Revision of the species confused with “Nereis falsa” de Quatrefages, 1866 (Annelida, Nereididae)

Nereis falsa de Quatrefages, 1866 has been regarded as a cosmopolitan species, and several species described from diff erent localities have been regarded as junior synonyms of N. falsa. The present study is an attempt to resolve the taxonomic confusion in N. falsa, which seems to contain several distinct species due to previous inappropriate synonymy, widely distributed in the Atlantic and eastern Pacifi c Oceans. For this purpose, the authors fi rst propose the resurrection of the synonymy of N. falsa with Hediste diversicolor that was concluded during the 19th century but disregarded later. After the fi xation of the identity of N. falsa sensu stricto, the authors re-evaluate the proper taxonomic status of species which have previously been confused with N. falsa. Type, topotype and non-type specimens were examined; most species are redescribed, and others are reinstated. Nereis splendida Grube, 1840 is a valid Mediterranean species, and a neotype is proposed; it includes the Mediterranean populations of what is currently regarded as N. falsa. Consequently, N. falsa is transferred to Hediste Malmgren, 1867, and some taxonomic comments are added for the latter genus and a key to species is also included. Nereis callaona Grube & Kröyer in Grube, 1857, N. marginata Grube & Örsted in Grube, 1857 and N. riisei Grube & Örsted in Grube, 1857 are restricted to tropical American shores and are all redescribed. Nereis pelagica lunulata Ehlers, 1901, formerly regarded as a junior synonym of N. falsa by Fauvel (1941), is redescribed and elevated in rank to species level. Nereis lucipeta Ehlers, 1908, formerly regarded as a junior synonym of N. splendida by Ehlers (1913) and of N. falsa by Fauvel (1919), is reinstated. Nereis occidentalis Hartman, 1945 is also redescribed. Furthermore, N. ambigua Treadwell, 1937, formerly regarded as a junior synonym of N. riisei by Monro (1933), deserves to be reinstated. Western Africa specimens recorded as N. falsa are newly described as N. mezianei sp. nov.


Introduction
Parapodial glands can be separated into three basic patterns: tubular, granulose and solid. Tubular glands have a fine mesh of thin tubules, with varying intensities of pigmentation. Granulose glands are rather irregular, with margins ill-defined and heterogenous cores, but differing from adjacent tissues in density or pigmentation. Solid glands are regular, with well defined margins, especially laterally, and homogeneous cores.
Tubular glands are present in Nereis mezianei sp. nov., a species formerly recorded as N. falsa by Fauvel (1936). The glands have a dark pigmentation, giving a dark or even blackish appearance to parapodial ligules, but they are not present inside cirri. The pigmentation is less intense in anterior chaetigers ( Fig. 2A), and becomes darker in median (Fig. 2D) and posterior chaetigers (Fig. 2G). These glands extend along most of the available space in notopodial and ventral ligules; its tubes are rather smooth in anterior chaetigers ( Fig. 2B-C). In median and posterior chaetigers these glands become more complex, with an expanded convolute basal area, penetrating inside the parapodial lobe beyond the widest ligule base. In all ligules, tubes extend along them but become regularly corrugated or monilate (Fig. 2E, H), and even in neuropodial ligules these glandular tubes extend distally, reaching the ligular tips ( Fig. 2F, I), although distal areas are less heavily pigmented. Tubular glands are also present in N. occidentalis.
Granulose parapodial glands are present in N. callaona, N. lucipeta and N. lunulata stat. nov. Solid parapodial glands are shown by specimens of N. marginata, N. splendida and N. riisei. However, some transitional forms are shown by non-type specimens of N. marginata and N. riisei.

