Taxonomic Status and Composition of the Genera Caulaster, Porcellanaster and Eremicaster (Asteroidea) Based on Juvenile Morphology and Molecular Phylogenetic Data

Abstract

The genus Porcellanaster Thomson 1878 has hitherto included two species, the type species P. ceruleus Thomson, 1878 and P. ivanovi Belyaev, 1969. According to WoRMS, the full list of junior synonyms of P. ceruleus consists of 15 specific names, including porcellanasterids of the genera Caulaster Perrier 1882 and Albatrossia Ludwig 1905. In this paper, the morphology of juvenile and adult Porcellanaster and synonymized species from the Atlantic, Pacific, Indian and Southern Oceans are studied. As a result, the composition of the genus Porcellanaster has been revised. The genus Caulaster is re-established and now includes two species, and two new morphological forms of Caulaster are described. The genera Albatrossia and Damnaster H.E.S Clark & McKnight, 1994 are considered junior synonyms of Caulaster. The number of species of the genus Porcellanaster has increased to five, including the recovered P. caulifer, P. fragilis and P. sladeni. The study of representatives of the closely related genus Eremicaster Fisher, 1905 has not led to a change in its species composition. The main diagnostic feature of Caulaster is the presence of adambulacral and dorsal pedicellariae both in adults and juveniles with a major radius (R) greater than 3.5 mm. Pedicellariae have never been found in Porcellanaster or Eremicaster at any stage of postlarval development. The species of Caulaster and some species of Porcellanaster are the smallest porcellanasterids, with the most simplified morphology and reduced papulae and paxillae responsible for respiration. These genera are located on the phylogenetic tree in different clades, which demonstrates the parallel evolution of these taxa and confirms the validity of the genus Caulaster. One of the reasons for miniaturization is likely the burrowing mode of life with feeding on subsurface sediment of low nutritional value. The simplification of morphology can be traced by many morphological charactercs in many ways, including the reduction in papulae and paxillae.