PEDICELLASTERIDAE, Perrier, 1884

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 : 651-652

THE PEDICELLASTERIDAE

The family Pedicellasteridae was established based on a number of reduced skeletal characters, including the lack of fused proximal adambulacral plates (i.e. an adoral carina), a more decalcified body wall, and several other characters interpreted as intermediate between the derived Asteriidae and non-forcipulate asteroids ( Fisher, 1928; Blake, 1990). For example, most pedicellasterids possess only two rows of tube feet versus four in the Asteriidae . Two rows of tube feet are considered plesiomorphic for most other living Asteroidea (e.g. Blake, 1987). Four of the six genera of nominal Pedicellasteridae – Ampheraster , Hydrasterias , Pedicellaster , and Tarsaster – were included in the analysis, as well as three pedicellasterid genera that are new to science and are currently being described (C. Mah, unpubl. data).

Our trees recover a non-monophyletic Pedicellasteridae , which places putative pedicellasterids on three different clades: the Pedicellasteridae ; the Ampheraster clade, including new genus 2; and the six-rayed pedicellasterid clade (new genus 3). The Pedicellasteridae clade includes the name-bearing Pedicellaster , Hydrasterias , and a new genus and species of pedicellasterid (new genus 1). The second ‘pedicellasterid’ clade contains the pedicellasterids Tarsaster alaskanus , Ampheraster marianus , the Hawaiian asteriid Tarsastrocles , and a new pedicellasterid genus and species 2. Finally, the third clade includes the six-rayed new genus/species 3, which was collected from the Gorda Ridge region and adjacent areas in the North Pacific.

The genus Tarsaster is not supported as monophyletic, with Tarsaster galapagensis recovered among the Stichasteridae and Tarsaster alaskanus placed with Ampheraster , Tarsastrocles , and new genus/species 1. Although Tarsaster has historical seniority over Ampheraster , the lack of monophyly in Tarsaster has dictated that for the time being, Ampheraster be used to describe the non-Stichasteridae clade, which includes Tarsaster alaskanus , until taxonomic issues in Tarsaster can be fully resolved. Depending on whether the type species for Tarsaster , Tarsaster stoichodes is placed among the Stichasteridae or among the members of the ‘ Ampheraster ’ clade, assignments to new genera will probably be necessary.

Although not recovered as monophyletic, pedicellasterids were never recovered as part of the restricted Asteriidae or any of the more recently derived forcipulatacean lineages, supporting the interpretation of at least some pedicellasterids as basal or stemward forcipulataceans. Although the multiple pedicellasterid lineages suggest that the characters associated with pedicellasterids are independently derived, it seems more likely, especially based on phylogenetic hypotheses based on fossils (e.g. Blake & Hagdorn, 2003), that these characters are plesiomorphic for the Forcipulatacea.