Gracilechinus acutus? ( Lamarck, 1816 )

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 : 109

Gracilechinus acutus? ( Lamarck, 1816)

Reports for the Azores:

Echinus acutus Lamarck, 1816 —? Koehler 1898: 7, 23; Nobre 1938: 114–115, figs. 48, 51; García-Diez et al. 2005: 50; p.p.? $ Wisshak et al. 2010: 2382, fig. 2L; Micael & Costa 2010: 323;

Gracilechinus acutus ( Lamarck, 1816) — Micael et al. 2012: 4.

See: Mortensen (1943a: 43–52, pl. 3, fig. 3, pl. 5, figs. 1–5, pl. 6, figs. 1–5, pl. 7, figs. 7–9, pl. 8, figs. 1–10, pl. 10, figs. 1–2, pl. 54, fig. 26, as Echinus acutus ).

Occurrence: Mediterranean Sea and Northeast Atlantic, in the north from the Denmark Strait, Iceland, the Barents Sea, and Scandinavia [ G. acutus norvegicus ( D̹ben & Koren 1846); Mortensen 1943a], southwards along the European ( Koehler 1898, Nobre 1938) and North African coasts ( D̂derlein 1906, Cadenat 1938) to Sierra Leone ( Madsen 1957).

Depth: 20– 1,280 m ( Mortensen 1943a);? AZO : 380–500 m (herein).

Habitat: from detritic bottoms, where feeds on all kind of bottom living organisms, with preference for crustaceans and foraminifera ( Mortensen 1943a).

Larval stage: planktotrophic ( Emlet 1995).

Remarks: Koehler (1898) examined young specimens collected by Hirondelle in Azorean waters between 1,372 and 1,850 m, which he identified as possible G. acutus or G. alexandri though due to their small sizes (less than 1 cm) he could not identify them without doubt. Later, Koehler (1909) reviewed the material from Hirondelle and established that the specimens did not belong to G. acutus . The author also added it was not possible to identify the material because of their small size and lack of pedicellaria. Recently, Wisshak et al. (2010: 2383, fig. 2L) presents a photograph of an echinoid taken at 380 m in the southern Faial Channel, which they identified as G. acutus (= Echinus acutus ). They also observed that this large echinoid was abundant at a depth of 500 m. However, the photograph portraits a large white animal basketball-shaped with relatively short spines. The spherical white test and the short spines points towards E. melo ( Fig. 24 ) and not to G. acutus , which is generally characterized in the Atlantic by a subconical brightly coloured test ( Koehler 1921b). However, images provided by Max Wisshak of additional specimens observed at 460 m, suggest that they indeed observed both G. acutus , as well as E. melo . Unfortunately, no material was collected by Wisshak and co-workers precluding to verify the identification based on images taken by the submersible Lula. Both species are very variable in colour, shape and spine length (see Mortensen 1943a) and thus are difficult to distinguish even in the lab. It is, therefore, usually impossible to confirm their identity based on photographs alone (especially in specimens exhibiting slightly intermediate characteristics). Consequently, unless collected and verified by direct examination, the presence of G. acutus in the Azorean EEZ, though likely, remains unconfirmed.

Figures

FIGURE 24. Echinus melo Lamarck, 1816 (EMEPC–LUSO L09D17B1:A–D).Aboral view (A); lateral view (B); oral view (C); animal in situ (D); echinoid most possibly belonging to E. melo in situ in Azorean deep waters (EMEPC–LUSO, 38°47'50"N, 27°28'57W", 455 m: E).