Leptolaimus octavus, 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 : 60-63

Leptolaimus octavus sp. n.

( Figs 25 C–D , 26 ; Table 17)

Type material. Holotype male (slide # Type-8493) and five male and 11 female paratypes (slides # Type-8493 - Type-8497) each deposited in the invertebrate type collection of the Department of Zoology , Swedish Museum of Natural History, Stockholm, Sweden.

Additional material. Five males and six females (slides # 131245–131248) deposited in the general invertebrate collection of the Department of Zoology , Swedish Museum of Natural History, Stockholm, Sweden .

Type locality. Coarse sediment with algae from 45–55 m deep, Skagerrak off the west coast of Sweden (N 58° 17' 32'', E 11° 11' 24''), 09 August 2011, legit O. Holovachov (six males and 11 females) .

Additional localities. Gravel , mud and algae from 30–70 m deep, Skagerrak off the west coast of Sweden (N 58° 22' 14'', E 11° 05' 00''), 09 August 2011, legit O. Holovachov (one male and one female) ; coarse gravel from 30–50 m deep, Skagerrak off the westcoast of Sweden (N 58° 17' 58'', E 11° 10' 05''), 09 August 2011, legit O. Holovachov (one male and two females) ; soft mud from 30 m deep, Gullmarn Fjord near Fiskebäckskil, Sweden (N 58° 15' 25'', E 11° 27' 30''), 11 August 2011, legit O. Holovachov (one male and two females) ; soft mud from 44 m deep, Gullmarn Fjord near Fiskebäckskil, Sweden (N 58° 15' 37'', E 11° 27' 43''), 11 August 2011, legit O. Holovachov (two males and one female) .

Etymology. The specific epithet " octavus " is translated as " the eighth " 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 2.2–3.1 µm wide at mid-body, without ornamentation. Lateral field present, consists of single ala (two incisures), 2.0–3.0 µm wide at mid-body; originating at level of posterior part of stoma or stoma base (anterior to or at the same level as first body pore) and extending posteriorly to middle of tail. Lateral field expands to create a bursa-like structure along the proximal part of tail in females and in males. Prominent body pores in sublateral position at both sides of lateral field present, arising from oval lateral epidermal gland cells; usually three 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 stoma base or procorpus. Labial region truncate, 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 at level of anterior third of stoma. Nerve ring surrounding pharynx at level of anterior part of isthmus. Hemizonid not seen. Secretory-excretory system indistinct. 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. Short setae emerging through first, second and third pairs of body pores. Reproductive system diorchic; anterior testis outstretched; posterior one reflexed. Spicules paired, symmetrical, with subcylindrical arcuate calamus and ovoid shaft. Gubernaculum plate-like, with double dorsal apophyses. Accessory apparatus composed of one midventral precloacal papilliform sensillum located on anterior cloacal lip, four evenly spaced midventral tubular supplements extending for 110–133 µm from cloaca towards anterior end; alveolar supplements absent. Tubular supplements weakly S-shaped, with dentate tips. Posteriormost tubular supplement 27.0–29.5 µm anterior to cloaca, anterior to spicules. Sublateral precloacal and caudal sensilla present: two (one pair) precloacal setae at level of spicules and usually four (two pairs) caudal setae arranged in one subventral and one subdorsal pair.

Female. Reproductive system didelphic, amphidelphic; ovary branches reflexed antidromously. Anterior genital branch 72–110 µm long (equal to 11.6–17.5% of total body length), located on right-hand side of intestine (n=5), posterior genital branch 85–98 µm long (equal to 13.5–15.7% of total body length), located on left-hand side of intestine (n=5). 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 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 1.0–1.3 anal body diameters long; surrounded by three gland-like cells at intestine-rectum junction.

Diagnosis. Leptolaimus octavus sp. n. is particularly characterised by the 541–638 µm long body; truncate labial region continuous with body contour; cephalic setae 1.5–2.0 µm long; amphid located 8.5–12.0 µm from anterior end; first body pore located 31.5–41.0 µm from anterior end; lateral field originating 26.0–40.0 µm from anterior end and expanding into bursa-like structure along the proximal part of the tail; female without supplements, vagina without pars refringens, vulva midventral; male with four tubular and without alveolar supplements, tubular supplements weakly S-shaped with dentate tips; spicules arcuate and 30.0–31.5 µm long.

Relationships. Leptolaimus octavus sp. n. is unique among other species of Leptolaimus in having a bursa-like expansion of the lateral field along the proximal part of the tail of both females and males. It should be further compared with other species of the genus Leptolaimus , males of which have only four evenly spaced tubular supplements, i.e.: L. gerlachi , L. praeclarus , L. septimus sp. n. (see above), some specimens of L. nonus sp. n. and L. elegans . The new species differs from L. gerlachi in smaller body (541–638 µm vs. 760–840 µm in L. gerlachi ), shape of tubular supplements (with dentate tips vs. with bifid tips in L. gerlachi ), shape of spicules (with thin subcylindrical shaft vs. with broad conoid shaft in L. gerlachi ), and absence of subterminal setae on tail (vs. present in L. gerlachi ). It differs from L. praeclarus in length of spicules (30.0–31.5 µm vs. 24.0 µm in L. praeclarus ) and anteriormost body setae well posterior to amphid (vs. at amphid base in L. praeclarus ). It differs from L. nonus sp. n. in longer stoma (30–36 µm vs. 17–22 µm in L. nonus sp. n.), longer spicules (30.0–31.5 µm vs. 17.0–26.0 µm in L. nonus sp. n.), position of vulva (midventral vs. right-subventral in L. nonus sp. n.), and absence of pars refringens vaginae (vs. present in L. nonus sp. n.). It furthermore differs from L. elegans in having longer stoma (30–36 µm vs. 18–24 µm in L. elegans ), longer spicules (30.0–31.5 µm vs. 20.0–24.0 µm in L. elegans ), position of vulva (midventral vs. right-subventral in L. elegans ).

Figures

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.

FIGURE 26. Leptolaimus octavus sp. n., holotype male (A–C) and paratype female (D–F). A: Anterior end, surface view; B: Pharyngeal region, median section; C: Male posterior region; D: Female tail; E: Female reproductive system (anterior part). F: Female tail, ventral view. Scale bar: A–F = 20 µm.