Disk circular (dd = 4.16 mm). Covered by numerous imbricating scales of irregular shapes (Fig. 4f). Primary plates very conspicuous (Fig. 4f). Central primary plate slightly pentagonal, surrounded by the radial primary plates. Radial shields enlarged distally, contiguous, except at proximal end, where there is a small, elongate, triangular scale (Fig. 4f). Ventral interradius covered by small, imbricating scales (Fig. 4g). Bursal slits long and broadened. Oral shields diamond-shaped (Fig. 4h). Adoral shields enlarged laterally. Two oral papillae on each side of jaw angle, the distal one a little larger than the proximal one (Fig. 4h). Infradental papillae rectangular and robust. Dorsal arm plate broader than long, rectangular, with the distal border rounded (Fig. 4i). Ventral arm plate pentagonal. Three arm spines slightly bigger than one arm segment, which is laterally flattened, with blunt tip (Fig. 4j). Two tentacle scales subequal and perpendicular.

Off Florida, the Antilles, possibly Panama and Puerto Rico, and Brazil (Hendler et al. 1995). In Brazil from Amapá, Pará (Albuquerque 1986), Bahia (Magalhães et al. 2005), Rio de Janeiro (Lütken 1859, type locality), São Paulo (Tommasi 1970), and Paraná (Borges and Amaral 2005). Depth 1-311 m. Found for the first time in the State of Paraíba, at 16 m, in the present study.

This species is known from sand and mud bottoms (Tommasi 1970). Thomas (1962) suggests that the species may be found in shallow waters, given that several reports collected specimens from 37m. Thomas (1962) suggests that Ophiophragmus brachyactis and Amphiodia riisei are synonyms. However, we have considered them distinct species belonging to different genera, on the basis of several noted differences, among which we stress the presence of a fence of papillae on the margin of the disk in Ophiophragmus brachyactis and the presence of well developed primary plates in Amphiodia riisei. In the original description of Ophiophragmus brachyactis, based on a specimen of 7 mm in disk diameter (dd), H.L. Clark (1915) did not observe the presence of well developed primary plates, a character emphasized by Tommasi (1970) for individuals of Amphiodia riisei with different dd (1.64 to 9 mm). Manso (1988) analysed a specimen of Ophiophragmus brachyatis with4 mm in dd and Thomas (1962) examined a specimen with a dd of 8 mm and none of them noticed the presence of well developed primary plates. However, Tommasi (1970) remarked that young individuals of Amphiodia riisei may present marginal scales slightly elevated on the border of the disk. In these specimens a single tentacle scale is observed, and the scales on the dorsal surface of the disk, mainly the primary plates, are well developed and elevated, characters that do not agree with the diagnosis of Ophiophragmus brachyatis. According to H.L. Clark (1918), one of the most important characters of the genus Ophiophragmus is the presence of a fence of papillae along the margin of the disk, although he notes that some species of Amphiodia may also have elevated scales on the interbrachial areas, despite their appearance being different from those in Ophiophragmus. Thus the proposed synonymy and the combination Ophiophragmus riisei proposed by Thomas (1962) and accepted by authors such as Hendler et al. (1995), and Stöhr and O’Hara (2013), are not followed herein. We emphasize that the previously mentioned authors did suggest that this complex of species must be revised.