Leptolaimus septimus, 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 : 56-59

Leptolaimus septimus sp. n.

( Figs 24 , 25 A–B ; Table 16)

Type material. Holotype male (slide # Type-8488) and four male and eight female paratypes (slides # Type-8488 - Type-8492) deposited in the invertebrate type collection of the Department of Zoology , Swedish Museum of Natural History, Stockholm, Sweden.

Additional material. One female (slide # 131244) deposited in the general invertebrate collection of the Department of Zoology, Swedish Museum of Natural History, Stockholm, Sweden.

Type locality. Shells and sand from 15–22 m deep, Skagerrak off the west coast of Sweden (N 58° 12' 37'', E 11° 18' 53''), 09 August 2011, legit O. Holovachov (five males and eight females) .

Additional localities. Coarse gravel from 30–50 m deep, Skagerrak off the west coast of Sweden (N 58° 17' 58'', E 11° 10' 05''), 09 August 2011, legit O. Holovachov (one female) ;

Etymology. The specific epithet " septimus " is translated as " the seventh " 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; strongly 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 2.2–3.1 µm wide at mid-body, without ornamentation. Lateral field present, consists of single ala (two incisures), 1.5–2.0 µm wide at mid-body; originating at level of posterior part of stoma or stoma base (anterior to first body pore) and extending posteriorly to middle 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; 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 50–70% 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. Secretoryexcretory system present; excretory pore located at level with or 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 (longer but plumper and more curved ventrad in male), elongate-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 subcylindrical calamus and ovoid manubrium. Gubernaculum plate-like, with double dorsocaudal apophyses. Accessory apparatus composed of one midventral precloacal papilliform sensillum located on anterior cloacal lip, four (five in one male) evenly spaced midventral tubular supplements extending for 144–184 µm from cloaca towards anterior end; alveolar supplements absent. Tubular supplements weakly S-shaped, with bifid tips in posteriormost supplements and blunt tips in anteriormost supplements. Posteriormost tubular supplement 29.5–34.0 µm anterior to cloaca, anterior to spicules. Sublateral precloacal and caudal sensilla present: two (one pair) precloacal setae at level of spicules and usually two (one pair) caudal setae arranged subventrally. One subventral pair of papilliform sensilla located somewhat posterior to the bases of caudal setae.

Female. Reproductive system didelphic, amphidelphic; ovary branches reflexed antidromously. Anterior genital branch 64–109 µm long (equal to 8.0–15.5% of total body length), located on right-hand side of intestine (n=6), posterior genital branch 62–102 µm long (equal to 7.6–15.0% of total body length), located on left-hand side of intestine (n=6). 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 1.4–1.8 anal body diameters long; surrounded by three gland-like cells at intestine-rectum junction.

Diagnosis. Leptolaimus septimus sp. n. is particularly characterised by the 679–850 µm long body; truncate labial region offset from body contour; cephalic setae 2.5–3.5 µm long; amphid located 8.5–11.5 µm from anterior end; first body pore located 37.0–44.0 µm from anterior end; lateral field originating 26.5–37.0 µm from anterior end; female without supplements, vagina without pars refringens, vulva midventral; male with four (rarely five) tubular and without alveolar supplements, tubular supplements weakly S-shaped, with bifid or blunt tips; spicules arcuate and 31.0–33.5 µm long.

Relationships. The new species is most similar to L. alatus and L. sextus sp. n. in having distinct large papilliform outer labial sensilla. Leptolaimus septimus sp. n. differs from L. alatus in having fewer tubular supplements (4–5 vs. 6–8 in L. alatus ), bifid tips of posteriormost tubular supplements (vs. blunt in L. alatus ), longer body (679–850 vs. 376–595 µm in L. alatus ), longer tail in both males (91–106 µm, c'=4.7–5.3 vs. 48–84 µm, c'= 2.8–4.2 in L. alatus ) and females (73–91 µm, c'=5.1–7.1 vs. 38–80 µm, c'= 3.4–4.4 in L. alatus ). It differs from L. sextus sp. n. in having shorter spicules (31–34 µm vs. 39–46 µm in L. sextus sp. n.) and longer tail in both males (91–106 µm, c'=4.7–5.3 vs. 64–71 µm, c'= 2.6–3.2 in L. sextus sp. n.) and females (73–91 µm, c'=5.1–7.1 vs. 56–61 µm, c'= 3.4–3.9 in L. sextus sp. n.). From other species of the genus Leptolaimus , males of which have only four evenly spaced tubular supplements ( L. gerlachi Murphy, 1966 , L. praeclarus Timm, 1961 , L. octavus sp. n., some specimens of L. nonus sp. n. and L. elegans ), the new species differs in the shape of the labial region with distinct large papilliform outer labial sensilla. It furthermore differs from L. gerlachi in the shape of tubular supplements (S-shaped vs. weakly arcuate in L. gerlachi ), shape of gubernaculum (with dorsocaudal vs. with dorsal apophysis in L. gerlachi ), shape of spicules (with thin subcylindrical shaft vs. with broad conoid shaft in L. gerlachi ), absence of subterminal setae on tail (vs. present in L. gerlachi ). It also differs from L. praeclarus in length of spicules (31–34 µm vs. 24 µm in L. praeclarus ), longer body (679–850 µm vs. 442–518 µm in L. praeclarus ), and anteriormost body setae well posterior to amphid (vs. at amphid base in L. praeclarus ). It also differs from L. octavus sp. n. in the absence of bursa-like expansion of lateral field (vs. present in L. octavus sp. n.), shape of tubular supplements (S-shaped with bifid or blunt tips vs. weakly arcuate with dentate tips in L. octavus sp. n.), shape of gubernaculum (with dorsocaudal vs. with dorsal apophysis in L. octavus sp. n.), and number and arrangement of sensilla along pharyngeal region and male tail. It also differs from L. nonus sp. n. in the shape of tubular supplements (S-shaped with bifid or blunt tips vs. weakly arcuate with dentate tips in L. nonus sp. n.), shape of gubernaculum (with dorsocaudal vs. with dorsal apophysis in L. nonus sp. n.), longer spicules (31.0–34.0 vs. 17.0–26.0 µm in L. nonus sp. n.), position of vulva (midventral vs. right-subventral in L. nonus sp. n.), absence of pars refringens vaginae (vs. present in L. nonus sp. n.), larger body size (679–850 µm vs. 403–633 µm in L. nonus sp. n.) and other measurements, and number and arrangement of sensilla along pharyngeal region and on male tail. It also differs from L. elegans in the shape of tubular supplements (S-shaped with bifid or blunt tips vs. weakly arcuate with dentate tips in L. elegans ), shape of gubernaculum (with dorsocaudal vs. with dorsal apophysis in L. elegans ), longer spicules (31.0–34.0 vs. 20.0–24.0 µm in L. elegans ), position of vulva (midventral vs. rightsubventral in L. elegans ), absence of pars refringens vaginae (vs. present in L. elegans ), and number and arrangement of sensilla along pharyngeal region and on male tail.

Figures

FIGURE 24. Leptolaimus septimus 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 25. Leptolaimus septimus sp. n. (A–B) and Leptolaimus octavus sp. n. (C–D). A, C: Entire female; B, D: Entire male. Scale bar: A–D = 50 µm.