A new species of Chaetopterus (Annelida: Chaetopteridae) from eastern Canada, with a redescription of Chaetopterus norvegicus M. Sars, 1835

Chaetopterus is a globally distributed genus of marine Annelida with a long history of taxonomic confusion. Here, we describe Chaetopterus bruneli sp. nov. from a depth of 350 m in the St. Lawrence Estuary, eastern Canada. The new species represents the northernmost record for Chaetopterus in the western Atlantic to date. The similar European species Chaetopterus norvegicus M. Sars, 1835 is resurrected from long-standing synonymy and redescribed from type material, and a lectotype is designated.


Introduction
Chaetopteridae Audouin & Milne-Edwards, 1833 is a globally distributed family of marine Annelida Lamarck, 1809, and currently comprises 73 valid species in four genera (Britayev & Martin 2019;Read & Fauchald 2019;Tilic & Rouse 2020). The genus Chaetopterus Audouin & Milne-Edwards, 1833 was established for C. pergamentaceus Cuvier, 1830, a large, infaunal, tube-dwelling annelid described from the Caribbean Sea. Members of the genus Chaetopterus have the most extreme notopodial specialization among chaetopterids, with all benthic species sharing a highly conserved complement of specialized, modifi ed notopodial structures for single mucus net suspension feeding in the middle body region. The uniformity of their unusually tagmatized body plan, coupled with a fl exible capacity for anterior and posterior regeneration (Berrill 1928), contributes to diffi culty in distinguishing among species on the basis of morphology alone.
The genus Chaetopterus was fi rst revised by Joyeux-Laffuie (1890), who regarded most European representatives as belonging to Chaetopterus variopedatus (Renier 1804). Subsequent authors expanded this view to eventually place all species of Chaetopterus from the North Atlantic, Indo-Pacifi c, and Antarctic under C. variopedatus, as a single, highly variable and cosmopolitan species (Crossland 1904;de St. Joseph 1894;Fauvel 1927). Recent phylogenetic studies provide evidence that the genus is far more diverse than refl ected in the current taxonomy (Osborn et al. 2007;Zhang et al. 2015;Moore et al. 2017). While several Pacifi c species have been resurrected from synonymy (Nishi 2001), most species remain synonymized with C. variopedatus.
There are nine nominal species of Chaetopterus described from North Atlantic and Mediterranean waters; however, only C. pergamentaceus and C. variopedatus are currently considered valid (Read & Fauchald 2019). While both C. pergamentaceus and C. variopedatus are large, infaunal species, there are several epifaunal species names currently synonymized under C. variopedatus. One of these, Chaetopterus norvegicus M. Sars, 1835, was described from the Bergen fjord in western Norway, and is a longstanding junior synonym of C. variopedatus (Joyeux-Laffuie 1890; de St. Joseph 1894;Fauvel 1927). Despite this status, some recent workers have published records that recognized C. norvegicus from the northeastern Atlantic, from western Sweden in the east (GBIF 2019) and west to the Faroe Islands Shelf at 250 m (Jensen & Frederiksen 1992).
In the western North Atlantic, Chaetopterus pergamentaceus has been recorded as far north as Cape Cod (GBIF 2019). During benthic sampling of the St. Lawrence Estuary in eastern Canada in 1991 and 1992, 18 specimens of a very small, epibenthic Chaetopterus were found on soft substrates at a depth of 350 m, representing the northernmost record of the genus in the western North Atlantic. These specimens most closely resemble C. norvegicus; however, several morphological and ecological features distinguish these taxa. The Canadian specimens are newly described below as Chaetopterus bruneli sp. nov. Chaetopterus norvegicus is resurrected from synonymy and redescribed from original syntype material, and a lectotype is designated.

