Aulostomonema abyssum, Leduc, 2023

Leduc, Daniel, 2023, New nematode species and genera (Nematoda: Chromadorea) from cold seeps on Hikurangi Margin, New Zealand, European Journal of Taxonomy 856, pp. 1-45 : 17-22

Aulostomonema abyssum gen. et sp. nov.

urn:lsid:zoobank.org:act:105F5B86-DC27-4689-8279-10549DAC2C21

Figs 7–9 , Table 4

Diagnosis

Aulostomonema abyssum gen. et sp. nov. is characterized by body length 7.1–8.8 mm; short, 3 µm long outer labial setae and cephalic setae in single circle; amphids ca 0.5 cbd from anterior extremity; narrow mouth opening followed by constriction expanding posteriorly into cuticularized, cylindrical buccal cavity 19–23 µm long and 3 µm in diameter; excretory pore located at level of nerve ring or slightly posterior; spicules 1.5 cloacal body diameters long, gubernaculum with dorsocaudal apophyses, at least 10–13 papilliform precloacal supplements present; short conical tail with rounded posterior extremity.

Etymology

The species name is derived from the Latin ʻ abyssus ʼ meaning ʻa deep pit, the deep seaʼ, ʻhellʼ and refers to the deep type locality.

Material examined

Holotype NEW ZEALAND • ♂; Hikurangi Margin , Mungaroa cold seep site; 41.9382° S, 175.3128° E; 2077 m water depth; collected on 7 Jul. 2019; sandy mud (96% silt/clay, mean particle size 20 µm), voyage TAN1904, station 21; NIWA154911 .

Paratypes NEW ZEALAND – Hikurangi Margin, Mungaroa cold seep site • 1 ♂; 41.9403° S, 175.3157° E; 2091 m water depth; collected on 7 Jul. 2019; sandy mud (98% silt/clay, mean particle size 16 µm), voyage TAN1904, station 23; NIWA154912 • 2 juveniles; 41.9354° S, 175.3076° E; 2070 m water depth; collected on 7 Jul. 2019; sandy mud (98% silt/clay, mean particle size 16 µm), voyage TAN1904, station 15; NIWA154913 .

Type habitat and locality

New Zealand continental slope, Hikurangi Margin, Mungaroa cold seep.

Description

Male

Body cylindrical, colourless, tapering slightly towards both extremities. Cuticle finely striated, no lateral differentiation. Somatic setae short and sparse. Rounded cephalic region, not set-off from rest of body. Lip region poorly developed; inner labial papillae not observed. Six short outer labial setae, 3 µm or 13– 14% cbd long, situated at same level as four cephalic setae of same length. Additional and subcephalic setae absent. Amphidial fovea circular; outline cuticularized, surrounded by cuticle striations, ca 0.5 cbd from anterior extremity. Narrow mouth opening followed by constriction 20–22 µm in length, apparently surrounded by several small glands, expanding posteriorly into cuticularized, cylindrical buccal cavity, 19–23 µm long and 3 µm in diameter. Pharynx muscular, not surrounding cylindrical buccal cavity; posterior portion of pharynx swollen into pharyngeal bulb; ducts of pharyngeal glands not observed. Nerve ring located slightly posterior to middle of pharynx. Secretory-excretory system with large ventral gland situated at level of cardia; excretory pore located at level of nerve ring or slightly posterior. Cardia not surrounded by intestine, well-developed, 43–93 µm long. Multiple pseudocoelomocytes present in pharyngeal region. Intestine with amorphous brown content.

Reproductive system with one anterior outstretched testis located to the left of intestine. Sperm cells globular 12–17 × 18–22 µm. Spicules short, arcuate, with velum, 1.5 cloacal body diameters long, strongly cuticularized, tapering distally. Gubernaculum with dorsocaudal apophyses tapering distally or with bifid tip. At least 10–13 papilliform precloacal supplements present, difficult to observe, beginning ca 30 µm anterior to cloaca and 30–80 µm apart. Several large rectal glands present; multiple ejaculatory glands present on either side of vas deferens extending 5–6 cloacal body diameters anterior to cloaca Tail short, conical with rounded posterior extremity. Caudal glands not observed.

Juvenile

Similar to males but with shorter body length, lower ratios of a, b and c, slightly smaller amphids, and longer conical tail with pointed posterior extremity.

Figures

Fig. 7. Aulostomonema abyssum gen. et sp. nov. A, E–F. Holotype (NIWA154911). B, D. Paratype (NIWA154912). C, G. Paratype (NIWA154913). A–B. Anterior body portion of male. C. Anterior body region of juvenile. D. Posterior body region of male. E. Copulatory apparatus. F. Posterior body region of male. G. Posterior body region of juvenile. Scale bar: A = 100 µm; B, D, G = 75 µm; C = 70 µm; E = 80 µm; F = 200 µm.

Fig. 8. Aulostomonema abyssum gen. et sp. nov. Light micrographs of male, holotype (NIWA154911). A. Cephalic region showing amphid. B. Cephalic region showing anterior sensilla. C. Cephalic region showing pharynx. D. Cephalic region showing buccal cavity. E. Copulatory apparatus and precloacal supplements. Scale bar: A–D = 20 µm; E = 18 µm.

Fig. 9. Aulostomonema abyssum gen. et sp. nov. Composite light micrograph image of entire male, paratype (NIWA154912). Scale bar = 1000 µm.