Ophiactis savignyi ( Müller & Troschel, 1842 ),

Alitto, Renata A. S., Bueno, Maristela L., Guilherme, Pablo D. B., Domenico, Maikon Di, Christensen, Ana Beardsley & Borges, Mic, 2018, Shallow-water brittle stars (Echinodermata: Ophiuroidea) from Araçá Bay (Southeastern Brazil), with spatial distribution considerations, Zootaxa 4405 (1), pp. 1-66: 51-53

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Ophiactis savignyi ( Müller & Troschel, 1842 )


Ophiactis savignyi ( Müller & Troschel, 1842) 

( Fig. 18View FIGURE18)

Type locality. Egypt, Africa. 

Maximum size. dd up to 8.5 mm ( Paim et al. 2015).

Material examined. 84 specimens (dd: 0.9–4.1 mm). Subtidal: ZUEC OPH 2186, St. XXI, 5 spms; ZUEC OPH 2206, St. XXII, 1 spm; ZUEC OPH 2273, St. XXVI, 2 spms. From rocky shore in sponge: ZUEC OPH 2146, St. 1C, 3 spms; ZUEC OPH 2147, St. 1C, 3 spms; ZUEC OPH 2148, St. 2C, 5 spms; ZUEC OPH 2153, St. 9C, 4 spms; ZUEC OPH 2155, St. 8C, 1 spms; ZUEC OPH 2432, St. 11C, 9 spms; ZUEC OPH 2434, St. 13C, 9 spms; ZUEC OPH 2438, St. 10C, 2 spms; ZUEC OPH 2453, St. 15C, 40 spms.

Description. Disc: (dd: 3.2 mm) circular, covered by irregular and imbricating scales, approximately 18 between the centrodorsal and the edge of the disc and some small spines, more numerous at the edges. Radial shields acute proximally, large (approximately one-third of dd), internally straight and externally slightly curved, separated proximally by two scales ( Fig. 18AView FIGURE18). Ventral interradius covered with scales smaller than the dorsal and with sparse spines. Bursal slits broad ( Fig. 18BView FIGURE18). Oral shields diamond-shaped with distal lobe, as long as wide. Adoral shields broadened distally and united proximally. One lateral oral papilla spatulate, sometimes two. One rectangular apical papilla ( Fig. 18CView FIGURE18).

Arms: typically hexamerous, occasionally pentamerous. Dorsal arm plates rectangular, twice as wide as long, distal edge rounded and proximal straight and contiguous ( Fig. 18D,FView FIGURE18). Ventral arm plates pentagonal, as long as wide, distal edge straight and proximal acute angle, contiguous ( Fig. 18E,GView FIGURE18). One tentacle scale larger (nearly half the length of one ventral arm plate) and attached at lateral arm plate. Five to six arm spines blunt and denticulate, the ventral one smaller ( Fig. 18EView FIGURE18).

Lateral arm plates ( Fig. 18H,IView FIGURE18): general outline: ventral portion projecting ventro-proximalwards; ventro-distal tip not projecting ventralwards. Outer surface ornamentation: trabecular intersections protruding to form knobs larger than stereom pores on most of outer surface. Outer proximal edge: surface lined by discernible band of different stereom structure, restricted to central part; without spurs; central part protruding; proximal edge of outer surface with horizontal striation, but restricted to small area. Spine articulations: on same level as remaining outer surface, middle arm spine articulation larger; distance between spine articulations increasing dorsalwards. Lobes simply separated, dorsal lobe clearly larger than the ventral lobe; lobes parallel, bent, and tilted orientation; stereom massive; sigmoidal fold absent. Inner side, ridges and knobs: inner side dominated by two separate (rarely merged) central knobs; without additional dorsal structure on inner side; single large perforation on inner side.

Vertebrae: zygospondylous universal type and non-keeled. Proximal side of vertebrae dorsally without large groove on the dorsal-distal muscular fossae ( Fig. 18JView FIGURE18). Zygocondyles nearly parallel and zygosphene fused with pair of zygocondyles ( Fig. 18KView FIGURE18). Dorso-distal muscular fossae transformed distalwards projecting far from distal edge of zygocondyles ( Fig. 18LView FIGURE18). Zygosphene projecting beyond ventral edge of zygocondyles with projecting part longer than zygocondyles ( Fig. 18MView FIGURE18).

