Cervonema shiae Chen & Vincx, 2000

Leduc, Daniel, 2012, Deep-sea nematodes (Comesomatidae) from the Southwest Pacific Ocean: five new species and three new species records, European Journal of Taxonomy 24, pp. 1-42 : 3-7

Cervonema shiae Chen & Vincx, 2000

Figs 1-2 , Table 1

Material examined

1 Ƌ and 2 ♀♀, collected 6 Apr. 2007, southern flank of Chatham Rise (1240 m water depth), 44.4864°S, 177.1407°E. Characteristics of surface sediment layer (0-5 mm): mostly silt/clay (82.9%), with very fine sand (10.2%), and fine sand (8.4%); calcium carbonate content: 38.4%; total organic matter content: 1.9%; chloroplastic pigment concentration: 3501 ng /gDW sediment (NIC 84438). 1 Ƌ collected 5 Jun. 2007, Challenger Plateau (532 m water depth), 40.8814′S, 170.8603′E. Characteristics of surface sediment layer (0-5 mm): mostly silt/clay (67.6%), with fine sand (15.2%), and very fine sand (11.4%); calcium carbonate content: 56.0%; total organic matter content: 2.1%; chloroplastic pigment concentration: 1344 ng /gDW sediment (NIC 84439).

Description

Males

Body cylindrical, tapering towards both extremities but more pronounced in tail region. Cuticle faintly striated, no lateral differentiation. Somatic setae short and sparse. Head not set-off by constriction. Inner labial papillae indistinct, six outer labial setae, and four slightly longer cephalic setae, the latter two in separate circles close to each other. Amphideal fovea spiral, at 6.0-6.5 turns, 1.8-2.3 head diameters from anterior. Small buccal cavity, cup-shaped. Pharynx widening posteriorly into a weakly marked elongated bulb. Cardia short. Nerve ring near middle of pharynx length. Secretory-excretory pore near two thirds of pharynx length from anterior. Cellular body of ventral gland small- at level of cardia. Intestine wall consisting mostly of cells containing colourless granules, interspersed with clusters of clear globular inclusions.

Reproductive system diorchic, opposed, outstretched. Anterior testis to left of intestine, posterior testis to right of intestine. Anterior testis with relatively large oval sperm cells (5-8 μm wide by 12-15 μm long) without nuclei ( Fig. 2A ). Posterior testis with smaller, oval-shaped sperm cells (up to 8×5 μm) with lenticular nuclei situated peripherally ( Fig. 2B ). Spicules paired, equal, 0.5-0.6 abd long, with lightly cuticularised, swollen proximal portion, and heavily cuticularised, pointed distal portion. Gubernaculum not observed. Large rectal gland surrounds spicules. Four small, tubular pre-cloacal supplements, one pre-cloacal seta. Tail conico-cylindrical, with several short caudal setae and three short terminal setae. Three caudal glands and spinneret.

Females

Similar to males, but with slightly larger maximum body diameter, amphideal fovea smaller, 5.0-5.5 turns. Reproductive system didelphic, opposed, ovaries outstretched, with anterior branch to left of intestine and posterior branch to right of intestine. Both types of sperm observed in uterus. Spermathecae not observed. Vulva at median or slightly post median. Granular vaginal glands present, pars proximalis vaginae surrounded by constrictor muscle.

Discussion

My specimens closely resemble the description of Chen & Vincx (2000) based on specimens from the Beagle Channel (255-257 m water depth), although specimens from Chatham Rise and Challenger plateau have slightly shorter cephalic setae (0.3-0.4 vs. 0.5 cbd) and longer tail (5.5-6.4 vs. 4.8 abd). The specimens are also characterised by sperm dimorphism (anterior testis with large oval sperm cells without nuclei, posterior testis with smaller nucleated sperm cells); Chen & Vincx (2000), however, did not provide details of the sperm in their description. This is the first record of this species outside the type locality.

Figures

Fig. 1. Cervonema shiae Chen & Vincx, 2000. A. Ƌ anterior body region. B. Lateral view of Ƌ head region. C. ♀ reproductive system. D. ♀ tail. E. Ƌ posterior body region showing reproductive system and copulatory apparatus. Scale bar: A = 40 μm; B = 35 μm; C = 65 μm; D = 30 μm; E = 60 μm.

Fig. 2. Cervonema shiae Chen & Vincx, 2000 and Cervonema kaikouraensis sp. nov. light micrographs. A. Large sperm cells without nuclei in anterior testis of C. shiae. B. Small nucleated sperm in posterior testis of C. shiae. C. Large sperm cells without nuclei in anterior testis of C. kaikouraensis sp. nov. D. Small nucleated sperm in posterior testis of C. kaikouraensis sp. nov. Arrows point to the lenticular nuclei situated on the periphery of the small sperm cells in the posterior testes of both species. Scale bar = 10 μm.