Collections
The holotype and 17 paratypes of Chaetopterus bruneli sp. nov. are deposited in the annelid collections of the Canadian Museum of Nature, Ottawa (18 specimens, CMNA 2015-0001 to CMNA 2015-0018). These specimens were collected by the second author, using a 0.2 m 2 box corer, from fi ne silt and sand sediments at a depth of 350 m in the St. Lawrence Estuary (Station 23, 48°42.20′ N, 68°33.98′ W), during seven sampling events from February 1991 to October 1992. A total of 52 samples were brought up to the surface, undisturbed, and transported to the laboratory as described in Silverberg et al. (1995). There, the benthic communities were maintained alive in mesocosms where specimens of Chaetopterus could be observed under a stereo microscope. Eighteen specimens were maintained alive during the mesocosm experiments and relaxed by gradually adding drops of 70% ethanol before fi xation in a 4% buffered formaldehyde solution, then washed in freshwater and transferred to 70% ethanol for long-term preservation.

Terminology
The chaetopterid body plan is unique among annelids for its division into three distinct, functionally specialized body regions (tagmata). Following Crossland (1904), we refer to these anterior, middle and posterior tagmata as A, B and C, respectively. Counting of chaetigers is done within each tagma; e.g., A1-A9 refer to chaetae-bearing segments 1-9 of the anterior tagma. A-last refers to the last chaetiger in tagma A, as the number of segments can vary within this tagma.

Morphological observations
Preserved specimens were examined, measured, and photographed at 7.1-25X magnifi cation using a Leica stereo microscope mounted with a Nikon D7000 DSLR camera. To characterize notochaetal features, A4 parapodia were dissected and mounted whole on glass microscope slides in Canada balsam and photographed using the camera above mounted on a Leica compound microscope. Uncini-bearing tissues were sampled from A9 neuropodia (if present), the anterior and posterior neuropodial lobes of B1, ventral lateral tori of B3, and ventral and lateral lobes of C1. Uncini were teased away from surrounding tissue using fi ne needles and mounted on microscope slides in Euparal. Measurement data were collected from compound light micrographs. Drawings of specimens were made from photographs to illustrate selected structures for comparison.

Additional known material
The following specimens were examined and identifi ed as Chaetopterus norvegicus by M.E. Petersen; however, their current location was not verifi ed or ascertained. We include them here to contribute additional distributional information for this species:

