Oreaster reticulatus ( Linnaeus, 1758 )

Cunha, Rosana, Tavares, Marcos & Jr, Joel Braga De Mendonça, 2020, Asteroidea (Echinodermata) from shallow-waters of the remote oceanic archipelago Trindade and Martin Vaz, southeastern Atlantic, with taxonomic and zoogeographical notes, Zootaxa 4742 (1), pp. 31-56 : 44-46

Oreaster reticulatus ( Linnaeus, 1758)

Figures 4E , 8

Asterias reticulata Linnaeus, 1758: 661 [type locality: “Spanish West Indies”, viz. Clark & Downey, 1992].

Oreaster reticulatus – Hendler et al., 1995: 82 , figs. 25–26; Fernandes et al. 2002: 422; Magalhães et al. 2005: 63; Ventura et al. 2007: 238; Manso et al. 2008: 185, fig. 8c–e; Xavier, 2010: 75; Alves & Dias, 2010: 157; Benavides-Serrato et al., 2011: 179–180. Miranda et al. 2012: 143–144; Gondim et al. 2014: fig. 8a–g, 12c.

Trindade specimens. Brazil, Espírito Santo, Trindade Island , Enseada dos Portugueses, Farol, 20°29’52.3”S, 29°19’15.6”W, 23.x.2014, 12.5 m: 1 spm, R=100, r=45 ( MZUSP 1611 ); 6.vii.2015, 12.6 m: 1 spm, R=105, r=52 ( MZUSP 1612 ) .

Comparative material. Bermuda, Ferry Reach , 32º21’58”N, 64º41’56”W, iv.1939: 1 spm, R=170, r=90 ( MCZ AST–3727) . Brazil, São Paulo, São Sebastião , 23º47’55”S, 45º 23’45”W: 1 spm R=125, r=60 ( MZUSP 1956 ) ; San- tos, 23º57’39”S, 46º20’01”W, 1.vi.1999, 76 m: 2 spms R= 130 cm, r=70; R=140, r=80 ( MZUSP 1617 ) .

Distribution. Mexico, Bahamas, Cuba, Belize, Haiti, Dominican Republic, Puerto Rico, Guatemala, Honduras, Nicaragua, Costa Rica, Panama, Venezuela, Guyana, Surinam, Brazil (Ceará, Paraíba, Pernambuco, Bahia, Trindade Island, Cabo Frio, São Paulo), Canary Islands, Cape Verde ( Verrill, 1915; Caso, 1944; Tommasi, 1958; Brito, 1960; 1962; 1968; Walenkamp, 1976; Clark & Downey, 1992; Hendler et al. 1995; Guzman & Guevara, 2002; Ventura et al. 2007; Entrambasaguas, 2008; Alvarado & Solis-Marin, 2013; Hernandéz et al. 2013; Gondim et al. 2014). Depth range: 0–69 m ( Clark & Downey, 1992).

Recognition characters. Highly inflated disc. Five (4–6) short arms, distally tapered. Abactinal plates with tubercles or spines, reticulated, attached by elongated, sometimes narrow, secondary plates ( Fig. 8D ). Adambulacral plate with seven spines, five unequal in size, smallest two positioned at extremities of plate. One large, heavy subambulacral spine. Actinal pedicellariae not in alveoli. Pedicellariae abundant ( Clark & Downey, 1992; present study).

Color in life. Variable. In juveniles the abactinal surface is usually mottled with green, brown, beige and gray, whilst adults are yellow, brown, or orange on the abactinal surface. The actinal region is beige or yellowish in both, juveniles and adults ( Ummels, 1963; Hendler et al. 1995). Trindade specimens ( Figure 8 A–C).

Habitats. Inhabits shallow, protected waters, such as calm reef waters, lagoons and mangrove canals. This is species has been found on coral reefs, mangroves, rocky bottom, sandy bottom, seagrass, and rubble bottom, where it feeds upon different benthic organisms ( Scheibling, 1980; Alvarado & Solis-Marin, 2013). In Trindade O. reticulatus inhabits mixed bottoms of rhodolith beds, sand, gravel, and small rocks, between 12.5 m and 12.6 m ( Figure 8A ). This species is vulnerable to human exploitation ( Hendler et al. 1995; Alves & Dias, 2010; Lawrence, 2013).

