New Spirinia and Stygodesmodora species (Nematoda, Spiriniinae) from the Southwest Pacific, and a revision of the related genera Spirinia, Chromaspirina and Perspiria

Two new species of the family Desmodoridae are described from the upper continental slope of New Zealand, Southwest Pacific, and the genera Spirinia, Chromaspirina and Perspiria are revised. Spirinia verecunda sp. nov. is characterised by a short, stout body, cuticle covered in minute, hair-like structures, unispiral amphideal aperture and cryptospiral amphideal fovea, buccal cavity with small dorsal tooth and minute subventral teeth, eight oblong glands surrounding anterior portion of pharynx, large sperm cells, spicules with weak capitulum, and the absence of precloacal supplements. Stygodesmodora confusa sp. nov. is characterised by a relatively short body, spiral amphids with 1.2– 1.4 turns, cephalic setae situated at or slightly posterior to mid-level of amphid, and males with four precloacal supplements consisting of short setae on wide bases. Like other species of the genus, S. confusa sp. nov. is characterised by an annulated head region, but in some specimens the cuticle annulations are restricted to the dorsal and ventral sides of the head. S. confusa sp. nov. shows similarities with species of other desmodorid genera (i.e., Echinodesmodora, Bolbonema), but can be differentiated from them by the presence of an annulated head region and amphideal plates. The genera Spirinia, Chromaspirina and Perspiria have very similar morphologies and differ mainly in the size and structure of the buccal cavity (Spirinia vs Chromaspirina) or the shape of the tail and placement of the amphids relative to the cuticle annulations (Spirinia vs Perspiria); their diagnoses are clarified and some nomenclatural changes are proposed to eliminate overlap in the definitions of these genera.

the head region, amphids, pharynx, and male copulatory apparatus. The main distinction between the two genera is the shape of the buccal cavity: Spirinia is characterised by a narrow and lightly cuticularised buccal cavity with no or a small dorsal tooth and no or minute subventral teeth, whereas Chromaspirina is characterised by a more heavily cuticularised, medium to large buccal cavity with a large dorsal tooth and smaller subventral teeth. A third genus, Perspiria Wieser & Hopper, 1967, is also similar to Spirinia and differs from the latter in having a conico-cylindrical to fi liform tail and by the amphids not completely surrounded by body annulations. Species of these three genera show considerable overlap in the above-mentioned morphological characteristics, however, and the boundaries between them have become somewhat blurred. Here, we describe S. verecunda sp. nov. from the Chatham Rise crest (350 m water depth) on the continental margin of New Zealand, and we propose several nomenclatural changes to species of Spirinia and Chromaspirina to allow a more consistent distinction between the genera based on buccal morphology. Several nomenclatural changes are also suggested for the genus Perspiria to refl ect differences in tail shape and body annulations of the head region between the latter genus and Spirinia.
Stygodesmodora Blome, 1982 is a relatively uncommon genus comprising only two species: S. bacillicauda (Gerlach, 1963) and S. epixantha Blome, 1982. These species were described from shallow sandy sediments in the Indian Ocean and North Sea, respectively. Here a third species, S. confusa sp. nov., is described from the continental margin of New Zealand (350 and 686 m water depth); it is the fi rst species of the genus to be described from the deep sea.

