Thyone crassidisca Pawson & Miller, 1981

Martins, Luciana & Tavares, Marcos, 2018, New species of the genera Havelockia and Thyone (Echinodermata: Holothuroidea) and first record of T. crassidisca from the southwestern Atlantic Ocean, Zootaxa 4407 (4), pp. 533-542 : 534-535

Thyone crassidisca Pawson & Miller, 1981

( Figs. 1–2 )

Material examined. Brazil: Marataízes, Espírito Santo , Brazil, ii.1990, depth unknown, 1 spm, 35 mm ( MZUSP 1353 ) . Santos , São Paulo, 3.x.1967, 2 spms 45–60 mm ( MZUSP 1519 ) .

Comparative material examined. United States: Off Georgia, 19.ii. 1981, 41 m, 1 spm, 40 mm ( USNM 19573).

Distribution. Western Atlantic: from Florida to Brazil (Espírito Santo and São Paulo, present paper). Bathymetric range: currently known to inhabit sand and crushed shell bottoms ( Miller & Pawson 1984) mostly between 4 and 54 m.

Description. Body U-shaped, slightly upturned at both ends ( Fig. 1A ), rough to touch. Color whitish or brownish in ethanol. Tube feet scattered throughout body. Ten tentacles, ventral pair reduced. Anal papillae present. Internal organs degraded, not observed. Calcareous ring tubular, mosaic-like, about 50% of total body length; radial plates notched anteriorly with long and subdivided posterior processes; interradial plate pointed anteriorly. Radial and interradial plates equal in length, united along entire length ( Fig. 1B ).

Body wall and anal ossicles: tables two-pillared; handle present, disc oval, four-holed, margins knobbed. Spire terminating into single, blunt point (80–100 µm long, Fig. 2A–B ). Introvert ossicles: tables two-pillared, disc oval, completely perforated; spire high, ending in three teeth (40–60 µm long, Fig. 2D–E ) and rosettes (30–40 µm long, Fig. C). Tentacle ossicles: tables (also in introvert). Tube feet ossicles: supporting two-pillared tables; disc curved, 4 central holes, single perforated ends; spire tapering (100–120 µm long, Fig. 2F ). Small end plate with large holes around margin, smaller ones medially (100 µm long).

Remarks. The species of Thyone are separated into four groups according to their types of introvert ossicles: Itables only; II- rosettes only; III- tables and rosettes; IV- plates only (Panning, 1 949; Pawson & Miller, 1981; Thandar, 1990). Thyone crassidisca belongs to the third group, along with 24 other already known species, among which Thyone pseudofusus Deichmann, 1930 . Thyone crassidisca and T. pseudofusus are unique in the group III in possessing tables with handles in the body wall ( Fig. 2A ). However, Thyone crassidisca differs from T. pseudofusus in having low spires terminating in a single blunt point (versus truncate spires ending in a crown of spines in T. pseudofusus ).

Thyone crassidisca was previously known only from North Carolina to Florida and is recorded herein for the first time from the southeastern Brazilian coast (Espírito Santo ~21° S and São Paulo ~24° S).

Figures

FIGURE 1. (A-D) Thyone crassidisca Pawson & Miller, 1981 (MZUSP 1353). (A) Specimen preserved in ethanol; (B) Calcareousring; (C)Anterior portion of thecalcareous ring after iodine treatmentto show the subdivisionsof the radial (R)and interradial plates (IR) (black arrow); (D)Posterior portion of the calcareous ringafter iodine treatmentto show the subdivisions of posterior processes (white arrow). Scale bars: A, 5 mm.B–D 0,5 mm.

FIGURE 2. (A–F) Thyone crassidisca Pawson & Miller, 1981 (MZUSP 1353). SEM images of the ossicles. (A) Body wall tables, lateral view. (B) Body wall tables, top view. (C) Rosettes from introvert, top view. (D) Tables from introvert and tentacles,lateral view.(E)Tables from introvert, bottomview.(F)Supportingtables from tubefeet,lateral view.Scale bars: A– B,50 µm. C, 20 µm. D–E, 30 µm.F, 50 µm.