Hypodontolaimus ventrapophyses Huang & Gao, 2016, sp. nov.

Hypodontolaimus ventrapophyses sp. nov.

(Figs 3–4)

Type material. Two males and three females were measured and studied. Holotype: ♂1 on slide 5-7(0-2)-2; paratypes: ♂2, ♀1, ♀2, and ♀3 on slides 5-7(0-2)-2, 5-7(0-2)-4, 5-7(0-2)-4 and 548(0-2)-1, respectively. Type specimen was deposited in the Qingdao Institute of Oceanology, Chinese Academy of Sciences.

Type locality and habitat. Intertidal silt sediment from the coast of Kangmei Town, Dongshan Island, East China Sea (117°29' E, 23°43' N). Sample comprised surface layer sediment to a depth of 0–2 cm.

Etymology. Species name refers to the structure of the gubernaculum which has a ventral apophyses.

Measurements. Table 2.

Description. Males. Body cylindrical with blunt (or slightly expanded) anterior end and tapered tail end. Cuticle annulated, with homogeneous transverse rows of small dots, lateral differentiation of two longitudinal rows of enlarged dots not linked by slender transverse bars. Somatic setae 7–12 µm long and in four longitudinal rows. Anterior end slightly rounded. Amphidial fovea not seen. Inner labial setae inconspicuous, outer labial setae short (5 µm long) while the four cephalic setae are long, 9–10 µm (or 0.7 h.d. long). Buccal cavity with a large S-shaped dorsal tooth. Pharynx 100 µm long, enveloping the buccal cavity in the form of a dorsally strongly enlarged bulb and a well-developed oval terminal bulb 22 µm long. Ventral gland oblong, located at anterior of intestine, 150 µm from the anterior end. Excretory pore opening at level of median part of pharynx. Reproductive system monorchic, composed of an outstretched testis and a long vas deferens. Spicules 1.6–1.8 a.b.d. long, strongly curved, slender and slightly cephalate proximally and tapered distally. Gubernaculum 1 a.b.d. long, plate with a 6.5 µm ventral apophysis and pointed at the posterior end. Precloacal supplements absent. Tail elongate conical and with a prominent spinneret.

Females. Similar to males in most aspects except that somatic setae not present. Reproductive system amphidelphic with opposed, reflexed ovaries, anterior branch to right and posterior to left of intestine. Vulva located at mid-body length.

Diagnosis. Hypodontolaimus ventrapophyses sp. nov. is characterized by having a homogeneous cuticle with lateral differentiation of two longitudinal rows of larger dots; pharynx with well developed oval-shaped buccal bulb and terminal bulb; a large ventral gland; slender spicules, and gubernaculum with ventral apophysis; and precloacal supplements absent. It differs from all other related species in the genus, except Hypodontolaimus dimorphus Wieser 1954, by the structure of the gubernaculum.

Hypodontolaimus ventrapophyses sp. nov. is similar to Hypodontolaimus dimorphus in having a ventral apophysis of the gubernaculum, similar to H. pumilio Gerlach, 1956 in most aspects, and similar to H. interruptus Wieser & Hopper 1967 and H. steineri Wieser 1954 by the size and shape of body. However, it differs from H. dimorphus by having longer cephalic setae (9–10 µm vs 5 µm) and absence of precloacal supplements (vs seven precloacal supplements in H. dimorphus). It differs from H. pumilio by having a longer body (610–669 vs 436–464 µm) and the structure of gubernacular apophysis (ventral apophysis vs dorsal apophysis). The new species differs from H. interruptus by having shorter cephalic setae and somatic setae (9–10 µm and 12 µm vs 15 µm and 35 µm long, respectively), and the gubernaculum is small and without a ventral apophysis in H. interruptus. It differs from H. steineri by having shorter cephalic setae and somatic setae (9 µm and 12 µm vs 15 µm and 20 µm long, respectively), and in having a gubernaculum plate with a strong hook-shaped dorsal apophyses in H. steineri.

To date more than 40 nominal species have been described under Hypodontolaimus or moved to it from other genera. However, only about 25 may be accepted as valid for the genus (http://nemys.ugent.be/aphia.php?p=taxlist; Andrássy & Gibson 2007). The others are either synonyms or have been transferred to other genera. Hypodontolaimus heymonsi (Steiner, 1922), H. sivertseni Allgén 1951 and H. punctulatus (Cobb, 1920) Filipjev 1934, known only from females, should be considered as invalid species. The new species described here belongs to the second group of Hypodontolaimus, lacking supplements.