Remarks
The taxonomic history of Hediste diversicolor is rather complex and has not been fully resolved. The original description was "body subdepressed, parapodia tapered with chaetae" (Müller 1776: 217), and no Greenlandic name or type locality was indicated; after invoking the ICZN, the Commission has moved to conclude that "the type locality has not been clarified" (Oug et al. 2014: 220). However, recommendation 76A1.3 is to take into account "the original description of the taxon". The second line for the original description includes two references: "Würm. 104, t. 6, Str. S. 1, p. 198, 2?" The first is a previous paper by the author (Müller 1771), whereas the latter is a paper: "Physik og oeconomisk Beskrievelse over fogderiet Söndmör" by Hans Ström (published in Soröe [Sorø, Denmark] in 1762).
We could not find the latter, but we found two editions of the former which contain an extended description (Müller 1771: 102-111, pl. 6 figs 1-6) and indications that the specimens were collected in Copenhagen. This information complies with the recommendation, and consequently the type locality should be Copenhagen, Denmark. It was reiterated in the second edition (Müller 1880: 110). Furthermore, specimens identified as H. diversicolor from the Baltic Sea include at least two different species, and this has complicated solving what we should regard as this biological species (Virgilio et al. 2009;Tosuji et al. 2019).
Örsted (1843: 23) provided a description of Nereis diversicolor and included illustrations of the anterior end, one jaw and one parapodium (pl. 4 figs 66, 68, 73). From the description, he emphasized that the tentacular cirri could reach segments 5-6, that dorsal cirri were short, parapodial ligules tapered and the notopodia had three ligules. He also indicated that this was a very common species living in sediments along Danish coasts, and in the synonymy he listed the species that Rathke (1837a) had recorded as Lycoris pulsatoria? Örsted relied on the original description by Rathke (1837a) and on the additional detailed account of its anatomy published separately (Rathke 1837b). Because the typical N. diversicolor and the recorded specimens of L. pulsatoria? have three notopodial ligules, he regarded them as synonymous.
On the other hand, Malmgren (1867: 48-49) used the number of notopodial ligules in his key to genera, and for species having three ligules he proposed Hediste, with N. diversicolor as its only species and listing N. sarsi Rathke, 1843, described from Molde, Norway, and N. depressa Frey & Leuckart, 1847, described from Helgoland, as synonyms. Malmgren did not use the diagnostic anchylosed neurofalcigers in his diagnosis, nor in the species description, and did not illustrate them. Ehlers (1868: 554) added N. brevimanus Johnston, 1840, described from Ireland, to the list of synonyms, provided a complete description and indicated that Hediste diversicolor could also be found in fresh-water environments.
Key to species of Hediste Malmgren, 1867 1. Areas VII-VIII with a single row of denticles (rarely 2-5 supernumerary paragnaths  (Izuka, 1908) (Japan) -Area II with more than 20 tiny paragnaths per side; longest tentacular cirri reaching chaetigers 8-9; areas VII-VIII with 9  (Hartman, 1938) (California) -Longest tentacular cirri reaching chaetiger 2 ......H. rabatensis (Mohammad, 1989) (Müller, 1776) sensu Khlebovich 1996 (Black Sea;matching N. falsa (de Quatrefages, 1866)) Remarks Smith (1959), after comparing the types, concluded that H. lighti was a junior synonym of H. limnicola. They differ in pigmentation in living specimens, H. limnicola being reddish, whereas H. lighti is transparent. A more detailed comparison is needed to confirm this synonymy. Day (1967) described Nereis gilchristi based on a single small specimen (8 mm long, 40 chaetigers) collected in South Africa. He indicated that it has only two notopodial ligules in anterior chaetigers, which is an important difference and deserves a separate assessment when assigning it to a genus. The key above should be used cautiously because the status of the type species must be clarified, since there are two cryptic species in the Baltic Sea (Röhner et al. 1997;Virgilio et al. 2006;Audzijonyte et al. 2008), and some Mediterranean and Black Sea forms (Virgilio et al. 2009;Cossu et al. 2012) might necessitate the reestablishment of some names currently regarded as junior synonyms.
Parapodia. Not dissected to avoid further damage (see below).
Pattern of parapodial ligules. Anterior chaetigers with ligules blunt, longer than wide in first few chaetigers, soon becoming as long as wide; natatory region with ligules tapered, 3-4 × as long as wide.
Pattern of parapodial ligules. Anterior chaetigers with ligules blunt, as long as wide, or slightly longer than wide; median and posterior chaetigers with ligules tapered or digitate, about 2 × as long as wide, or longer.
Posterior region. Tapered into a blunt cone (Fig. 6H). Pygidium with anus terminal, anal cirri as long as last 7-8 chaetigers (MNHN 495-1). Fauvel (1916: 81) used the name N. falsa for some Mediterranean nereidids and he included as junior synonyms of N. falsa two species described from Naples by Claparède (1868): N. parallelogramma and N perivisceralis; he also included N. lucipeta Ehlers, 1908 from South Africa. In a subsequent publication, Fauvel (1916: 81) added N. splendida Grube, 1840 as a synonym, another Mediterranean species, as well as a record by Ehlers (1913: 496) for the Cape Peninsula, South Africa. By expanding this synonymy, Fauvel's conclusions generated the "N. falsa species group," which he would define later (Fauvel 1923: 337). The list of synonyms includes, after Fauvel, N. parallelogramma Claparède, 1868, N. perivisceralis Claparède, 1868, Lycoris pulsatoria Rathke, 1843and N. lucipeta Ehlers, 1908. This group contains species of Nereis with pharyngeal area V without paragnaths and areas VII-VIII with a single row or 2-3 rows of paragnaths, anterior parapodia with two blunt notopodial ligules, notopodial homogomph falcigers in posterior chaetigers, with blades sinulose, sometimes with a distal ligament or tendon (Fauvel 1923). Two other species, N. callaona and N. victoriana Augener, 1918, were regarded as similar to N. falsa by Salazar-Vallejo & Jiménez-Cueto (1997: 374), and Reish (1954: 104)  This progression of synonymies based on generally similar specimens of different species, without paying attention to some features of the pharynx, was incorrect, especially because N. falsa was based on L. pulsatoria? from the Black Sea, which does not match these features. Furthermore, some aspects of the taxonomic history of Hediste diversicolor deserve mention, as it is also complex and not fully resolved. For example, there are no type specimens and there was no indication of the type locality. Furthermore, specimens identified as H. diversicolor from the Baltic Sea, which could be the type locality, include at least two different species, and this has complicated resolving what we should regard as this biological species (Oug et al. 2014). Some names are available for the regional forms, in case there is more than one, taking into account that Malmgren (1867: 48-49) proposed Hediste to include N. diversicolor, listing N. sarsi Rathke, 1843, described from Molde, Norway, and N. depressa Frey & Leuckart, 1847, described from Helgoland, Germany, as junior synonyms. Ehlers (1868: 554) added N. brevimanus Johnston, 1840, described from Ireland, to the list of synonyms. Black Sea population haplotypes differ from those present in nearby areas (Vasileiadou et al. 2016); if this difference promotes regarding Black Sea specimens as belonging to a different species, N. falsa de Quatrefages, 1866 would be available for them.

Remarks
It has been indicated that Nereis splendida cannot be used as a senior synonym for N. falsa (Salazar-Vallejo et al. 2017), because it was preoccupied by Nereis splendida de Blainville, 1825. Because this is a junior homonym, its name should be replaced (ICZN 1999, arts 52.2, 57.2), and the next available name should be used instead. However, contrary to previous conclusions, there is an alterative for retaining N. splendida Grube, 1840, and this refers to the fact that the two species involved do not belong in the same genus (ICZN 1999, art. 59.2). Nereis splendida de Blainville, 1825 refers to a nephtyid polychaete, which would be a junior synonym of Nephtys hombergi Savigny in Lamarck, 1818 according to Audouin & Milne-Edwards (1833: 257) and de Quatrefages (1866a: 434). Consequently, "the junior name is not to be rejected, even if one species-group name was originally proposed in the current genus of the other" (ICZN 1999, art. 59.2). Alós et al. (2004: 513) did not indicate their reasons for retaining N. splendida Grube, 1840, but the above article provides the explanation for it. Some additional details must be understood. First, the composition of the type material. Augener (1918: 186) noted that what was then regarded as the type material of N. splendida Grube, 1840 actually contained three specimens, two of them belonging to Ceratonereis Kinberg, 1865, and the originally described specimen of N. falsa.
Second, the type material is lost. Birger Neuhaus (ZMB, 2019 in email) indicated "We had unspecified type material of Nereis splendida, catalogue number ZMB 'Vermes' 5160; the material was lost at some time. I checked our loan records and found that Augener received this lot on loan to Hamburg around 19.II.1914 from my predecessor Anton Collin, and returned the specimens on 11.VIII.1921. He does not seem to have had the specimens on loan a second time." The next available name is N. splendida Grube, 1840. This name could be used for Mediterranean records of what has been regarded as N. falsa. As indicated above, N. falsa would be available for the Black Sea populations currently regarded as Hediste diversicolor, once significant differences are found and its independent specific status is confirmed. However, Claparède left no type material because he emphasized that (Claparède 1867: 12 [341 in translation]) "the Annelida can only be well studied at the seaside and by means of living individuals." Because there is no type material, and especially because the species-group name is in conflict, the designation of a neotype is necessary to define the nominal taxon (ICZN 1999, art. 75.1). These are the qualifying conditions: -a neotype of Nereis splendida Grube, 1840 is proposed to clarify the taxonomic status of the species (ICZN 1999, art. 75.3.1) -the above description, the key below, and the publication by Gravina et al. (2015, as Nereis falsa) characterize the species and its differences from similar species in the area or from elsewhere (ICZN 1999, art. 75.3.2) -the description above matches the original description and the labeling ensures the recognition of the neotype (ICZN 1999, art. 75.3.3) -as indicated above, the type material was lost (ICZN 1999, art. 75.3.4) -the neotype is a mature male specimen with some modifications for swimming and swarming. Despite the modifications of cephalic appendages and parapodia, the pharynx armature is not modified (Fauvel 1916;Pamungkas & Glasby 2015), and the neotype matches the original description. Because no other topotype specimen was available, this different life stage is code compliant (ICZN 1999, art. 75.3.5) -the neotype was collected in Naples harbor, and Grube (1840: 2) indicated that most of his specimens, if no locality was given, as is the case for N. splendida, were collected in the Gulf of Naples, and the neotype was collected from the same area (ICZN 1999, art. 75.3.6) -the neotype has been deposited in the Muséum national d'histoire naturelle, Paris, a recognized scientific institution (ICZN 1999, art. 75.3

