Paraleptopentacta tergestina Mezali, Thandar & Khodja, 2020, n. comb.

Paraleptopentacta tergestina n. comb. (Sars, 1859)

Figures 1–3

Cucumaria tergestina Sars, 1859: 127; Koehler, 1921: 158–160.

Trachythyone tergestina Tortonese, 1965: 83–85.

Leptopentacta tergestina Panning, 1966: 62 (passim).

Remarks. Paraleptopentacta (n. gen.) tergestina n. comb. is a cucumariid sea cucumber, a fairly well known Mediterranean species. Unlike its sister species P. elongata, which has spread into the North-West Atlantic, P. tergestina n. comb. is restricted to the Mediterranean sea (Tortonese 1965), being reported from France (Koehler 1921), Italy (Tortonese 1965; 1977; Milisenda et al. 2017), the Malta Islands (Tanti & Schembri 2006), the Aegean Sea (Voultsiadou et al. 2011), the Adriatic Sea (Petovic 2011) and the Marmara Sea (Turkey) (Öztoprak et al. 2014). It is often caught by trawlers as a bycatch, frequenting muddy, detrital waters and Posidonia and Caulerpa bottoms.

The specimens here studied correspond well with the description of the species by Koehler (1921) and require no further comment.

Material examined. LPVCMRMS2020.101, Mostaganem, Algeria, 36º 6.38374’N, 0º 8.34821’E, 60 m, March 2020, 5 spec.

Description. Contracted individuals 20-50 mm in length and 10-15 mm in breadth. Body somewhat pentagonal, curved, with a broad mid-body and narrower posterior end. Tegument rigid, smooth, dark brown, interradial areas devoid of pedicels (Figure 2A). Pedicels light brown, rigid, non-retractable, in five double rows arranged in a zigzag fashion, elongated, slender in living specimen and short, thorn-shaped in preserved individuals. Tentacles 10, dendritic, ventral two reduced, white, with brown spots (Figure 2B). Each tentacle consists of a central trunk from which lateral branches emerge, giving rise to terminal papillate branches.

Ossicles. Ossicles from the anterior end (Figure 3A), dorsal surface (Figure 3B), ventral surface (Figure 3C), anal region (Figure 3D) and podia (Figure 3E) appear identical, without any noticeable differences. They include an external layer of small baskets and an inner layer of thick, multilocular, non-imbricating plates of various sizes, with smooth margins and nearly always with a paired series of small holes, plates of the dorsal surface are smaller and thinner than those of the ventral surface. The plates occur in a variety of shapes, usually elongated, but often round- ed or oval, the elongated ones are the most abundant with a maximum length of 844.901 µm and a maximum width of 169.774 µm [according to Koehler (1921), they can reach up to 1.5 mm (1500µm) in length]. The baskets have a quadrilocular base and a rim bordered by numerous thick projections directed outward and inward. The baskets occur dorsally and at the anal end. The rosettes are characteristic of this species and do not occur in the congenerics but are present in at least one species of Leptopentacta (s.s.). They occur in the dorsal body wall and in the anal region. The body wall also contains rods, which are present at the anterior end, in the anal region, the podia and tentacles. The tentacles (Figure 3F) contain plates like those of the body wall and curved, thin rods provided with a few perforations, whereas only perforated plates like those of the body wall characterize the introvert (Figure 3G). The podia also contain plates of different shapes like those of the body wall as well as rods; end plates are reduced.

Behaviour (in vitro). The specimen kept alive in a tank usually adheres to the wall of the tank with its posterior end while waving and twisting the unattached end freely in the water column (Figure 2C). This behavior was described by Monticelli (1896) as one of the three autotomy mechanisms in Ocnus planci (Brandt, 1835), of fission by constriction and stretching. According to Crozier (1917), sometimes the posterior part, which is glued to the substrate, can divide again. When exposed to intense light the tentacles retract, which may indicate that the species exhibits the “shade-seeking” behavior described by Yoshida (1966).