Leptolaimus sextus, 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 : 49-53

Leptolaimus sextus sp. n.

( Figs 21 , 22 A–B ; Table 14)

Type material. Holotype male (slide # Type-8479) and 15 male and 18 female paratypes (slides # Type-8479 - Type-8487) 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 (16 males and 18 females) .

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

Description. Adult. Body fusiform, strongly tapering anteriorly in pharyngeal region and posteriorly on tail; ventrally curved or coiled 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 2.5–3.3 µm wide at mid-body, without ornamentation. Lateral field present, consists of single ala (two incisures), 2.0–3.5 µm wide at mid-body; originating at level of posterior part of stoma (anterior to first body pore) and extending posteriorly to proximal part of tail. Prominent body pores in sublateral position at both sides of lateral field present, arising from oval lateral epidermal gland cells; usually five pairs of body pores are present along pharyngeal region, and one at level of cardia; numerous body pores scattered over rest of the body. Anteriormost body pore located at level of procorpus. Labial region truncate, offset from body contour, lips fused. Inner labial sensilla indistinct; outer labial sensilla large and papilliform, located on the outer surface of lips. Cephalic sensilla setiform, equal to 20–50% of labial region diameter. Subcephalic and cervical sensilla and ocelli absent. Amphidial fovea round, located at level of anterior third of stoma. Nerve ring surrounding pharynx at level of anterior part of isthmus. Hemizonid not seen. Secretory-excretory system present; excretory pore located posterior to nerve ring. 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 (more curved ventrad in male), conoid, gradually narrowing distally. Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Male. Long setae emerging through first, second and fifth pairs of body pores. Reproductive system diorchic; anterior testis outstretched; posterior one reflexed. Spicules paired, symmetrical, with arcuate cylindrical calamus and ovoid manubrium. Gubernaculum plate-like, with double caudal apophyses. Accessory apparatus composed of one midventral precloacal papilliform sensillum located on anterior cloacal lip, five (six in one specimen) evenly spaced midventral tubular supplements extending for 177–232 µm from cloaca towards anterior end; alveolar supplements absent. Tubular supplements weakly S-shaped, with bifid tips. Posteriormost tubular supplement 20.0–28.0 µm anterior to cloaca, at level of spicules. Sublateral precloacal and caudal sensilla present: two (one pair) precloacal setae at level of spicules and usually four (two pairs) caudal papillae arranged in two subventral pairs.

Aberrant male. Similar to typical males except for the larger body size and presence of nine midventral tubular supplements extending for 281 µm from cloaca towards anterior end.

Female. Reproductive system didelphic, amphidelphic; ovary branches reflexed antidromously. Anterior genital branch 69–129 µm long (equal to 10.3–18.3% of total body length), located on right-hand side of intestine (n=11), posterior genital branch 76–122 µm long (equal to 11.2–17.6% of total body length), located on left-hand side of intestine (n=11). Oviduct a narrow tube. Spermathecae obscure. Uterus a wide tube. Vagina straight, 0.3 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 1.6–2.2 anal body diameters long, often S-shaped in lateral view; surrounded by three gland-like cells at intestine-rectum junction.

Diagnosis (single aberrant male excluded). Leptolaimus sextus sp. n. is particularly characterised by the 626– 728 µm long body; truncated labial region offset from body contour; cephalic setae 1.5–2.0 µm long; amphid located 8.0–12.0 µm from anterior end; first body pore located 41.0–48.5 µm from anterior end; lateral field originating 28.0–41.0 µm from anterior end; female without supplements, vagina without pars refringens, vulva midventral; male with five (rarely six) tubular and without alveolar supplements, tubular supplements weakly Sshaped with bifid tips; spicules arcuate and 39.0–46.0 µm long.

Relationships. Current specimens are similar to the type specimen of L. alatus Vitiello, 1971 in general morphology, shape of labial region, distinct papilliform cephalic setae, position of amphid, anterior body pore, lateral field, number and shape of tubular supplements, shape of gubernaculum. The major differences are body size (626–728 µm vs. 595 µm in L. alatus ), length of spicules (39.0–46.0 µm vs. 26.0 µm in L. alatus ), shape of supplements (with bifid tips vs. without in L. alatus ). Unfortunately, the original description of L. alatus is not complete and insufficiently illustrated to allow any further comparisons. However, we found a population that we think belongs to L. alatus (see description below). L. sextus sp. n. differs from this population of L. alatus in larger body (626–728 µm vs. 376–518 µm in L. alatus ) and other measurements, number and shape of tubular supplements (usually five and with bifid tips vs. usually seven and with blunt tips in L. alatus ). In having bifid tips of tubular supplements, the new species shows similarities to L. gerlachi Murphy, 1966 , L. praeclarus Timm, 1961 and L. vipriensis Gagarin & Nguyen Vu Thanh, 2005 , but it can be easily distinguished from all three species by the shape of the labial region with distinct papilliform outer labial sensilla (vs. outer labial sensilla indistinct), among other characters. Leptolaimus limicolus Lorenzen, 1972 has similar number of supplements and shape of spicules, however it can be easily separated from L. sextus sp. n. in the shape of lip region and size of outer labial sensilla (indistinct vs. large distinct papilliform in L. sextus sp. n.) and asymmetrical spicules (vs. symmetrical in L. sextus sp. n.).

Figures

FIGURE 21. Leptolaimus sextus 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 22. Leptolaimus sextus sp. n. (A–B) and Leptolaimus alatus Vitiello, 1971 (C–D). A, C: Entire male; B, D: Entire female. Scale bar: A–D = 50 µm.