Leptolaimus gracilis, 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 : 385-389

Leptolaimus gracilis sp. nov.

( Figures 1–2 , Table 1 )

Holotype and paratype material. Three males and one female were obtained and measured. Holotype (male 1) on slide SPG2-5-3. Paratype 1 (male 2), paratype 2 (male 3) and paratype 3 (female 1) all on slide SPG3-5-7.

Type locality and habitat. Holotype and paratypes were all collected from intertidal fine sandy sediments at Dongtou Island of Wenzhou City along the East China Sea (27°51′45″ N; 121°9′4″ E) in May 2023 .

Etymology. The species epithet comes from the Latin word gracilis , referring to the new species with slender body.

Measurements. All measurement data are given in Table 1 .

Leptolaimus gracilis sp. nov. Leptolaimus hamatus sp. nov. ♂1 ♂2 ♂3 ♀1 ♂1 ♂2 ♂3 ♀1 ♀2 Total body length 980 978 1001 936 690 642 624 700 682 Maximum body diameter 14.7 12.8 13.3 14.5 20 21 19.5 24 20 Head diameter 5 4.5 4.5 4 5 4.5 4 4 4 Length of cephalic setae 6 5 6 6 2.5 2 2 3 2.5 Length of buccal cavity 21 22 20 19 24 - 18 18 16 Diameter of amphidial fovea 4.5 3.5 4 4 4 4 3.5 3 3 Body diameter at amphidial fovea 8 7.5 7.5 7.5 8 8 8 8 8 Amphidial fovea from anterior end 14 14 15 11 13 12 12.5 13 12 Length of pharynx 137 143 150 128 136 145 128 139 134 Body diameter at pharyngeal base 13 13 12 13 18 19 18.5 21 19 Length of cardia 6.5 7 10 7 8 9 7 9 8.5 Spicules length along arc 18 18 18 - 22 22 24 - - Length of gubernaculum 12 13 11 - 8 9 11 - - Number of precloacal supplements 8 8 8 - 6 6 6 - - Vulva from anterior end - - - 456 - - - 334 341 Body diameter at vulva - - - 14 - - - 24 20 V% - - - 49 - - - 48 50 Body diameter at cloaca or anus 14.4 12.5 12.5 9.5 17 18 17 15 14 Tail length 105 111 84 116 110 102 101 118 106 a 66.7 76.4 75.2 64.6 34.5 30.6 33.1 29.2 34.1 b 7.1 6.9 6.7 7.3 5.1 4.4 5.0 5.0 5.1 c 9.3 8.8 11.9 8.0 6.3 6.3 6.4 5.9 6.4 c′ 7.3 8.9 6.2 12.2 6.5 5.7 5.9 7.7 7.6

Characters

Descriptions

Males

Body very slender. Cuticle annulated, annuli about 2.0 µm wide at mid-body, without ornamentation. Lateral field and body pores indistinct. Setae along pharyngeal region not seen. Labial region rounded, offset from body contour by a constriction. Inner and outer labial sensilla indistinct. Cephalic sensilla setiform, equal to 1.2–1.5 times of labial region diameter. Subcephalic and cervical sensilla and ocelli absent. Amphidial fovea unispiral, round in outline, 47–56% corresponding body diameter, located at level of post-mid of stoma. Nerve ring surrounding pharynx at level of middle of pharynx, i.e. 78–94 µm from anterior end of the body. Secretory-excretory system not seen. Buccal cavity uniformly tubular, 4.2–4.9 head diameter deep. Pharynx cylindrical, with distinct oval basal bulb. Cardia cylindrical, its posterior part embedded in intestine. Tail elongate conical, gradually narrowing distally. Three to four pairs of subventral and two pairs of subdorsal caudal setae 4–5 µm long. Three caudal glands present. Spinneret functional.

