Marginaster Perrier 1881

Mah, Christopher L. & Foltz, David W., 2014, New taxa and taxonomic revisions to the Poraniidae (Valvatacea; Asteroidea) with Comments on Feeding Biology, Zootaxa 3795 (3), pp. 327-372 : 344-345

Marginaster Perrier 1881

Fig. 4 A–D

Marginaster Perrier 1881: 16 ; 1884: 229; Sladen 1889: 364; Perrier 1894: 164 –165; Ludwig 1897: 189; Verrill 1914b: 18 –19; 1915: 75–76; Downey 1973: 82; A.M. Clark 1984: 25 –27; McKnight 2006: 106.

Cheilaster Bell 1893: 81 (superfluous replacement name for Marginaster Perrier )

PoraniscaVerrill 1914b: 19; A.M. Clark 1984: 25 [type: P. lepidus Verrill 1914b ]

Type species: Marginaster paucispinus Fisher 1913 (by subsequent designation)

Diagnosis. Poraniid taxon of small size, with R<2.0 cm. Body flattened, subpentagonal to stellate in outline (R/r=1.1–2.0), disk large, arms short. Skeleton covered by discrete layer of skin. Abactinal plates reticulate with variable degrees of plate distribution and arrangement (i.e., some denser where others are wider). Open skin regions around primary circlet largest. Plates with multiple spinlets. Papulae single. Superomarginal plates form distinct fringe around dorsolateral edge. Multiple spinelets present on superomarginal plate surface. Intermarginal papulae present. Inferomarginal plates form dorsolateral fringe, with spinelets present on edge and presenting a discrete border around the actinal surface. Actinal plates imbricate, forming transverse rows. Furrow spines one or two. Subambulcral spines two to three.

Included taxa: M. capreensis (Gasco 1876) , M. patriciae McKnight 2006 , M. paucispinus Fisher 1913 (by subsequent designation), M. pectinatus Perrier 1881

Taxonomic comments. Marginaster ’s small size and weakly developed skeleton have led to skepticism regarding its taxonomic status and indeed, other apparent species of Marginaster , such as M. littoralis Dartnall 1970 , have been shown to be other taxa ( M. littoralis = unidentified Asterinidae ). Verrill (1914) has suggested that M. pectinatus is the juvenile form of Porania . However, Downey (1973) noted that small Marginaster from the West Indies were “sexually mature.” This led to Clark and Downey’s (1992: 205) statement that Marginaster will be recognized as a synonym of Porania , suggesting that Marginaster species will be shown to be a “stunted species” with a “neotenous retention of the juvenile abactinal armament…” Further interpretations of Marginaster include the possibility that it is a distinct, separate, widely distributed, poraniid taxon or that it represents the juvenile form of a poorly known or undiscovered poraniid taxon.

One of the persistent inconsistencies of the “ Marginaster as the juvenile of a known poraniid” hypotheses has been the lack of sampling and the disjunction between known taxa and Marginaster species. Herein, we can address the former of these issues in that appropriately sized individuals were available for examination. Specimens of the Atlantic M. pectinatus and descriptions of other Marginaster species were compared with other specimens of Porania from the Northern and Southern Hemispheres in order to provide insight on these perspectives ( Fig. 4 A, B). Marginaster pectinatus (tropical Atlantic, R= 0.6 –1.0) was examined alongside similarsized P. pulvillus (R=0.9–1.0) (see Figs 4 A, C). Porania pulvillus shows a more stellate body form, a strongly imbricate abactinal skeleton (more openly reticulate in M. pectinatus ), an absence of spinelets on plate surfaces in P. pulvillus , and a more blocky, chevron-like superomarginal in P. pulvillus (more wing-shaped in M. pectinatus ). Actinal surface and plate arrangements between Porania and Marginaster appear to be similar but may be plesiomorphic across the Poraniidae . Comparisons between M. pectinatus and the southern hemisphere “ Porania ” antarctica show even more starkly different morphology with the latter demonstrating a more strongly stellate body shape and the same imbricate vs. reticulate abactinal plate arrangements and marginal plate differences at comparable sizes to Marginaster species in the southern hemisphere.

The second consideration, which is the lack of distributional overlap between Marginaster and its proposed “adult” species remains a consistent one. Marginaster pectinatus is known only from the tropical Atlantic, including San Salvador the Yucatan Channel, the Bahamas and southern Brazil but Porania pulvillus is not known south of Cape Hatteras. Lack of distributional overlap is also observed between species considered in the Southern Hemisphere as well. “ Porania ” antarctica , for example, shows no direct overlap with Marginaster paucispinus or other Marginaster species in the region ( McKnight 2006). However, little is known regarding the smaller (R=2.0 cm) sizes of subantarctic poraniids such as Spoldaster.

For the moment, available morphological evidence shows a disjunction between Marginaster spp. and known adult poraniid taxa. Population phylogenetics will likely play an important role, but ultimately the collection of further specimen samples and understanding ontogenetic stages in the Poraniidae will be crucial to understanding of this issue. Future phylogenetic treatments of the Poraniidae should include Poraniella echinulata (Asteropseidae) , which has previously been classified within Marginaster (e.g., Hotchkiss & Clark 1976) but occurs in the same general region as M. pectinatus .

Material examined. USNM E30129 East of Arrowsmith Bank, Yucatan Channel, Caribbean Sea. 21°00N, 86°23’W, 174–348 m, Coll. R/V Pillsbury (1 dry spec. R=1.0, r=0.7); USNM E30130 Brazil, North Atlantic Ocean. 0°18’N 44°17’W, 275 m, Coll. R/V Oregon (2 dry specs. R=0.9, r=0.5; R=0.6, r=0.3).

Figures

FIGURE 4. Marginaster pectinatus & size comparisons. A. USNM E 30130 Marginaster pectinatus Abactinal surface. (R = 0.9). B. M. pectinatus actinal surface. C. USNM Paralectotype 18496, abactinal surface Porania pulvillus. (R = 0.9) D. USNM 1136790 Glabraster antarctica abactinal surface (R = 1.2)