Sclerasterias richardi? (Perrier, in Milne-Edwards, 1882 )

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 : 68-69

Sclerasterias richardi? (Perrier, in Milne-Edwards, 1882)

( Fig. 14 )

Reports for the Azores:

Sclerasterias richardi (Perrier, in Milne-Edwards, 1882) — $ Madeira et al. 2017b: 11–18.

Type locality: Mediterranean Sea.

See: Perrier (in Milne-Edwards 1882: 20–21, as Asterias richardi ; 1894: 109–112, pl. 9, fig. 4, as Hydrasterias richardi ); Ludwig (1897: 403–418, pl. 12, figs. 18–22).

Occurrence: known only from the Mediterranean Sea ( Tortonese 1965),?Azores ( Madeira et al. 2017b) and Cape Verde ( Perrier 1894).

Depth: 80–710 m ( Falconetti et al. 1976); AZO: 135 m ( Madeira et al. 2017b).

Habitat: soft, detritic to hard substrata ( Gautier-Michaz 1958, Tortonese 1965).

Larval stage: planktotrophic; also reproduces asexually through fission ( Falconetti et al. 1976, 1977).

Material examined: DBUA-ECH 357 (Vila Franca do Campo, SMG, AZO, 37°41’42”N, 25°25’22”W, 2006.07. 17, 135 m; 3 spms, R = 5–6 mm, r = 1 mm);

Description: two specimens presenting six arms of unequal sizes (three larger and three smaller) and one animal with three arms of similar dimensions to the larger arms of the six-rayed specimens. Arms broad, pentagonal in cross-section, narrowing gradually into a round arm tip covered by the terminal plate; arms weakly attached to the disc. Reticular plating on the arms arranged in fairly regular longitudinal plate series (carinal, dorsolateral, superomarginal, inferomarginal, adambulacral); arm plates with a round four-lobed shape with exception of the small bridge-like dorsolateral plates. Papulae occupying the interstices between plates, forming two longitudinal rows on each side of the arm. Arm spines forming fairly regular longitudinal series. Carinal plates carrying up to three short and round spines bearing small spinelets at their tips. Dorsolateral plates bearing one small spine. Superomarginal plates armed with two spines similar in size and shape to the carinal and dorsolateral ones. Spine number and size gradually reduced to one small spine near the arm tip in both carinal and superomarginal plates and none in the dorsolateral plates. Inferomarginal plates with one or two flattened, spatulate to clavate enlarged spines, arranged obliquely and slightly enlarged towards the tip. Adambulacral plates diplacanthid bearing two flattened spines arranged obliquely with the internal spines slightly smaller than the external one. Dorsal surface of all specimens partially damaged, preserving at least two madreporites (S-shaped) near the interradial edges; disc also densely covered with small spines, identical in size and shape to those found on the dorsal surface of the arms. Numerous crossed pedicellaria almost as large as the dorsal spines dispersed over the body surface, not forming a wreath around the spines; presence of a slightly enlarged unpaired tooth on the outer face of each valve of the crossed pedicellaria. Straight pedicellaria felipedal, slightly larger than the crossed pedicellaria and restricted to the interradial areas.

Remarks: currently, only two other Sclerasterias species are known to the NE Atlantic and Mediterranean Sea: S. neglecta ( Perrier, 1891) (Bay of Biscay and Mediterranean Sea, 166–887 m) and S. guernei Perrier, 1891 (Bay of Biscay, 160–490 m) (A.M. Clark & Downey 1992). Unlike S. richardi , the crossed pedicellaria in these species is distributed in a fashion typical of the genus (i.e. in wreaths around the spines; Perrier 1891: 264) and none is known to asexually reproduce by fission. Nonetheless, neither the fissiparous nature nor the distribution of the crossed pedicellaria observed in S. richardi appears to be unique in Sclerasterias . While adults of Hawaiian S. euplecta present all the typical characters of the genus, the juvenile stages were described by Fisher [1906, as Coscinasterias (Distolasterias) euplecta ] as fissiparous and presenting a scattered distribution of crossed pedicellaria. These observations have led Fisher (1928) to believe that S. richardi was also a juvenile of another Sclerasterias , possibly S. neglecta . Later, A.M. Clark & Downey (1992) further suggested that S. richardi was an invalid species since the description by Perrier (in Milne-Edwards 1882, 1894) was based on immature specimens. However, the smallest known specimens of both S. neglecta and S. guernei (R = 15 mm, r = 3 mm and R = 17 mm, r =? mm, respectively) were described as having five arms with crossed pedicellaria arranged in circles around the spines ( Perrier 1891, 1896a). More recently, Mastrototaro & Mifsud (2008) argued that the unequal number and size of the arms, the presence of multiple madreporites and the documented sexual reproduction by Falconetti and co-workers (1976, 1977) suffice to prove that it was a valid species. Though we agree with Mastrototaro & Mifsud (2008), the position of S. richardi (or even of S. euplecta ) should be re-addressed in future revisions of this genus.

The only other fissiparous sea star known from the coastal waters of the Azores Coscinasterias tenuispina can be easily distinguished from S. richardi by the arrangement of the crossed pedicellaria in wreaths around the spines and by the monocanthid arrangement of the adambulacral spines. Furthermore, C. tenuispina appears to be restricted to the first few meters in the Azores (± 12 m) as opposed to much deeper local record of S. richardi (135 m). Sclerasterias richardi is one of the latest additions to the Azores echinoderm fauna. Madeira et al. (2017b) have identified the specimens herein enumerated among the material collected off the coast of Vila Franca do Campo (S„o Miguel Island) by the International Workshop of Malacology and Marine Biology (2006), one of the rare efforts in the Azores targeting deeper coastal waters (i. e. between 50 m and 200 m depth). Nevertheless, the specimens were small and probably immature shedding some doubt on whether they belong to an established population or represent a recent arrival, a question that can only be answered in future studies as further material becomes available.

Figures

FIGURE 14. Sclerasterias richardi (Perrier, in Milne-Edwards, 1882) (DBUA-ECH 357). Dorsal view (A); ventral view (B); madreporite (C); detail of the arm, ventral view (D).