Amphiodia riisei ( Lütken, 1859 ),

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: 33-35

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Amphiodia riisei ( Lütken, 1859 )


Amphiodia riisei ( Lütken, 1859) 

( Fig. 11View FIGURE 11)

Type locality. Rio de Janeiro, Brazil. 

Maximum size. dd up to 11 mm ( Borges & Amaral 2005).

Material examined. 3 specimens (dd: 2.3–9.2 mm) from subtidal: ZUEC OPH 2252, St. 15, 1 spm; ZUEC OPH 2253, St. XVI, 1 spm; ZUEC OPH 2357, St. XXXIV, 1 spm.

Description. Disc: (dd: 9.2 mm) circular with soft radial incisions above the arms, covered by irregular scales of medium size, approximately ten between the central primary plate and the edge of the disc. Primary radial plates evident and larger than the scales. Radial shields twice as long as wide, with a whitish spot on distal portion, separated proximally by two scales ( Fig. 11AView FIGURE 11). Ventral interradius covered by smaller scales than the dorsal and imbricated. Bursal slits long and narrow ( Fig. 11BView FIGURE 11). Oral shields diamond-shaped with rounded edges. Madreporite larger than other oral shields. Adoral shields broadened distally and touching proximally. Two lateral oral papillae, distal slightly larger and triangular. One pair of infradental papillae widely separated from each other ( Fig. 11CView FIGURE 11).

Arms: dorsal arm plates wide fan-shaped, three to four times as wide as long and contiguous ( Fig. 11D,FView FIGURE 11). Ventral arm plates trapezoid, twice as wide as long and contiguous ( Fig. 11E,GView FIGURE 11). Two subequal tentacle scales, one attached to the ventral arm plate and the other to the lateral arm plate. Three short (shorter than a half segment) and blunt arm spines ( Fig. 11EView FIGURE 11).

Lateral arm plates ( Fig. 11H,IView FIGURE 11): 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 of not protruding; surface without horizontal striation. Spine articulations: on same level as remaining outer surface, middle spine articulation larger; distance between spine articulations increasing dorsalwards. Lobes simply separated, dorsal lobe clearly larger than the ventral lobe; lobes parallel, bent, and oriented nearly horizontal; stereom with perforations, sigmoidal fold absent. Inner side, ridges and knobs: inner side dominated by two separate central knobs; without additional dorsal structure on inner side; single large perforation on inner side.

Vertebrae: zygospondylous of universal type and non-keeled. Proximal side of vertebrae dorsally without large groove on the dorsal-distal muscular fossae ( Fig. 11JView FIGURE 11). Zygocondyles dorsalwards converging and zygosphene fused with pair of zygocondyles ( Fig. 11KView FIGURE 11). Dorso-distal muscular fossae transformed distalwards projecting far from distal edge of zygocondyles ( Fig. 11LView FIGURE 11). Zygosphene projecting beyond ventral edge of zygocondyles with projecting part longer than zygocondyles ( Fig. 11MView FIGURE 11).

Taxonomic comments. The smallest specimens collected had a single tentacle scale. Primary plates on the dorsal surface of the disc were well developed and elevated, features which match with juvenile specimens ( Tommasi 1970). We do not follow the new synonymizing with Ophiophragmus riisei  as proposed by Hendler et al. (1995). We consider A. riisei  and O. brachyactis  distinct species and additional information concerning their differences can be found in Gondim et al. (2013a). Indeed, they are very closely related species, and a broader taxonomic revision with greater details is necessary.

Remarks. It occurs in mud and sandy bottom ( Borges & Amaral 2005; Manso et al. 2008). A. riisei  was collected from sand (coarse and fine sand) and rubble bottom with dredge and van Veen grab (66% of spms).

Distribution. Tropical Atlantic (realm), Tropical Northwestern Atlantic (province): Southern Gulf of Mexico to Eastern Caribbean ( Miloslavich et al. 2010); Tropical Southwestern Atlantic (province): Northeastern and Eastern Brazil ( Magalhães et al. 2005; Manso et al. 2008; Gondim et al. 2013a). Temperate South America (realm), Warm Temperate Southwestern Atlantic (province): Southeastern Brazil ( Lütken 1859; Tommasi 1970; Manso & Absalão 1988; Manso 1991; Pires-Vanin et al. 1997; Netto et al. 2005; Pires-Vanin et al. 2014).

From 1 to 300 m depth ( Borges & Amaral 2005). The present study samples occurred at depths ranging from 2.5 to 15.5 m.

Selected references. Lütken (1859): p. 258 [as Amphiura riisei  ]; Clark (1915): p. 249; Parslow & Clark (1963): p. 30; Albuquerque (1986): p. 91, fig. 16 a –d, est. IV fig. 1a –c; Monteiro (1987): p. 45, est. IIIa –c; Borges & Amaral (2005): p. 257, fig. a –c; Manso et al. (2008): p. 189, fig. 16a,b; Gondim et al. (2013a): p. 58, fig. 4 f –j [as Amphiodia riisei  ]; Rathbun (1879): p. 155 [as Amphipholis riisei  ]; Fell (1962): p. 14; Tommasi (1970): p. 28, fig. 22,23 [as Diamphiodia riisei  ]; Hendler et al. (1995): p. 175, fig. 90, 106 c –e; Alitto et al. (2016): p. 7, fig. 5a,b [as Ophiophragmus riisei  ].