Microlaimus tenuispiculum de Man, 1922

Revkova, Tatiana N., 2017, First records of Microlaimus tenuispiculum de Man, 1922 (Nematoda: Microlaimidae) from the Black Sea, Ecologica Montenegrina 14, pp. 74-79 : 75-78

Microlaimus tenuispiculum de Man, 1922

Figure 1 , Table 1

Material examined: five males, three females. Glycerin-gelatin slides. Males on slides from # FlN/BS–16 to FlN/BS−20; same for females, from FlN/BS−21 to FlN/BS−23.

Type locality. Black Sea. Submarine Dnieper Canyon, specimens were found on 8 stations at depths 120– 190 m (st. 256, 120 m, 44°47.54'N, 31°57.34'E; st. 258, 130 m, 44°47.41'N, 31°57.50'E; st. 259, 140 m, 44°47.36'N, 31°57.61'E; st. 260, 150 m, 44°47.29'N, 31°57.72'E; st. 261, 160 m, 44°47.15'N, 31°57.99'E; st. 262, 170 m, 44°47.04'N, 31°58.16'E; st. 324, 180 m, 44°46.72'N, 31°58.36'E; st. 326, 190 m, 44°46.67'N, 31°58.36'E). Bottom sediments are sandy silt with large quantities of bivalve, ostracod and foraminifera shells at 120–140 m depth, and silt with molluscan shell debris and bacterial aggregations at 150–190 m depth. The sediment surface is covered by various kinds of organic detritus, including the remains of macroalgae and micro-algae, as well as bacterial mats of different sizes. The maximum abundance was recorded at depth 160 m (73895 ind./m 2, 10.1 % of the total community), minimum – at depth 180 m (456 ind./m 2, 4.4 %).

Zernov’s Phyllophora Field : specimens were found on 7 stations at depths 20–36 m (st.11, 27 m, 45°38.417'N, 30°36.35'E; st.14, 21 m, 45°58.967'N, 30°53.233'E; st.15, 34 m, 46°5.3'N, 31°5.933'E; st.16, 35 m, 45°58.917'N, 31°5.367'E; st.18, 36 m, 45°45.45'N, 31°6.883'E; st.24, 20 m, 46°4.117'N, 31°21.033'E; st.25, 20 m, 46°4.05'N, 31°35.083'E). Bottom sediments are silt with light smell of hydrogen sulphide and with dead shells at 27 (st. 11) and 21 m (st. 14) depths; dense silt clay with dead shells at 34 (st. 15) and 35 m (st. 16); silty debris shells at 36 m (st. 18); silty debris shells at 20 m (st. 24 and 25). Maximum abundance was at depth 35 m (st. 16) – 20580 ind./m 2 (81 % of the total community), minimum – 36 m (st. 18) – 605 ind./m 2 (0.5 %).

Shallow waters: Kruglaya and Sevastopolskaya Bays. In Kruglaya Bay, specimens were found on 3 stations at the exit of the Bay (depths 8–16 m). Bottom sediments are sand with dead shells. Maximum abundance was at depth 15 m (790 ind./m 2, 1.2 % of the total community), minimum – at depth 8 m (575 ind./m 2, 1%). Sevastopolskaya Bay, specimens were found along the whole of the Bay area on 12 stations at depths 5– 17 m. Bottom sediments are silty-sand with hydrogen sulphide (depths 5–10 m), black silt with smell hydrogen sulphide (depths 8–17 m). Maximum abundance (17725 ind./m 2, 15.3 % of the total community) was recorded in the mouth of the Bay.

Description. Male. Body spindle-shaped, tapering gradually to both ends. Cuticle finely annulated (width of annuli 1 μm). Head rounded. Sensillae of cephalic end arranged in 3 circles: 6 inner labial papillae indistinct and 6 short outer labial papillae 1 μm long. Four cephalic setae 4 μm long, situated 6 μm behind the anterior end. Somatic setae 3 μm long, scattered along the body. Сryptocircular amphidial fovea (45.5−50 % of corresponding body diameter), situated 12−14 μm from anterior edge. Buccal cavity narrow with one dorsal and two ventrosublateral teeth. Pharynx cylindrical, muscular with well-developed bulb, oval-shaped 14−16 μm in wide. Nerve ring is situated at the level of middle of pharynx. Secretory-excretory system present; renette cell situated posterior to cardia on ventral side of the body; secretory-excretory pore not visible. Cardia small.

Reproductive system diorchic, with opposed and outstretched testes lying to the left of intestine. Sperm cells oval-shaped, 10 × 16 μm. Spicules medium-sized (2.6−3.4 a.b.d.), slender and S-shaped. Gubernaculum (0.7−0.8 a.b.d.), simple and thin. One precloacal seta (3 μm long), situated 12 μm from anus. Tail conical, with swollen tip. One caudal seta on the terminal part of the tail, 2.8 μm long. Three caudal glands present. Spinneret present.

Females. Similar to male in most parameters. Reproductive system didelphic, amphidelphic, with outstretched ovaries. Vulva situated slightly anterior to mid-body, not protruding outside the body contour. Vagina short, with muscular walls. Large oocyte 24 μm long and 20 μm wide. Spermatozoa of round-shape visible in uterus.

Figures

Figure 1. Microlaimus tenuispiculum de Man 1922 А: female, total view; В: male 1, tail; C: male 1, total view; D: female, head; E: male 1, head. Scale bars: A = 100 µm; B, C, D, E = 50 µm.