Thyone inermis? Heller, 1868

Madeira, Patrícia, Kroh, Andreas, Cordeiro, Ricardo, De, António M., Martins, Frias & Ávila, Sérgio P., 2019, The Echinoderm Fauna of the Azores (NE Atlantic Ocean), Zootaxa 4639 (1), pp. 1-231 : 137

Thyone inermis? Heller, 1868

Reports for the Azores:

Thyone inermis Heller, 1868 —? $ Marenzeller 1892: 66, 1893: 17;? $ Hérouard 1902: 45; Perrier 1902: 276; Mortensen 1927a:

408, fig. 246; Nobre 1938: 142; Deichmann 1954: 397; Miller & Pawson 1984: 40–41, figs. 32, 33; Pereira 1997: 333;

Bohn 2004: 518; García-Diez et al. 2005: 51; Havelockia inermis (Heller) — Tortonese 1965: 90–91, fig. 37B; Micael & Costa 2010: 323; Micael et al. 2012: 4.

Type locality: Adriatic Sea, Mediterranean Sea.

See: Koehler (1921b: 167, fig. 167); McKenzie (1991: 141–146); Bohn (2004); Pawson et al. (2010: 28).

Occurrence: Northeast Atlantic and Mediterranean Sea, reported from the English Channel south to Portugal ( Bohn 2004, Jesus & Fonseca 1999) and the? Azores ( Marenzeller 1892).

Depth: mostly above 30 m ( McKenzie 1991);? AZO:?130–? 1,385 m ( Marenzeller 1892, Hérouard 1902).

Habitat: lives buried in muddy to sandy habitats ( Tortonese 1965).

Remarks: the shallow-water cucumarid Thyone inermis was recorded in the archipelago by Marenzeller (1892, 1893) and Hérouard (1902) at unusual depths, both well below the maximum depth accepted for this species. The first author identified this species among the material collected by Hirondelle (sta 226) between Pico and Faial islands, at a depth of 130 m. However, it is possible that material was collected at shallower depths than what was reported (see remarks under Pawsonia saxicola ). In the second report, Hérouard recorded T. inermis at two stations sampled by Princesse Alice in the Azorean waters (sta 553: 37°42’40”N, 25°05’15”W; sta 575: 38°27’00”N, 26°30’15”W) between 1,165 –1,385 m. The depth values alone seem to suggest that the material was neither T. inermis nor a species of Thyone , a shallow-water genus ( Pawson & Miller 1981).

The taxonomy of the Thyone as in other dendrochirote holothurians is rather intricate (with a resulting problematic synonymy) particularly in the case of the European species, which are still awaiting an extensive revision ( McKenzie 1991). Most of the characters used to separate species show a great degree of overlap, frequently forcing the identifications to be based on a sum of characteristics rather than on a single character. Moreover, dendrochirote holothurians are also characterized by species showing a large degree of morphological plasticity resulting from ontogenetic, environmental and genetic variability, coupled with the occasional drastic effects of fixation (e.g., partial to total dissolution of ossicles) ( Pawson & Miller 1981; McKenzie 1991) making the identification rather difficult and in some cases impossible. The inclusion of this species in the Azorean extant fauna should be considered under caution, until new material belonging to T. inermis is taken in the area that could corroborate the historical records.