.7)
Most specimens that have been preserved for about 100 years risk having the blades of compound falcigers detach, and this is why additional specimens must be studied to reveal the specific morphology of the homogomph falcigers in median or posterior chaetigers. It seems that the blades in median chaetigers have tips better defined and more acute than those present along more posterior chaetigers.
Observations of the inner margin denticulation are also difficult because it can be eroded, and we think this feature is also better defined along median chaetigers.
"Nereis falsa" resembles N. pelagica Linnaeus, 1758, the type species of the genus (Fauvel 1923: 335-336), in pharyngeal ornamentation and parapodial development; their main differences are in the size and dentition of the homogomph falciger blades. In "N. falsa" the blades of falcigers are longer (3 × as long as wide), the distal tooth is incurved and they have denticulate cutting edges, whereas in N. pelagica the blades are shorter (2.0-2.5 × as long as wide), without a distal tooth and the cutting edges are smooth to barely rugose. On the other hand, Gravina et al. (2015: 162, key) indicated that "N. falsa" is more similar to N. rava Ehlers, 1864, because both have similar parapodial development in posterior chaetigers, without expanded dorsal ligules, and because the homogomph falciger blades are denticulate. These two species differ because of some fine details in the blades of homogomph falcigers. In N. rava, these blades are medially expanded, and there is a thicker distal tooth, without a ligament, whereas in "N. falsa" the blades are tapered, and the distal tooth is incurved, with a ligament or tendon. Another relevant difference is that in N. rava there is a single transverse row of paragnaths in areas VII-VIII, whereas there are 2-3 rows in "N. falsa". In the latter species, most accounts indicate that there can be 3 or 4-5 paragnaths in area VI in the same population (Fauvel 1923;Gravina et al. 2015), and it would be interesting to evaluate whether these differences are linked with some other morphological features.
It must be emphasized that according to Hartman (1959), N. pelagica includes 18 junior synonyms (and some subspecies) described from the Atlantic; the Northwestern Pacific records (Imajima 1972) differ from the Northeastern Atlantic forms, as illustrated by Chambers & Garwood (1992: 38), in cephalic appendages, as well as parapodial and chaetal features, including in epitokes. Some of the junior synonyms have also been confused with "N. falsa" due to the pigmented glandular parapodial ligules.
As indicated below, N. splendida resembles "N. falsa" recorded for the Caribbean Sea (Liñero-Arana & Reyes-Vásquez 1979) in having anterior chaetigers with digitate notopodial ligules, ventral ligules longer than neuracicular ligules in median and posterior chaetigers, and pharyngeal areas VII-VIII with 2-3 transverse rows of paragnaths. Their main differences are in prostomial shape and pharyngeal paragnath numbers in area II. In N. splendida the anterior prostomial lobe is 2 × as long as wide, and area II has about 22 paragnaths, whereas in the Caribbean specimens the anterior prostomial lobe is wider than long, and area II has about 30 paragnaths.

Distribution
Mediterranean Sea and adjacent localities in the Northeastern Atlantic, in shallow water. The record by Rullier & Amoureux (1969: 120) cannot be confirmed because their specimens could not be located.
Prostomium. Pyriform, longer than wide; eyes round, of similar size, in trapezoidal arrangement, posterior eyes closer to each other (Fig. 7A). Antennae swollen basally, as long as palps, without gap between them. Palpophores globose, 1.5 × as long as wide, palpostyles rounded. Pattern of parapodial ligules. Anterior chaetigers with ligules blunt, globose, as long as wide, becoming digitate, 2-3 × as long as wide in median and posterior chaetigers; ventral ligule slightly longer than neuracicular ligules in anterior chaetigers, in median and posterior ones markedly longer than them.
Posterior region. Tapered. Pygidium with terminal anus and two anal cirri.

Remarks
Nereis callaona was described based on specimens from El Callao port, Peru. It differs from other species in the group by the presence of massive, dark glands in parapodial ligules throughout the body. The record by Augener (1918) for West Africa resembles typical specimens because it has the posterior eyes exposed, pharyngeal areas VII-VIII with 2-3 rows of denticles and pigmented glandular areas in posterior parapodia. They differ, however, because the Eastern Pacific species has 11 paragnaths in two rows in pharyngeal area II, whereas the West African form has 28 paragnaths in three rows in the same area. Reish (1954) regarded N. pseudonereis Hartman, 1940, described from the Galapagos and Peru, as a junior synonym of N. callaona after a comparison of the type specimens (see above). We follow Reish's conclusion.
Nereis callaona was regarded as identical to N. falsa by Berkeley & Berkeley (1964), probably following Hartman (1940: 224), who indicated some affinities of her N. pseudonereis, a junior synonym of N. callaona (as indicated above), with N. falsa. However, the status of this latter species has been confused, because it belongs in Hediste Malmgren, 1867 (see above). (1913) by recording N. splendida Grube, 1840 from Southern Africa. However, N. callaona differs from N. splendida by having dark glandular masses in the parapodial ligules. Augener (1918) recorded N. callaona, from Western Africa, and although specimens of this latter region were not seen, they differ in the number of paragnaths in area II. There are 11 cones in the American specimens and 28 in the African ones. On the other hand, the male epitoke reported as N. falsa by Berkeley & Berkeley (1964) has 26 chaetigers in the pre-natatory region instead of 27, as indicated for "N. falsa" by Fauvel (1923: 338). Their account should be referred to N. callaona, as indicated above, and not to any other species.

Diagnosis
Nereis with posterior eyes partially covered by anterior margin of tentacular belt; tentacular belt 2 × as long as first chaetiger; tentacular cirri short, reaching chaetiger 4; pharyngeal areas VII-VIII with 5 large paragnaths in a single row; posterior chatigers with dorsal ligules 2-3 × as wide as median ones.

Material examined
Holotype UNITED STATES VIRGIN ISLANDS • Saint John (the vial has a label signed by Kröyer inside that says it is Nereis riisei, i.e., a very incorrect label); Kröyer leg.; NHMD 109266 (previously ZMUC POL-1483).

Remarks
Nereis (Nereis) marginata is a neglected Caribbean species; it was originally described based on a single specimen with about 90 chaetigers from St John, U.S. Virgin Islands (formerly St Jean).
The original description is succinct and has no illustrations; perhaps because of this, Hartman (1959) regarded N. marginata as indeterminable. The type material of N. (Nereis) marginata (NHMD 109266) was examined. The holotype consists in a single specimen with the pharynx previously removed. The parapodia have black spots on the distal part of the ligules throughout body. Additional specimens from the Caribbean Sea were examined and match the type material.
Nereis marginata resembles N. rava, from the Mediterranean Sea (following Gravina et al. 2015). These two species have posterior eyes partially covered by the tentacular belt's anterior margin and short tentacular cirri reaching chaetigers 2-4. Their main differences are in pigmentation pattern and in the relative size of the notopodial ligules on posterior chaetigers. In N. marginata the dorsum has transverse irregular bands, its dorsal ligules are 2-3 × as wide as median ones and the ventral ligules surpass neuracicular ligules, whereas in N. rava the dorsum has two transverse bands, its dorsal and median ligules are of similar width and ventral ligules reach neuracicular ligules in length.
On the other hand, N. marginata also resembles N. riisei in pharyngeal formula and both parapodial and chaetal morphology, but they can be separated by using several features of the anterior end, parapodia and chaetae. In N. marginata, the posterior eyes are partially covered by the tentacular belt, whereas in N. riisei they are completely exposed; in N. marginata, the dorsal ligules are wider than long throughout body and become markedly wider toward posterior chaetigers, whereas in N. riisei they are of subequal length and width, becoming slightly wider toward posterior chaetigers; in N. marginata, median ligules in anterior chaetigers are much wider than neuroacicular ligules, whereas in N. riisei they are of similar width; in N. marginata, the ventral cirri become longer than ventral ligules toward posterior chaetigers, whereas in N. riisei they are shorter than the ventral ligules throughout the body; N marginata has neuropodial heterogomph falcigers with blades of different sizes in supra-and infracicular neuropodial fascicles, whereas in N. riisei they are of similar size. These differences are consistent within the material examined, so Nereis marginata is here regarded as a valid species.

