Ophioplocus januarii ( Lütken, 1856 ),

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: 16-18

publication ID

https://doi.org/10.11646/zootaxa.4405.1.1

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lsid:zoobank.org:pub:D33BF380-5AF7-4645-86C7-9981C528EAF0

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http://treatment.plazi.org/id/03C3B82F-9223-C969-07C8-FF59FB193ED3

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Plazi

scientific name

Ophioplocus januarii ( Lütken, 1856 )
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Ophioplocus januarii ( Lütken, 1856) 

( Fig. 4View FIGURE 4)

Type locality. Rio de Janeiro, Brazil. 

Maximum size. dd up to 21.9 mm ( Borges, 2006).

Material examined. 1 juvenile specimen (dd: 4.4 mm) from subtidal: ZUEC OPH 2207, St. XXII, 1 spm.

Description. Disc: (dd: 4.4 mm) pentagonal, covered by large and imbricating scales, becoming smaller and granulated in interradial portions of the disc. Central primary plate circular and primary radial plates evident. Radial shields oval, small, twice as long as wide, convergent proximally and separated by several scales ( Fig. 4AView FIGURE 4). Ventral interradius covered with scales smaller and more imbricated than the dorsal. Bursal slits broad ( Fig. 4BView FIGURE 4). Oral shields proximal angle obtuse, lateral rounded angles and lobed distal edge. Madreporite larger than other oral shields, but with similar shape. Adoral shields comma-shaped, distally convex, proximally deeply concave (tentacle pore), bordering proximal angle of oral shield and separated proximally. Four block-shaped lateral oral papillae, distal one larger. One small apical papilla. 2nd tentacle pore broad, laterally opening in the mouth slit, at the adoral shield ( Fig. 4CView FIGURE 4).

Arms: dorsal arm plates fan-shaped, the most proximal ones irregularly fragmented in two, and contiguous ( Fig. 4D,FView FIGURE 4). Ventral arm plates broadly convex distally, acute angle proximally, with deep notches for the tentacle tube feet laterally and contiguous ( Fig. 4E,GView FIGURE 4). Three tentacle scales at first arm pore and two from the second pore. Three arm spines blunt ( Fig. 4EView FIGURE 4).

Lateral arm plates ( Fig. 4H,IView FIGURE 4): general outline: ventral portion projecting ventro-distalwards; ventro-distal tip 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 over most of the proximal edge; without spurs; central part not protruding; surface without horizontal striation. Spine articulations: on same level as remaining outer surface, ventralwards increasing in size; distance between spine articulations increasing dorsalwards. Two parallel ridges, ventral larger than the dorsal, separated at both ends, and oriented nearly horizontal; stereom with perforations; sigmoidal fold absent. Inner side, ridges and knobs: inner side apparently without ridges or knobs (potentially due to its juvenile stage); 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. 4JView FIGURE 4). Zygocondyles dorsalwards converging and zygosphene fused with pair of zygocondyles ( Fig. 4KView FIGURE 4). Dorso-distal muscular fossae transformed distalwards not projecting ( Fig. 4LView FIGURE 4). Zygosphene projecting beyond ventral edge of zygocondyles with projecting part longer than zygocondyles ( Fig. 4MView FIGURE 4).

Taxonomic comments. The specimen described here was a juvenile, with characters that may change in an adult: i) the central primary plate is pentagonal; ii) primary radial plates are trapezoid; iii) five tentacle scales at first arm pore, four at the second pore and three at third pore. Similar to Ophioderma  , Ophioplocus januarii  has arm ossicles, especially the lateral arm plates and vertebrae, more robust than the other brittle stars of our study. This robustness of the arms ossicles could aid in its epifaunal lifestyle, as stouter arms are more suitable for life on the surface. However, like in Ophioderma januarii  , this hypothesis needs to be tested. Ophioplocus januarii  is similar to O. imbricatus  , but the latter differs in having fragmented dorsal arm plates more symmetrical than O. januarii ( Thomas 1975)  .

Remarks. It appears to be a microphagous species feeding on macroalgae fragments, plant debris, and animal cuticle structures ( Brogger et al. 2015). It is gonochoric with no evident sexual dimorphism. It breeds continuously; however, spawning intensity may be higher in some months than in others ( Brogger et al. 2013). This species can be often found on rocky, sandy, and rubble bottom ( Alvarado & Solís-Marín 2013), but it has also been observed associated with molluscs, arthropods, and annelids ( Arribas et al. 2008). A single specimen was collected on rubble bottom with a dredge.

Distribution. Tropical Atlantic (realm), Tropical Northwestern Atlantic (province): Southern Caribbean; Tropical Southwestern Atlantic (province): Trindade and Martin Vaz Islands ( Tommasi & Aron 1987). Temperate South America (realm), Warm Temperate Southwestern Atlantic (province): Southeastern Brazil ( Tommasi 1970; Manso 1989; Monteiro et al. 1992; Oliveira et al. 2010).

From intertidal to 180 m depth ( Alvarado & Solís-Marín 2013). The present study samples occurred at 19 m depth.

Selected references. Lütken (1856): p. 10 [as Ophiolepis januarii  ]; Lyman (1865): p. 62; Tommasi (1970): p. 72, fig. 72–75 [as Ophioceramis januarii  ]; Bernasconi & D'Agostino (1977): p. 95, lam. VIII, fig. 1,2; Monteiro (1987): p. 98, est. Xc –f; Borges (2006): p. 70–71, fig. 1.20 A –E [as Ophioplocus januarii  ].