Microphiopholis subtilis ( Ljungman, 1867 )

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 : 38-40

Microphiopholis subtilis ( Ljungman, 1867)

( Fig. 13 )

Type locality. Rio de Janeiro, Brazil.

Maximum size. dd up to 5.8 mm (present study).

Material examined. 105 specimens (dd: 1.5–5.8 mm) from subtidal: ZUEC OPH 2120, St. 27, 7 spms; ZUEC OPH 2134, St. I, 6 spms; ZUEC OPH 2135, St. 26, 3 spms; ZUEC OPH 2136, St. 35, 1 spm; ZUEC OPH 2137, St. 31, 1 spm; ZUEC OPH 2138, St. 33, 1 spm; ZUEC OPH 2139, St. 30, 1 spm; ZUEC OPH 2140, St. 32, 1 spm; ZUEC OPH 2141, St. III, 5 spms; ZUEC OPH 2142, St. 36, 1 spm; ZUEC OPH 2143, St. 32, 1 spm; ZUEC OPH 2144, St. 37, 1 spm; ZUEC OPH 2145, St. 37, 1 spm; ZUEC OPH 2157, St. 65, 1 spm; ZUEC OPH 2159, St. 70, 1 spm; ZUEC OPH 2160, St. 74, 1 spm; ZUEC OPH 2161, St. 74, 1 spm; ZUEC OPH 2162, St. VII, 2 spms; ZUEC OPH 2163, St. 68, 1 spm; ZUEC OPH 2165, St. 64, 1 spm; ZUEC OPH 2167, St. 74, 1 spm; ZUEC OPH 2168, St. 73, 2 spms; ZUEC OPH 2169, St. 71, 1 spm; ZUEC OPH 2170, St. 74, 3 spms; ZUEC OPH 2171, St. 72, 2 spms; ZUEC OPH 2173, St. 63, 2 spms; ZUEC OPH 2174, St. 66, 1 spm; ZUEC OPH 2180, St. VIII, 1 spm; ZUEC OPH 2184, St. 69, 2 spms; ZUEC OPH 2255, St. XVII, 3 spm; ZUEC OPH 2256, St. XX, 2 spms; ZUEC OPH 2257, St. XV, 4 spms; ZUEC OPH 2259, St. 111, 1 spm; ZUEC OPH 2260, St. 103, 1 spm; ZUEC OPH 2262, St. XVIII, 1 spm; ZUEC OPH 2263, St. 101, 1 spm; ZUEC OPH 2264, St. 104, 1 spm; ZUEC OPH 2265, St. XV, 1 spm; ZUEC OPH 2281, St. XXVI, 3 spm; ZUEC OPH 2284, St. XXVII, 9 spms; ZUEC OPH 2287, St. 147, 1 spm; ZUEC OPH 2289, St. XXII, 1 spm; ZUEC OPH 2294, St. 137, 1 spm; ZUEC OPH 2295, St. 148, 1 spm; ZUEC OPH 2297, St. 139, 1 spm; ZUEC OPH 2299, St. 148, 1 spm; ZUEC OPH 2300, St. 137, 1 spm; ZUEC OPH 2301, St. 143, 1 spm; ZUEC OPH 2302, St. 141, 1 spm; ZUEC OPH 2303, St. 143, 1 spm; ZUEC OPH 2304, St. 144, 1 spm; ZUEC OPH 2333, St. 5H, 1 spm; ZUEC OPH 2334, St. 6H, 1 spm; ZUEC OPH 2335, St. 11H, 1 spm; ZUEC OPH 2337, St. 8H, 2 spms; ZUEC OPH 2342, St. 7H, 1 spm; ZUEC OPH 2343, St. 29H, 1 spm; ZUEC OPH 2344, St. 16H, 1 spm; ZUEC OPH 2345, St. 16H, 4 spms; ZUEC OPH 2349, St. 27H, 1 spm; ZUEC OPH 2350, St. 17H, 1 spm.

Description. Disc: (dd: 3.7 mm) pentagonal, covered by numerous small, imbricating and slender scales, approximately 40 between the centrodorsal and the edge of the disc. Radial shields narrow, five times as long as wide, touching distally and separated proximally by two or three elongated scales ( Fig. 13A ). Ventral interradius covered with scales smaller than the dorsal and more imbricated. Bursal slits broad and long ( Fig. 13B ). Oral shields oval with slight lateroposterior indentations. Madreporite larger than other oral shields and more whitish. Adoral shields triangular, broadened distally, and tapered proximally. Two lateral oral papillae, distal twice as wide than the proximal. A pair of rectangular infradental papillae, similar to proximal oral papilla ( Fig. 13C ).