Diagnosis
Nereis with posterior eyes completely exposed; tentacular belt 2 × as long as first chaetiger; pharyngeal areas VII-VIII with a single row of large denticles; median and posterior parapodia with ventral ligules surpassing neuracicular ligule tips.
Prostomium. Slightly longer than wide, dorsal groove present. Eyes black (Fig. 12A-B), larger in preepitoke (Fig. 16A), or reddish, of similar size, anterior eyes oval, directed anteroventrally, about ⅒ of prostomial width, slightly more separated than posterior eyes. Antennae terminal, without gap between them, tips surpassing tips of palpophores, not surpassing palpostyles, half as long as prostomium. Palpophores conical, truncate, 2 × as long as wide; left palpostyle longer than wide, right one as long as wide.
Pattern of parapodial ligules. On first few chaetigers, as well as on medial and posterior ones, with ligules tapered, blunt, about 2 × as long as wide, with massive dark glands, projected beyond ligular bases; anterior chaetigers with ligules massive, shorter, slightly tapered. First chaetigers with ligules granulose or verrucose, in a small area, progressively larger in anterior chaetigers, but missing in medial and posterior chaetigers. Glandular masses leave apical ligular spaces empty in medial and posterior chaetigers.

Remarks
Salazar-Vallejo & Eibye-Jacobsen (2012) incorrectly indicated Puntarenas, Costa Rica (Pacific Ocean) as the type locality of Nereis riisei. Rather, St Croix is the correct type locality as indicated both in the description (Grube 1857: 163) and the index for the series (Grube 1858: 119). The label in the holotype material deposited in NHMD indicates that the type locality is St Croix and the collector was Kröyer (Danny Eibye-Jacobsen, pers. comm.).
Although it is a relatively easy species to identify, Nereis riisei has a largely confused taxonomic history and has been widely reported for both coasts of America in temperate to tropical waters. It is likely that the confusion regarding the type locality has given this species its current amphiamerican status. The first amphiamerican report was made by Monro (1933), synonymizing several species with N. riisei, and Hartman followed this conclusion in subsequent papers (Hartman 1938(Hartman , 1940(Hartman , 1944(Hartman , 1954. This decision has been widely followed, except for some species such as N. glandulata Hoagland, 1919(e.g., Treadwell 1924, 1928. We disagree and regard N. ambigua Treadwell, 1937 as a distinct species (see below). Day (1973) and Gardiner (1976) recorded Nereis (Nereis) riisei from North Carolina, but their specimens differ from Caribbean ones by having tentacular cirri reaching chaetiger 6, ventral ligules as long as neuracicular ligules in posterior chaetigers, and notopodial homogomph falcigers with longer blades. Furthermore, Day (1973) described the dorsal cirri of anterior parapodia as being 3 × as long as dorsal ligules and the dorsal ligules as half as long as median ones, subconical instead of rounded.
On the other hand, N. riisei resembles N. ambigua Treadwell, 1937 by having the posterior eyes completely exposed and pharyngeal areas VII-VIII with a single row of paragnaths (the latter characterized in Dean 2001). These two species differ because in N. riisei the ventral ligules in median and posterior parapodia surpass the neuracicular ligules, and fresh specimens have a blackish tentacular belt, whereas in N. ambigua the ventral ligules reach the neuracicular ligule tips in median and posterior parapodia, and fresh specimens have a pale tentacular belt. However, these differences must be taken as preliminary pending the collection of topotype specimens of N. ambigua and confirming these diagnostic features.
Nereis (Nereis) puncturata Grube & Örsted in Grube, 1857 was described based on specimens from two distinct localities. Salazar-Vallejo & Eibye-Jacobsen (2012) located the type material in two museums: a specimen from St Croix is deposited in the Natural History Museum of Denmark (NHMD), while specimens from Valparaiso are deposited in the Zoological Museum, Berlin (ZMB 4040). Grube did not include type localities in the descriptions. but included them for the index to species (Grube 1858). One syntype of N. puncturata (NHMD 109269, previously ZMUC POL-1486) was studied and within it a label by Kröyer was found indicating that this species is similar to N. riisei; the syntype is in poor condition, the body being crystallized, but morphological characters could be observed that place it closer to Platynereis dumerilii (Audouin & Milne Edwards, 1833). The species requires the proposition of lectotypes to separate the Atlantic from the Pacific forms.
The syntypes of Nereis albipes (ZMB Q3441) are similar to N. riisei, and they are herein regarded as snynonyms. This southern Brazilian species has the same pattern of black glandular spots in the parapodial ligules; however, a slight variation is observed in the paragnath formula: I: 1; II: 11-20 in two rows; III: 11-23 in oval group; IV: 18-28 in a crescent-shaped patch; V: 0; VI: 4-10 in a rounded patch; VII-VIII: 5 in a single band. Incidentally, this species name was indicated, on the same page (Grube 1874: 60), as "N. albipes Gr." and 20 lines below as "albipes Gr. Müll." We are following the latter because Fritz Müller provided some identifications to the specimens sent to Grube.
Other species have been referred to as synonyms of N. riisei, but the material needed to corroborate their status were not examined. These species deserve to be studied in further detail to clarify their affinities, but that is beyond our objectives for this contribution. The species are the following ones (in chronological order): Heteronereis fasciata Schmarda, 1861. Schmarda (1861) described this species based on epitokes from Jamaica, preventing an adequate comparison with atoke specimens of N. riisei. Augener (1925) revised the type material and based upon the paragnaths on pharyngeal areas VII-VIII and the chaetae, he concluded that it was identical to N. riisei. Diagnostic features include jaws with five teeth, areas VII-VIII with few paragnaths in one band, neuropodial heterogomph falcigers with short blades and natatory region starting at chaetiger 22-23. Several specimens of this species (with labels V900 and V901), supposed to be the type material observed by Augener, are deposited at the Natural History Museum in Vienna (H. Sattmann, pers. comm.). Ehlers, 1868. Ehlers (1868 described this species based on specimens from Haiti and Florida. Augener (1925) regarded N. nigripes as identical to N. riisei, and Monro (1933) synonymized it with N. riisei without further explanation. Hartman (1938), based on Monro's decision, synonymized this species and N. bicruciata Augener, 1906 (see below) with N. riisei. The database of the Museum of Comparative Zoology (Harvard University, Cambridge, MA) indicates they have the specimen from Haiti (ANNa-54). Ehlers (1868) detailed the following paragnath formula: I: irregular patch; II: arc patch; III: transverse patch; IV: arc patch; V: 0; VI: 8-13; VII-VIII: 5. Based on the original description, N. nigripes differs from N. riisei by having the antennae as long as the prostomium, tentacular cirri reaching chaetiger 9 and dorsal ligules longer than median ones in posterior chaetigers.