Material and Methods
Samples for species descriptions were obtained from the Chatham Rise and southern Hikurangi margin, Southwest Pacifi c. The Chatham Rise is a submarine ridge that extends eastwards from the South Island of New Zealand, over water depths ranging from ca. 250 to 3000 m. The highly productive Subtropical Front (STF) is geographically constrained near the southern fl ank of the rise at around 44° S (Murphy et al. 2001). The southern Hikurangi margin lies on the south-eastern extremity of the North Island of New Zealand and is situated north of the Chatham Rise. Samples were collected at two sites: one situated near the head of a canyon on the southern Hikurangi margin during National Institute of Water and Atmospheric Research (NIWA) cruise TAN1004 (station 92, 686 m water depth, 41.8921° S, 174.6347° E), and one at an open slope site located near the central Chatham Rise crest during NIWA cruise TAN1103 (station 69, 350 m water depth; 43.331° S, 178.288° E). Sediment samples were collected using an Ocean Instruments MC-800A multicorer (MUC; core internal diameter = 9.52 cm). Each sample consisted of one subcore of internal diameter 26 mm taken to a depth of 5 cm. Samples were fi xed in 10% formalin and stained with Rose Bengal. Samples were subsequently rinsed on a 1 mm sieve to remove large particles and on a 45 m sieve to retain nematodes. Nematodes were extracted from the remaining sediments by Ludox fl otation and transferred to pure glycerol (Somerfi eld & Warwick 1996). Species descriptions were made from glycerol mounts using differential interference contrast microscopy, and drawings were made with the aid of a camera lucida. Specimens for scanning electron microscopy (SEM) were transferred to a 2% glutaraldehyde solution with sodium cacodylate buffer overnight, then transferred to a 4% osmium tetroxide solution for 2 hours. They were then gradually transferred to pure ethanol using a graded ethanol series, critical point dried, and mounted onto stubs before being coated with gold using a sputter coater. Observations were made using a Hitachi TM3000 tabletop SEM at high vacuum mode.
All measurements are in m, and all curved structures are measured along the arc. Type specimens are held in the NIWA Invertebrate Collection, Wellington, New Zealand. Abbreviations in the text are as follows: a = body length/maximum body diameter abd = anal body diameter b = body length/oesophagus length c = body length/tail length cbd = corresponding body diameter %V = vulva distance from anterior end of body × 100/total body length.
Emended diagnosis (modifi ed from Lorenzen 1981 andSmol 2006) Member of Desmodoroidea. Cuticle with coarse annulations, at least in anterior body region, or striated. Specialised somatic setae, such as adhesion tubes (Draconematidae) or ambulatory setae (Epsilonematidae) not present. Amphideal fovea usually spiral, unispiral, cryptospiral, or cryptocircular, and sometimes loop-or pore-shaped. Buccal cavity with small to large dorsal tooth and smaller or indistinct subventral teeth. Pharynx usually with round muscular posterior bulb, with or without cuticularised lumen; sometimes bulb is pyriform, elongated, or indistinct. Gubernaculum without dorsal apophyses. Males usually monorchic, except in Onepunema Leduc & Verschelde, 2013 (diorchic). Vulva usually posterior to middle of body. Tail conical. Armenteros et al. (2014) recently argued that the genus Onepunema Leduc & Verschelde, 2013 is more closely related to the Microlaimidae than to the Desmodoridae because of the presence of two testes (a feature common in the former but not found in the latter). The Microlaimidae, however, are characterised by the presence of outstretched ovaries, while Onepunema possesses refl exed ovaries, a characteristic of the Desmodoridae. This trait, in combination with the presence of a cephalic capsule in Onepunema (an important characteristic for the classifi cation of supraspecifi c taxa within the Desmodorida and never found within the Microlaimoidea) suggests closer affi nities with the Desmodoridae (and Desmodorinae in particular) than with the Microlaimidae. Armenteros et al. (2014: 26) incorrectly stated that "… the presence of refl exed ovaries […] suggest a relationship with Bolbolaimus Cobb, 1920, Calomicrolaimus Lorenzen, 1976and Microlaimus de Man, 1880. Refl exed ovaries are not found in any of these genera; perhaps Bolbolaimus was confused with Bolbonema Cobb, 1920(see comments under Chromaspirina longisetosa Jensen, 1985, which belongs to the Desmodoridae due to the presence of refl exed ovaries and a globular cephalic capsule.

European Journal of Taxonomy 118: 1-25 (2015)
Diagnosis (from Decraemer & Smol 2006) Member of Desmodoridae. Body cuticle with fi ne annulations. Head not demarcated as a cephalic capsule. Amphideal fovea usually a simple spiral. Buccal cavity small or large, with a distinct or a minute dorsal tooth; two small ventrosublateral teeth may be present or absent.

Differential diagnosis
This subfamily is similar to the Desmodorinae but can be differentiated from the latter by the absence of a head capsule.

