Zoological Journal of the Linnean Society (2001), 133: 53-62. With 3 figures dW:10.1006/zj1s.2000.0279. available online at httpi/w-.idealibrary.com on lDEalX Phylogeny of the Apodan Holothurians (Echinodermata) inferred from morphology ALEXANDER M. KERR* Department of Ecology and Evolutionary Biology, Osborn Zoological Laboratories, Yale University, PO Box 2081 06, New Haven, CT 06520-81 06, USA Received February 2000; accepted for publication December 2000 The Apodida is an order of littoral to deep-sea, largely infaunal sea cucumbers with about 270 extant species in 32 genera and three families, Synaptidae, Chiridotidae and Myriotrochidae. In this study, I perform the first phylogenetic test of the taxonomic and palaeontological hypotheses about evolutionary relationships within Apodida by using cladistic analyses of 34 morphological characters. I introduce several previously unconsidered synapomorphic characters, examine the relationships between all recognized suprageneric taxonomic groups and assess the assumptions of monophyly for each family. Maximum-parsimony analyses of type species from 14 genera and use of three rooting methods recovered identical topologies at the subordinal level and subfamily level within Synaptidae. Overall, the current higher-level classification of Apodida was well corroborated. Within Synaptidae, the relationships (Synaptinae, (Leptosynaptinae, Rynkatorpinae)) are well supported. The rnonophyly of Chiridotidae was not supported and appears paraphyletic at the subfamily level. Calibrating the phylogenetic hypothesis of Apodida sgainst the fossil record indicated that most higher-level divergences occurred within the Palaeozoic, unlike that (of extant non-holothuroid echinoderms, which radiated in the early Mesozoic. Synaptidae appears to have radiated (duringthe Lower Cretaceous. Alternatively, and if one discounts the considerable ghost lineage duration that this liypothesis requires, they may have radiated during the Eocene. i? 2001 The Llnnean Society of London .4DDITIONAL KEY WORDS: holothuroids - Holothuroidea - Synaptidae - Chiridotidae -- Myriotrochidae - inorphology - sea cucumbers. INTRODUCTION Apodida is a group of littoral to deep-sea, largely infaunal holothuroid echinoderms. Apodans are unique among holothuroids in lacking tubefeet, papillae and radial water canals. Apodans are invariably vermiform ~~ith a thin, often transparent body wall and range in length from a few millimetres to more than 3 m, making them the largest echinoderms. They are distributed worldwide, with about 270 extant species in 32 genera and three families (Smiley, 1994; Smirnov, 1998). In this study, I make the first phylogenetic test of the t,axonomic and palaeontological hypotheses about c:volutionary relationships within Apodida by using cladistic analyses of morphological characters. I in- t.roduce several previously unconsidered, but im- portant, characters, examine the relationships among Vurrent address: Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 513106, USA. E-mail: alexander.kerr@aya.yale.edu 14 terminal taxa representing all currently recognized supergeneric groups and perform a preliminary test of the monophyly of apodan families. The taxonomic history of the apodans has been re- viewed most recently by Smirnov (1998). Briefly, Os- tergren (1898) divided the group into three subfamily- level groups that largely correspond to the present family designations. His classification was modified by Clark (1907) and by Heding (1928, 1929, 1931, 1935), who described numerous new species and introduced important suprageneric distinctions. Several more gen- era have since been described, notably by Belyaev & Mironov (1980) and Gage & Billett (1986). More re- cently, Smirnov (1989) revised Synaptidae to include fossil taxa with the stated aim of having the group's taxonomy reflect evolutionary relaltionships. Smirnov (1998) soon expanded this goal to include the entire 00244082/01/090053 + 10 S35 UO/0 5 3 ( 2001 The I,inncxan Society of Lortdon Downloaded from https://academic.oup.com/zoolinnean/article-abstract/133/1/53/2631213 by guest on 13 June 2020