Actinonema diplobulba, Chu, Hao & Huang, 2023

Chu, Mengdi, Hao, Yingdong & Huang, Mian, 2023, Two new species of Chromadorida (Nematoda) from the intertidal zone of the Yellow Sea, China, Journal of Natural History 57 (25 - 28), pp. 1364-1376 : 1365-1369

Actinonema diplobulba sp. n.

( Figures 1 , 2 and Table 1 )

Type material

Two males and one female were collected from the sand beach of Huangdao at the west coast of Qingdao (35.917°N, 120.2°E). Holotype male 1 on slide HDYST 71–2 , paratypes: male 2 and female 1 on slides HDYST 71–4 and HDYST 71–7 , respectively.

Type locality and habitat

Holotype was found in the surface layer of silver sand at the sandbeach of Huangdao.

Etymology

The specific name is derived from the Greek adjective diploos (double) and Latin noun bulbus, referring to its double pharyngeal bulbs.

Measurements

All measurement data are given in Table 1 .

Description

Males. Body small, cylindrical and gradually tapering towards both ends, with anterior end blunt. Cuticle ornamentation heterogeneous with lateral differentiation as a ridge beginning at posterior of amphid (about 80 μm to anterior body end), and disappearing at posterior quarter of tail (about 84 μm to cloaca). Somatic setae not seen.Six inner labial papillae, minute and inconspicuous. Six outer labial setae together with four cephalic setae in one circle. Cephalic setae slightly longer than outer labial setae,25–43% of head diameter. Cuticular solid cone absent (cf. Muthumbi and Vincx 1998). Buccal cavity conical, with one distinct sharply pointed dorsal tooth in anterior portion of buccal cavity. Amphideal fovea conspicuous, transversely oval, with a central slit; occupying 54–64% of corresponding body diameter, located at level of cephalic setae. Pharynx with distinct double posterior bulbs. Cardia indistinct. Nerve ring located posterior to middle of pharynx. Excretory pore just posterior to nerve ring, about 61 μm to anterior body end. Ventral gland large, located posterior of the pharyngo-intestinal junction. Tail conical, with an elongate tapering tip and lacking any annulation from 4–5 μm from the end, caudal glands unclear. Terminal spinneret developed. except a, b, c, c ′ and V%). posterior bulbs; (c) anterior end of male, showing amphidial fovea and cephalic setae; (d) posterior portion of male, showing spicules (arrow); (e) cloacal region of male, showing telamon and gubernaculum (arrow); (f) posterior portion of female, showing lateral differentiation and tail. Scale bars: 10 μm.

Reproductive system monorchic with single outstretched testis located to the right of intestine. Single spicule slender, arcuate, 1.5–1.7 cloacal body diameter long, cephalated proximally and tapered distally. Single gubernaculum spinous, extra hammer-shaped lateral pieces (telamon) hollow, 13 μm long. Precloacal supplement absent.

Females. Overall morphological features similar to males. Reproductive system amphidelphic with two opposite and reflexed ovaries, anterior to the right of the intestine, posterior to the left of it. Vulva raised, located in the middle of the body.

Differential diagnosis and discussion

Actinonema diplobulba sp. nov. is characterised by large amphideal fovea transverse oval-shaped, pharynx with double posterior bulbs, single spicule slender, arcuate with cephalated proximal end, gubernaculum spinous, and an extra hammer-shaped telamon present.

The genus Actinonema Cobb, 1920 belongs to the subfamily Euchromadorinae Gerlach and Riemann,1973 of the family Chromadoridae Filipjev, 1917 ,which contains five subfamilies ( Hodda 2022). It was erected by Cobb (1920) with the type species A. pachydermatum Cobb, 1920 . It includes 16 nominal species worldwide, but only 11 have been identified as valid species (Nemys eds 2022). Among them, A. dolichurum Gagarin and Long, 2017 has no male described; it should be considered as a species inquirenda. Shi et al. (2018) provided an updated key to nine species of the genus (excluding A. dolichurum Gagarin and Long, 2017 , A. longicaudatoides Gagarin, 2015 and A. parvum Gagarin, 2015 ).

Among the 10 valid species within the genus, three species – A. falciforme Shi, Yu and Xu, 2018 , A. longicaudatum Steiner, 1918 and A. smolae Muthumbi and Vincx, 1998 – have no spicules, only having telamon or gubernaculum. Seven species – A. celtica Boucher, 1976 , A. fldata Vitello, 1970 , A. grafi Jensen, 1991 , A. longicaudatoides Gagarin, 2015 , A. paraceltica Muthumbi and Vincx, 1998 , A. pachydermatum ( Cobb, 1920) and A. parvum Gagarin, 2015 – have spicules. Among them, A. celtica , A. paraceltica and A. pachydermatum have telamons; A. fldata , A. grafi and A. parvum lack telamons. Actinonema longicaudatoides has an extended cuticle in front of the cloaca in males. Detailed investigation suggests the nematode studied here is a new species of the genus Actinonema . The new species has double pharyngeal bulbs (a character unique within the genus), and both spicule and telamon, by which it can be easily distinguished from its congeners. The difference between A. diplobulba sp. nov. and other known species in the genus can be inferred from the key below.

Figures

Figure 1. Actinonema diplobulba sp. nov. (a) entire male; (b) anterior end of male, showing amphidial fovea and cephalic setae; (c) pharyngeal region of male, showing buccal cavity teeth, posterior pharyngeal bulbs; (d) posterior portion of male; (e) spicule, gubernaculum and telamon; (f) entire female. Scale bars: a, f = 30 μm; b, d, e = 10 μm; c = 20 μm.

Figure 2. Actinonema diplobulba sp. nov. (a) Pharyngeal region of male, showing buccal cavity teeth, posterior pharyngeal bulbs; (b) pharyngeal region of male, showing amphidial fovea and double