Nereis nigripes
Nereis (Lycoris) trifasciata Grube, 1878. Grube (1878) described this species from Bohol, Philippines. He provided the following paragnath formula: I: 0; II: 11 in two rows; III: 8 in two rows; IV: 15 in two rows; V: 0 or 1; VI: 5-6; VII-VIII: a single band. The original description is succinct and prevents any further comparison between N. trifasciata and N. riisei. Monro (1933) regarded this species as a synonym of N. riisei without further explanation, but this conclusion must be evaluated based upon topotype specimens because of the different type localities for these species. The species was transferred to Neanthes Kinberg, 1865 by Villalobos-Guerrero & Idris (2021). Hansen, 1882. Hansen (1882 described this species based on one specimen from Rio de Janeiro, Brazil. Augener (1934) concluded that this species must be regarded as a synonym of N. riisei because of the presence of ligules with dark glands in middle and posterior chaetigers and the presence in pharyngeal areas VII-VIII of 4 paragnaths in a single band. The original description and Augener's redescription were very short, preventing further comparisons with N. riisei. Records of Nereis sp. by Nonato & Luna (1970) and of N. riisei by Santos & Lana (2003) might belong to N. lata if they are shown to be different from N. riisei. Hansen, 1882. This species was also described based on specimens from Rio de Janeiro (Hansen 1882). According to Augener (1934), the type material contains two species, one of them very similar to N. lata and therefore, in his opinion, probably conspecific with N. riisei. Augener (1934) detailed the following paragnaths in the oral pharyngeal ring: V: 0; VI: 11-15; VII-VIII: 4 in a single band. Based on the original description, N. scolopendroides differs from N. riisei by having shorter antennae, dorsal and median ligules shorter than neuracicular ligules and heterogomph falcigers with shorter blades. Willey, 1905. Willey (1905 described this species from Sri Lanka (formerly Ceylon) and provided the following paragnath formula: I-IV: unknown; V: 0; VI: small patch; VII-VIII: a single band. Fauvel (1919) thought that this species differed from N. trifasciata only in its pigmentation. Monro (1933) regarded N. unifasciata as a synonym of N. riisei without further explanation. Based on the original description, N. unifasciata differs from N. riisei by having tentacular cirri reaching chaetiger 7 and lacking notopodial homogomph falcigers. This explains why Day (1967: 318) regarded it as belonging in Neanthes. Pamungkas & Glasby (2015) provided an account of this species. Augener, 1906species inquirenda. Augener (1906 described this species based on an incomplete specimen from St Croix, Virgin Islands, dredged from sediments at a depth of 210 m. Hartman (1938) examined the type specimen and determined that N. bicruciata and N. nigripes Ehlers, 1868 were synonyms of N. riisei, although she identified some differences in jaw dentition and paragnath numbers. The type material was supposedly deposited in the Museum of Comparative Zoology, Harvard University (MCZ ANNc-2277) but has been lost since 1983, requiring the proposal of a neotype. Augener (1906) detailed the following paragnath formula: 1: 1; II: several rows; III: 7; IV: triangular patch; V: 0; VI: 4-5; VII-VIII: 3 in a single band. Based on the original description, N. bicruciata differs from N. riisei by having tentacular cirri reaching chaetigers 10-11 and fewer paragnaths in pharyngeal area III. Treadwell, 1932. Hartman (19381956: 255) synonymized this species from Ilha de São Sebastião, Brazil, with N. riisei, but made no comments about this decision. Treadwell (1932) detailed the following paragnath formula: I: 1; II: about 15 in two rows; III: oblong patch; IV: oval patch smaller than in III; V: 0; VI: 6-8; VII-VIII: 4-5 in a single band. Based on the original description, N. decora differs from N. riisei mainly by having antennae as long as the prostomium and tentacular cirri reaching chaetiger 7, while the parapodia are very similar in both species. Treadwell, 1941 (replacement name for Nereis (Neanthes) paucidentata Treadwell, 1939). Hartman (1956) synonymized this species with N. riisei, notwithstanding the fact that she detailed clear differences between them, such as the presence in N. varia of paragnaths in area V, a single paragnath in areas VI and two rows of paragnaths in areas VII-VIII. Moreover, in the middle parapodia of N. varia, the dorsal cirri are half as long as the dorsal ligules, and the dorsal ligules are 2 × as long as the median ligules; in N. riisei, the dorsal cirri are longer than the dorsal ligules, and the dorsal and median ligules are subequal. Finally, notopodial homogomph falcigers were not noticed for N. varia. All these mentioned features are enough to separate it from N. riisei.
Prostomium. Longer than wide, subpyriform, dorsal groove present. Eyes black, in trapezoidal arrangement, anterior eyes slightly longer than posterior ones. Antennae half as long as prostomium, not reaching tips of palpostyles, with a small gap between them. Palpophores globose, 2 × as long as wide, palpostyles rounded (Fig. 14A).
Pattern of parapodial ligules. Anterior and median chaetigers with ligules massive, blunt, round, slightly longer than wide, posterior chaetigers with ligules conical, blunt, as long as wide, or slightly longer than wide in posterior chaetigers; ventral ligule reaching tip of neuracicular ligules.
Prostomium. 2 × as long as wide, dorsal groove present. Eyes blackish, of similar size, anterior ones oval, directed anteroventrally, diameter ⅙-⅐ of prostomial width, slightly more separated than posterior eyes (Fig. 6B). Antennae half as long as prostomium, without gap between them, tips reaching palpostyle tips. Palpophores 2 × as long as wide; palpostyles longer than wide (left) or rounded (right).
Tentacular belt. 2 × as long as first chaetiger; anterior margin projected anteriorly (less pronounced in smaller specimen), with an unpigmented irregular area along its right side. Tentacular cirri smooth, integument detached along almost all their length, longest ones reaching chaetigers 3-4.
Pattern of parapodial ligules. Anterior and median chaetigers with ligules blunt, slightly longer than wide, becoming blunt triangular, slightly longer than wide in posterior chaetigers. Ventral ligules as long as neuracicular ligules, tapered.
Posterior region. Tapered into a blunt cone. Pygidium regenerating, almost completed in smallest specimen, anus terminal, anal cirri as long as last 5-6 chaetigers.

