Molecular phylogeny of extant Holothuroidea (Echinodermata)

Abstract

Sea cucumbers (Holothuroidea) are a morphologically diverse, ecologically important, and economically valued clade of echinoderms; however, the understanding of the overall systematics of the group remains controversial. Here, we present a phylogeny of extant Holothuroidea assessed with maximum parsimony, maximum likelihood, and Bayesian approaches using approximately 4.3kb of mt- (COI, 16S, 12S) and nDNA (H3, 18S, 28S) sequences from 82 holothuroid terminals representing 23 of the 27 widely-accepted family-ranked taxa. Currently five holothuroid taxa of ordinal rank are accepted. We find that three of the five orders are non-monophyletic, and we revise the taxonomy of the groups accordingly. Apodida is sister to the rest of Holothuroidea, here considered Actinopoda. Within Actinopoda, Elasipodida in part is sister to the remaining Actinopoda. This latter clade, comprising holothuroids with respiratory trees, is now called Pneumonophora. The traditional Aspidochirotida is paraphyletic, with representatives from three orders (Molpadida, Dendrochirotida, and Elasipodida in part) nested within. Therefore, we discontinue the use of Aspidochirotida and instead erect Holothuriida as the sister group to the remaining Pneumonophora, here termed Neoholothuriida. We found four well-supported major clades in Neoholothuriida: Dendrochirotida, Molpadida and two new clades, Synallactida and Persiculida. The mapping of traditionally-used morphological characters in holothuroid systematics onto the phylogeny revealed marked homoplasy in most characters demonstrating that further taxonomic revision of Holothuroidea is required. Two time-tree analyses, one based on calibrations for uncontroversial crown group dates for Eleutherozoa, Echinozoa and Holothuroidea and another using these calibrations plus four more from within Holothuroidea, showed major discrepancies, suggesting that fossils of Holothuroidea may need reassessment in terms of placing these forms with existing crown clades.

Epitomapta simentalae sp. n., a new species of apodous sea cucumber from the Central Eastern Pacific coast of Mexico (Echinodermata, Holothuroidea, Apodida)

“…Sea cucumbers of the family Synaptidae (order Apodida), while resolved as a non-monophyletic group in recent molecular analyses (Miller et al 2017), includes the genus Epitomapta , a shallow water transisthmian taxonomic group of burrowing apodous sea cucumbers. The genus was created by Heding (1928) to include the previously described Epitomaptaroseola (Verrill, 1873) and his new species E.tabogae Heding, 1928.…”

Filogenia morfológica das famílias Phyllophoridae e Sclerodactylidae (Echinodermata: Holothuroidea: Dendrochirotida)

“…É consensual entre os pesquisadores deste grupo, a necessidade iminente de revisão morfológica dos caracteres taxonômicos, especialmente sob a luz da cladística. Miller et al (2017) destacam ainda a necessidade de um estudo direcionado que abranja o mapeamento sobre a evolução de tais caracteres, especialmente do anel calcário, uma das estruturas menos conhecidas e com alto valor sistemático (Pawson & Fell, 1965;Reich, 2015;Smirnov, 2012).…”

“…Embora esteja além do objetivo deste trabalho, é importante destacar que com a incorporação de Dactylochirotida à ordem Dendrochirotida Miller et al (2017), torna-se necessário um estudo do relacionamento das famílias de Dactylochirotida com as famílias de Dendrochirotida (sensu Pawson & Fell, 1965). …”

“…Compreendem cerca de 1700 espécies (Paulay & Handson, 2013) distribuídas em sete ordens: Apodida, Elasipodida, Holothuriida, Synallactida, Persiculida, Molpadida e Dendrochirotida (Miller et. al., 2017).…”

“…No campo medicinal atuam no controle de patógenos (Toral-Granda, 2006), e diversas substâncias biologicamente ativas com ação antimicótica, antibacteriana (Ridzwan et al, 1995) e antitumoral (Kuznetsova et al, 1982, Micael et al, 2009 As espécies da ordem Dendrochirotida (sensu Miller et al, 2017) são caracterizadas pela presença de introverte, tentáculos do tipo dendrítico ou digitiforme, anel calcário com prolongamentos posteriores desenvolvidos ou simples, parede do corpo com ossículos dispersos ou imbricados formando uma testa, até duas vesículas de Poli e gônadas organizadas em tufo (Grube, 1840). Os principais tipos de ossículos encontrados na parede corporal são torres, botões e placas perfuradas (Deichmann, 1941 (Miller et al, 2017). Destas, aproximadamente 80% das espécies encontram-se distribuídas entre Cucumariidae Ludwig, 1894; Phyllophoridae Östergren, 1907 e Sclerodactylidae Pawson & Fell, 1965).…”