Description
Based mostly on lectotype and paralectotypes. Uncini data based on LACM specimens, and their tooth counts and measurements are given in Table 1. GROSS MORPHOLOGY AND PRESEGMENTAL STRUCTURES. Small to medium-sized epibenthic Chaetopterus, 26 mm total body length for 26 chaetigers in lectotype, segmental formula 9A+5B+7-12C. Peristomium ventrally broad, horseshoe-shaped in dorsal view, with broad dorsolateral lobes that sometimes obscure A1 notopodia, sometimes with medium-brown pigment on dorsal surface. Grooved palps short, thin and fi liform, inserted at dorsal inner margins of peristomium, 1.5 mm in length (n = 5). Eyes small, faint black spots positioned laterally near the outer base of the palps and obscured by the laterodorsal lobes of the peristomium. REGION A. Anterior region with 9 segments (Fig. 1A); 4.9 mm mean length (range 4.5-6 mm, n = 6) and 4.5 mm mean width (range 3-6 mm, n = 6), slightly longer than wide or as wide as long; ventral surface of A with broad, rectangular glandular shield (Figs 1B, 3A). Region A notopodia shortest at A1 or A4, increasing from A4 to a maximum at A6 and decreasing in length again to segment A9; A4 notopodia shorter than neighboring notopodia. Small swellings not visible at dorsal base of A notopodia. Segment A4 notopodia bearing 5-10 relatively large apically blunt, light brown, cutting chaetae, with a distinct ventral tooth, on the ventral side of the notopodia (Fig. 1A). Other notopodia and the distal side of A4 notopodia bear lanceolate and simple chaetae. Region A chaetigers uniramous except the last, A9, also with fan-shaped neuropodia in 4 of 5 specimens; mean width 1.3 mm (range 1-1.5 mm, n = 4) and furnished with uncini on posterior margin (Figs 1B, 3A). A9 uncini asymmetrically pyriform to D-shaped, apically blunt and pointed at base, widest at middle or slightly below, with a curved proximal margin (Fig. 1D).
REGION B. Middle body region 10 mm in length in complete specimen. B1 with long aliform notopodia, 6 mm mean length (range 5-7 mm, n = 6), reaching anteriorly to the peristomium ( Fig. 1A-B). B1 and B2 neuropodia bilobed, with four completely unfused, discrete lobes, with uncini on distal lobe margins (Figs 1B, 3A). Anterior pair of neuropodial lobes in B1 narrow and situated medially (Figs 1B, 3A); uncini ovate to D-shaped, sometimes slightly pyriform, apically blunt and pointed or rounded at base, widest at middle or slightly below (Fig. 1E). Posterior neuropodial lobes of B1 broader than anterior and situated laterally (Figs 1B, 3A); uncini asymmetrically pyriform to ovate, apically blunt and pointed or rounded at base, widest at middle or slightly below, with a curved proximal margin (Fig. 1F). Segment B2 relatively short, 5 mm in length in one posterior fragment specimen; neuropodia bilobed with four completely unfused, discrete lobes; anterior pair of neuropodial lobes situated more laterally than posterior pair. Neuropodia of B3-B5 with a single pair of short, medially fused and ridge-like lobes, bearing uncini on posterior margins. B3 uncini of piston tori ovate to D-shaped, apically blunt and pointed at base, widest at middle, with straight proximal margin (Fig. 1G). B3 ventral lobe uncini asymmetrically pyriform to D-shaped, apically blunt and pointed at base, widest at middle or slightly below, with straight proximal margin (Fig. 1H).
REGION C. Posterior body region mean length 6 mm (range 2-10 mm, n = 4), with 7-12 chaetigers. Region C notopodia long and thin, tapering evenly to apex; C1 notopodia mean length 3.3 mm (range 2.5-4.5 mm, n = 4). Neuropodia bilobed, ventral lobes medially unfused, C1 ventral neuropodial lobes broader than those in succeeding segments; lateral lobes of C neuropodia lacking dorsal and ventral cirri, one specimen with small dorsal infl ations on dorsal margin of lateral lobes. Both neuropodial lobes bear a row of uncini on distal margin. C1 lateral lobe uncini asymmetrically pyriform to D-shaped, apically blunt and pointed at base, widest at middle or slightly below, with straight or curved proximal margin (Fig. 1I). C1 ventral lobe uncini long D-shaped, apically blunt and pointed or rounded at base, widest at middle, sometimes with marked curvature toward proximal side (Fig. 1J). TUBE. Tube straight or irregularly bent, pale cream-white and paper-like, very thin and delicate, composed of laminated proteinaceous material, without externally affi xed sediment (Fig. 1C).

Ecology and distribution
Chaetopterus norvegicus is an epifaunal species found on rocky substrates, sometimes among the branches of the  (Malmgren 1867); not known from the Baltic Sea.