Remarks
Nereis pelagica lunulata Ehlers, 1901 differs from the stem species, N. pelagica Linnaeus, 1758 as defined by Chambers & Garwood (1992: 16, figs 17-18), because its ventral ligules are tapered in posterior chaetigers, instead of being blunt, lobate, and because its notopodial homogomph falcigers are spinulose, with a barely defined tendon, as opposed to dentate or smooth in N. pelagica. Consequently, it is herein elevated in rank from subspecies to species.
As indicated in the key below, because of the presence of 2-3 transverse rows of paragnaths in pharyngeal areas VII-VIII, and by having digitate notopodial ligules in anterior chaetigers, N. lunulata stat. nov. resembles N. splendida Grube, 1840, from the Mediterranean Sea, and "N. falsa" sensu Liñero-Arana & Reyes-Vásquez (1979), from the southeastern Caribbean. These three species differ by the relative size of ventral ligules and by the number of paragnaths in pharyngeal area II. In N. lunulata stat. nov., ventral ligules are as long as neuracicular ligules, and area II has 16 paragnaths, whereas N. splendida and "N. falsa" have ventral ligules longer than neuracicular ligules, and there are 22 paragnaths in area II in the former, and about 30 in the latter.
It is worth noting that the presence of some unidentified, solitary peritrich ciliates on the parapodial cirri modifies their appearance, making them look wider, and the surface also becomes more irregular, i.e., it is not as smooth as in other similar species.
Posterior region. Tapered into a blunt cone. Pygidium with anus terminal, anal cirri as long as last 6-8 chaetigers.
The main difference between the male epitokes of N. lucipeta and those of N. splendida is in the number of chaetigers in the non-natatory region, as indicated in the key below. In N. lucipeta the anterior region includes 20 chaetigers, whereas in N. splendida, it has 27. An additional difference is in the shape of the prostomium and the size of the palpophores. In N. lucipeta the anterior prostomial region is longer than the posterior, ocular one, and the palpophores are markedly swollen, projected laterally beyond the level of the lateral eyes, whereas in N. splendida the anterior prostomial region is as long as, or shorter than, the posterior ocular one, and the palpophores are not so markedly swollen.
The atokes of what could be regarded as N. lucipeta were briefly characterized by Day (1962: 639), under the name of N. falsa, based on some specimens from Natal, and later he keyed out the atokes and provided an extended diagnosis (Day 1967: 317). These records are herein regarded as N. lucipeta because of the similarities in parapodial and pharyngeal features, although the anterior end of an atoke has not been illustrated before.
As indicated in the key below, by having short tentacular cirri N. lucipeta resembles N. callaona and N. callaona sensu Augener 1918 from Western Africa. However, typical N. callaona can be separated from the two other species because its jaws only have 4 denticles, whereas the two other species have 6-7 denticles. The main difference between N. lucipeta and N. callaona from Western Africa are in the pharyngeal areas II and III, because N. lucipeta has 18-20 paragnaths in II and about 30 paragnaths in III, whereas N. callaona sensu Augener has 28 paragnaths in II and about 50 in III.

Material examined
None.

Remarks
Dark pigmented glands in parapodial ligules have been reported several times for West African specimens recorded as N. callaona. Augener (1918: 184) and later Fauvel (1936: 35) noted 2-3 transverse rows of paragnaths in pharyngeal areas VII-VIII. Fauvel recorded this species with a single specimen from Agadir (30°25′00″ N, 09°35′00″ W), on ascidians. He gave the paragnath formula as: I: 0, 2; II: two arches; III: rectangular group; IV: arched groups; V: 0; VI: 3-5 large paragnaths in a cross on each side; VII-VIII: 2-3 irregular series with subequal paragnaths. The presence of a dorsal homogomph falciger was indicated with a blade denticulated, and with a ligament from the top. The pigmentation was given as greenish with transverse brownish bands along the anterior region. However, West African specimens differ from typical N. callaona from western South America in several features. In West African specimens, jaws have 6 denticles, but only 4 are present in western South American specimens. In African specimens, the pharyngeal area II has about 28 paragnaths in three rows, whereas American specimens have about 11 in two rows. Augener (1918: 186) indicated some resemblance of his specimens to N. lucipeta Ehlers, 1908, and to N. splendida; we have not seen these specimens and their affinities must be clarified in the future.

Diagnosis
Nereis with posterior eyes completely exposed; tentacular belt 2 × as long as first chaetiger; pharyngeal areas VII-VIII with a single row of large denticles; median and posterior parapodia with ventral ligules reaching tip of neuracicular ligules.

Description (abridged from several sources)
Body. Dark brownish pigmentation on dorsal surfaces of prostomium and tentacular belt, often continued as two transverse bars per segment along anterior chaetigers.
Prostomium. Pyriform, longer than wide; eyes round, of similar size, in a rectangular arrangement. Antennae slightly surpassing palp tips. Palpophores globose, as long as wide, palpostyles rounded.
Pattern of parapodial ligules. Anterior chaetigers with ligules blunt, slightly longer than wide, of similar length and width, becoming tapered, blunt, slightly longer than wide in median and posterior chaetigers; ventral ligule progressively smaller, thinner, 2 × as long as wide.
Posterior region. Tapered. Pygidium with anus terminal with two anal cirri, as long as last 11 chaetigers.

Remarks
The specific epithet must be modified because the original one was masculine (‛ambiguus', ‛uncertain'), but the gender of Nereis is feminine. Therefore, the epithet must be used in the feminine form (ambigua).
There are some problems regarding the type material of N. ambigua. Treadwell (1937: 149) selected and described as "type" a juvenile collected in the Revillagigedo Islands. It was 25 mm long, 1 mm wide, without the posterior region, and he recorded another, smaller specimen. Surprisingly, he indicated "the type retained only one anal cirrus" (Treadwell 1937: 150), and this might correspond to the heteronereis he referred to in the last line of his description. Treadwell (1937) described the largest specimen, 25 mm long and 1 mm wide, and its pharynx was not exposed, preventing him to clearly count the numbers of paragnaths. Hartman (1940) synonymized this species with N. riisei on the basis of parapodial ligules and homogomph falciger shape only, but no further comments were made. Later, Hartman (1956) studied one of the type specimens, but she failed to indicate which one it was or whether there was only a single specimen remaining in the jar, the largest one being destroyed after dissection. She dissected the pharynx and found a paragnath distribution different from the one originally indicated by Treadwell (1937). Treadwell indicated that areas I and II were smooth, whereas Hartman found 3 paragnaths in I and a patch of larger paragnaths in II; furthermore, larger differences relate to areas VI and VII-VIII, because Treadwell indicated 3-4 cones in VI, 7-8 cones in VII and a circular patch with about 20 paragnaths in VIII, but Hartman noted 12 cones in VI and a single continuous band with about 10 alternating larger and smaller cones in VII-VIII. On the other hand, Hartman (1940: 222) found a different pattern in her Eastern Pacific specimens, with 4-5 cones in VI and a single band with 4-5 in VII-VIII. A similar pattern, matching Hartman's account, was recorded by Dean (2001) for his Costa Rican specimens. Hartman (1956) also detailed 9 teeth on the jaws, dark aciculae and homogomph falcigers (presumably notopodial ones) appearing from chaetiger 26.
Because of this series of differences, which were more or less corroborated in the Gulf of California material, and because Treadwell (1937) indicated he had two specimens, the chances are that those two specimens belong to different species. An alternative is that Treadwell confused the pharyngeal areas in the non-everted pharynx, as he indicated, and that would explain the specific epithet. The specimens that Hartman (1940) and Dean (2001) studied were more similar to N. riisei than the specimen Hartman (1956) studied. Regretfully, subsequent collecting trips to the Revillagigedo Islands (Hartman 1939;Rioja 1960) did not provide topotype specimens of N. ambigua.
Consequently, the key below indicates that N. ambigua resembles N. riisei because both have posterior eyes completely exposed and a single row of paragnaths in areas VII-VIII, after the careful characterization by Dean (2001). Based on the original description, N. ambigua differs from N. riisei mainly by having larger eyes, tentacular cirri reaching chaetiger 9 and dorsal cirri in posterior chaetigers shorter than dorsal ligules. These two species further differ because in N. ambigua the ventral ligule in median and posterior parapodia reach the tips of the neuracicular ligules, and in fresh specimens the tentacular belt is pale. On the contrary, in N. riisei the ventral ligules in median and posterior parapodia surpass the neuracicular ligules, and fresh specimens have a blackish tentacular belt. Nevertheless, these differences must be taken as preliminary pending the finding of topotype specimens and confirming their diagnostic features.

