Desmodora parapilosa Leduc 2023, sp. nov.

Desmodora parapilosa sp. nov.

urn:lsid:zoobank.org:act: 4ED46F36-0AEA-43BA-9EF5-0A2D799E7135

Figs 16–18, Tables 7–8

Diagnosis

Desmodora parapilosa sp. nov. is characterized by body length 2.3–3.2 mm, jointed inner labial setae, outer labial setae and cephalic setae, main portion of cephalic capsule with numerous, irregularly distributed pores (or vacuoles), large amphideal fovea with 2.25 turns in males (smaller in females with 1.75–2.0 turns), buccal cavity with large cuticularised dorsal tooth, two smaller ventrosublateral teeth and two lateral, transverse rows of small denticles, arcuate spicules 1.3–1.5 cloacal body diameters long, short, plate-like gubernaculum, vulva at almost two thirds of body length from anterior and conical tail 2.6–3.5 cloacal or anal body diameters long.

Differential diagnosis

The new species is most similar to Desmodora pilosa Ditlevsen, 1926 in the shape of the amphids (spiral), presence of pores/vacuoles in the cephalic capsule, buccal cavity armature with rows of denticles and structure of the copulatory apparatus. Desmodora parapilosa sp. nov. can be differentiated from the latter by the jointed anterior sensilla (vs not jointed in D. pilosa), larger amphids (in males: 51–63 vs 37 % cbd in D. pilosa), number of amphid turns (2.25 in males and 1.75–2.0 in females vs 1.25 turns in males and females of D. pilosa), and shorter spicules (61–66 vs 72–96 µm in D. pilosa).

Etymology

The species name refers to the morphologically similar species Desmodora pilosa Ditlevsen, 1926.

Material examined

Holotype NEW ZEALAND • ♂; Hikurangi Margin, Uruti South cold seep site; 41.4251° S, 176.3510° E; 1226 m water depth; collected on 13 Jul. 2019; sandy mud sediment (91% silt/clay, mean particle size 23 µm), voyage TAN1904, station 62; NIWA154921.

Paratypes NEW ZEALAND – Uruti South cold seep site • 3 ♂ ♂; same collection data as for holotype; NIWA 154922 • 1 ♀; 41.4260° S, 176.3506° E; 1237 m water depth; collected on 14 Jul. 2019; sandy mud sediment (94% silt/clay, mean particle size 18 µm); voyage TAN1904, station 68; NIWA154923 • 1 ♀; Uruti South cold seep site; 41.4253° S, 176.3509° E; 1235 m water depth; collected on 14 Jul. 2019; voyage TAN1904, station 70; NIWA154924.

Type habitat and locality

New Zealand continental slope, Hikurangi Margin, Uruti South cold seep.

Description

Male

Long cylindrical body, widest at level of pharynx, with slight golden-brown colouration throughout except for main portion of cephalic capsule and intestine wall which which may be strongly stained by Rose bengal; rounded anterior end and conical tail. Cuticle coarsely annulated with annulations ca 1.2 µm apart; minute cuticle spines present on surface of cuticle, difficult to observe using light microscopy. Several protists often attached throughout body length and some specimens with patches of dense rod-shaped bacteria on outer cuticle, 4–8 µm long. Eight longitudinal rows of somatic setae along entire body length, 4–6 µm long in pharyngeal and mid-body regions, and up to 10 µm long in precloacal region; subventral row of precloacal somatic setae associated with conspicuous epidermal glands. Welldeveloped cephalic capsule, 40–46 µm wide and 40–46 µm high, consisting of two parts separated by a sutura: a lip portion with relatively thin cuticle and extendable anterior portion and a main region with thickened cuticle (up to 7 µm thick) and comprising at least three quarters of cephalic capsule. Main portion of cephalic capsule with numerous, dense pores (or vacuoles) irregularly distributed except near base where pores may be arranged in transverse rows; sparse subcephalic setae present at base of cephalic capsule, 2–6 µm long. Six inner and six outer labial setae present on lip region; inner labial setae 2–4 µm long, outer labial setae 4–6 µm long. Four cephalic setae present at level of sutura, 3–5 µm long. Inner labial setae, outer labial setae and cephalic setae all with a single joint near tip where sensilla becomes markedly narrower.Amphideal fovea and aperture large, spiral with 2.25 turns and cuticularized outline, located on main portion of cephalic capsule; amphideal fovea slightly wider than amphideal aperture. Buccal cavity with large cuticularised dorsal tooth and two smaller ventrosublateral teeth; two lateral, transverse rows of small denticles also present. Cylindrical pharynx slightly swollen anteriorly and with oval posterior pharyngeal bulb. Secretory-excretory system not observed. Cardia 12–19 µm long, partially surrounded by intestine.

