Mudwigglus plebeius

Leduc, Daniel, 2013, Mudwigglus gen. n. (Nematoda: Diplopeltidae) from the continental slope of New Zealand, with description of three new species and notes on their distribution, Zootaxa 3682 (2), pp. 351-370 : 362-366

Mudwigglus plebeius gen. et sp. n.

( Figs 7–9 , Table 1)

Type specimens. Holotype male, collected on 20 February 2011 ( NIWA cruise TAN1103, station 69), central Chatham Rise (43.331° S, 178.288° E), water depth: 350 m, sediment depth: 1–5 cm (NIC 865980). Paratype male, collected on 5 June 2007 ( NIWA cruise TAN0707, station 112), western Challenger Plateau (40.879° S, 170.859° E), water depth: 537 m, silt/clay content: 67.6%, CaCO3 content: 56%, sediment chlorophyll a concentration: 21 ng /gDW sediment (NIC 865981). Two paratype males and one paratype female, collected on 6 April 2007 ( NIWA cruise TAN0705, station 45), southwestern Chatham Rise (44.486° S, 177.141° E), water depth: 1238 m, silt/clay content: 93.9%, CaCO3 content: 13%, sediment chlorophyll a concentration: 32 ng /gDW sediment (NIC 865 982). One paratype male and four paratype females, collected on 4 October 2001 ( NIWA cruise TAN0116, station U2581D), central Chatham Rise (42.968° S, 178.500° E), water depth: 450 m, sediment depth: 0–5 cm, silt/clay content: 96.7%, CaCO3 content: 13%, sediment chlorophyll a concentration: 88 ng /gDW sediment (NIC 865983).

Etymology. The species name is derived from the Latin plebeius (= common) and refers to high abundance and widespread distribution of this species in the New Zealand region relative to the other known species of the genus.

Description. Males. Cylindrical body, colourless, tapering slightly towards both extremities. Cuticle 0.6 Μm thick, with annuli beginning posterior to cephalic setae to near tail tip, situated 2–3 Μm apart, no lateral differentiation. Two subventral and two subdorsal rows of short (1 Μm long), sparse somatic setae extending from posterior edge of fovea amphidialis to level of cloaca. Hypodermal glands not observed. Lateral chords with honeycomb-like appearance and clusters of small, elongated inclusions always situated ventrally ( Figure 9 B). Two pairs of subventral setae and one pair of subdorsal setae on tail. Two terminal setae.

Labial region rounded, not set off. Inner labial sensillae not observed. Six minute outer labial sensillae and four cephalic setae, 1Μm long. Subcephalic setae absent. Fovea amphidialis an elongated loop, with cuticularised outline, two times longer than wide. Buccal cavity short, cylindrical, with small cuticularised ring (difficult to observe in some specimens), separated from anterior extremity by narrow, 2–3 Μm long mouth opening surrounded by bulge of inner portion of lip region. Walls of buccal cavity slightly cuticularised. Teeth not observed. Pharynx short, cylindrical, without subdivisions except for oval-shaped basal bulb. Pharyngeal lumen not cuticularised, valvular apparatus absent. Muscular tissue of basal bulb arranged in bundles. Pharyngeal glands and their orifices indistinct. Nerve ring at 65–70% of pharynx length. Secretory-excretory system present, renette cell at level with intestine, ampulla and pore at level of pharyngeal bulb or slightly anterior. Pore opening surrounded by small but distinct cuticularised ring ( Figure 7 A). Cardia short.

Reproductive system diorchic with two testes directed anteriorly. Anterior testis outstretched, to the right of intestine, posterior testis antidromously reflexed, situated ventrally. Mature sperm globular to elongated, nucleated, width 4–5 Μm, length 6–7 Μm. Spicules paired, equal, short, arcuate, with weak capitulum, pointed distally. Velum absent. Gubernaculum with straight dorso-caudal apophyses. Rectal gland surrounds spicules, ejaculatory glands not observed. Two small tubular pre-cloacal supplements, one pre-cloacal seta, 1–2 Μm long. Tail conico-cylidrical with clavate tip. Three caudal glands present, structure of spinneret not clear.

Females. Similar to males. Female reproductive system didelphic, amphidelphic with reflexed ovaries. Position of ovaries relative to intestine difficult to ascertain. Spermathecae not observed. Vulva located mid-body or slightly posterior. Vagina not at right angle with body surface but directed posteriorly ( Figure 8 B and 9C). Pars proximalis vaginae surrounded by constrictor muscle.

Diagnosis and relationships. Mudwigglus plebeius gen. et sp. n. is characterised by relatively short body length (487–673 Μm), cylindrical buccal cavity with cuticularised ring, males with arcuate spicules and gubernaculum with dorso-caudal apophyses, females with vagina directed posteriorly, and conico-cylindrical tail with two terminal setae. M. plebeius gen. et sp. n. is similar to M. macramphidum gen. et sp. n. but can be differentiated from the latter based on the shape of the fovea amphidialis (2 vs> 3.5 times longer than wide in M. macramphidum gen. et sp. n.), cylindrical buccal cavity with cuticularised ring (vs ring absent), gubernaculum with apophyses (vs no apophyses), and vagina directed posteriorly (vs vagina at right angle with body surface).

Figures

FIGURE 7. Mudwigglus plebeius gen. et sp. n. A: Male anterior region; B: female head; C: male anterior body region; D: male chord, right hand side view; E: male posterior region. Scale bar = 25 Μm.

FIGURE 8. Mudwigglus plebeius gen. et sp. n. A: Entire male; B: entire female. Scale bar = 50 Μm.

FIGURE 9. Mudwigglus plebeius gen. et sp. n. light micrographs. A: Male head, right hand side view; B: male lateral chord, left hand side view; C: vulva, right hand side view; male posterior region. Arrows point to the pre-cloacal supplements. Scale bar: A and D = 20 Μm; B and C = 12 Μm.