Phylogeny of the Holothuriidae (Echinodermata: Holothuroidea) inferred from morphology
Appeltans, W. (2002). Phylogeny of the Holothuriidae (Echinodermata: Holothuroidea) inferred from morphology. MSc Thesis. Vrije Universiteit Brussel: Brussel. 94 pp.
Despite the efforts of numerous notable taxonomists, the taxonomy and systematics of the grand family Holothuriidae (Holothuroidea: Aspidochirotida) remain vague for some groups. As such, a cladistically substantiated phylogeny based upon clearly defined morphological characters can bring insights into the evolution of the holothuriids. Thus, here I present a phylogeny of the group based on morphological characters. Cladistic analysis was performed by an heuristic search under the maximum-parsimony optimality criterion. 27 ingroup taxa, representing all currently recognized genera and subgenera and 6 outgroup taxa, belonging to the closely related Stichopodidae and deep-sea Synallactidae, were scored for a total of 68 characters concerning gross external and internal morphology and ossicle assemblage in the body wall, the tentacles and the tube feet. Moreover, often ignored body parts such as longitudinal muscles, cloacal muscles and anal papillae were examined for the presence of ossicles. Preliminary analysis revealed that for the synallactid genus Mesothuria, the species used as outgroup (e.g. M. sufflava) clustered in the ingroup. As it is here argued that this is the result of erroneous identification, Mesothuria was omitted as outgroup taxon. On the other hand, two genera of the Stichopodidae successfully lent themselves as outgroup. For the Holothuriidae, the monophyly of the genera Actinopyga, Bohadschia and Labidodemas was confirmed. Labidodemas, however, clustered in the paraphyletic lineage Holothuria. The enigmatic genus Pearsonothuria turned out to be the sister group of Actinopyga. From the resulting phylogeny, inferences on character evolution are made.
