Disk pentagonal (dd = 5.67 to 12.16 mm). Covered by thick and naked tegument (Fig. 2a). Radial shields enlarged along internal margin. Marginal interradius with a row of 8 to 10 large and overlapping scales (Fig. 2a). Bursal slits short and narrow (Fig. 2b). Oral shields triangular to circular, distal margin rounded. Adoral shields narrow and enlarged laterally. Three enlarged oral papillae on each side of jaw angle, distal free end totally dentate, the two proximal papillae being longer and wider than distal papilla (Fig. 2c). Dorsal arm plate long, narrow, fragmented into two (Fig. 2d). Ventral arm plates small, pentagonal, with a small notch on the distal margins. Four to five small, compressed, arm spines, with denticles on tips. Without tentacle scale (Fig. 2e).

Bermuda, the islands off southern Florida, the Bahamas, the Antilles, Mexican Caribbean, Belize, Guatemala, Honduras, Panama, islands off Caribbean Colombia, Venezuela, and Brazil (Devaney 1974, Hendler et al. 1995, Chavarro et al. 2004, Durán-Gonzáles et al. 2005, Trujillo-Luna and González-Vallejo 2006, Alvarado et al. 2008, Hernandéz-Herrejón et al. 2008). In Brazil it has been recorded from the States of Amapá, Pará, Maranhão, Ceará, Rio Grande do Norte, Paraíba, Pernambuco, Alagoas (Gondim et al. in press), Abrolhos islands off southern Bahia (Rathbun 1879), Bahia (Alves and Cerqueira 2000), and Rio de Janeiro (Manso 1993). Intertidal to 367.5 m. In this study it occurred between 11 and 33m.

According to Hendler et al. (1995), young individuals live associated with the phytal community, while adults are more commonly found on gravel bottoms from seagrass beds. This species feeds ingesting large portions of algae and sponges, detritus being collected by lateral movements of the arms. We observed specimens with stomachs filled with sponge spicules. Although Ophiomyxidae is a taxonomically problematic family (Franklin and O’Hara 2008), with the placement of several genera being uncertain (Martynov 2010). The identification of Ophiomyxa flaccida is easy, because the taxonomic characters are relatively constant intraspecifically, except for coloration that can vary between geographic areas (green, yellow, orange, red, reddish with a white spot on the disc or brown). Individuals analyzed in this study had a number of interradial scales smaller than observed by Tommasi (1970) for specimens from southeastern Brazil (about 12 scales). This is apparently a rare species in reef environments of Paraiba, and has been reported only in two reefs of this coast (Gondim et al. 2008, 2011).