Benthodytes violeta Martinez, Solís-Marín & Penchaszadeh, 2014, sp. nov.

Benthodytes violeta sp. nov.

(Figures 1–3)

Diagnosis. Body flattened when alive, sub-cylindrical when fixed; colour, including tentacles, violet. Mouth ventral, anus terminal. Sixteen shield-shaped tentacles distributed in only one circle. Eight pairs of dorsal appendages, each 1–3 mm long, occupying half anterior part of body. Ventrally one ambulacra with four rows of tube feet. Festooned edges on the dorsal-ventral interface. Body wall deposits as rods and crosses with three or four arms and primary cross with central bipartite apophysis; tentacles and gonad with rods and crosses also with 3 or 4 arms.

Etymology. The specific name is a noun in apposition.

Materials examined. Holotype, MACN-In 39098, length 122 mm and 2 slides, Mar del Plata Canyon (37º57´S – 54º11´W), 1508 m, 13 Aug. 2012; Paratypes: MACN-In 39099, length 195, 151, 171 mm, same data as holotype (3 paratypes); MACN-In 39100, length 207 mm, Mar del Plata Canyon (37º52´S – 54º11´W), 1950 m, 15 Aug. 2012 (1 paratype); MACN-In 39101, length 117, 158, 173, 134, 155 mm, Mar del Plata Canyon, (38º2´S – 53º58´W), 1601 m, 16 Aug. 2012 (5 paratypes); MACN-In 39102, length 142 mm, Mar del Plata Canyon (38º2´S – 53º55´W), 1783 m, 16 Aug. 2012 (1 paratype).

Description. Body flattened in life, sub-cylindrical when fixed, up to 200 mm length in life but when fixed up to 190 mm; both body and tentacles violet in life and when fixed. Mouth ventral, anus terminal but directed dorsally, with two papillae on its dorsal side (Fig. 1 a, b, c). Tentacles 16, in a single circle, all 2 mm length and shield-shaped (Fig. 1 c). Dorsal appendages eight pairs, each 1–3 mm long, occupying half anterior of body (Fig. 1 a, b). Festooned edges on the dorsal ventral interface. Ventrally one ambulacra with four rows of tube feet (Fig. 1 c). Body wall gelatinous and thick. Polian vesicles two, drop-shaped, one 30 mm, other 10 mm in length. Stone canal ~ 0.5 mm, attached to dorsal side of mesentery, madreporite globular, 0.3 mm, attached to mesentery. Respiratory trees not observed. Gonad branched, with two tufts.

Body wall ossicles comprise primarily rods 200–400 µm long, with multiple spines more common on the edges of small rods and crosses of 120–310 µm with three or four arms, more common on the posterior part of the body. Also primary cross of 120–700 µm with central bipartite apophysis more common on anterior and middle of the body, all crosses with multiple spines (Fig. 2 a, 3a) ventral ossicles, less abundant than dorsal ossicles, also crosses and rods with multiple spines, crosses few and localised particularly anteriorly (Fig. 2 b). Ossicles of tentacles (Fig. 2 c, 3b) and gonad (Fig. 2 d, 3c) comprise rods with central spines and crosses of three and four axis.

Remarks: After preservation in ethanol (96º) for several days all specimens suffer a body size reduction of up to 50%. All measurements given above were from fixed individuals except where live length is recorded in the description. Size reduction makes more difficult to observe the podia arrangement on the fixed material.

Habitat: muddy sediments.

Distribution: Mar del Plata Canyon, off Buenos Aires (around 38ºS–54ºW), Argentina.

Depth: 1508–1950 m.