Leptolaimus hamatus, Gu & Sun & Huang, 2024

Gu, Huimin, Sun, Lingyun & Huang, Yong, 2024, Two new species of Leptolaimus (Nematoda: Plectida) from Chinese sea area, Zootaxa 5507 (2), pp. 384-394 : 389-392

Leptolaimus hamatus sp. nov.

( Figures 3–4 , Table 1 )

Holotype and paratype material. Three males and two females were obtained and measured. Holotype (male 1) on slide 3800-1-2-5. Paratype 1 (male 2) on slide 3825-2-2-5, paratype 2 (male 3) on slide 3800-1-2-5, paratype 3 (female 1) on slide 3800-1-2-5, and paratype 4 (female 2) on slide 3800-1-2-5.

Type locality and habitat. Holotype and most paratypes were collected from sea floor muddy sediment at Station 3800-1 (38°0′ N, 122°30′ E, water depth 46 m) in the Yellow Sea, and one paratype was collected from subtidal muddy sediment at Station 3825-2 (38°25′ N, 122°30′ E, water depth 50 m) in the Yellow Sea in 2008.

Etymology. The species epithet comes from the Latin word hamatus , referring to procloacal supplements with hooked distal end.

Measurements. All measurement data are given in Table 1 .

Descriptions

Males

Body slender, tapering anteriorly in pharyngeal region and posteriorly on tail. Cuticle annulated, annuli about 2.0 µm wide at mid-body, without ornamentation. Lateral field present, consists of single alae (two incisures), 3 µm wide at mid-body; originating from anterior third of pharyngeal length, and extending posteriorly to the middle of tail. Numerous body pores present with short and stout setae in sublateral position at both sides of lateral field, and scattered over the body from the pharynx to the proximal part of tail. The first body pore located 22–26 µm from anterior end. Labial region rounded, offset from body contour by a constriction. Inner and outer labial sensilla indistinct. Cephalic setae short, 2–2.5 µm long. Subcephalic sensilla and ocelli absent. Amphidial fovea round, located at level of just post-mid of stoma. Nerve ring surrounding pharynx at level of pre-mid of pharynx, about 40% pharyngeal length from anterior end of the body. Secretory-excretory system not seen. Buccal cavity uniformly tubular. Pharynx cylindrical, with distinct oval basal bulb. Cardia cylindrical. Tail conico-cylindrical with a slightly swollen tip. A pair of precloacal subventral setae 3–4 µm long, 5 µm anterior to cloaca. Two to three pairs of subventral and two pairs of sundorsal caudal setae 3–4 µm long. Three caudal glands present. Spinneret functional.

Reproductive system diorchic; anterior testis outstretched, posterior one reflexed. Spicules paired, knife-like, with broad proximal half part and narrow curved distal half part. Gubernaculum plate-like, with a straight dorsal apophysis. Accessory apparatus composed of one midventral precloacal papilliform sensillum located on anterior cloacal lip, six midventral tubular supplements extending for 120–130 µm from cloaca towards anterior end; alveolar supplements absent. Tubular supplements slightly curved, rounded proximal ends and hooked distal ends, 11–14 µm long, weakly S-shaped. Posteriormost tubular supplement 21 µm anterior to cloaca, anterior to spicules, the space between adjacent supplements increasing from the posteriormost supplement to the anteriormost one, varying from 13 to 23 µm.

Females

Similar to males in most morphological characters, except tail longer (c′> 7.5) without setae, and supplements absent. Reproductive system didelphic, with two opposed, reflexed ovaries, the anterior ovary located to the right side of the intestine, and the posterior one located to the left side of the intestine. Oviduct a narrow tube. Spermathecae indistinct. Vagina straight, 0.3 times vulval body diameter long. Vulva right ventrosublateral, located in the middle of the body, 48–50% of the total body length from the anterior end.

Diagnosis. Leptolaimus hamatus sp. nov. is characterized by body 624–690 µm long; rounded labial region offset from body contour; cephalic setae 2–3 µm long; amphidial fovea located 12–13 µm from anterior end; first body pore located 22–26 µm from anterior end; males with six tubular and without alveolar supplements, tubular supplements hooked distally; spicules slightly curved, knife-like and 22–24 µm long; gubernaculum with a straight dorsal apophysis; tail conico-cylindrical; females without supplements, vulva situated at right subventral side of body.

Remarks. Leptolaimus hamatus sp. nov. is similar to L. octavus Holovachov & Boström, 2013 and L. elegans (Schuurmans-Stekhoven & De Coninck, 1933) Gerlach, 1958 in tubular supplements weakly S-shaped, but differs from L. octavus by supplements hooked distally (vs strongly cuticularized distally with dentate tips in L. octavus ), spicules knife-like (vs slender), vulva right-subventral (vs midventral). Additionally L. octavus is the only species within Leptolaimus in having a bursa-like expansion of the lateral field along the proximal part of the tail of both females and males. The new species differs from L. elegans by different shape of supplements (hook-like distally with point tips vs knot-like distally with dentate tips), and different shape of gubernaculum (plate-like with a straight dorsal apophysis vs triangular with a pointed dorsal apophysis). The new species is also similar to L. septempapillatus Platt, 1973 in having knife-like spicules and similar number of tubular supplements, but it differs from L. septempapillatus by supplements hook-like distally without cuticular collars around their distal ends (vs knot-like distally with dentate tips and with cuticular collars around their distal ends), and vulva right ventrosublateral (vs midventral in the latter species). The new species is also similar to L. gabinoi Villares & Pastor de Ward, 2012 and L. papilliger de Man, 1876 in having tips of supplements hook-like, but it differs from L. gabinoi by shorter cephalic setae (2–3 µm vs 5–6 µm long) and more numerous tubular precloacal supplements (6 vs 3); it differs from L. papilliger by setiform cephalic setae (vs papilliform cephalic setae) and lack of alveolar supplements (vs presence of 12–15 alveolar supplements in L. papilliger ). The new species furthermore differs from L. gracilis sp. nov. by shorter cephalic setae (2-3 µm vs 5–6 µm long), conico-cylindrical tail (vs elongated conical tail), spicules knife-like, and six weakly S-shaped precloacal supplements with hooked distal ends (vs shorter arcuated spicules and eight sickle-shaped supplements). The new species distinguishes from other known species by combination of characters of cephalic setae 2–3 µm long, males with six tubular precloacal supplements with hooked distal ends, without alveolar supplement, spicules knife-like, 22–24 µm long, gubernaculum with a straight dorso-caudal apophysis, females without supplements, vulva right subventral, tail conico-cylindrical.

Figures

FIGURE 3. Drawings of Leptolaimus hamatus sp. nov. (A) entire view of male holotype; (B) entire view of female paratype, showing reproductive system; (C) anterior end of male holotype, showing cephalic setae, amphidial fovea, cuticle pore and cuticle alae; (D) cloacal region of male holotype, showing spicule, gubernaculum and precloacal supplements. Scale bars: A, 20 µm; B, 30 µm; C, D 10 µm.

FIGURE 4. Micrographs of Leptolaimus hamatus sp. nov. (A) anterior end of male holotype, showing cephalic setae, amphidial fovea and first body pore (arrow); (B) posterior region of male 2 paratype, showing tubular supplements; (C) posterior end of male holotype, showing tubular supplements, spicule and gubernaculum; (D) middle region of female paratype, showing vulva (arrow1), ovaries (arrow 2) and eggs (arrow 3). Scale bars: A, C, D 10 µm; B 20 µm.