Comments. Oreaster consists of only two species in the Atlantic Ocean: O. reticulatus ( Linnaeus, 1758) (WA) and O. clavatus Müller & Troschel, 1842 (EA). Clark & Downey (1992) differentiated the two species primarily based upon the presence, in O. reticulatus , of a highly inflated disc, abactinal plates with tubercle or spine ( Fig. 8D ), subambulacral spine large and heavy, and actinal pedicellariae not in alveoli (versus more or less flat disc, granules in the abactinal plates, slender and blunt subambulacral spine, and actinal pedicellariae in alveoli in O. clavatus ).

However, the variation in shape, from pentagonal to stellate, and the differing degrees of swollenness of the disc make this an extremely variable species. Morphological variations appeared to have led H. L. Clark (1942) astray in describing one specimen from Bermuda as a new subspecies (i. e., O. reticulatus var. bermudensis ). Downey (1973) found that the disc in small individuals of O. reticulatus was not inflated, and the marginal plates are relatively larger and more conspicuous than in the adults. One specimen from São Sebastião (R=125; MZUSP 1956) has a flattened disc, whereas the remaining studied specimens have strongly arched discs.

Ummels (1963) reported that most of the specimens of O. reticulatus from Saint Martin (Caribbean Sea) have a second subambulacral spine, which vary greatly in size. The Trindade specimens have only one spine in the subambulacral row ( Fig. 8G ) and the actinal granules are arranged in mosaics; whereas the coastal specimens from São Sebastião and Santos, São Paulo (see under comparative material) have two such spines, the smaller being positioned behind the larger one. In the specimens from Santos, the granules are more distant from one another and hence not forming a mosaic.

The spines in the center of the actinal plates are smaller in the specimens from Trindade comparatively to São Sebastião, which also have comparatively much larger spines in the interradial region near the mouth.

The Trindade specimens have seven ambulacral spines, being five larges and two very small spines. The smaller ones are not easily detected and this is, probably, why in most of the literature only five ambulacral spines have been recorded for this species. The coastal specimens studied have 5–7 spines.

The number of pedicellariae in the proximal interradial region and above the ambulacral furrow also vary between the Trindade and the coastal specimens (São Sebastião and Santos), in which the pedicellariae in the proximal interradial region and above the ambulacral furrow are much more numerous. The abactinal pedicellariae are abundant in the Santos specimens, whereas they were detected in only one specimen from Trindade, and they were not found in the specimens from São Sebastião. Furthermore, we have noticed that the number of pedicellariae increase with the size of the specimens.

Despite Clark & Downey’s (1992) assertion that the two species are separated by an east and west Atlantic distribution, the species O. reticulatus is also recorded from the Cape Verde Islands ( Caso, 1944; Hendler et al. 1995; Guzman & Guevara, 2002; Entrambasaguas, 2008), and Canary Island ( Hernandéz et al. 2013), however in this last record the authors did not provide any morphological information.

Figures

FIGURE 4. A. Copidaster lymani A. H. Clark, 1948, Trindade Island, Enseada das Orelhas. B–D. Mithrodia clavigera (Lamarck, 1816). B, C. Trindade Island, Príncipe beach. D. Fernando de Noronha, tide pool at Boldró beach. Photograph by Gabriela C. Zeineddine. E. Oreaster reticulatus (Linnaeus, 1758), Trindade Island, Enseada dos Portugueses, Farol. F. Luidia alternata alternata (Say, 1825) Trindade Island, Ponta da Calheta.

FIGURE 8. Oreaster reticulatus (Linnaeus, 1758). A–R. MZUSP 1611: A. specimen from Trindade Island photographed in situ. B, C. Abactinal and actinal views. D. Detail of the reticulate area. E. Madreporite. F. Mouth. G. Ambulacral spines. H–R. Scanning electron microscope. H–J. Adambulacral plates. K. Stereom, ambulacral plate. L–N. Ambulacral plates. O. Actinal plate. P. Marginal spine. Q. Superomarginal plate. R. Stereom, superomarginal plate. Scale bars: B–C, 20 mm; D, 10 mm; E, 1 mm; F–G, 3 mm. H–J, O, Q, 600 μm; K, R, 90 μm; L–N, 900 μm; P, 400 μm.