Gracilechinus alexandri

Gracilechinus alexandri (Danielssen & Koren, 1883) Reports for the Azores:

Echinus alexandri Danielssen & Koren, 1883 — $ Koehler 1895b: 229, 1909: 230; Mortensen 1927a: 304–305, figs. 167.1, 172– 173, 1943a: 65–68, figs. 20a, 21a–b, pl. 11, figs. 8–11; Grieg 1932: 42; Gage et al. 1985: 184; Serafy & Fell 1985: 4, 20, 21–22, fig. 29;? $ Pérès 1992: 255; García-Diez et al. 2005: 50 $ Desbruyères et al. 2006: 479, figs. 1–4; Gracilechinus alexandri (Danielssen et Koren, 1883) — Mironov 2014: 123–124.

Type locality: off Lofoten (69°18’N, 14°32’E), Norway.

See: Danielssen & Koren (1883: 294–296, pl. 3–4, figs. 7–16; as Echinus alexandri); Mortensen (1903: 146– 150, pl. 5, figs. 2, 3, 5,7, pl. 15, figs. 13, 17, pl. 16, fig. 8, pl. 17, figs. 9, 11, 19, 23, 25, pl. 19, figs. 16, 31, 34, 38, pl. 20, figs. 1, 2, 27, pl. 21, figs. 18–20, 27; 1943a); Desbruyères et al. (2006).

Occurrence: North Atlantic, in the west, along the east side of North America (Serafy & Fell 1985) and in the east from Icelandic, Scandinavian and British deep waters (Mortensen 1903, 1927a), southwards to the Bay of Biscay and the Azores (Koehler 1909); possibly also in Tristan da Cunha (Mortensen 1943a).

Depth: 230– 3,150 m (Desbruyères et al. 2006); AZO: 1,165 –1,940 (?2,560) m (Koehler 1909, Pérès 1992).

Habitat: soft substrates, ooze to sand (Koehler 1909, Gage et al. 1985); diet consisting of bottom mud with foraminiferans (Serafy & Fell 1985); feeds also on deep-sea reef building corals such as Lophelia pertusa and Madrepora oculata (Stevenson & Rocha 2012); can be found in the vicinity of deep-water hydrothermal vents (Desbruyères et al. 2006).

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 Gracilechinus acutus (= Echinus acutus) or Gracilechinus alexandri (= Echinus alexandri) but due to the small size of the animals (less than 1 cm) he could not ascertain without doubt. The confirmation of G. alexandri presence in the archipelago was made later by Koehler (1895b, 1909) who identified material belonging to this species collected by Princesse Alice at several stations located inside the Azorean waters. During a dive made by the bathyscaphe Archimède north of the S„o Miguel, Pérès (1992) claimed to observe an animal of this species at a depth of 2,560 m, though no specimen was collected. More recently, a small population of G. alexandri was found at one time in the vicinity of the Azorean Mid-Atlantic hydrothermal vent field Lucky Strike, from which a specimen has been figured in the Handbook of Deep-Sea Hydrothermal Vent Fauna by Desbruyères et al. (2006).