Remarks
The lectotype is delicate and in fair condition, and represents the sole complete specimen within the original syntype lot. The paralectotypes consist of the remaining original syntypes and are in a similar condition. To avoid destructive sampling of the original type material, we examined uncini from a Norwegian specimen in the collections of the LACM. The external morphological features of this specimen agree with those of the lectotype and paralectotypes. Three additional specimens of Chaetopterus norvegicus from Denmark and western Sweden were examined and fi gured in detail by the late M.E. Petersen (see Additional known material, above). The present location of these specimens is unknown, but the notes and drawings agree well with the features present in the type material.
Chaetopterus norvegicus M. Sars, 1835 was the second species described within the genus Chaetopterus.
The original description of Chaetopterus norvegicus is detailed and includes illustrations; however, Sars mistook the dorsal side for the ventral, and included segment B1 in the anterior body region, as fi rst remarked by Quatrefages (1866 Additionally, several morphological features distinguish between these species. While the original description of C. variopedatus is brief and without fi gures (Renier 1804), the examination of six specimens of C. variopedatus from the Mediterranean and Adriatic Seas (USNM 5102, UF 4254 to UF 4258) revealed several characters clearly distinguishing these species. Chaetopterus variopedatus has a body size of 7-14 cm, medially fused, bilobed, sucker-like neuropodia in segments B1 and B2, and over 20 segments in tagma C. Furthermore, C. variopedatus secretes a large (~30 cm), infaunal tube of heavily laminated, fl exible, brown parchment-like material covered externally in coarse sediment. Chaetopterus norvegicus, in contrast, has a body size of approximately 2-3 cm, distinctive unfused bilobed neuropodia in segments B1 and B2, 7-12 chaetigers in tagma C, and inhabits a relatively small, stiff, delicate and somewhat translucent white tube, and is epifaunal on hard substrates. The unusual unfused neuropodia of B1 in C. norvegicus contrast with the sucker-like, fused neuropodia found in C. variopedatus and other species of Chaetopterus (Fig. 3). These strong genetic, morphological and ecological differences warrant the resurrection of C. norvegicus as a valid species. Mean and range values are given in parentheses for the holotype and six paratypes. Uncini data are based on paratype specimen CMNA 2015-0018, and their tooth counts and measurements are given in Table 1. GROSS MORPHOLOGY AND PRESEGMENTAL STRUCTURES. Small, epibenthic Chaetopterus, 10.5 mm total body length for 19 chaetigers (mean 11.6 mm, range 8.0-15.0 mm, n = 7); segmental formula 9-10A+5B+5-6C. Peristomium ventrally narrow, horseshoe-shaped in dorsal view, with narrow dorsolateral lobes that sometimes obscure A1 notopodia, without pigment in preserved specimens. Grooved palps short and stout, inserted at dorsal inner margins of peristomium, 2.1 mm in length (mean 2.1 mm, range 2.0-2.5 mm). Eyes absent.
REGION B. Middle body region 6 mm in length (mean 5.9 mm, range 4.5-7.0 mm, n = 7). B1 with long aliform notopodia, approximately the length of region A (2.0-4.0 mm), reaching anteriorly to the peristomium ( Fig. 2A). B1 and B2 neuropodia bilobed, with four completely unfused, discrete lobes, with uncini on distal lobe margins (Figs 2B, 3B). Anterior pair of neuropodial lobes in B1 narrow and situated medially (Figs 2B, 3B); uncini pyriform to D-shaped, apically rounded and pointed or rounded at base, widest slightly below middle (Fig. 2E). Posterior neuropodial lobes of B1 broader than anterior lobes and situated laterally (Figs 2B, 3B), uncini ellipsoid to D-shaped, apically blunt and rounded and pointed at base, widest at middle or slightly below (Fig. 2F). Segment B2 short relative to total body length; neuropodia bilobed with four completely unfused, discrete lobes; anterior pair of lobes situated more laterally than posterior pair of lobes (Fig. 2B). Neuropodia of B3-B5 each with a single pair of well-developed, unfused lobes, bearing uncini on posterior margins. Uncini of B3 piston tori ellipsoid to pyriform, apically rounded and rounded or pointed at base, widest at middle, proximal margin sometimes with a medial notch (Fig. 2G). B3 ventral lobe uncini ellipsoid to pyriform, apically blunt and pointed at base, widest at middle or slightly below, proximal margin with a medial notch (Fig. 2H).
TUBE. Tube short and curved, pale cream to tan, thin and composed of laminated proteinaceous material, externally covered in mud (Fig. 2D).

Ecology and distribution
The new species is known only from the type locality in the lower St. Lawrence Estuary, epibenthic on fi ne sediments at a depth of 350 m. Tubes resembling those of this species were also observed on bottom photographs from stations 18 and 20, at 390 and 331 m depth, respectively (Belley et al. 2010).   In the late spring to early autumn of 1990 and 1991, several physico-chemical and biological measures were studied near the type locality of C. bruneli sp. nov. in the lower St. Lawrence Estuary (Station 26 in Savenkoff et al. 1994). These measurements were collected around the same time as some of the type specimens presented here. At that time, the type locality was in an upwelling area of the Laurentian trough, characterized by moderate productivity, low vertical stratifi cation, higher salinity, and lower temperatures compared to the more productive plume region downstream (Savenkoff et al. 1994). The bottom water in the lower St. Lawrence Estuary is now being reported as increasingly and persistently hypoxic in recent years (Belley et al. 2010;Gilbert et al. 2005), which may explain why attempts to recollect this species from the type locality in September 2015 and August 2020 proved unsuccessful. Future benthic surveys of the St. Lawrence Estuary and Gulf of St. Lawrence may provide revised information about the distribution of this species.