Distribution
Originally described from the Revillagigedo Islands, the potential distribution of Nereis ambigua might extend along the Eastern Pacific, from the Gulf of California to the Galápagos Islands and Ecuador, in shallow water. Hartman, 1945 Fig. 17 Nereis pelagica occidentalis Hartman, 1945: 20, pl. 4 figs 1-6.
Posterior region. Tapered. Pygidium damaged, anus terminal; anal cirri as long as last 17 chaetigers (Fig. 17B). Hartman (1945) regarded this species as a subspecies of Nereis pelagica Linnaeus, 1758, but Pettibone (1956) thought they were different and regarded it as a distinct species, although further comments about this conclusion were not given. Because there is no available redescription of N. pelagica, here the description and illustrations in Chambers & Garwood (1992: 38-40) are followed. Hartman, 1945 differs from N. pelagica in the following features: N. occidentalis has larger paragnaths basally in pharyngeal areas VII-VIII, whereas N. pelagica has larger paragnaths distally; in N. occidentalis, the ventral ligules are longer than the neuracicular ligules in middle and posterior chaetigers, whereas in N. pelagica they are subequal; in N. occidentalis, parapodial ligules are subconical with pointed tips, whereas in N. pelagica they are digitiform with blunt tips; in N. occidentalis, the notopodial homogomph falcigers have several narrow teeth and a distal, stout tooth with a tendon, whereas in N. pelagica these falcigers are not denticulate.

Nereis occidentalis
As discussed elsewhere (Conde-Vela & Salazar-Vallejo 2015), Pettibone (1956) raised this species to species level and described it with specimens from Laguna Madre, Texas, Gulf of Mexico. Some features of those specimens resemble those of N. occidentalis, such as the length of the tentacular cirri, the arrangement of paragnaths on the pharynx (although she did not indicate most paragnath numbers) and the shape of blades of both notopodial and neuropodial falcigers. However, there are some relevant parapodial differences between specimens from Texas and typical N. occidentalis: in the anterior chatigers of N. occidentalis, median ligules are rounded and neuracicular ligules are as long as ventral ligules, whereas in specimens from Texas the median ligules are digitiform and neuracicular ligules are shorter than ventral ligules; in the middle chaetigers of N. occidentalis, medial ligules are 3 × as long as neuracicular ligules, whereas in specimens from Texas, median ligules are 2 × as long as neuracicular ligules; in the posterior chaetigers of N. occidentalis, ventral ligules are 2 × as long as neuracicular ligules, whereas in specimens from Texas, ventral ligules are shorter than neuracicular ligules. These variations might be intraspecific variations, but clarifying this will depend of a future study. Taylor (1984: 31.39, fig. 31.38) identified specimens from the Gulf of Mexico Florida coasts as Nereis falsa, and he included a plate combining figures made of North Carolinean specimens by Hartman (1945) and Gardiner (1975); Taylor's specimens are similar to ones from Texas, requiring a further examination of them to clarify the affinities between these local populations. Dueñas-Ramírez (1980) reported N. occidentalis from the Colombian Caribbean and included a brief description and illustration; his specimens differ from N. occidentalis in having larger overlapping eyes, in contrast to the smaller and separated eyes and dorsal ligules with relatively narrow bases in the Carolinian specimens of N. occidentalis.

Distribution
North Carolina, United States.

Material examined
None.

Remarks
Because no specimens were available, we cannot clarify the status for this record. There is a discrepancy between the description and the illustration regarding the tentacular cirri; in the illustration they reach about chaetiger 5, but the description indicated that they were twice as long. Based on the available data and by following the key below, the Venezuelan specimens resemble N. splendida Grube, 1840, by having anterior notopodial ligules digitate, median and posterior chaetigers with ventral ligules longer than neuracicular ligules and pharyngeal areas VII-VIII with 2-3 transverse rows of paragnaths. Their main differences are in the prostomial shape and the pharyngeal paragnath numbers in area II. In the specimens reported by Liñero-Arana & Reyes-Vázquez (1979) the anterior prostomial lobe is wider than long, and there are about 30 paragnaths in area II, whereas in N. splendida the anterior prostomial lobe is 2 × as long as wide, and there are about 22 paragnaths in area II.

Distribution
Venezuela, Gulf of Cariaco, in intertidal rocky shores.

Diagnosis
Nereis with posterior eyes partially covered by anterior margin of tentacular belt; tentacular belt 1.5 × as long as first chaetiger; tentacular cirri long, reaching chaetigers 7-8; pharyngeal areas VII-VIII with 5 large paragnaths in a single row; posterior chatigers with dorsal and median ligules of similar width.

Etymology
This species is named after Dr Tarik Meziane, curator of polychaetes at the Muséum national d'histoire naturelle, Paris, in recognition of his curatorial activities and especially as a means of gratitude for his long-standing support of our research activities.
Prostomium. Slightly longer than wide; eyes blackish, of similar size, anterior eyes oval, longer than wide, about ⅙ of prostomial width, slightly more distant from each other than posterior eyes (Fig. 18B). Antennae terminal, without gap between them, tips reaching palpophore ends. Palpophores 2 × as long as wide; palpostyles rounded, small. Tentacular belt. 1.5 × as long as first chaetiger; anterior margin partially covering posterior eyes. Tentacular cirri corrugate to articulate, tips broken, posterior dorsal cirri lost, remaining ones reaching chaetiger 2.

Variation
The paratypes are anterior fragments, regarded as mature females due to the presence of oocytes in their coelom (Fig. 19), as damaged as in the holotype. Body with dorsum brownish, especially along anterior third of body ( Fig. 19A-B, E), and parapodial ligules with brownish glandular regions from chaetigers 3-4, often darker in posterior chaetigers. They are 12-23 mm long, 1-2 mm wide, with 61-62 chaetigers; all parapodial ligules with dark brown glands, many chaetae broken. The left posterior dorsal tentacular cirri in the largest paratype are broken, reaching chaetiger 6 (Fig. 19E). The right one is longer, but it was broken during manipulation, such that tentacular cirri might reach chaetiger 8. The tentacular belt partially covers the posterior eyes (Fig. 19B, F), and the eyes are of similar size, with the posterior eyes slightly closer to each other than the anterior ones. Both paratypes with oocytes from about chaetiger 30 (Fig. 19C), although they can appear from chaetiger 18 (MNHN 372-T28), and continue throughout most segments, even in the smallest paratype (Fig. 19D); each oocyte about 150 μm in diameter.
Another mature female (MNHN 372-T28), defined as such by the presence of oocytes in its coelom, is 12 mm long, 1.2 mm wide, with 72 chaetigers, and has an almost complete histolysis such that most of the coelomic space is filled with oocytes ( Fig. 20A), first visible from chaetiger 8-9, but more abundant from chaetiger 18, each about 150 μm in diameter. Tentacular cirri articulate, broken. Antennae slightly longer than palps. the parapodia do not show any trace of epitokal transformation.

