Daptonema amphorum, Leduc, Daniel, 2015

Leduc, Daniel, 2015, One new genus and five new nematode species (Monhysterida, Xyalidae) from Tonga and Kermadec Trenches, Southwest Pacific, Zootaxa 3964 (5), pp. 501-525 : 509-513

Daptonema amphorum n. sp.

( Figs 5–7 )

Measurements. See Table 1.

Type specimens. Holotype female (99743), collected 10 October 2013 (JAMSTEC cruise YK13-10, deployment 2-1, core 1). One paratype female (99744), collected 10 October 2013 (JAMSTEC cruise YK13-10, deployment 2-1, core 3). One paratype male (99745), collected 12 October 2013 (JAMSTEC cruise YK13-10, deployment 2-3, core 1).

Type habitat. Horizon Deep, Tonga Trench (174.74971º W, 23.27382º S and 174.75224º W, 23.27514º S), water depth: 10817 and 10811 m, sediment depth: 3–10 cm.

Etymology. The species name is derived from the latin amphora (= two-handled vase, pitcher, jar) and refers to the distinctive shape of the prevulvar uterine sac (spermatheca).

Description. Females. Body cylindrical, tapering towards anterior and posterior extremities. Cuticle striated, ~1.0 µm thick, with 10 annulations every ~16–22 µm. Cellular structure of chords indistinct. Sub-cephalic setae absent; somatic setae short and sparse, 2 µm long.

Head blunt, narrow; labial region 4 µm in height. Six inner labial papillae; six long outer labial setae and four cephalic setae in one circle, ~0.4 cbd long, jointed, cephalic setae of same length as outer labial setae. Amphideal fovea circular, with cuticularised outline and central spot, 1.7–1.9 cbd from anterior. Buccal cavity small, 4–7 µm deep, not cuticularised, with shallow anterior cylindrical portion and funnel-shaped posterior portion ( Figs 5 B & 7A). Pharynx muscular, widening posteriorly but not forming true posterior bulb. Cardia short, 6–8 µm long. Nerve ring situated at 33–42% of pharynx length from anterior. Secretory-excretory system not observed.

Reproductive system, monodelphic, prodelphic, with ovary to the left of intestine. Vagina directed anteriorly, situated slightly posterior to mid-body; small vaginal glands present on either side of vagina; muscular pars proximalis vaginae. Prevulvar uterine sac conspicuously cuticularised, cylindrical, with rounded distal end ( Figs 6 C and 7C). Prevulvar uterine sac is connected to uterine wall by cuticularised rim (or fold) at one third of uterine sac length from proximal end; another cuticularised rim surrounds opening. Several sperm cells present in uterus and prevulvar uterine sac. Postvulvar uterine sac absent. Tail conico-cylindrical, with a few sparse somatic setae and two terminal setae, 5 µm long. Two (perhaps three) caudal glands present.

Males. Similar to males but with slightly higher a values. Reproductive system diorchic with two outstretched and opposed testes; anterior testis to the left and posterior testis to the right of intestine. Sperm cells nucleated, globular, 10 × 12–17 µm ( Fig. 7 B). Spicules 1.1 cbd long, arcuate, strongly cuticularised, with pointed distal end and capitulum; velum present. Gubernaculum thin, 11 µm long, surrounding spicules distally, without apophyses. Four to five ejaculatory glands present on either side of vas deferens ( Fig. 5 D). Pre-cloacal setae and supplements absent.

Diagnosis. Daptonema amphorum n. sp. is characterised by medium body length (955–1030 µm), short (2 µm) somatic setae, narrow head region, amphideal fovea relatively far (1.7–1.9 cbd) from anterior body extremity, arcuate spicules 1.1 cbd long, thin gubernaculum without apophyses surrounding spicules distally, and cuticularised prevulvar uterine sac with two rims (one at proximal end and one at one third of uterine sac length from proximal end).

Differential diagnosis. Daptonema amphorum n. sp. differs from all other species of the genus by the presence of a cuticularised prevulvar uterine sac. The presence of a prevulvar uterine sac has been noted in a few Daptonema species, but they are never cuticularised. Daptonema conicum (Filipjev, 1922) and D. williamsi Vincx & Coomans, 1983 are characterised by a prevulvar uterine sac, but both also possess a posteriorly-directed vagina (versus anteriorly-directed in D. amphorum n. sp.), and a postvulvar uterine sac (versus absent). It should be noted that the structure of the postvulvar uterine sac in D. williamsi is similar to that of the prevulvar uterine sac in D. amphorum n. sp., i.e., cuticularised with a distinct rim surrounding the proximal end. The other Daptonema species with prevulvar uterine sac are: D. arcticus Steiner, 1916 , D. conicum (Filipjev, 1922) , D. nanum (Lorenzen, 1972) , D. pratti (Murphy & Canaris, 1964) , D. procerum (Gerlach, 1951) , D. proprium (Lorenzen, 1972) , D. sentiens (Cobb, 1914) , and D. setosum (Butschli, 1874) . D. trabeculosum (Schneider, 1906) is listed by Neres et al. (2010) among the species possessing a prevulvar uterine sac, but no description of it could be found in the original description, or the re-description by Lorenzen (1977).

Daptonema amphorum n. sp. is similar to D. xyaliforme (Wieser & Hopper, 1967) , D. paratortum (Vitiello, 1971) , and D. nanum (Lorenzen, 1972) in the narrow head shape and position of the amphideal fovea relatively far from anterior end of body. Daptonema amphorum n. sp. can be differentiated from the latter three species by the absence of gubernacular apophyses (present in the other three species).

Remarks. A female was designated as holotype because the main diagnostic characteristic of this species is the presence of a cuticularised prevulvar uterine sac.

Figures

FIGURE 5. Daptonema amphorum n. sp. Male paratypes. A: Lateral view of anterior body region; B: lateral view of head; C: copulatory apparatus; D: posterior body region; E: entire male. Scale bar: A = 25 µm; B = 18 µm; C = 14 µm; D = 40 µm; E = 88 µm.

FIGURE 6. Daptonema amphorum n. sp. Female holotype. A: Lateral view of anterior body region; lateral view of posterior body region; C: gonad, showing structure of prevulvar uterine sac; D: entire female. Scale bar: A = 25 µm; B = 28 µm; C = 31 µm; D = 90 µm.

FIGURE 7. Daptonema amphorum n. sp. Micrographs of holotype. A: Female head; B: sperm; C: lateral view of prevulvar uterine sac. Scale bar = 10 µm.