PAULASTERIIDAE, Mah & Linse & Copley & Marsh & Rogers & Clague & Foltz, 2015

Mah, Christopher, Linse, Katrin, Copley, Jon, Marsh, Leigh, Rogers, Alex, Clague, David & Foltz, David, 2015, Description of a new family, new genus, and two new species of deep-sea Forcipulatacea (Asteroidea), including the first known sea star from hydrothermal vent habitats, Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 174 (1), pp. 93-113 : 95-98

PAULASTERIIDAE FAM. NOV.

Mah & Foltz 2011b: 649–653, 658; figures 2–3.

Type genus/species

Paulasterias tyleri gen. et sp. nov.

Diagnosis

Pedicellasterid-like forcipulataceans with small disc and between six and eight arms. Reticulate skeleton, weakly developed, concealed by fleshy body wall or dense spinelets. Fleshy body wall with abactinal spinelets and/ or pedicellariae and furrow spines sheathed in tissue. Adoral carina either minimal (one or two adambulacrals abutting) or absent altogether. Madreporite encircled by spines. One shared, crossed pedicellariae type, with jagged teeth on valve edge and multiple shanks on valve roof (sensu Lambert et al., 1984). Tube feet biserial or quadraserial (distally biserial). Both known members were collected from deep-sea settings below 2000 m in depth, either from or in the vicinity of hydrothermal vents.

ESTABLISHMENT OF THE PAULASTERIIDAE AND COMPARISONS WITH THE PEDICELLASTERIDAE

Based on the molecular evidence presented in Figure 2 and the morphological data outlined below, it is argued that the two new species presented herein are members of a new, previously undescribed clade, which we now name as a new family, the Paulasteriidae , for the newly described type genus Paulasterias . This clade represents the first new taxon (i.e. based on undescribed or previously unknown material) within the Forcipulatacea since the 1800s. Many of the newer families, such as the Pycnopodiidae Fisher, 1928 or the Freyellidae Downey, 1986 have been based on, or elevate, previously recognized taxa. Within the Asteroidea as a whole, the two most recently described families include the Caymanostellidae , described by Belyaev (1974), and the Podosphaerasteridae Fujita & Rowe (2002) , although in the latter case, the recognition of Podosphaeraster was made by Clark & Wright (1962).

The clade discussed in the results section, including the ‘6-rayed pedicellasterid’ (sensu Mah & Foltz, 2011b) and the ‘Antarctic stichasterid’ or ‘Stichasterid n. sp. ’ (e.g. Rogers et al., 2012) included in the analysis are supported as a distinct clade, previously unrecognized and separate from other forcipulataceans. Some characters used in the description of the taxa, such as a weakly developed adoral carina, occur among multiple forcipulatacean lineages, suggesting that these characters are convergent. Morphological synapomorphies for the group are not abundant but there are diagnostic characters for the lineage that further support its distinction as a new family.

Prior classifications of the Forcipulatacea, when considering the Pedicellasteridae , focused on the characters that were most comparable with the Asteriidae , the group to which pedicellasterids were most similar. Characters such as tube foot rows, development of the abactinal/marginal/actinal skeleton as well as the adoral carina (= the number of adambulacral plates abutted proximal to the oral plates) were the primary emphasis (e.g. Fisher, 1928). As indicated earlier, prior molecular data on forcipulataceans ( Mah & Foltz, 2011b) show that the Pedicellasteridae was not a monophyletic group, being instead composed of several clades occupying stemward locations.

Although they occur on different clades within the Forcipulatacea, comparisons between the Paulasteriidae and various ‘pedicellasterid’ genera are inevitable given the characters present, such as a minimal or absent adoral carina, biserial tube foot rows, and fleshy body tissue/weakly developed abactinal skeleton. Our results ( Fig. 2 ) show the Paulasteriidae as separated from other pedicellasterids, including ‘ Tarsaster ’, which was present on two different clades, and Pedicellaster and Hydrasterias on another more distant clade.

In addition to the paraphyly of the group as a result of the molecular trees presented by Mah & Foltz (2011b), however, further taxonomic issues have since been discovered for taxa within the Pedicellasteridae (e.g. paraphyletic genera, etc.). A more comprehensive summary of diagnostic characters distinguishing Paulasterias from other ‘Pedicellasteridae’ is being developed, but full treatment is beyond the scope of this account. Thus, diagnostic treatments presented herein should be considered only as a means of broadly distinguishing the Paulasteriidae from other members of the Forcipulatacea. Comparisons between Paulasterias tyleri gen. et sp. nov. and other Antarctic Asteriidae are listed in Table 2.

Figures

Figure 2. Phylogenetic tree for the Paulasteriidae and related taxa, based in large part on a three-gene data set from Mah & Foltz (2011b). The scale bar shows the number of substitutions per site; see Material and methods for additional details.