Paramphimonhystrella scutula, Leduc, Daniel, 2014

Leduc, Daniel, 2014, Four new Paramphimonhystrella species (Nematoda: Xyalidae) from the continental slope of New Zealand, Zootaxa 3814 (4), pp. 478-494 : 488-491

Paramphimonhystrella scutula n. sp.

( Figs 7–9 , Table 2 )

Type specimens. Holotype male ( NIWA 89977), collected on 21 April 2010 ( NIWA cruise TAN1004, station 72), open slope habitat on southern Hikurangi Margin (176.1958ºE, 41.3657ºS); water depth: 985 m. One paratype male ( NNCNZ 3169), collected on 20 April 2010 ( NIWA cruise TAN1004, station 58), canyon habitat on southern Hikurangi Margin (175.8977ºE, 41.4080ºS); water depth: 670 m. One paratype female ( NIWA 89978), same data as holotype. One paratype female ( NNCNZ 3170), collected on 19 April 2010 ( NIWA cruise TAN1004, station 38), open slope habitat on southern Hikurangi Margin (175.8532ºE, 41.5937ºS); water depth: 1121 m.

Etymology. The species name is the diminutive of the latin word scuta (= diamond-shaped dish), and refers to the shape of the buccal cavity in this species.

Description. Males. Body cylindrical, tapering slightly towards both extremities. Cuticle ~1.0–1.2 µm thick, with fine striations ~1.2–1.4 µm apart beginning halfway between cephalic setae and anterior edge of amphids. Somatic setae very short and sparse, irregularly arranged. Head tapering anteriorly. Inner labial sensillae not observed; six outer labial setae, 2 µm long, situated immediately anterior to four cephalic setae, 3–4 µm long. Two rings of sub-cephalic setae; anterior ring consists of eight 1 µm long setae at level of amphids; second ring consists of eight setae 6–7 µm long, situated 1.0–2.0 cbd posterior to first ring of sub-cephalic setae ( Figure 7 A–C). Amphids with round or slightly oval outline, cuticularised. Buccal cavity 12 µm deep, 2–3 µm wide, lozengeshaped, lightly cuticularised, almost completely surrounded by pharyngeal tissue. Pharynx muscular, widening posteriorly but not forming true bulb. Cardia elongated, ~6 µm long, surrounded by intestine tissue. Nerve situated at middle of pharynx. Secretory-excretory system not observed.

Male reproductive system diorchic with outstretched testes; both testes situated to the left of intestine. Sperm cells round to globular in shape, nucleated, ~2–4 µm in diameter ( Figure 7 F). Spicules scythe-shaped, 1.4–1.5 abd long, lightly cuticularised, with straight, blunt thick proximal one third and curved, distal two thirds ( Figure 7 H); gubernaculum and pre-cloacal supplements absent. Tail conico-cylindrical, with two pairs of sub-lateral setae. Two terminal setae, 6–8 µm long. Three caudal gland; one or two anterior-most glands conspicuously larger than other(s) ( Figure 7 G, H).

Female. Similar to males. Reproductive system monodelphic with outstretched anterior branch to the left of intestine; small spermatheca present; postvulvar sac present, sperm cells not observed in postvulvar sac ( Figure 7 D, 8A). Mature egg 81–116×9–10 µm. Vulva situated posterior to mid-body, at almost two thirds of body length from anterior. Granular vaginal glands present; distinctive hammer-shaped cuticularised piece situated ventrally and immediately posterior to vagina, flanked on either side by vaginal glands, ~10 µm long and 2 µm wide in narrow portion ( Figure 7 D, 9).

Diagnosis. P. scutula n. sp. is characterised by lozenge-shaped buccal cavity, round amphids, two rings of eight sub-cephalic setae with anterior ring consisting of very short (1 µm) setae, males with scythe-shaped spicules, females with vulva at almost two thirds of body length from anterior and hammer-shaped cuticularised piece immediately posterior to vagina, and tail with two terminal setae.

Differential diagnosis. P. s c ut u l a n. sp. can be differentiated from all other species of the genus except P. glossalga n. sp. in the presence of a hammer-shaped cuticularised piece immediately posterior to the vagina. P. scutula n. sp. differs from the latter most notably in the size and shape of the buccal cavity, number and length of sub-cephalic setae, and spicule shape. P. s c ut u l a n. sp. is similar to P. m inor in the number and arrangement of subcephalic setae, size and shape of the amphids and tail, and position of the vulva, but differs from the latter in buccal cavity shape (lozenge-shaped in P. scutula n. sp. vs funnel-shaped in P. minor ), spicule shape (scythe-shaped vs curved and slender), and the presence of a hammer-shaped cuticularised piece immediately posterior to the vagina (vs absent).

Figures

FIGURE 7. Paramphimonhystrella scutula A: Lateral view of male head; B: lateral view of female head; C: female anterior body region; D: left-hand side view of vulva and hammer-shaped cuticularised piece; E: male posterior body region; F: sperm; G: female posterior body region; H: male posterior body region. Scale bar = 20 µm.

FIGURE 8. Paramphimonhystrella scutula A: entire female; B: entire male. Scale bar: A = 100 µm; B = 55 µm.

FIGURE 9. Paramphimonhystrella scutula Light micrograph. Left-hand side view of vulva and hammer-shaped cuticularised piece. Scale bar = 10 µm.