ASTERINIDAE Gray, 1840

As outlined elsewhere, molecular phylogenetic results (Mah & Foltz 2011) have placed members of these two families on the same clade and created ambiguity with regards to the taxonomic boundary between them (see further discussion below). For reasons that will be evident, a general treatment of these two groups is combined herein.

The Asterinidae includes over 150 species in over 25 genera with occurrence all over the world in temperate, tropical and cold-water settings ranging from shallow to deep-water habitats. They have been heavily studied in biogeography (e.g., Ayers & Waters 2005). Asterinids have long been a model animal for developmental biology (e.g., Miyawaki et al. 2003) and possess the greatest range of life histories known for the Asteroidea (Byrne 2006) making them relevant for experimental biology and have been well studied in ecology (e.g., Emson & Crump 1984). Although systematics of the Asterinidae were heavily revised by O’Loughlin and Waters (2004), the group shows a broad morphological range and many taxa displayed characters which led to confusion with other families. For example, the endangered Derwent River seastar, “ Marginaster ” littoralis was in fact a species within the genus Patiriella and had been misidentified as a poraniid due to its fleshy body wall (O’Hara et al. 2018). Some asterinids, such as Paxillasterina (now Asterinides) displaying paxillate abactinal plates show superficial resemblance with some Ganeriidae.Although a diagnosis for the Asterinidae is included, we suggest O’Loughlin & Waters (2004) and references therein to survey full morphological diversity.

As described in more detail below, new subfamilial groupings are proposed for the Asterinidae to accommodate phylogenetic relationships illustrated by Mah & Foltz (2011). This includes a return of the Ganeriidae to subfamily status within the Asterinidae and establishment of the Hyalinothricinae as proposed by Fisher (1911).

Diagnosis (truncated). Body shape highly diverse, ranging from pentagonal to strongly stellate, thickness ranges from flattened to paper-thin to thick and round with short to extended arms, mostly five but with some genera up to 15. Interradial regions, with variably flattened edges to thick and confluent with disk. Abactinal plates variably crescentic, lobate, polygonal in imbricate to fenestrate arrangement. Surficial accessories highly diverse, ranging from granules, spinelets, paxillae to thick dermal covering with highly variable expression. Marginal plate morphology highly variable, similar in appearance with abactinal and/or actinal plates, but tracking to terminal plate as per Blake (1978). Superambulacral and superactinal plates present or absent. Actinal plates in chevron formation, but variably imbricate to abutted in arrangement, each plate with diverse accessories ranging from spinelets singly or in clusters and more documented in O’Loughlin & Waters (2004). Pedicellariae present or absent. Furrow spines forming palmate series in many but as with other accessories, highly variable.