Remarks
Nereis mezianei sp. nov. has been recorded as "N. falsa" de Quatrefages, 1866 from the Gulf of Guinea, herein regarded as resembling N. splendida instead. However, these two species differ in relevant pharyngeal and parapodial features, and the main difference is that N. mezianei sp. nov. has a single row of paragnaths in areas VII-VIII, whereas N. splendida has 2-3 rows. Furthermore, because the posterior eyes are partially covered by the anterior margin of the tentacular belt, N. mezianei sp. nov. groups with N. marginata Grube & Örsted in Grube, 1857 from the Caribbean Sea, and with N. rava Ehlers, 1868 from the Mediterranean Sea. However, N. mezianei sp. nov. can be separated from these two other species because its tentacular cirri are longer. Nevertheless, N. mezianei sp. nov. approaches N. rava by having dorsal and median ligules in the posterior parapodia of similar width. Although the depth of the sampling site was not given in the original description of N. rava, the type locality (Gulf of Quarnero) has a maximaum depth of 128 m. There are at least three different morphs regarded as belonging to N. rava in the Mediterranean region, and it has been reported from sediments in depths of 130-1685 m (Fauvel 1914: 169). Herein, we follow Gravina et al. (2015) regarding the specific features of N. rava. Nereis mezianei sp. nov. and N. rava have corrugate or articulate tentacular cirri. They especially differ in pigmentation pattern, in the relative size of tentacular cirri and in some parapodial features. In N. mezianei sp. nov., anterior segments have a solid brownish pigmentation, their longest tentacular cirri reach chaetigers 7-8, and the ventral ligule is longer than the neuracicular ligule, whereas in N. rava, anterior segments have two transverse brownish bands, their longest tentacular cirri reach chaetigers 2-3, and the neuracicular ligule is as long as the ventral ligule. Another important difference relies on mature females. In N. mezianei sp. nov., there is no metamorphosis or parapodial modification in mature females, whereas female heteronereis are known for N. rava (Núñez 2004: 374-375).
Nereis mezianei sp. nov. also resembles N. caparti Fauvel, 1953 described from off Namibia, because they have the longest tentacular cirri reaching chaetiger 7-8, parapodial ligules tapered and pharynx areas VII-VIII with a single row of paragnaths. They differ, however, because in N. mezianei sp. nov. the posterior eyes are partially covered by the anterior margin of first segment, notopodial ligules are of similar length and width, and compound notofalcigers have spinulose blades, whereas in N. caparti, posterior eyes are fully exposed, dorsal ligules are progressively longer than median ones, and the blades of the notofalcigers are smooth.

Remarks
Nereis perivisceralis Claparède, 1868 is not included in the key because it has notopodial homogomph falcigers with blades with 1-2 large basal denticles, instead of a series of spines (Gravina et al. 2015: 152, fig. 4).
On the other hand, Nereis rava Ehlers, 1868 apparently has three different body patterns in the Mediterranean, especially regarding the anterior end features. The original illustration by Ehlers (1868: pl. 21 fig. 10) was repeated by Fauvel (1923: 340, fig. 131e), and it shows the anterior margin of the tentacular belt as crenulated, not covering the posterior eyes, the anterior eyes are not round, but oval with their longest axis horizontal, and the tentacular cirri are long, reaching about chaetiger 6. Núñez (2004: fig. 138a) illustrated an alternative anterior end pattern: the anterior margin of the tentacular belt is smooth, not covering the posterior eyes, the anterior eyes are round, and the tentacular cirri are short, reaching about chaetiger 2-3, although they were described as reaching chaetiger 8 (Núñez 2004: 373).
The third pattern was illustrated by Gravina et al. (2015: 158, fig. 8e): they show the anterior margin of the tentacular belt as smooth, partially covering the posterior eyes, the anterior eyes are round, and the tentacular cirri are very short, barely reaching chaetiger 2. These differences might be explained by the use of different fixatives, ethanol by Ehlers, formaline by the others, but in the key above we follow the characterization of Gravina et al. (2015) for this Mediterranean species.

Discussion
The widespread confusion regarding what Nereis falsa de Quatrefages, 1866 is can be partially solved if it is regarded as belonging in Hediste Malmgren, 1867, and probably as a junior synonym of H. diversicolor (Müller, 1776). However, with the indication of a distinct species in the Black Sea, the name N. falsa would be available for it once it is accepted as a valid species. This conclusion was reached early, but influential scientists like McIntosh and Fauvel overlooked it. As a means to encourage the solution of this problem, some notes on the taxonomy of Hediste and a key to identify species of Hediste are also included.
The alternative delineation by Fauvel (1914Fauvel ( , 1923 of N. falsa was widely used, and eventually it was further expanded to include other species as junior synonyms. However, this species-group name must be changed. The next available name, N. splendida Grube, 1840, is an alternative for what has been regarded as N. falsa de Quatrefages, 1866 from the Mediterranean and adjacent eastern Atlantic region. A neotype has been proposed, and atoke and epitoke species have been fully described and illustrated.
Most of the species previously regarded as junior synonyms of "N. falsa" deserve to be reinstated, and one, Nereis lunulata Ehlers, 1901 stat. nov., is elevated to species rank. Furthermore, the expansion of "N. falsa" resulted in the inclusion of other morphological patterns, including some species having a single row of paragnaths on pharyngeal areas VII-VIII. These species would not strictly belong to the group, but were included in this contribution and in the key to species, to emphasize their resemblances and differences.
The grouping of species under N. falsa, now Nereis splendida, is restricted to encompass a homogeneous set of species including N. splendida, N. callaona, N. lucipeta, N. lunulata stat. nov. and N. occidentalis. They share the presence of anterior parapodia with blunt ligules, becoming blunt conical to digitate in median and posterior parapodia, as well as having dorsal cirri or notopodia of similar proportions along the body or a similar paragnath pattern on the pharynx. The pharynx has conical paragnaths in both maxillary rings, but none in area V, and areas VII-VIII have 2-3 rows of paragnaths. The notopodial homogomph falcigers have blades spinulose, tips incurved, and well defined tendons.
Harris for the amenities given during the visit at the LACM. VMCV received funding from CONACYT and ECOSUR. Maestros Drs Masanori Sato and Torkild Bakken, and Rudy C.A.M. Jocqué carefully read a previous draft and recommended many positive means to improve this contribution. This final presentation was accomplished by the careful reading and editing by Danny Eibye-Jacobsen.