Ocnus planci Brandt, 1835

Mezali, Karim, Zerroual, Hanane, Lebouazda, Zineb & Khodja, Ihcene, 2024, On the presence of Ocnus planci Brandt, 1935 (Echinodermata: Dendrochirotida: Cucumariidae) in the Mostaganem region (Western Algerian coast), Zootaxa 5403 (4), pp. 479-487 : 481-483

Ocnus planci Brandt, 1835

Figure 2 , 3

Cladodactyla planci : Brandt, 1835, p.45.

Cucumaria dodiolum ( Pallas, 1766) : Sars, 1857, p. 129, tav. I. f. 18–23.

Cucumaria planci : Marenzeller, 1874, p. 300; 1893, p. 15— Ludwig, 1879, p.565 — Lampert, 1885, p. 140 — Bell, 1892, p. 37, tav. II f. 2, VIII f. 1— Koehler, 1921, p. 153, f. 101–104; 1927, p. 164, tav. XVI f. 3— Mortensen, 1927, p. 403, f. 241 (1)— Cherbonnier, 1951, p. 39, tav. XVIII f. 1–16; 1951, p. 11; 1956, p. 20. Rowe, 1970, p. 686.

Ludwigia planci : Panning, 1949, p. 433, f. 26— Cherbonnier, 1958, p. 60.

Material examined. LPVRMLSM.2020.501, Mostaganem, Algeria, 36°6.38374’N, 0°8.34821’E, 60 m, Mars 2020, 1 spec.

Description. Body cylindrical, barely curved ( Figures 2A & 2 Bb), light to dark brown with thick, soft cuirassed skin. Body length 68 mm, contracted width 9 mm, weight 2.028 g. Five double rows of retractile podia aligned in a zigzag pattern in the ambulacral regions. Eight oral long tentacles visible, branched, arboreal, brown in colour, identical to the body, with some whitish spots ( Figure 2C ). Two other tentacles are atrophied. Four anal teeth ( Figure 2 Ba). Introvert present. Tegument thickness 0.35 mm. Longitudinal muscles thin and whitish, attached to body wall, paired, each about 0.28–0.38 mm thick. Cuvierian tubules absent. Single Polian vesicle, average length about 3.75 mm. Single stone canal 3.10 mm long, calcareous ring 6.18 mm ( Figure 3H ).

Ossicles. The ossicles of both ventral and dorsal sides ( Figures 3A & 3B ), podia ( Figure 3D ), anal region ( Figure 3E ) and anterior end ( Figure 3F ) appear to be similar. Contains knobs and 4 to 13 holes of different sizes ( Figures 3 Aa, Ba, Da, Ea & Fa), and small knobbed buttons which are also present in the introvert. Rosettes occur only in the tentacles ( Figure 3 Gb), while baskets occur in the ventral and dorsal body wall, the anterior extremity, the anal region and in the tentacles ( Figures 3 Ad, 3Bb, 3Dd, 3Ed, 3Fd & 3Gb). Numerous nodules with small perforations are present only in the ventral side and in the tentacles ( Figures 3 Ab & 3Gf). Rods of various shapes (with some perforations at their periphery) are present in the introvert, podia, anal region and tentacles. Perforated plates of varying thicknesses are evident in the tentacles, as depicted in Figures 3 Ga and 3Gc. Notably, large plates featuring 23 holes are observed in the anal region, as shown in Figure 3 Eb. The podia also contain knobbed buttons of various shapes as well as rods like those on the body wall ( Figure 3D ). The calcareous ring plates are posteriorly forked, the radial plates are longer than the interradial plates, with an anterior depression for the retractor muscle; interradial plates triangular, with medial depression ( Figure 3H ).

Ecology and geographic distribution. Ocnus planci , like most holothurians, is an epibiont species. According to Lo Bianco (1888), it reproduces in Naples from September to December. Fertilised eggs develop well in columns of seawater containing a few pieces of the green seaweed Ulva sp. , until they develop into small holothurians with tentacles 1–2 mm long. The adult lives in seagrass beds, on detrital and coral bottoms from five to nearly 100 m depth (Lo Bionco 1888). Ocnus planci is the preferred host for the commensal amphipod Tritaeta gibbosa and the parasitic Eulimidae Melanella bosci ( Delongueville & Scaillet 2009, Laetz et al. 2013). It has been reported for the first time from the Ligurian Sea, Naples, the Adriatic Sea, Menton, Monaco, Marseille, Banylus-sur-mer and the Sea of Marmara ( Tortonese 1987), North Sea ( Massin & De Ridder 1989) and Mauritania ( Massin 1993). Many studies, had mentioned its presence in the north east of the Atlantic Ocean, West Africa, France, Portugal, Ireland, United Kingdom, Scotland and the Irish Sea and St. George’s Channel ( Madsen & Hansen 1994, Hanson 2001, 2004, Davoult 2002, Muller 2004, Southward & Campbell 2006, Guiry & Guiry 2011). In 2010, Koukouras reported its presence in the Eastern Mediterranean. It lives on different types of bottoms and is resistant in polluted environments ( Tortonese 1987).

Figures

FIGURE 2. External morphology of Ocnus planci. A. General view (a. ventral side b. dorsal side), B. Posterior part (a. anus with 4 anal teeth indicated by red arrows, b. whole individual), C. Tentacles indicated by red arrows (a. lateral view, b. top view), D. Internal anatomy (a. whole individual, b. buccal part).

FIGURE 3. Ossicles of O. planci. A. Ventral side. B. Dorsal side. C. Introvert. D. Podia. E. Anal region. F. Anterior end. G. Tentacles. H. Calcareous ring (R = radial plates, IR = interradial plates). Scale bar A–G = 50 µm, H = 1 mm.