Cervonema kaikouraensis, Leduc, 2012

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 : 7-10

Cervonema kaikouraensis sp. nov.

urn:lsid:zoobank.org:act:00FCA18B-AB7B-4464-8DBC-A75F17F3BC72

Figs 2-4 , Table 1

Etymology

This species is named after the type locality.

Material examined

Holotype

Ƌ, collected 5 May 2010, Kaikoura Canyon axis (1061 m water depth), 42.5081°S, 173.6325°E (NIC 84440).

Paratypes

2 ♀♀, same data as holotype (NIC 84441).

Description

Males

Body cylindrical, tapering towards both extremities. Cuticle faintly striated, no lateral differentiation. Somatic setae very short and sparse, 1-2 μm long, except in pre-cloacal region, 4 μm long. Head not setoff by constriction. Six inner labial papillae, six jointed outer labial setae, and four cephalic setae, not jointed. Amphideal fovea spiral, 5.5 turns, at 1.7 head diameters from anterior. Golden-coloured granular material in lateral, ventral, and dorsal chords, forming two continuous bands ( Fig. 4D ). Small buccal cavity, cup-shaped. Pharynx gradually widening posteriorly into an elongated bulb. Dorsal pharyngeal gland nucleus conspicuous. Cardia short. Nerve ring near middle of pharynx length. Secretory-excretory pore situated just posteriorly to nerve ring. Cellular body of ventral gland small, at level of cardia. Intestine wall with numerous granules, orange-brown in anterior portion, colourless in posterior portion. Reproductive system diorchic, opposed, outstretched.Anterior testis to left of intestine, posterior testis to right of intestine. Anterior testis with relatively large elongated sperm cells (up to 5 μm wide and 20 μm long), without nuclei ( Fig. 2C ). Posterior testis with smaller, globular sperm cells (4-6 μm diameter) with lenticular nuclei situated peripherally ( Fig. 2D ). Spicules paired, equal, narrow, straight, 0.9 abd long, with small capitulum. Rectal gland present. Five, possibly six tubular pre-cloacal supplements, difficult to observe, one pre-cloacal seta. Tail conico-cylindrical, with several caudal setae, 2-5 μm long, and three short terminal setae. Three caudal glands and well-developed spinneret ( Fig. 4C ).

Females

Similar to males, but with slightly larger maximum body diameter, amphideal fovea smaller, 4.5 turns. Reproductive system didelphic, opposed, with anterior branch to left of intestine and posterior branch to right of intestine. Terminal (i.e., distal) portion of anterior ovary bent in one paratype specimen ( Fig. 4A ), but not other paratype specimen; germinal portion of posterior ovary bent in both paratypes. Both types of sperm observed in uterus and spermathecae. Vulva at body median. Granular vaginal glands present, pars proximalis vaginae surrounded by constrictor muscle.

Diagnosis and relationships

Cervonema kaikouraensis sp. nov. is characterised by body length 1636 μm, amphid with 5.5 turns situated 1.7 head diameter from anterior end, jointed outer labial setae, equal in length to cephalic setae, anterior testis with large elongated sperm cells without nuclei, posterior testis with smaller nucleated sperm cells, 5 small pre-cloacal supplements, straight spicules 32 μm in length, and tail 5.5 abd.

C. kaikouraensis sp. nov. can be differentiated from all other species of the genus, except C. allometricum Wieser, 1954 and C. pseudodeltensis Barnes et al., 2012 by the presence of jointed outer labial setae. The presence of jointed outer labial setae in C. allometricum was not described in the original description of Wieser (1954) but was later noted by Lorenzen (1981). C. kaikouraensis sp. nov. can be distinguished from C. allometricum and C. pseudodeltensis by the absence of gubernaculum and gubernacular apophyses (gubernaculum with conspicuous posterior apophyses present in C. allometricum and C. pseudodeltensis ).

The presence of jointed outer labial setae may have been overlooked in previous descriptions and may not be a reliable trait to use for differentiating between all species of Cervonema . C. kaikouraensis sp. nov. can further be differentiated from most other species of the genus (except C. deltensis Hope & Zhang, 1995 and C. papillatum Jensen, 1988 by the presence of sperm dimorphism. C. kaikouraensis sp. nov. differs from C. deltensis in body length (1636 vs. 1201 - 1237), length of cephalic setae (6 vs. 3-5 μm), amphideal fovea turns (5.5 vs. 3-5), position of amphid (1.7 vs. 1.4 hd from anterior), and absence of gubernaculum (plate-like gubernaculum in C. deltensis ). C. kaikouraensis sp. nov. differs from C. papillatum in body length (1636 vs. 1140 - 1230), and by the absence of a weakly cuticularised cap surrounding the spicules proximally. The presence or absence of sperm dimorphism was not noted in the descriptions of C. brevicauda Gourbault, 1980 and C. jenseni Gourbault, 1980 , but these species differ most notably from C. kaikouraensis sp. nov. in the presence of a gubernaculum (absent in C. kaikouraensis sp. nov.). C. brevicauda also has a shorter body length (800- 1090 vs. 1636), shorter cephalic setae (3 vs. 6 μm), and shorter spicules (0.6 vs. 0.9 abd) than C. kaikouraensis sp. nov. C. jenseni can also be differentiated from C. kakouraensis sp. nov. by the greater number of amphid turns (7 vs. 5.5) and absence of supplements (5 in C. kaikouraensis sp. nov.).

Remarks

The presence of bent ovaries, as observed in C. kaikouraensis sp. nov., is unusual for the family Comesomatidae . The ovaries, however, are bent only in the terminal portion. Because the ovaries in both female specimens are quite large and occupy most of the available space in the pseudocoel ( Fig. 3D ), this trait is considered to be a secondary feature resulting from lack of space, rather than true reflexed ovaries.

Figures

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.

Fig. 3. Cervonema kaikouraensis sp. nov. A. Ƌ anterior body region. B. ♀ head. C. Ƌ reproductive system. D. Entire ♀. E. Ƌ copulatory apparatus. Scale bar: A = 50 μm; B = 30 μm; C = 170 μm; D = 200 μm; E = 40 μm.

Fig. 4. Cervonema kaikouraensis sp. nov. light micrographs. A. Anterior ovary, showing bent germinal portion. B. Ƌ head, showing jointed outer labial seta. C. Ƌ spinneret. D. Granules in the lateral chords of Ƌ. Scale bar: A = 40 μm; B = 18 μm; C = 12 μm; D = 24 μm.