Remarks
The tribe Spirinacea was originally established by Chitwood (1936), before being raised to subfamily, family and superfamily rank by De Coninck (1965). According to the Principle of Coordination (ICZN, 1999, Article 36), "a name established for a taxon at any rank in the family group is deemed to have been simultaneously established for nominal taxa at all other ranks in the family group; (…). The name has the same authorship and date at every rank." The appropriate authorship for Spiriniinae should therefore be attributed to Chitwood (1936), and not Gerlach & Murphy (1965), as is often done (e.g., Armenteros et al. 2014).
Valid genera Armenteros et al. 2014) Alaimonema Cobb, 1920Chromaspirina Filipjev, 1918Metachromadora Filipjev, 1918Onyx Cobb, 1891Papillonema Verschelde et al., 1995Paradesmodora Schuurmans Stekhoven, 1950Parallelocoilas Boucher, 1975Perspiria Wieser & Hopper, 1967Polysigma Cobb, 1920Pseudometachromadora Timm, 1952Sigmophoranema Hope & Murphy, 1972Spirinia Gerlach, 1963Spirodesma Cavalcanti et al., 2009Stygodesmodora Blome, 1982 We provide emended diagnoses and updated lists of valid species for Chromaspirina, Spirinia, and Perspiria below to clarify the distinctions between them. These lists are based on the original and any subsequent descriptions; as many of the original descriptions (especially early ones) lack type material, we often had to rely on short descriptions and/or illustrations.
Chromaspirina rabosa (Gerlach, 1956). This species was originally described as Desmodora rabosa and later transferred to Chromaspirina by the same author (Gerlach 1963). Muthumbi et al. (1995) argued that the species should be left in the genus Desmodora because it has "… a well-developed head capsule with the amphids situated outside the rings." We note, however, that the cephalic setae are situated posterior to the amphids, and this species is therefore transferred to the genus Bolbonema. Thus, we propose the combination Bolbonema rabosum (Gerlach, 1956) comb. nov. with the synonyms Desmodora rabosa Gerlach, 1956 and Chromaspirina rabosa (Gerlach, 1956).

Species inquirenda
Perspiria sabulicola (Filipjev, 1918/1921) comb. nov. (synonym: Spirina sabulicola Filipjev, 1918/ 1921). This species was described with a 'long tail (length 4 × width)' and hence should be transferred to the genus Perspiria. However, as the species was described based on only one female, it is regarded as a species inquirenda.

Emended diagnosis
Robust body with rounded or conical head region and conical tail, fi ne body annulations. Annulated head region; body annulations normally completely surround the amphideal fovea, with few exceptions. Spiral amphideal fovea. Buccal cavity narrow, lightly cuticularised; no or small/inconspicuous dorsal tooth, no or minute subventral teeth. Pharynx with small pyriform, oval, or rounded posterior bulb without cuticularised lumen. Precloacal supplements usually absent. Short conical tail.

Valid species
Spirinia gerlachi (Luc & De Coninck, 1959). Main diagnostic characters: "Annulations beginning halfway down the lateral organ…long attenuated conical tail"; also clear in drawings (Luc & De Coninck 1959: fi g. 25). Despite the presence of an amphid only partially surrounded by cuticle annulations, this species is left within Spirinia because of the shape of the tail (conical), which is the primary trait for differentiating between Spirinia and Perspiria.
Spirinia gnaigeri Ott, 1977. Amphids almost entirely located within the body annulations in one male, but only the posterior half of another male's amphid is surrounded by body annulations (compare fi gs 42 and 43 in Ott 1977); however, as the species has a conical tail, it belongs within Spirinia.
S. guanabarensis (Maria et al., 2009) comb. nov. (synonym: Chromaspirina guanabarensis Maria et al., 2009). Main diagnostic characters: "Buccal cavity large with an acute dorsal tooth and two smaller ventrosublateral teeth." However, later in the text it is stated that: "Chromaspirina guanabarensis sp. nov. belongs to the group of species characterized by a poorly developed dorsal tooth." Drawings also show a small buccal cavity with a small dorsal tooth and minute subventral teeth (Maria et al. 2009: fi g. 1). Tail is conical. This species is therefore transferred to Spirinia.

S. laevis
S. okemwai (Muthumbi et al., 1995) comb. nov. (synonym: Chromaspirina okemwai Muthumbi et al., 1995). We studied the type material, which shows that this species has a cylindrical pharynx with only a slightly swollen terminal bulb, whose shape cannot be described. The teeth are diffi cult to distinguish and hence cannot be called 'large' or 'distinct'; therefore, we transfer this species to the genus Spirinia.

Species inquirendae
Spirinia granulata (Allgén, 1929) comb. nov. (synonym: Spirina granulata Allgén, 1929). This species was described based on two juveniles only, with very poor drawings and inadequate descriptions. Hence, we have to regard this species as species inquirenda.
S. paucispira (Schuurmans Stekhoven, 1950) comb. nov. (synonym: Chromaspirina paucispira Schuurmans Stekhoven, 1950. This species was considered species inquirenda by Wieser & Hopper (1967) and Muthumbi et al. (1995), because the original description was based on a single female specimen. It was stated that the buccal cavity of this species has an "indication of a dorsal tooth". Based on this character, which is suffi cient to distinguish between Spirinia and Chromaspirina, this species is transferred to the genus Spirinia (but remains species inquirenda due to the incomplete nature of the original description). (Cobb, 1898) (synonym: Spira similis Cobb, 1898). Considered invalid by Coles (1987) due to lack of illustrations.

