Antomicron lorenzeni, Holovachov, Oleksandr, 2012

Holovachov, Oleksandr, 2012, Swedish Plectida (Nematoda). Part 2. The genus Antomicron Cobb, 1920, Zootaxa 3380, pp. 39-54 : 43-44

Antomicron lorenzeni sp. n.

( Fig. 2 ; Table 2 )

Type material. Holotype male (slide # 8358), as well as one female and two male paratypes (slide # 8359) each deposited in the type collection of the Department of Invertebrate Zoology, Swedish Museum of Natural History, Stockholm, Sweden.

Type locality. Soft mud from 44 m deep, Gullmarn Fjord near Fiskebackskil, Sweden (N 58° 15' 37'', E 11° 27' 43''), 11 August 2011, legit O. Holovachov (one female and three males).

Etymology. The species is named in honour of well-known German nematologist S. Lorenzen.

Description. Adult. Body tapering anteriorly in pharyngeal region and posteriorly on tail; straight or ventrally curved upon fixation, weakly curved ventrad in posterior part in males. Maximum body diameter at vulva in female; male body more cylindrical. Cuticle annulated; annuli 2.4–2.8 µm wide at mid-body, without ornamentation. Lateral field present, consists of single alae (two incisures), 1.7–2.3 µm wide at mid-body; originating just posterior to amphid and extending posteriorly to middle of tail. Crystalloids absent. Prominent body pores in sublateral position at both sides of lateral field present, arising from oval lateral epidermal gland cells; 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. Somatic sensilla absent in female, present in male (see below). Labial region bluntly rounded, continuous with body contour, lips fused. Anteriormost body annule, which demarcates labial region, located at level of posterior end of amphid. Inner and outer labial sensilla indistinct. Cephalic sensilla setiform, equal to 25–30 % of labial region diameter. Subcephalic and cervical sensilla and ocelli absent. Amphidial fovea an inverted U-shaped, 2.5–3.1 times as long as it is wide. Nerve ring surrounding pharynx at level of anterior part of isthmus. Hemizonid not seen. Secretory-excretory system present; renette cell large, located opposite to ventral side of cardia and anterior part of intestine, extends anteriorly along ventral side of pharynx and forms an excretory ampulla just posterior to nerve ring level. Excretory canal weakly cuticularised, extends from excretory ampulla for a short distance anteriorly and opens to the exterior via a pore. 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 almost similar in shape in both sexes (shorter and more curved ventrad in male), elongate-conoid, gradually narrowing proximally. Unstriated tail tip swollen. Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Female. Sensilla associated with epidermal glands absent. Reproductive system didelphic, amphidelphic; ovary branches reflexed antidromously. Anterior genital branch 81 µm long (equal to 12.6% of total body length), located on right-hand side of intestine, posterior genital branch 85 µm long (equal to 13.3% of total body length), located on left-hand side of intestine. Oviduct a narrow tube. Two offset, oval, sack-like spermathecae located on each (right and left) side of each (anterior and posterior) gonoduct. Spermathecae filled with oval spermatozoa. Uterus a wide tube. Vagina straight, 0.3 times vulval body diameters long; pars proximalis vaginae encircled by single sphincter muscle. Epiptygmata and sensitive structures around vulva (advulval sensilla) absent. Rectum 1.6 anal body diameters long; surrounded by three gland-like cells at intestine-rectum junction.

Male. Sensilla associated with epidermal glands absent. Reproductive system diorchic; anterior testis outstretched; posterior one reflexed. Spicules paired, symmetrical, with arcuate subcylindrical shaft and ovoid manubrium. Gubernaculum plate-like, with dorso-caudal apophysis. Accessory apparatus composed of one midventral precloacal papilliform sensillum located on anterior cloacal lip, two midventral tubular supplements extending for 69–72 µm from cloaca towards anterior end, and nine alveolar supplements extending anteriorly. Anteriormost alveolar supplement is located just posterior to cardia, 150–163 µm from anterior end. Posteriormost tubular supplement 50–52 µm anterior to cloaca, anterior to spicules. Sublateral precloacal and caudal sensilla present: two (one pair) precloacal setae at level of spicules and six-eight (three-four pairs) caudal setae arranged in two subventral and one-two subdorsal pairs. One pair of small papilliform sensilla is located just posterior to the second pair of subventral caudal setae.

Diagnosis. Antomicron lorenzeni sp. n. is particularly characterised by the 0.6–0.68 mm long body; an inverted U-shaped amphid; straight vagina without sclerotizations; female without sensilla in pharyngeal region and without supplements; male without sensilla in pharyngeal region, two tubular and nine alveolar supplements, one pair of precloacal and four pairs of caudal setae, 23 µm long spicules.

Relationships. The new species belongs to a group of species, which males have both tubular and alveolar supplements: A. pratense Lorenzen, 1966 , A. profundum Vitiello, 1971 , A. intermedius Gagarin & Nguyen Vu Thanh, 2005 and A. alveolatum Villares & Pastor de Ward, 2011. A. lorenzeni sp. n. differs from A. pratense in having longer cephalic setae (1.8–2.0 µm vs. 0.5 µm), shape of specloacal sensilla (setiform vs papilliform), and lesser number of tubular (2 vs. 3) and alveolar (9 vs. 8) supplements; from A. profundum in having longer spicules (23 µm vs. 17.5 µm) and lesser number of tubular (2 vs. 5–10) and alveolar (9 vs. 14) supplements; from A. intermedius in the shape of amphid (inverted U-shaped vs doughnut-shaped) and different number of tubular (2 vs. 5–9) and alveolar (9 vs. 29–36) supplements; and from A. alveolatum in having shorter cephalic setae (1.8–2.0 µm vs. 5.0 µm) and number of tubular (two vs three) and alveolar (9 vs. 35) supplements. Further characters summarising the differences between all species of the genus Antomicron are given in Table 3.

Vu Thanh, 2005 (all measurements are in µm, except for the ratios a, b, c, c', V, T, EP and NR).

Body diameter 18.0 17.0; 17.0 21.5 30.0 30.0

Pharynx length 147.0 134.0; 141.0 147.0 120.0 111.0

Tail length 91.0 84.0; 92.0 89.0 99.0 108.0

Figures

FIGURE 2. Antomicron lorenzeni sp. n., holotype male (A – C) and paratype female (D – E). A: Male posterior region; B: Anterior end, surface view; C: Pharyngeal region, median section; D: Female tail; E: Female reproductive system (only posterior part is shown). Scale bar: A – E = 20 µm.

Tables

TABLE 2. Morphometrics of Antomicron lorenzeni sp. n., A. pratense Lorenzen, 1966 and A. intermedius Gagarin & Nguyen

Species	A. lorenzeni sp. n. Holotype, 3 2 3	1 Ƥ	A. pratense A. intermedius 1 3 1 3
Body length a	648.0 603.0; 676.0 35.7 35.4; 39.7	641.0 29.7	552.0 698.0 18.4 23.3
b c c' V or T (%)	4.4 4.5; 4.8 7.1 7.2; 7.3 5.3 5.7; 5.8??;?	4.4 7.2 6.0 52.2	4.6 6.3 5.6 6.5 4.6 4.4 46.1 51.5