Reproductive system monorchic with outstretched testis located to the right or left of intestine. Mature sperm cells globular or spherical, 8 × 8–10 µm. Short, arcuate spicules with well-developed capitulum, tapering shaft and distal end, 1.3–1.5 cloacal body diameters long; short, plate-like gubernaculum. Precloacal supplements and seta not observed. Conical tail with subventral and subdorsal rows of setae. Non-annulated tail tip without perforations. Caudal glands and spinneret present.

Female

Similar to males, but with smaller amphideal fovea with 1.75–2.0 turns and slightly longer tail. Reproductive system didelphic, amphidelphic with reflexed ovaries; position of ovaries relative to intestine not clear in one specimen, in other specimen, anterior ovary located to the left of intestine and posterior ovary to the right. Spermatheca not observed. Vulva located at almost two thirds of boody length from anterior. Proximal portion of vagina cuticularised; proximal portion of vagina surrounded by constrictor muscle. Vaginal glands present.

Remarks

The original description of D. pilosa by Ditlevsen (1926) based on Northwest Atlantic specimens did not include observations of male specimens or of buccal cavity armature. Ditlevsen (1926) did not describe pores in the cephalic capsule. Desmodora gorbunovi Filipjev, 1946 and Desmodora gorbunovi perforata Filipjev, 1946 were described based on Arctic Ocean specimens and later synonymized with D. pilosa by Gerlach (1963). The former lacks pores in the cephalic capsule whereas the latter is characterized by numerous pores in the cephalic capsule. Both of these are described by Filipjev (1946) as having a buccal cavity with a small dorsal tooth (although small ventrosublateral teeth may be present based on the drawings) without denticles. In his redescription of D. pilosa based on specimens from the Norwegian Sea, Jensen (1991) noted strong similarities between his specimens and Desmodora gorbunovi including the cephalic capsule with numerous pores, size and arrangement of anterior sensilla and somatic setae, structure of the amphideal fovea, and tail shape. Jensen’s specimens, however, have a buccal cavity with a band of numerous denticles, whereas Filipjev’s specimens do not have denticles. The descriptions of Filipjev (1946) and Jensen (1991) also show some inconsistencies in body dimensions and size of anterior sensilla and amphideal fovea (Table 8).

Leduc (2021) recently described abyssal nematode specimens from the Southwest Pacific showing similarities to D. pilosa although inconsistencies in body size, dimensions, amphid size and cuticle ornamentation were noted. Despite the morphological differences between the Southwest Pacific specimens and the specimens described by Ditlevsen (1926), Filipjev (1946) and Jensen (1991), Leduc (2021) did not erect a new species because further data are required from the type locality of D. pilosa (upper continental slope of NW Atlantic) to determine the structure of the buccal cavity armature, presence or absence of pores in the cephalic capsule and male morphology of this species.

A new species, Desmodora parapilosa sp. nov., is erected here because the Hikurangi margin specimens can be differentiated from the specimens described by Ditlevsen (1926), Filipjev (1946), Jensen (1991) and Leduc (2021) based on several key characters, i.e., the jointed anterior sensilla, larger amphids with greater number of turns, and shorter spicules. The new species also differs from the Southwest Pacific abyssal specimens in having a lower ratio of a, longer tail, longer gubernaculum, and smaller sperm (8 × 8–10 µm vs 10–11 × 16–19 µm) (Table 8).