S. similis
S. tenuicauda (Allgén, 1959) (synonym: Spirina tenuicauda Allgén, 1959). This species has to be regarded as a species inquirenda, as the only description Allgén made was to write "differing from Sp. parasitifera," and his drawings are inadequate.

Etymology
The species name is derived from the Latin word verecundus (bashful, shy, coy), in reference to the anterior part of the head region deeply folded inwards.

Male
Body stout, cylindrical, pale orange colour, tapering slightly towards both ends. Annulated cuticle, no lateral differentiation; annulations 0.6-0.8 m apart; cuticle slightly thicker in pharyngeal region than elsewhere (2.2-2.5 vs 1.6-2.0 m). Cuticle covered with dense layer of minute hair-like structures from posterior to amphid to near tail tip (barely visible under light microscope; Fig. 3A-B); larger, 1 × 5 m bacteria-like structures with narrow base also attached in pharyngeal region (Fig. 1D). A single protist, 74 m long and 18 m wide attached subdorsally near cloaca (Fig. 3E). Short somatic setae arranged in eight longitudinal rows along entire body length. Blunt, slightly rounded annulated head region with annulations completely surrounding amphid ( Fig.  1A-B). Four cephalic setae near anterior edge of amphid; inner and outer labial sensillae not observed because labial region is folded inwards from level of cephalic setae. Cryptospiral amphideal fovea with slightly cuticularised outline and unispiral amphideal aperture (Fig. 3A-B).
Reproductive system monorchic, with relatively large, outstretched testis situated to the left of intestine. Mature sperm large, globular to elongated in shape, up to 16 m in length. Short, arcuate spicules with weak capitulum and tapering distally; velum present (Fig. 1G). Gubernaculum with cuneus broadest in middle portion and tapering proximally and distally; poorly developed lateral crurae (Fig. 1H). Precloacal supplements not observed. Tail conical, with two pairs of short subventral setae and one pair of subdorsal setae; three caudal glands restricted to tail region and spinneret present.

Female
Similar to male, but with wider body. One specimen bears a single protist (suctorian) on tail. Reproductive system didelphic, amphidelphic with refl ected ovaries situated either both on the right or both on the left of intestine. Vulva located slightly post median. Cuticular pars distalis vaginae and pars proximalis vaginae surrounded by constrictor muscle.
Emended diagnosis (modifi ed from Blome 1982) Cuticle with coarse annulations; numerous long somatic setae may be present; annulated head region (sometimes intraspecifi c variation, with the head of some specimens only partially annulated in dorsal and ventral regions). Amphid unispiral or spiral located on amphideal plate; small to medium sized buccal cavity with dorsal tooth and (usually) smaller subventral teeth. Pharynx with rounded or pyriform posterior bulb, without cuticularised lumen. Pre-cloacal supplements present or absent; spicules short, arcuate, and with well-developed capitulum; gubernaculum present.

Etymology
The species name is derived from the Latin adjective confusus, meaning confused, perplexed or obscure (feminine form used, as -dora is feminine), and refers to the close affi nities of this species with other desmodorid genera (see Remarks), which resulted in initial confusion in the placement of this species.

Male
Relatively short cylindrical body, pale golden colour, tapering slightly towards both ends. Cuticle 0.9-1.4 m thick, with coarse annuli, approximately 1 m apart, no lateral differentiation. Ventral ala absent. Somatic setae of different sizes (4-19 m long; Fig. 5A), set out in eight longitudinal rows in anterior one fi fth of body length and in six longitudinal rows along rest of body except on tail, where they are irregularly arranged.
Annulated head region with annulations completely surrounding amphid (Figs 6A-C, 7C); in some specimens, there is a seemingly non-annulated head region, but some partial annulation of the dorsal  and ventral sides of the head can be observed (Fig. 7A-B); both forms are considered annulated head regions, even though the degree of annulation differs between the two morphotypes. Labial region folded inwards in all specimens. Six papilliform outer labial sensillae and four cephalic setae, 44-57% cbd long, situated at or slightly posterior to mid-level of amphid. Spiral amphideal fovea, 1.2-1.4 turns, located on a cuticularised amphideal plate (Figs 6B, 7B), larger in holotype than in paratype (~0.6 vs 0.4 cbd, respectively; Fig. 4C-D); amphideal aperture with similar shape to amphideal fovea but tapering proximally (compare Fig. 6A and 6B).
Buccal cavity small, with small dorsal tooth; subventral teeth not observed (Fig. 6C). Pharynx muscular, slightly swollen at anterior extremity, and with pyriform bulb at posterior extremity. Nerve ring at 60-62% of pharynx length. Secretory-excretory system not observed. Cardia short.

