Gebrukothuria profundus, Rogacheva & Cross, 2009

Gebrukothuria profundus View in CoL sp. nov. Rogacheva and Cross

Fig. 1 – 2 View FIGURE 1 View FIGURE 2

Type locality. Southern Indian Ocean, to east of Crozet Isles, 45˚40’S, 56˚35’E, 4269–4275 m.

Holotype: NHM, Cat. Nr. NHM 2008.993, held at Natural History Museum, London. Discovery St. 15773#23, 45˚40’S, 56˚35’E, 4269–4275 m mud bottom, collected 16 th December, 2005 by semi-balloon otter trawl (single specimen preserved in 4% buffered formaldehyde and then transferred to 80% ethanol) GoogleMaps .

Diagnosis. As for the genus.

Etymology. The name profundus means ‘deep’ and it corresponds to the bathymetric range of this species: Gebrukothuria profundus is among the deepest known laetmogonids. Only Laetmogone wyvillethomsoni Théel, 1879 and Psychronaetes hanseni occur at greater depths – 4410 m and 4800 – 5200 m respectively.

Description. Body elongated, 21 cm long, attaining a maximum width of 3.6 cm in the middle part of the body. Colour in alcohol uniform dark violet. Skin relatively thin, wrinkled ( Fig. 1 View FIGURE 1 ; A, B; Fig. 2 View FIGURE 2 : A, B, D).

Tube feet 18 on each side, conspicuous, separate not forming a brim; located evenly along the ventrolateral radii; almost not evident when viewed from dorsal surface; tube feet in the middle of the body slightly larger than others; the 2 posteriormost tube feet of each side are significantly smaller in size. Midventral tube feet tiny, located in a narrow channel which is probably a result of contraction.

Anus dorsal, sub terminal.

Dorsal papillae approximately 65 on each dorsal radius, evenly distributed. Papillae small, of equal size; retracted into long longitudinal wrinkles ( Fig. 2 View FIGURE 2 : D). 2 additional irregular rows of papillae on both dorsal radii on the anterior part of the body; papillae of these irregular rows are smaller than others ( Fig. 1 View FIGURE 1 : A). Rows of papillae occur close to each other; some of the posteriormost papillae are slightly smaller than others.

Tentacles 15; tentacle disk slightly convex with conspicuous knobs on the disk margin ( Fig. 2 View FIGURE 2 : E).

Circum-oral papillae absent.

Deposits consist of rods in body wall ( Fig. 1 View FIGURE 1 : C), papillae, tube feet and tentacles; not abundant in the body wall. Wheels never observed. The rod-shape deposits in the body wall are 0.09 – 0.35 mm in length. They are curved, often tetrahedral in cross section, with few spines close to the ends or without spines; a few with larger, blunt spines or knobbed processes. Rods in papillae abundant, between 0.09 – 0.3 mm, some with irregular blunt spinous processes, knobbed ends, or spear-like tips, rarely with a central swelling. Abundant deposits in tentacles and tube feet, tending to be in the upper size-range and thicker than those found in the body wall and papillae. Blunt spinous processes and central swellings common in deposits from tube feet and tentacles. Deposits absent in the gonad.

Calcareous ring not present.

Gonad consisting of clusters of multi-branched tubules ( Fig. 2 View FIGURE 2 : C).

Remarks. The specimen is referred to the family Laetmogonidae based on the morphology of gonads consisting of clusters of branched tubules. Also rods found in G. profundus resemble rods typical for species of the genus Laetmogone . We suggest that the absence of wheels in the body wall was not a result of preservation history. Wheels in laetmogonids are relatively large compared to in other elasipodids, and if destruction of deposits took place, it is likely rods would dissolve first (before massive wheels). Furthermore we found no traces of wheels. In the Laetmogonidae wheels are abundant and if they were present it is likely we would have seen traces of them. The absence of wheel-shaped deposits in this specimen is sufficient to consider it as representing a new genus.

Relationships. Based on the presence of midventral tube feet and absence of ventrolateral papillae, Gebrukothuria profundus most resembles species of Pannychia and Laetmogone . It differs from the Pannychia by the absence of wheel-shaped deposits and ventrolateral papillae. It differs from Laetmogone by the absence of wheel-shaped deposits and the presence of midventral tube feet.

The specimen is similar in appearance to another Antarctic holothurian, Benthodytes browni Vaney, 1908 , known from one specimen in the Antarctic. Hansen assigned this specimen to the family Laetmogonidae based on discrete and cylindrical tube feet with a strictly ventral position. However, Hansen did not refer it to any genus or species in the family because the specimen lacked deposits. Nevertheless, G. profundus differs from Benthodytes browni by possessing a higher number of dorsal papillae and tube feet.