Remarks
Chaetopterus bruneli sp. nov. is likely closely related to C. norvegicus. A summary of morphological features for both species is given in Tables 1 and 2. These species are unusual among described species of Chaetopterus for having unfused neuropodial lobes in segments B1 and B2 (see Discussion). Chaetopterus bruneli sp. nov. differs from C. norvegicus by its smaller body size, its lack of neuropodia in tagma A, and by its club-shaped notopodia and fewer chaetigers in tagma C. Chaetopterus bruneli sp. nov. builds mud-covered tubes on the surfaces of fi ne sediments at upper continental slope depths, whereas C. norvegicus is found in rocky areas on hard substrates at continental shelf depths, with little sediment on the external surface of the tubes.
Some characters distinguishing these species may vary ontogenetically in Chaetopterus, including the body size and the number of segments in tagma C. There is, however, evidence from studies on the development of Chaetopterus that the neuropodia in the anterior tagma are present one day postmetamorphosis in a species that bears these structures as adults (Irvine et al. 1999: fi g. 8b). Thus, the absence of neuropodia in tagma A should be reliable for distinguishing post-settlement individuals. While no mature gonads were observed in the preserved material of C. bruneli sp. nov., long-term preservation in alcohol can sometimes make distinguishing fat deposits from gametes diffi cult in specimens of Chaetopterus. The specimens of C. bruneli sp. nov. described here were collected over several seasons over two years and do not vary substantially in their morphology, nor in size. Genetic evidence is not available, as the specimens were preserved in formalin and no new material is available for tissue collection. The morphological and ecological differences between these species outlined above are substantial enough to provide suffi cient grounds for the establishment of a new species.
Only one other described species of Chaetopterus, C. longipes Crossland, 1904, lacks neuropodia in tagma A (Fig. 3C). Chaetopterus longipes was originally described from the Maldive Archipelago and was redescribed from Japanese material (Nishi 1996). Phylogenetic analyses suggest that C. longipes may represent a species complex distributed in both the tropical Indo-Pacifi c and Caribbean (Moore et al. 2017). Like C. norvegicus, C. longipes builds epibenthic tubes; these, however, occur gregariously and are embedded within elevated crevices on rocky coral reef substrates or found attached to the undersides of rocks rather than on the surface of soft sediments (Nishi 1996(Nishi , 2001). Neither C. bruneli sp. nov. nor C. norvegicus are known to occur gregariously. C. bruneli sp. nov. lacks the fused, suckerlike neuropodia of segments B1 and B2 that are present in C. longipes and in most other species of Chaetopterus (Fig. 3). There are no records of any Chaetopterus species lacking neuropodia in tagma A north of 33º N latitude. The morphological and ecological differences among these species warrant the establishment of a distinct taxon, C. bruneli sp. nov.
Chaetopterus bruneli sp. nov. is the northernmost record of the genus in the western Atlantic. Prior to this study, the northernmost western Atlantic records belong to Chaetopterus pergamentaceus Cuvier, 1830 from Woods Hole, Massachussetts, USA, a large, widespread, infaunal species which was originally described from the Caribbean Sea. There are currently 18 valid species within the genus Chaetopterus (Read & Fauchald 2019;Tilic & Rouse 2020); however, most of these were either recently described or were resurrected in a relatively recent partial revision of Pacifi c species (Nishi 2001). The resurrection of C. norvegicus presented here is a fi rst step toward revising the taxonomy of Atlantic species of Chaetopterus. Fourteen nominal taxa remain in synonymy under the 'cosmopolitan' species C. variopedatus, originally described from the Adriatic Sea. Phylogenetic studies have shown that the true diversity of the genus Chaetopterus is under-represented in the current taxonomy (Osborn et al. 2007;Zhang et al. 2015;Moore et al. 2017). Forthcoming work will include a comprehensive revision of the genus to address the long-standing taxonomic issues.