HELIASTERIDAE AND THE

Mah, Christopher & Foltz, David, 2011, Molecular phylogeny of the Forcipulatacea (Asteroidea: Echinodermata): systematics and biogeography, Zoological Journal of the Linnean Society 162 (3), pp. 646-660 : 652-653

THE HELIASTERIDAE AND THE SYNONYMY OF THE LABIDIASTERIDAE

The monotypic Heliasteridae includes the sole genus Heliaster , which comprises a species complex in the tropical East Pacific from Baja California, west to the Galapagos, and south to Chile (H. L. Clark, 1907).

In our two-gene tree ( Fig. 2 ) the monotypic Heliasteridae , represented by the Eastern Pacific species Heliaster kubiniji , is supported (100% bootstrap) as the sister taxon to the Southern Ocean/sub-Antarctic Labidiaster . The three-gene tree, which lacks Heliaster , shows Labidiaster as sister taxa to a new genus and species of deep-sea six-rayed pedicellasterid from the Central Pacific (86% bootstrap support), but with much longer branch lengths, suggesting greater divergence between the two taxa. If Labidiaster and Heliaster are sister taxa, this would further suggest a close biogeographic relationship between the South American and Antarctic/sub-Antarctic asteroid faunas. Janosik et al. (2008) have shown pelagic larvae for Labidiaster annulatus present in the Drake Passage, suggesting gene flow between South American and Antarctic populations.

Support for Labidiaster as the sister taxon to Heliaster is consistent with the assertion that the Labidiasteridae (sensu Spencer & Wright, 1966) is a purely artificial grouping (e.g. Mah, 2000; Foltz et al., 2007). Labidiaster is a phylogenetically separate taxon from the other labidiasterids (sensu Clark & Mah, 2001), including Plazaster , Coronaster , and Rathbunaster . Because Labidiaster is the type genus for the Labidiasteridae , this places synonymy of the Labidiasteridae into the Heliasteridae rather than the Asteriidae , as has been implied by earlier studies (e.g. Mah, 2000). The other genera within the Labidiasteridae have emerged with phylogenetically distinct clades: Plazaster and Rathbunaster on separate clades within the boreal Asteriidae , and Coronaster with the pantropical Asteriidae . All members of the polyphyletic Labidiasteridae were characterized by large numbers of elongate arms (up to 50 in Labidiaster ), biserial tube foot rows, and prominent pedicellariae. Based on our phylogenetic trees, these characters may be independently derived adaptations for benthopelagic predation, which has been observed in Labidiaster ( Dearborn, Edwards & Fratt, 1991) and Rathbunaster ( Lauerman, 1998) .

Figures

Figure 2. Maximum-likelihood tree for 95 forcipulate taxa and nine velatidan taxa, rooted on 111 taxa belonging to the Valvatida, Paxillosida, and Notomyotida (these taxa have been omitted for clarity), and based on 261 bp of sequence data for the 12S rDNA gene and 437 bp for the 16S rDNA gene. Bootstrap support values are based on 250 pseudoreplicates and are shown as percentages when ± 50%. Named clades correspond either to traditional taxonomic groups or to geographically restricted lineages.