Poraniomorpha Danielssen & Koren 1881

Poraniomorpha Danielssen & Koren 1881

Figure 7 A–F, 8A–F

Poraniomorpha Danielssen & Koren 1881: 189; 1884: 67–70; Verrill 1895: 139; Grieg 1907: 41 –42; Fisher 1911: 248 (in key); 1919: 407; Koehler 1924: 157; Mortensen 1927: 92; Gallo 1937: 1664 –1667; Djakonov 1950: 58 –59 (1968: 48–49); Spencer & Wright 1966: U70; A.M. Clark 1984: 33 –41; Clark & Downey 1992: 212.

Rhegaster Sladen 1883: 155; 1889: 367; Bell 1893: 80; Verrill 1914b: 17.

Lasiaster Sladen, 1889: 371 –372; Bell 1893: 81; Verrill 1899: 198.

Type species: Poraniomorpha rosea Danielssen & Koren, 1881, now regarded as a subspecies of Goniaster hispidus M. Sars, 1872 by original designation.

Diagnosis. Body form pentagonal to stellate (R/r=1.2 to 2.75), disk large, thick. Arms triangular, variably short to elongate. Abactinal plates imbricate to fenestrate, boundaries obscured by discrete layer of skin. Papulae large, number ranging from single up to 15, with some species ranging in groups up to 10–15. Abactinal, marginal surface covered by fine, numerous and frequently abundant spinelets. Marginal plates variably shaped, from irregularly imbricate to blocky and in regular series. Intermarginal papulae present or absent. Actinolateral fringe discrete with larger, thicker spines variably present. Actinal regions relatively large, plates imbricate in transverse series. Plate boundaries obscured by discrete skin, covered by spinelets, variable in size, homogeneity, and density. Adambulacral armature prominent, forming a discrete, spiny fringe along tube foot groove similar in width to inferomarginal series. Furrow spines one to three, arranged in some as part of a transverse series with subambulacral spines but as a separate series in others.

Included species. Poraniomorpha abyssicola (Verrill 1895), Poraniomorpha bidens Mortensen 1932, Poraniomorpha hispida Sars in Sars 1872, † Poraniomorpha jurassica (Hess 1972), Poraniomorpha tumida (Stuxberg 1878).

Taxonomic considerations. Rhegaster & Species boundaries. Poraniomorpha hispida Sars 1872 shows significant morphological disparity from the other three living species of Poraniomorpha, P. abyssicola, P. bidens and P. tumida. Characters in P. hispida, including the large, blocky marginals, multiple papular pores, and the wide fenestrate abactinal plate arrangement show significant morphological disparity relative to the other three species which display more overall similarity of morphological characters. Poraniomorpha abyssicola, P. bidens, and P. tumida display characters more similar to one another than to P. h i s p i d a, including narrower arms, more inflated disk, more strongly stellate body form, single to few numbers of papular pores, and more irregularly shaped abactinal and marginal plates. The morphology present in the former three species of Poraniomorpha is consistent with the definition of Rhegaster sensu Sladen (1883, 1889). Although Rhegaster has been entered into synonymy of Poraniomorpha (Clark and Downey 1992) it has never been directly addressed. Because of the morphological distinctiveness of these three species (and “ Rhegaster ”) some discussion of their taxonomic limits is warranted and provides hypotheses for future studies.

Several specimens that conform to the taxonomic definition of P. t umida (the type species for Rhegaster) are morphologically consistent with P. h i s p i d a, showing overlap or possibly supporting synonymy. For example, CASIZ 121456 from the Beaufort Sea (at R=3.9) showed the subpentagonal body form, and fenestrate abactinal plate arrangement of P. h i s p i d a, but the relatively fewer papular pores and abactinal tubercles of P. t u m i d a. Smaller individuals of P. t u m i d a from the Beaufort Sea locality (e.g., CASIZ 142780, 122301) are more stellate, suggesting that the body shape becomes more swollen and more pentagonal as it increases in size. This may be applicable toward other individuals showing this morphology, possibly including other Poraniomorpha “species”, which all tend to show relatively small size. It is unclear if the Beaufort Sea P. t u m i d a (or other Poraniomorpha spp.) and the Atlantic P. h i s p i d a are conspecific or even sister taxa, but external morphology, including the subpentagonal body shape, furrow spines, and few papular pores, of the two are extremely similar and may represent extension of P. hispida beyond the Atlantic.

Based on consideration of P. t u m i da and P. h i s p i d a it seems that there is some morphological contintuity between P. h i s p i d a and the “ Rhegaster ” type morphology (i.e., P. t um i d a) which at the moment does not separate them into clearly separate taxa. However, further specimens will likely provide further insight as morphology and population phylogeography clarify the phylogenetic limits of each taxon as well as any possible effects resulting from environmentally induced parallelism.

Other taxonomic considerations. Characters studied for Poraniomorpha (Culcitopsis) borealis did not support affinities within Poraniomorpha. Ambulacral ossicles, furrow spine arrangements, abactinal and marginal plate arrangements were all inconsistent with those of P. h i s p i d a with no observed characters supporting a monophyletic Poraniomorpha concept. Although the phylogenetic position of Culcitopsis was not tested using DNA, character distribution data suggests that it should be separated from Poraniomorpha and reinstated as a separate genus.

Hess (1972) described Sphaeriaster jurassicus from Jurassic deposits in the Northern Swiss Jura Mountains. Sphaeriaster Dons 1939 has been synonymized into Poraniomorpha Danielssen & Koren, 1881. Hess’ (1972) description of S. jurassicus appears to be significantly different from living Poraniomorpha and seems much older than timing of P. h i s p i d a would imply, suggesting the need for re-evaluation of S. jurassicus. It remains included herein for the sake of completeness and to draw attention for the question.