Female
Similar to males. Female reproductive system didelphic, amphidelphic with refl ected ovaries situated either to the right or left of intestine, with anterior and posterior ovaries always situated on opposite sides. Vulva located slightly post median. Cuticular pars distalis vaginae and pars proximalis vaginae surrounded by constrictor muscle. Mature eggs 66-73 × 25 m.

Remarks
Stygodesmodora confusa sp. nov. can most easily be differentiated from the other two species of the genus by the location of the cephalic setae at mid-level of amphids (vs anterior to amphids in S. bacillicauda and S. epixantha). S. confusa sp. nov. also differs from S. bacillicauda in the presence of pre-cloacal supplements (absent in S. bacillicauda) and the absence of lateral crurae on the gubernaculum (present in S. bacillicauda), and from S. epixantha by the presence of numerous long somatic setae (short somatic setae in S. epixantha).
Stygodesmodora confusa sp. nov. closely resembles species of other desmodorid genera, and distinguishing it from these other species requires careful examination of the head region. S. confusa sp. nov. resembles Echinodesmodora moensi Verschelde & Vincx, 1996 in the absence of a cephalic capsule, numerous long somatic setae, and cephalic setae at or slightly posterior to mid-level of amphids, but can be differentiated from the latter by the absence of pharyngeal lumen cuticularisation (present in E. moensi), amphid shape (< 1.25 turns vs 1.5-2.0 turns in E. moensi), presence of setose precloacal supplements (absent in E. moensi), and the absence of knotty protrusions on the tail (present in E. moensi). The most important distinction, however, is the presence of an amphideal plate in S. confusa sp. nov. This species is also superfi cially similar to species of Bolbonema, i.e., B. brevicolle (Cobb, 1920), B. longisetosum (Jensen, 1985) comb. nov., andB. spiralis Hourston &Warwick, 2010, in the presence of both short and long somatic setae, cephalic setae just posterior to mid-level of amphid, and in the structure of the copulatory apparatus. The amphideal plates in S. confusa sp. nov. give a swollen appearance to the head region laterally (see Fig. 7A), and in some specimens there is a gap in the body annulations in the head region (compare Fig. 7A and 7C), which may be wrongly interpreted as a nonannulated head region or even a head capsule. S. confusa sp. nov., however, is clearly defi ned by an annulated region, and not a head capsule, because (1) the swollen part of the head is mostly restricted to the area surrounding the amphids (i.e., the amphideal plates), (2) the cuticle is the same thickness in head and body regions (see Fig. 6C), and (3) annulations are present dorsally and ventrally at least to mid-level of amphids, with one continuous annulation anterior to the amphid (see Figs 6B, 7A-C). The genus Bolbonema, however, is characterized by a globular head capsule (i.e., conspicuously thicker cuticle and absence of annulations; Verschelde & Vincx 1996;Verschelde et al. 1998). Muthumbi et al. (1995) provided an emended diagnosis for Chromaspirina and, more recently, Silva et al. (2009) provided an emended diagnosis for Spirinia. Maria et al. (2009) briefl y discussed the relationship between Chromaspirina and Spirinia. They identifi ed the size of the buccal cavity and dorsal tooth, and the shape of the posterior pharyngeal bulb as the main distinguishing features between the two genera and noted that several Chromaspirina species have a small dorsal tooth which "emphasises the close relationship of this genus with Spirinia..." and that "further investigation is needed into the relationships [of] Spirinia with Chromaspirina" (Maria et al. 2009: 28). In his review of Spirinia, Coles (1987) identifi ed buccal morphology as the main distinguishing feature between the two genera.

