Metacomesoma macramphida, Huang & Huang, 2018

Huang, Mian & Huang, Yong, 2018, Two new species of Comesomatidae (Nematoda) from the East China Sea, Zootaxa 4407 (4), pp. 573-581 : 578

Metacomesoma macramphida sp. nov.

( Figs 3–4 )

Type material. Holotype male on slide DH 4-8-8-1.

Type locality and habitat. Seabed muddy sediment at Station DH 4-8 in the East China Sea (27°58´N, 125°52.5´E, water depth 116 m).

Etymology. The species name refers to the feature of large amphideal fovea.

Measurements. Measurements are given in the following formula.

Holotype ♂: — 252 M 1204 1322 µm; a=32.2, b=6.2, c=7.1, spicule = 136 µm

11 33 34 29

Description. Male. Body cylindrical, tapered toward both ends. Head diameter 11 µm. Cuticle with fine transverse rows of punctuations, starting at the anterior border of amphideal fovea and continuing to the tail end. Lateral differentiation absent. Multispiral amphideal fovea very large, with 4.5 turns, 12 µm in diameter i.e. equal to 86% of corresponding body diameters, located at a distance of 10 µm from the anterior border of amphideal fovea to the anterior body end. Buccal cavity very small, without teeth. Head sensilla arranged following the 6+6+4 pattern. Inner and outer labial sensilla papilliform; four cephalic setae very short, 1.5 µm long. Pharynx cylindrical, with thickened and plicated wall at the posterior third portion, not forming terminal bulb. Cardia small, conical and surrounded by the intestine. Nerve ring not obvious. Secretory–excretory pore in a distance of 140 µm from the anterior body end.

Reproductive system diorchic. Two testes arranged in tandem and outstretched, 506 µm and 460 µm from their anterior tip to the cloaca respectively. Spicules curved and elongated, 136 µm long, i.e. equal to 4.7 anal body diameters. Proximal end of spicules cephalated and distal end finger-shaped. Gubernaculum 18 µm long, plate-like, without apophysis. Precloacal supplements difficult to detect.

Tail conico-cylindrical, 118 µm long, i.e. equal to 4.1 anal body diameters in length with the posterior half cylindrical. Few caudal setae on the ventral side of tail. Three terminal setae 2 µm long.

Female. Not found.

Diagnosis and discussion. Metacomesoma macramphida sp. nov. is characterized by very small buccal cavity; inner and outer labial sensilla papilliform; four cephalic setae very short, multispiral amphideal fovea large, with 4.5 turns, i.e. equal to 86% of corresponding body diameters; spicules slender and long, 4.7 anal body diameters, with a proximal cephalate capitulum and distal end finger-shaped; gubernaculum plate-like, without apophysis; precloacal supplements difficult to detect. The new species differs from M. cyatholaimoides Wieser, 1954 , which is the only valid species of this genus, mainly in having shorter cephalic setae (1.5 µm vs 5 µm), larger amphideal fovea (4.5 vs 3 turns) and longer spicules (4.7 vs 3.5 anal body diameters). In M. cyatholaimoides , six outer labial setae are as long as four cephalic setae, 5 µm long and close together almost forming a single circle; amphideal fovea with 3 turns, i.e. equal to 53% of corresponding body diameters; pharynx with an elongated terminal bulb; spicules 103 µm; tail conical with the posterior fifth cylindrical ( Chen & Vincx, 2000). In the arrangement of the head sensilla, Metacomesoma macramphida sp. nov. is similar to Comesomoides deconincki Gourbault, 1980 which is the only discovered species in this genus. However, Comesomoides species typically has the following characters: cuticle with lateral differentiation composed of larger dots; gubernaculum with apophysis; precloacal supplements present. In the new species, cuticle is without lateral differentiation; gubernaculum without apophysis: precloacal supplements seemingly absent. Thus, we prefer to identify current species as Metacomesoma .

Figures

FIGURE 3. Metacomesoma macramphida sp. nov. (A) lateral view of male anterior end, showing cephalic seta, amphideal fovea and excretory pore; (B) lateral view of male posterior end, showing spicules, gubernaculum; (C) two testes with spermatozoa.

FIGURE 4. Metacomesoma macramphida sp. nov. (A) male anterior end; (B) lateral view of male anterior end, showing amphideal fovea; (C) male cloacal region, showing spicules; (D) lateral view of male cloacal region, showing spicules and gubernaculum.(Scales:A, B 10 µm; C, D 20 µm).