Arms: long and delicate. Dorsal arm plates 1.5 times as wide as long, rounded distally and tapered proximally, with an apparent line in the middle of the plate entire length of the arm, not contiguous ( Fig. 13D,F ). Ventral arm plates pentagonal, twice as long as wide, straight distally and tapered proximally, contiguous ( Fig. 13E,G ). Two tentacle scales, the larger attached to the ventral arm plate and the smaller to the lateral arm plate. Three slender arm spines, tip tapered.

Lateral arm plates ( Fig. 13H,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, middle spine articulation larger; distance between spine articulations equidistant. Lobes simply separated, ventral lobe clearly larger than the dorsal lobe; lobes parallel, straight, and oriented nearly horizontal; stereom massive; sigmoidal fold absent. Inner side, ridges and knobs: dominated by two separate central knobs (appear merged); 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. 13J ). Zygocondyles dorsalwards converging and zygosphene fused with pair of zygocondyles ( Fig. 13K ). Tapering tip on dorsal and ventral groove, visible on the proximal and distal surfaces of the vertebrae ( Fig. 13J,K ). Dorso-distal muscular fossae transformed distalwards projecting but far from distal edge of zygocondyles and with a vertical oval hole through the ossicle, almost a fifth as long as the vertebra ( Fig. 13L,M ). Zygosphene projecting beyond ventral edge of zygocondyles with projecting part as long as zygocondyles ( Fig. 13M ).

Taxonomic comments. This is the only species that was noted as having tapering tips visible on the proximal and distal surfaces of the vertebrae. This tapering tip is related to elevated structures involving the dorsal and ventral groove. M. subtilis is easily identified by the shape of radial shields and by the orange or reddish color on each arm segment in living or recently fixed specimens ( Monteiro 1987). These features were observed in most specimens in addition to other characters that clearly differentiate them from other species, such as long arms and lateral arm plates that touch dorsally. M. subitilis is similar to M. gracillima , but the latter has four to five arm spines and radial shields contiguous for almost their entire length ( Tommasi 1970).

Remarks. It occurs in mud and rubble bottoms ( Monteiro 1987), and has typical adaptations to this habitat, including very elongated arms, small disc, and well-developed tentacle scales which protect the pore from the sediment ( Tommasi 1970). M. subitilis was collected from sand (very fine, fine and medium), silt (medium, coarse and very coarse), and rubble bottom with a dredge (41% of spms), van Veen grab (37% of spms) and multicorer (21% of spms).

Distribution. Tropical Atlantic (realm), Tropical Northwestern Atlantic (province): Eastern Caribbean ( Tommasi 1970); Tropical Southwestern Atlantic (province): Northeastern and Eastern Brazil ( Tommasi & Aron 1988; Magalhães et al. 2005; Manso et al. 2008). Temperate South America (realm), Warm Temperate Southwestern Atlantic (province): Southeastern ( Tommasi 1970; Manso & Absalão 1988; Pires-Vanin et al. 1997; Netto et al. 2005; Oliveira et al. 2010; Pires-Vanin et al. 2014).

Common from 2 up to 50 m depth. The present study samples occurred at depths ranging from 8.5 to 23.5 m.

Selected references. Ljungman (1867): p. 314; Fell (1962): p. 13 [as Amphipholis subtilis ]; Lyman (1882): p. 146 [as Amphiura subtilis ]; Thomas (1966): p. 831; Tommasi (1970): p. 40, fig. 41–42 [as Micropholis subtilis ]; Monteiro (1987): p. 84, est. VII–f [as Microphiopholis subtilis ].

Figures

FIGURE13. Microphiopholis subtilis ZUEC OPH 2263 (3.7 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; d: dorsal; dap: dorsal arm plate; ddi: dorso-distal; ddmf: dorso-distal muscular fossae; di: distal; dp: dorso-proximal; ho: hole; ip: infradental papillae; lap: lateral arm plate; lop:lateral oral papillae; ma: madreporite; os: oral shields; p: proximal; pe: perforation; rs: radial shields; tn: tentacle notch; ts: tentacle scale; tap: tapering tip; v: ventral; vap: ventral arm plate; vdi: ventro-distal; vp: ventro-proximal; 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.