Microphiopholis atra ( Stimpson, 1852 )

Alitto, Renata A. S., Bueno, Maristela L., Guilherme, Pablo D. B., Domenico, Maikon Di, Christensen, Ana Beardsley & Borges, Michela, 2018, Shallow-water brittle stars (Echinodermata: Ophiuroidea) from Araçá Bay (Southeastern Brazil), with spatial distribution considerations, Zootaxa 4405 (1), pp. 1-66 : 36-38

Microphiopholis atra ( Stimpson, 1852)

( Fig. 12 )

Type locality. South Carolina, United States.

Maximum size. dd up to 11 mm (present study).

Material examined. 70 specimens (dd: 2.4–11.2 mm) from intertidal zone and subtidal: ZUEC OPH 2112, St. 16, 1 spm; ZUEC OPH 2113, St. 34, 3 spms; ZUEC OPH 2115, St. 28, 1 spm; ZUEC OPH 2116, St. 21, 1 spm; ZUEC OPH 2117, St. 11, 1 spm; ZUEC OPH 2119, St. 26, 1 spm; ZUEC OPH 2181, St. 71, 1 spm; ZUEC OPH 2182, St. 68, 4 spms; ZUEC OPH 2192, St. 68, 1 spm; ZUEC OPH 2196, St. VII, 3 spms; ZUEC OPH 2200, St. 68, 5 spms; ZUEC OPH 2208, St. 71, 5 spms; ZUEC OPH 2213, St. 71, 3 spms; ZUEC OPH 2242, St. 108, 1 spm; ZUEC OPH 2244, St. XIX, 1 spm; ZUEC OPH 2247, St. 105, 3 spms; ZUEC OPH 2261, St. XIV, 1 spm; ZUEC OPH 2275, St. XXVI, 7 spms; ZUEC OPH 2283, St. XXVI, 1 spm; ZUEC OPH 2285, St. 145, 3 spms; ZUEC OPH 2290, St. 132, 1 spm; ZUEC OPH 2296, St. 147, 1 spm; ZUEC OPH 2326, St. 9H, 10 spms; ZUEC OPH 2339, St. 20H, 2 spms; ZUEC OPH 2351, St. XXXIV, 9 spms.

Description. Disc: (dd: 9.1 mm) circular, covered by numerous small and imbricating scales, approximately 30 between the central primary plate and the edge of the disc. Primary radial plates evident. Higher marginal scales, forming a fringe. Radial shields twice as long as wide, straight inner edge and curved outer edge, touching distally and separated proximally by two to four elongated scales. Scales near a pair of radial shields slightly bigger than the rest of the disc ( Fig. 12A ). Ventral interradius covered with scales smaller than the dorsal and strongly imbricated. Bursal slits broad ( Fig. 12B ). Oral shields diamond-shaped, twice as long as wide with proximal and distal edges tapered. Madreporite larger than other oral shields, more whitish than other oral shields and with pores in the distal margin. Adoral shields triangular broadened distally and tapered proximally. Two lateral oral papillae, distal larger and wider than the proximal. A pair of infradental papillae, widely separated from each other ( Fig. 12C ).

Arms: dorsal arm plates broadly oval, three times as wide as long, contiguous ( Fig. 12D,F ). Ventral arm plates pentagonal, as long as wide, proximal part angled, distal edge straight and with a slight notch on each side, contiguous ( Fig. 12E,G ). Two well-developed tentacle scales, half as long as one ventral arm plate; the larger attached to the ventral arm plate and the smaller to the lateral arm plate ( Fig. 12E ). Three pointed arm spines ( Fig. 12D ).

Lateral arm plates ( Fig. 12H,I ): general outline: ventral portion projecting ventro-proximalwards; ventro-distal tip not projecting ventralwards. Outer surface ornamentation: trabecular intersections protruding to form knobs approximately the same size than stereom pores. Outer proximal edge: surface lined by discernible band of different stereom structure, restricted to central part; without spurs; central part not protruding; surface without horizontal striation. Spine articulations: on same level as remaining outer surface, sizes all similar; distance between spine articulation increasing dorsalwards. Lobes simply separated, dorsal lobe clearly larger than the ventral lobe; lobes parallel, bent, and oriented nearly horizontal; stereom massive; sigmoidal fold absent. Inner side, ridges and knobs: 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. 12J ). Zygocondyles dorsalwards converging and zygosphene fused with pair of zygocondyles ( Fig. 12K ). Dorso-distal muscular fossae transformed distalwards projecting but far from distal edge of zygocondyles and with a vertical hole through the ossicle, approximately one tenth as long as the vertebra ( Fig. 12L,M ). Zygosphene projecting beyond ventral edge of zygocondyles with projecting part longer than zygocondyles ( Fig. 12M ).

