Leptolaimus secundus, Holovachov & Boström, 2013

Holovachov, Oleksandr & Boström, Sven, 2013, Swedish Plectida (Nematoda). Part 4. The genus Leptolaimus de Man, 1876, Zootaxa 3739 (1), pp. 1-99 : 18-22

Leptolaimus secundus sp. n.

( Figs 6 , 7 A–B ; Table 5)

Type material. Holotype male (slide # Type-8454) and three male and four female paratypes (slides # Type-8455 - Type-8456) deposited in the invertebrate type collection of the Department of Zoology , Swedish Museum of Natural History, Stockholm, Sweden.

Type locality. Mud from 30–39 m deep, Gullmarn Fjord near Fiskebäckskil, Sweden (N 58° 15' 13'', E 11° 27' 31''), 21 August 2010, legit M. Clément (four males and four females) .

Etymology. The specific epithet " secundus " is translated as " the second " and refers to the sequential number of the new species described in this publication.

Description. Adult. Body tapering anteriorly in pharyngeal region and posteriorly on tail; straight or ventrally curved upon fixation, more strongly curved ventrad in posterior part in males. Maximum body diameter at vulva in female; male body more cylindrical. Cuticle annulated; annuli 1.1–1.3 µm wide at mid-body, without ornamentation. Lateral field present, consists of single ala (two incisures), 1.0–1.5 µm wide at mid-body; originating at level of stoma (anterior to the first body pore) and extending posteriorly to distal part of tail. Prominent body pores in sublateral position at both sides of lateral field present, arising from oval lateral epidermal gland cells; usually four pairs of body pores are present along pharyngeal region; several body pores scattered over rest of the body. Anteriormost body pore located at level of stoma base or procorpus. Labial region rounded, continuous with body contour, lips fused. Inner and outer labial sensilla indistinct. Cephalic sensilla setiform, equal to 30–50% of labial region diameter. Subcephalic and cervical sensilla and ocelli absent. Amphidial fovea round, located anterior to middle of stoma. Nerve ring surrounding pharynx at level of anterior part of isthmus. Hemizonid not seen. Secretory-excretory system obscure. Buccal cavity uniformly tubular: cheilostom and gymnostom short, undifferentiated; stegostom tubular, with uniformly thickened lumen. Pharynx muscular, cylindrical anteriorly, with distinct oval basal bulb; valvular apparatus absent. Anterior cylindrical part of pharynx subdivided by breaks in muscular pharyngeal tissue into cylindrical procorpus, cylindrical metacorpus and narrow isthmus. Pharyngeal glands and their orifices indistinct. Cardia cylindrical, its posterior part embedded in intestine. Tail similar in shape in both sexes (longer and more curved ventrad in male), elongate-conoid, gradually narrowing distally. Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Male. Four short setae emerging through first, second, third and fourth body pores. Reproductive system diorchic; anterior testis outstretched; posterior one reflexed. Spicules paired, symmetrical, with arcuate subcylindrical calamus and ovoid manubrium. Gubernaculum plate-like, with weak dorsocaudal apophysis. Accessory apparatus composed of one midventral precloacal papilliform sensillum located on anterior cloacal lip; single midventral tubular supplement; 9–15 alveolar supplements. Tubular supplement weakly arcuate in shape, with bluntly rounded tip, 42–47 µm anterior to cloaca, anterior to spicules. Alveolar supplements with thin sclerotized lining. Anteriormost alveolar supplement 147–153 µm from anterior end, at level of anterior part of intestine. Sublateral precloacal and caudal sensilla present: two (one pair) precloacal setae at level of cloaca and usually eight (four pairs) caudal setae arranged in two subventral and two subdorsal pairs. One subventral pair of papilliform sensilla located at the bases of the second (from cloaca) pair of caudal setae.

Female. Reproductive system didelphic, amphidelphic; ovary branches reflexed antidromously. Anterior genital branch 72–90 µm long (equal to 11.3–13.9% of total body length), located on right-hand side of intestine (n=4), posterior genital branch 62–83 µm long (equal to 10.5–12.9% of total body length), located on left-hand side of intestine (n=4). Oviduct a narrow tube. Two offset, oval, sac-like spermathecae located on each (right and left) side of each (anterior and posterior) gonoduct. Spermathecae often filled with oval spermatozoa. Uterus a wide and short tube. Vagina straight, 0.3–0.4 times vulval body diameters long; pars proximalis vaginae encircled by single sphincter muscle; pars refringens vaginae absent. Vulva midventral. Epiptygmata and sensitive structures around vulva (advulval sensilla) absent. Supplements absent. Rectum 1.3–2.6 anal body diameters long; surrounded by three gland-like cells at intestine-rectum junction.

Diagnosis. Leptolaimus secundus sp. n. is particularly characterised by the 576–645 µm long body; rounded labial region continuous with body contour; cephalic setae 2.0 µm long; amphid located 6.5–7.0 µm from anterior end; first body pore located 23.0–28.5 µm from anterior end; lateral field originating 18.0–23.0 µm from anterior end; female without supplements, vagina without pars refringens, vulva midventral; male with single tubular and 9–15 alveolar supplements, tubular supplement weakly arcuate with blunt tips, alveolar supplements with sclerotized lining; spicules arcuate and 23.0–26.5 µm long.

Relationships. The new species belongs to a group of species having both tubular and alveolar supplements in males. Leptolaimus secundus sp. n. differs from all known species in this group besides Leptolaimus donsi ( Allgén, 1947) comb. n. in having just one tubular supplement. Although, males of L. donsi usually have two tubular supplements, we also found two aberrant specimens with just single tubular supplement (see below). The new species can however be easily differentiated from L. donsi in the shape (amphid without thick sclerotized rim vs. with sclerotized rim in L. donsi ) and location of the amphid (6.5–7.0 µm from anterior end vs. 2.0–5.0 µm from anterior end in L. donsi ), position of the anteriormost body pore (23.0–28.5 µm from anterior end vs. 11.5–14.0 µm from anterior end in L. donsi ), position of the anterior end of lateral field (18.0–23.0 µm from anterior end vs. 8.0– 13.0 µm from anterior end in L. donsi ), orientation of vulva (ventral vs. right-ventrosublateral) and absence of pars refringens vaginae (vs. present in L. donsi ). The only other known species of Leptolaimus having single tubular supplement is L. ditlevseni ( Steiner, 1916) De Coninck, 1965 . The new species differs from L. ditlevseni in having alveolar supplements (vs. absent in L. ditlevseni ), length of spicules (23–27 µm vs. 11.5 µm in L. ditlevseni ), and presence of gubernaculum (vs. absent in L. ditlevseni ).

Figures

FIGURE 6. Leptolaimus secundus sp. n., holotype male (A–C) and paratype female (D–E). A: Anterior end, surface view; B: Pharyngeal region, median section; C: Male posterior region; D: Female tail; E: Female reproductive system (anterior part). Scale bar: A–E = 20 µm.

FIGURE 7. Leptolaimus secundus sp. n. (A–B), Leptolaimus mixtus Lorenzen, 1972 (C–D) and Leptolaimus quartus sp. n. (E). A, C: Entire female; B, D, E: Entire male. Scale bar: A–E = 50 µm.