Discussion
We argue that the shape of posterior pharyngeal bulb and the presence or absence of precloacal supplements show too much overlap to be useful diagnostic features to distinguish Spirinia and Chromaspirina. For example, S. okemwai comb. nov. and S. guanabarensis comb. nov. lack precloacal supplements (a trait usually associated with Spirinia), but possess relatively weakly developed, ovalshaped posterior pharyngeal bulbs (a trait usually associated with Chromaspirina; see Maria et al. 2009). S. sophia Silva et al., 2009 also appears to be intermediate between the two genera: it possesses precloacal supplements (absent in all other Spirinia species but present in some Chromaspirina species) and a round to oval-shaped posterior pharyngeal bulb (despite Spirinia being defi ned as having a round posterior pharyngeal bulb; see Silva et al. 2009). Differences in the morphology of the pharyngeal bulb and precloacal supplements are not reliable traits to distinguish between Chromaspirina and Spirinia because (1) differences in the shape of pharyngeal bulbs are often subtle (e.g., pyriform vs elongated or oval) and (2) precloacal supplements in these two genera are often diffi cult to distinguish and may have been omitted in some species descriptions. Buccal morphology provides the clearest and most consistent way to differentiate between Spirinia and Chromaspirina because it can easily be observed; morphological features of the head region are also the most important traits for differentiating between desmodorid genera.
Perspiria was originally described as a subgenus of Spirinia by Wieser & Hopper (1967). The only distinguishing feature of this subgenus given by the latter authors was "the more prominently striated and fl agellate tail." Coles (1987) also gave the same distinguishing features between the two subgenera. Vincx & Gourbault (1989) later raised Perspiria to generic status and included two key characteristics in their diagnosis of the genus: amphids only partially surrounded by cuticle annulations and a "prominently striated" and "fi liform" tail, which we interpret as a coarsely annulated, conico-cylindrical tail from the drawings (see fi gs 1 and 2 in Vincx & Gourbault 1989). Some Spirinia species, however, have coarsely annulated (e.g., S. verecunda sp. nov.) or conico-cylindrical tails (e.g., S. septentrionalis (Cobb, 1914)), and others have amphids not completely surrounded by the body annulations (e.g., S. lara Silva et al., 2009). Here, we propose to differentiate between Spirinia and Perspiria primarily based on tail shape (conical vs conico-cylindrical to fi liform), as well as position of amphids relative to cuticle annulations (entirely vs partially surrounded), and have suggested nomenclatural changes to refl ect these distinctions.
The monospecifi c genus Spirodesma was recently described by Cavalcanti et al. (2009) from continental slope sediments in the Southwest Atlantic. The authors argued that the genus is most similar to Chromaspirina based on the rounded shape of the head, annulated cuticle, spiral amphideal fovea, and conical tail. We consider these arguments invalid because (1) an annlated cuticle is also a characteristic of some Spirinia (e.g., Spirinia verecunda sp. nov.) and Perspiria species (e.g., P. papillata Vincx & Gourbault, 1989), (2) the spiral amphideal fovea in Spirodesma is in fact very similar in shape to the cryptospiral amphideal fovea found in some Spirinia species (e.g., S. verecunda sp. nov.) and to the spiral amphideal fovea of Perspiria papillata, and (3) the tail of Spirodesma is conico-cylindrical (as stated in the original description), not conical. In addition, head shape is not a particularly informative trait for differentiating between genera. In our opinion, Spirodesma is most closely related to Perspiria because of the similar buccal cavity (narrow with small or minute teeth), the position of the amphids (only partially surrounded by cuticle annulations), and the shape of the tail (conico-cylindrical). The only difference between these genera appears to be the relative size of the teeth: Perspiria is characterised by a narrow, lightly cuticularised buccal cavity with no or a small/inconspicuous dorsal tooth and no or minute subventral teeth, while Spirodesma is characterised by a narrow, lightly cuticularised buccal cavity with three small, equal teeth. Spirodesma and Perspiria may therefore need to be synonymised in the future as more information becomes available on the former genus.
Stygodesmodora rotundicephala (Cobb, 1920) was originally described as Amphispira rotundicephala and was included in the World Register of Marine Species list of Stygodesmodora species at the time the present study was conducted (WoRMS Editorial Board 2014). The original description, which is based on a single juvenile specimen, clearly shows a head capsule, whereas no amphideal plate was described. Based on the drawing, the specimen/species could possibly belong in Zalonema, but, as the original species description of Amphispira rotundicephala was based only on one juvenile, we regard A. rotundicephala Cobb, 1920 to be a species inquirenda.