Taxonomic comments. Ophiactis savignyi  is easily confused with O. lymani ( Hendler et al. 1995)  particularly during its juvenile period. There are differences in the arm ossicles (see more above in taxonomic comments of O. lymani  ). O. savignyi  is also similar to O. brasiliensis  , however, the latter differs in having larger and circular dorsal disc scales, fewer spines at the disc edge and four arm spines ( Manso 1988). Of the 84 specimens, 66 show some evidence of regeneration of disc and arms due to fission ( Hendler et al. 1995; McGovern 2002; Manso et al. 2008; Paim et al. 2015). A single regenerating specimen was observed to have three lateral oral papillae, while all others only possessed one. O. savignyi  occurs in various combinations of greenish, greenish brown, brown and cream color ( Hendler et al. 1995). The colors recorded for most specimens were greenish and brown. Three individuals, whom had recently split, exhibited two colors: greenish in most of the disc and cream in part being regenerated.

Remarks. This is one of the most studied species, particularly with respect to its reproduction ( Emson & Wilkie 1984; Hendler 1991; Chao & Tsai 1995; McGovern 2002), population genetics ( Roy & Sponer 2002), feeding ( Boffi 1972; Emson & Mladenov 1992) and habitat ( Boffi 1972; Sloan 1982; Hendler & Littman 1986; Neves et al. 2007). O. savignyi  can be found on rubble bottom and living associated with sponges, seagrass, bryozoans, polychaetes, and with other brittle stars Ophiothrix (Ophiothrix) angulata  ( Ophiotrichidae  ) and Amphipholis squamata  ( Amphiuridae  ) ( Hendler et al. 1995; Gondim et al. 2008; Granja-Fernández et al. 2014). O. savignyi  was sampled associated with the sponge Amphimedon viridis  (65% of spms) and on rubble bottom with a dredge (35% of spms).

Distribution. Circum-tropical and circum-subtropical. In Brazil, it has been recorded in Tropical Atlantic (realm), Tropical Southwestern Atlantic (province): Northeastern Brazil ( Lima-Verde 1969; Tommasi 1970; Alves & Cerqueira 2000; Gondim et al. 2008; Miranda et al. 2012; Paim et al. 2015). Temperate South America (realm), Warm Temperate Southwestern Atlantic (province): Southeastern Brazil ( Brito 1960; Tommasi 1970; Pires-Vanin et al. 1997; Borges & Amaral 2005; Netto et al. 2005; Pires-Vanin et al. 2014).

From intertidal up to 518 m depth ( Alvarado & Solís-Marín 2013). The present study samples occurred at depths ranging from intertidal to 21.5 m.

Selected references. Müller & Troschel (1842): p. 95, fig. 4,5 [as Ophiolepis savignyi  ];

de Loriol (1893): p 401, Pl. XIV fig. 1 [as Ophiactis brocki  ]; Koehler (1905): p. 25, Pl III, fig. 15-17 [as Ophiactis conferta  ]; von Martens (1870): p. 248 [as Ophiactis incisa  ]; Lütken (1856): p. 12; Lyman (1865): p. 111, fig. 10,11 [as Ophiactis krebsii  ]; von Martens (1870): p. 248 [as Ophiactis maculosa  ]; Lütken (1859): p. 262 [as Ophiactis reinhardtii  ]; Mortensen (1936): p. 264; Tommasi (1970): p. 24, fig. 16,17; Madsen (1970): p. 207, fig. 33; Albuquerque (1986): p. 150, fig. 25a –c; Hendler et al. (1995): p. 148, fig. 70; Borges & Amaral (2005): p. 250, fig. a –d; Manso et al. (2008): p. 188, fig. 14f –h; Gondim et al. (2013a): p. 70, fig. 8g –l; Paim et al. (2015): p. 10, fig. 6d –f [as Ophiactis savignyi  ]; Clark (1938): p. 262 [as Ophiactis savignyi var. lutea  ]; Lyman (1865): p. 115 [as Ophiactis sexradia  ]; Clark (1939): p. 81, fig. 36 [as Ophiactis versicolor  ]; Lütken (1856): p. 24; Lyman (1865): p. 113 [as Ophiactis virescens  ]; Grube (1857): p. 37, pl. III fig. 1–3 [as Ophiolepis sexradia  ].