Reproductive system diorchic, anterior testis outstretched, posterior one reflexed. Spicules paired, symmetrical, arcuated with expanded proximal end and tapered distal end. Gubernaculum with a straight dorso-caudal apophysis. Accessory apparatus composed of eight almost evenly spaced midventral tubular supplements extending for 211– 251 µm from cloaca towards anterior end, without alveolar supplements. Tubular supplements sickle-shaped, with rounded proximal ends and pointed distal ends, 8–8.5 µm long. Posteriormost tubular supplement 21–36 µm anterior to cloaca, and anterior to spicules. The spacing of adjacent supplements in the three male specimens is almost equal (27–30 µm, 22–24 µm and 22–29 µm, respectively) except that of the most anterior two supplements being slightly larger (37 µm, 34 µm and 31 µm, respectively).

Female

Similar to males in most morphological characters, except tail longer and slender (c′=12.2 vs 6.2–8.9 in males) without setae, amphidial fovea located in more anterior position, 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. Uterus a wide and short tube. Vagina straight, 0.2 times vulval body diameter long. Vulva midventral, located in the mid-body, 49% of the total body length from the anterior end.

Diagnosis. Leptolaimus gracilis sp. nov. is characterized by slender body 936–1001 µm long; rounded labial region offset from body contour; cephalic setae 5–6 µm long; amphidial fovea located 2.8–3.3 times of head diameter from anterior end; males with eight tubular and without alveolar supplements, tubular supplements sickle-shaped with pointed tips; spicules arcuated and about 18 µm long; gubernaculum with a straight dorso-caudal apophysis; female without supplements, vulva situated at midventral side of body.

Remarks. Leptolaimus gracilis sp. nov. belongs to the group of Leptolaimus species in which males have only tubular precloacal supplements and females have no supplements. The new species is similar to Leptolaimus macer Lorenzen, 1972 in having sickle-shaped tubular precloacal supplements, but differs by longer body length (936– 1001 µm vs 698–790 µm), larger amphidial fovea (3.5–4.5 µm vs 2 µm in diameter in males), straight dorso-caudal gubernacular apophysis (vs arcuated dorsal apophysis), males with eight tubular supplements with pointed tips and the spacing of adjacent supplements almost equal except that of the most anterior two supplements (vs seven tubular supplements with truncated tips, and there is a distinct gap between the second and the third supplements), female body slender (a=64.6 vs 36.8–43.6), vulva situated at midventral side of body vs right-ventrosublateral side in L. macer . In body size and number of precloacal supplements, the new species is also similar to L. elegans (Schuurmans-Stekhoven & De Coninck, 1933) Gerlach, 1958 and L. septempapillatus Platt, 1973 , but differs from L. elegans by spicules slender, arcuated and cephalated proximally vs spicules slightly bent, knife-like; eight tubular supplements sickle-shaped with pointed distal ends vs 5–8 tubular supplements weakly S-shaped with dentate tips. The new species differs from L. septempapillatus by spicules 18 µm long, slender and cephalated proximally vs spicules 22–26 µm long, knife-like; gubernaculum small with dorso-caudal apophyses vs rod-like without apophyses; eight tubular supplements sickle-shaped without cuticular collars around their distal ends vs seven tubular supplements straight and cephalated proximally and knot-like distally with dentate tips and with cuticular collars around their distal ends. The new species can be identified from other known species by combination of characters of cephalic setae 5–6 µm long, males with eight almost equal spaced sickle-shaped supplements, without alveolar supplement, gubernaculum with a straight dorso-caudal apophysis; female without supplements, vulva situated at midventral side of body.

Figures

FIGURE 1. Drawings of Leptolaimus gracilis sp. nov. (A) entire view of male holotype; (B) anterior end of male holotype, showing cephalic setae, buccal cavity and amphidial fovea; (C) entire view of female paratype, showing reproductive system; (D) cloacal region of male holotype, showing spicule, gubernaculum and precloacal supplement. Scale bars: A, C 20 µm; B, D 10 µm.

FIGURE 2. Micrographs of Leptolaimus gracilis sp. nov. (A) pharygeal region of male holotype, showing posterior bulb; (B) anterior end of male holotype, showing buccal cavity (arrows); (C) anterior end of female paratype, showing cephalic setae, amphid and buccal cavity (arrow); (D) precloacal region of male 2 paratype, showing precloacal supplements; (E) spicule and gubernaculum of male holotype; (F) middle portion of female paratype, showing vulva (arrow 1), ovary (arrow 2) and egg (arrow 3). Scale bars:10 µm.