The holothuroid family Rhopalodinidae – its composition, distribution, phylogeny and taxonomic status

Abstract

The holothuroid family Rhopalodinidae currently contains three genera and 16 species, all restricted in their distribution to the East Atlantic Ocean from Senegal to the Cape of Good Hope. Their peculiar morphology is discussed and new  information is presented on the southern African forms. A key for the identification of the 16 known species is provided. It is suggested that the appearance of the proboscis was probably a response to the shallow turbulent waters of the tropical East Atlantic. Because of the polytentaculate nature of most species, the branched nature of the tentacles of some species, the shape of the calcareous ring, the ambulacral restriction of the pedicels and the form of the body wall tables, the Rhopalodinidae could well be classified within the Dendrochirotida, close to the Phyllophorinae. However, this point of view is not  supported by recent work based on analysis of rDNA and numerous morphological characters. According to this analysis Rhopalodinidae should be included within the Dactylochirotida.Key words: Echinodermata, Holothuroidea, Dactylochirotida, sea cucumbers, taxonomy