Taxonomic comments. Approximately half of the specimens lacked the disc and one-fourth had a broadened disc due to mature gonads. Similar to Amphiodia pulchella and Microphiopholis subtilis , M. atra can voluntarily cast off the disc during spawning to aid in the dispersal of gametes ( Manso et al. 2008). M. atra can present morphological differences, like fragmented dorsal arm plates and rectangular radial shields ( Borges 2006). These variations may occur in specimens with a regenerating disc and can cause an erroneous identification, as happened with Amphiodia gyraspis H.L. Clark, 1915 , currently a synonym of M. atra ( Thomas 1964; Stöhr et al. 2016).

Remarks. It is possibly a deposit feeding infaunal species, due to the large amount of sediment found in its stomach contents ( Tommasi 1970; Borges & Amaral 2005). It is commonly sampled in benthic communities in large numbers with other burrowing brittle stars, like Hemipholis cordifera ( Valentine 1991; Hendler et al. 1995). It occurs in muddy, sandy and rubble bottom ( Tommasi 1970; Manso et al. 2008). M. atra was collected from sand (very fine, fine, medium and coarse sand), medium silt and rubble bottom with van Veen grab (60% of spms), dredge (26% of spms) and multicorer (14% of spms).

Distribution. Tropical Atlantic (realm), Tropical Northwestern Atlantic (province): Eastern Caribbean to Southwestern Caribbean ( Tommasi 1970; Alvarado 2011); Tropical Southwestern Atlantic (province): Northeastern and Eastern Brazil ( Albuquerque & Guille 1991; Magalhães et al. 2005; Manso et al. 2008; Lima & Fernandes 2009; Gondim et al. 2013b; Paim et al. 2015). Temperate South America (realm), Warm Temperate Southwestern Atlantic (province): Southeastern ( Tommasi 1970; Borges & Amaral 2005; Netto et al. 2005).

Common in the intertidal zone up to 38 m depth ( Alvarado & Solís-Marín 2013), but there are records of up to 100 m ( Borges & Amaral 2005). The present study samples occurred at depths ranging from intertidal to 21.5 m.

Selected references. Stimpson (1852): p. 225 [as Ophiolepis atra ]; Thomas (1964): p. 160, fig. 2,3; Albuquerque (1986): p. 80, fig.13a–c; Borges & Amaral (2005): p. 255, fig. a–c; Manso et al. (2008): p. 189, fig. 15a–d [as Amphiodia atra ]; Clark (1915): p. 245, plate 7, 1–4; Parslow & Clark (1963): p. 33 [as Amphiodia gyraspis ]; Verrill (1899b): p. 312 [as Amphipholis limbata ]; Fell (1962): p. 14 [as Diamphiodia atra ]; Thomas (1966): p. 830; Tommasi (1970): p. 38, fig. 37–38 [as Micropholis atra ]; Monteiro (1987): p. 77, fig. VIe–f; Paim et al. (2015): p. 6, fig. 3a–c [as Microphiopholis atra ]; Grube (1857): p. 34, Taf. II. fig. 1 [as Ophiolepis limbata ].

Figures

FIGURE 12. Microphiopholis atra ZUEC OPH 2116 (9.1 mm dd). (A) Dorsal view. (B) Ventral view. (C) Detail of the oral view.(D)Detail of dorsalarm.(E)Detailof ventral arm.(F)Dorsal arm plate.(G)Ventral arm plate.(H-I) Lateralarm plate. (J) Vertebra—proximal surface. (K) Vertebra—distal surface. (L) Vertebra—dorsal surface. (M) Vertebra—ventral surface. Abbreviations: ads: adoral shields; as: arm spine; bs: bursal slits; cpp: central primary plate; d: dorsal; dap: dorsal arm plate; ddi: dorso-distal; ddmf: dorso-distal muscular fossae; di: distal; dp: dorso-proximal; ho: hole; hms: higher marginal scales; ip: infradentalpapillae;ma:madreporite; lop:lateral oral papillae;os: oral shields; p:proximal; pe:perforation; prp:primary radial plate; rs: radial shields; tn: tentacle notch; ts: tentacle scale; v: ventral; vap: ventral arm plate; vdi: ventro-distal; vp: ventroproximal; zd: zygoscondyle; zp: zygosphene. Stereomicroscope photos: (A)–(E), scale bar equal to 0.5 mm. SEM photos: (F)–(M), scale bar equal to 100 µm.