Antomicron elegans

Holovachov, Oleksandr, 2012, Swedish Plectida (Nematoda). Part 2. The genus Antomicron Cobb, 1920, Zootaxa 3380, pp. 39-54 : 48-50

Antomicron elegans (de Man, 1922) De Coninck, 1965

( Fig. 4 ; Table 1 )

Material examined. One male deposited in the general collection of the Department of Invertebrate Zoology, Swedish Museum of Natural History, Stockholm, Sweden.

Habitat and locality. Littoral sediments, Oosterschelde, the Netherlands, August 1991, legit R. Alkemade (one male).

Description. Male. Body tapering anteriorly in pharyngeal region and posteriorly on tail; ventrally curved upon fixation, more strongly curved ventrad in posterior part. Cuticle annulated; annuli 2.8 µm wide at mid-body, without ornamentation. Lateral field present, consists of single alae (two incisures), 4.5 µm wide at mid-body; originating a few annules posterior to amphid and extending to posterior 1/4th of tail. Crystalloids absent. Prominent body pores in sublateral position at both sides of lateral field present, arising from oval lateral epidermal gland cells; seven pairs of body pores are present along pharyngeal region, and one at level of cardia; numerous body pores scattered over rest of the body. Sensilla associated with epidermal glands present, emerging through first, third and sixth pairs of body pores. Labial region bluntly rounded, continuous with body contour, lips fused. Anteriormost body annule, which demarcates labial region, located at level of posterior third of amphid. Inner and outer labial sensilla indistinct. Cephalic sensilla setiform, equal to 40% of labial region diameter. Subcephalic and cervical sensilla and ocelli absent. Amphidial fovea elongate doughnut-shaped, 1.9 times as long as it is wide, with elongated central elevation. 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 just posterior to nerve ring. Buccal cavity uniformly tubular: cheilostom short funnel-shaped, undifferentiated; gymnostom short, with small bacilliform gymnorhabdia; 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, embedded in intestine. Reproductive system diorchic; anterior testis outstretched; posterior one reflexed. Spicules paired, symmetrical, with strongly arcuate subcylindrical shaft and oval manubrium. Gubernaculum plate-like, with long dorsal apophysis. Accessory apparatus composed of one midventral precloacal papilliform sensillum located on anterior cloacal lip and four midventral tubular supplements extending for 152 µm from cloaca towards anterior end; alveolar supplements absent. Posteriormost tubular supplement 51 µm anterior to cloaca, anterior to spicules. Sublateral precloacal and caudal sensilla present: two (one pair) precloacal setae at level of spicules and eight (four pairs) caudal setae arranged in two subventral and two subdorsal pairs. One pair of small papilliform sensilla is located just posterior to the second pair of subventral caudal setae. Tail elongate-conoid, gradually narrowing proximally. Unstriated tail tip swollen. Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Diagnosis (supplemented with literature data). Antomicron elegans is particularly characterised by the 0.9–1.1 mm long body; elongate doughnut-shaped amphid; female without supplements; male with three pairs of sensilla in pharyngeal region, four tubular and no alveolar supplements, one pair of precloacal and four pairs of caudal setae, 36.5–39 µm long spicules.

Remarks. Current specimen agrees well with the male individual described by Lorenzen (1969) specimen in general morphology, measurements and shape of amphids and number of tubular supplements. Unfortunately, the original species description is incomplete and insufficiently illustrated to allow detailed comparison.

Figures

FIGURE 4. Antomicron elegans (de Man, 1922) De Coninck, 1965, male. A: Pharyngeal region, median section; B: Anterior end, surface view; C: Posterior region. Scale bar: A – C = 20 µm.