Pseudarchaster gracilis gracilis ( Sladen, 1889 )

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 : 84

Pseudarchaster gracilis gracilis ( Sladen, 1889)

( Fig. 16 )

Reports for the Azores:

Aphroditaster gracilis $ Sladen, 1889: 117–120 , pl. 17, figs. 1–2, pl. 18, figs. 7–8; Verrill 1899: 195; Astrogonium gracile Sladen, 1889 — Perrier 1894: 342; Astrogonium necator $ Perrier, 1894: 350–355 , pl. 23, fig. 1; $ Koehler 1909: 74–75; Pseudarchaster necator ( Perrier, 1894) — Verrill 1899: 195; Mortensen 1927a: 86; Astrogonium aequabile Koehler, 1907 a— $ Koehler 1909: 66–68, pl. 11, figs. 1–4; Astrogonium eminens, Koehler, 1907 a— $ Koehler 1909: 68–71, pl. 16, figs. 3–6; Astrogonium marginatum $ Koehler, 1909: 71–73 , pl. 14, figs. 1–4, 1921a: 2; Pseudarchaster aequabile ( Koehler, 1907a) — Mortensen 1927a: 86; Pseudarchaster eminens ( Koehler, 1907a) — Mortensen 1927a: 86; Pseudarchaster marginatus ( Koehler, 1909) — Mortensen 1927a: 86; Pseudarchaster gracilis ( Sladen, 1889) — Mortensen 1927a: 86; $ Halpern 1972: 360–366, figs. 1–2; Downey 1973: 59–60, pl. 23, figs. C, D; Walenkamp 1979: 44–47, figs. 16, 19, pl. 10, figs. 1–4; Gage et al. 1983: 279–280; Pseudarchaster gracilis gracilis ( Sladen, 1889) — $ A.M. Clark & Downey 1992: 262–263, pl. 62, figs. E–F; García-Diez et al. 2005: 47; Benavides-Serrato et al. 2011: 170–171.

Type locality: Azores (37°24’N, 2 5°13’W).

See: Halpern (1972); Walenkamp (1979); A.M. Clark & Downey (1992); Benavides-Serrato et al. (2011).

Occurrence: North Atlantic, from Flemish Cap, off Cape Cod ( Murillo et al. 2015), and from Faeroe waters (Lousy Bank; Sneli 1999), south to the Equator on the both sides of the Atlantic and in the Charlie-Gibbs Fracture Zone ( Dilman 2008) and the Azores Archipelago ( Koehler 1909) in the Mid-Atlantic Ridge; the subspecies P. gracilis tessellatus Sladen, 1889 is restricted to southern Africa (A.M. Clark & Downey 1992).

Depth: 270– 2,940 m ( Benavides-Serrato et al. 2011); AZO: 903– 1,940 m).

Habitat: soft substrates, Globigerina ooze to fine sand and stones ( Koehler 1909, Sneli 1999).

Larval stage: direct or lecithotrophic ( Halpern 1972).

Material examined: EMEPC-LUSO L09D18B1 (N of SJG, AZO, 38°42’18”N, 28°01’18”W, 2009.10.02, 903 m; 1 spm, R = 102 mm, r = 31 mm).

Description: stellate and flat body form (R/r = 3.3) with narrow, tapering arms terminating in an acute point; wide, rounded interbrachial arcs. Abactinal plates paxillose, extending to terminal plates. Paxillae proximally hexagonal becoming more square-shaped distally, covered with rounded, flattened central granules and one peripheral row of short, slender spinelets. Madreporite rhombic, small, about one and one-half times the size of the adjacent abactinals, located about three quarters from the centre of the disc and to middle of the interbrachial arc. Anus small, located more or less at the centre of the disc. Superomarginal and inferomarginal plates corresponding; 36 in each side of the arm. Lateral angle of superomarginals compressed so that plates are broad and mainly in the vertical plane; superomarginals closely covered by large, rounded, and flattened granules. Inferomarginals covered by short triangular spinules interspersed by conical spines which are about three times larger. Each actinal plate covered by short spinules and one, rarely two or three larger spines. Actinal spines and spinules similar to those on inferomarginals. One pectinate pedicellariae between every two adjacent actinal plates along row contiguous to adambulacrals, particularly conspicuous in the proximal region; pedicellaria along entire width of plate. Adambulacral plates with angular furrow margin bearing six up to nine somewhat flattened furrow spines with blunt tips. Subambulacral spines irregularly arranged in two rows of intermediate shape and size between the actinal and the furrow spines. Each mouth plates bearing ten furrow spines similar to the adambulacral furrow spines, with a large, thick, unpaired median spine at apex of each mouth plate pair. Rest of each plate covered by spines grading progressively into actinal spinules distally.

Remarks: the highly variable Pseudarchaster gracilis gracilis was described for the Azores under five different names ( Sladen 1889; Perrier 1894; Koehler 1909, 1921a). Halpern (1972) re-examined the type material from the archipelago and established the synonymy. A.M. Clark & Downey (1992) also analysed the type material of P. gracilis described by Sladen (1889; as Aphroditaster gracilis ) based on specimens collected in Azores by H.M.S. Challenger and demoted P. tessellatus to a subspecies of P. gracilis .

The North Atlantic subspecies P. gracilis gracilis can be distinguished from P. parelii also occurring in the Azores (see below) by the conical shape and larger size of the actinal and inferomarginal spines. Additionally, P. parelii generally has poorly developed pedicellaria and fewer adambulacral and mouth furrow spines ( Halpern 1972). This present record substantiates the historical records.

Figures

FIGURE 16. Pseudarchaster gracilis gracilis (Sladen, 1889) (EMEPC–LUSO L9D18B1). Dorsal view (A); ventral view (B); detail of the disc and arm, dorsal view (C) and ventral view (D); animal in situ (38°42'18"N, 28°01'18"W, 2009.10.02, 903 m; E).