Antomicron holovachovi, Zhai & Wang & Huang, 2020

Zhai, H. X., Wang, C. M. & Huang, Y., 2020, Two new species of Antomicron Cobb, 1920 (Nematoda: Leptolaimidae) from Jiaozhou Bay, China, Journal of Natural History 54 (19 - 20), pp. 1199-1212 : 1200-1205

Antomicron holovachovi sp. nov. ( Figures 1–3 and Table 1)

Type material

One male and two females were obtained . Holotype : male, on slide number JZW(17–8) . Paratypes : ♀ 1 and ♀ 2, on slides numbered JZW(17–7) and JZW(47–31), respectively . ( The holotype specimen is deposited in the Marine Biological Museum of Chinese Academy of Sciences, Qingdao, and the paratype specimens are deposited in the biodiversity laboratory of Liaocheng University.)

Type locality and habitat

Specimens were collected from the surface 0–2 cm sublittoral silt sediment in Jiaozhou Bay (JZW-17: 36.119°N, 120.217°E) . Water depth of 11 m.

Etymology

The species is named in honour of Dr Oleksandr Holovachov, Swedish Museum of Natural History, for his contributions to nematode taxonomy.

Measurements

All measurement data are given in Table 1.

Description

Male. Body cylindrical, tapering anteriorly in cervical region and posteriorly on tail. Cuticle with widely spaced transverse striation, 2.2 µm apart, without ornamentation. Lateral field present, consists of single ala (two incisures), 2 µm wide at mid-body; originating at base of amphideal fovea and extending posteriorly to anterior part of tail. Some body pores situated at both sides of lateral field in pharyngeal region. Labial region bluntly rounded, continuous with body contour, lips fused. Cephalic capsule obvious. Anteriormost body annule, which demarcates labial region, located at level of middle of amphid. Inner and outer labial sensilla indistinct. Cephalic sensilla setiform, 1.5 µm long. Amphidial fovea elongate, loop-shaped, 11 µm long and 4.5 µm wide (2.4 times as long as it is wide), 8 µm from the anterior end. Nerve ring surrounding pharynx at level of anterior to excretory pore. Secretory-excretory system present; ventral gland cell large, located anterior part of intestine (230 µm from the anterior end), extends anteriorly along ventral side of pharynx and forms an excretory ampulla just anterior to pharyngeal bulb, and opens to the exterior via a pore just posterior to nerve ring. Buccal cavity uniformly tubular. Pharynx cylindrical anteriorly, with distinct oval basal bulb with strong cuticular internal lining. Cardia cylindrical, its posterior part embedded in intestine. Tail conicocylindrical, gradually narrowing to posterior cylindrical part. Unstriated tail tip swollen. Caudal setae scattered. Three caudal glands present. Spinneret distinct.

Reproductive system diorchic; anterior testis outstretched; posterior one reflexed. Spicules slender, slightly ventral curved, with cephalated proximal end and tapered distal end. Gubernaculum rectangular, with a dorsal caudal apophysis, 5 µm long. Accessory apparatus composed of five 11–11.5 µm midventral straight tubular supplements extending for 122 µm from cloaca towards anterior end, and 41 evenly spaced alveolar supplements extending anteriorly. Anteriormost alveolar supplement located at level of cardia, 124 µm from anterior end,posteriormost alveolar supplement 21 µm from the anteriormost tubular supplement (i.e. 143 µm anterior to cloaca). Posteriormost tubular supplement 18 µm anterior to cloaca, anterior to spicules. One pair of subventral precloacal setae and one pair of postcloacal setae present, 2–3 µm long.

Female. Similar to male in most respects except slightly shorter body length. Reproductive system didelphic, with two opposed and reflexed ovaries. Oviduct a narrow tube. Two oval, saclike spermathecae located on each side (anterior and posterior) of vulva. Spermathecae filled with oval spermatozoa. Uterus a wide tube. Vagina straight, 0.3 times vulval body diameter in length. Vulva located just before middle of body.

Three females of Antomicron were found in sublittoral sediment of Jiaozhou Bay. One of them was found with a male of Antomicron holovachovi sp. nov. in the same locality, and its main measurement data match with the male of Antomicron holovachovi sp. nov. Therefore, the female was identified as Antomicron holovachovi sp. The other female, which was from the locality where the male of another new species was found, and which had a thicker body and slightly longer amphideal fovea, was identified as Antomicron chinensis sp. nov. The third female, which matches the first female, was identified as Antomicron holovachovi sp. nov. The female of Antomicron holovachovi sp. nov. differs from the female of Antomicron chinensis sp. nov. by a slender body (maximum body diameter 23–26 µm vs 33 µm), slightly shorter amphideal fovea (10–12 µm vs 14 µm) and anterior position of vulva (40–45% vs 51%).

Differential diagnosis and discussion

Antomicron holovachovi sp. nov. is characterised by loop-shaped amphideal fovea, central elevation ridge-like; male with five straight tubular and 41 alveolar supplements; short cephalic setae; one pair of precloacal subventral setae; slightly curved slender spicules with cephalated proximal end and tapered distal end; rectangular gubernaculum with a short dorsal caudal apophysis. The new species belongs to a group of species the males of which have both tubular and alveolar supplements. The new species is morphologically close to Antomicron intermedius Gagarin and Nguyen Vu Thanh, 2005 in most aspects, but differs from the latter species in having elongated loop-shaped amphideal fovea (vs doughnut-shaped amphideal fovea; 2.4 vs 1.6 times as long as its width), central elevation ridge-like (vs oval), many more alveolar supplements (41 vs 29–36) and the shape of tubular supplements. The new species differs from the similar species A. profundum Vitiello, 1971 by longer body length (747–813 vs 512–575 µm), longer spicules (20 vs 17.5 µm) and many more alveolar supplements (41 vs 0–14). Further differences between Antomicron holovachovi sp. nov. and other congeners are specified in Table 2 and the key below.

Figures

Figure 1. Antomicron holovachovi sp. nov. (A) Anterior end of male, showing buccal cavity, cephalic setae and amphideal fovea; (B) view of entire female; (C) posterior portion of male, showing spicule, gubernaculum, precloacal supplements and lateral alae; (D) anterior portion of male, showing nerve ring, pharyngeal bulb, secretory-excretory system and alveolar supplements; (E) cloacal region of male, showing spicule, gubernaculum and precloacal seta.

Figure 2. Antomicron holovachovi sp. nov. (A) View of entire male; (B) tail end of male, showing swollen tail tip; (C) view of entire female; (D) post-mid female body, showing lateral alae; (E) tail end of female, showing swollen tail tip. Scale bars: A, C= 50 μm; B, D, E= 20 μm.

Figure 3. Antomicron holovachovi sp. nov. (A) Anterior end of male, showing cephalic setae, buccal cavity and amphideal fovea; (B) anterior end of female, showing buccal cavity and amphideal fovea; (C) region of pharyngeal base of male, showing terminal bulb and alveolar supplements; (D) cloacal region of male, showing spicule; (E) spicule and tubular precloacal supplements. Scale bars: A, B, D= 10 μm; C, E= 20 μm.