Common Seastar

Asterias forbesi (Desor)

Asteracanthion forbesi Desor, 1848:67.

Asterias arenicola Stimpson, 1851:268.

Asteracanthion berylinus A. Agassiz, 1863:3; 1877:94, pl. 9.

Asterias forbesi.–Verrill, 1866:345.–H. L. Clark, 1902:552, pl. 1: figs. 1, 2, pl. 4: figs. 14, 15–Fisher, 1930:205.–Gray, Downey, and Cerame-Vivas, 1968:156, fig. 34.

Asteracanthion novae boracensis Perrier, 1869:41, pl. 1: fig. 9a.

This is probably the commonest shallow-water species on the east coast of North America; certainly, it is the best known, for it is the one commonly used in biology classes. The disc is small, and the five arms are moderately long, thick, and constricted at the base. There is an irregular carinal row of plates down the middle of each arm. The superomarginal plates define the ambitus and are connected to the inferomarginals by an elongate ossicle; the inferomarginal plates are connected to 3 or 4 adambulacral plates by a triangular, unarmed ossicle. All plates from the carinals to the inferomarginals are connected by small, elongate secondary ossicles, forming an open meshwork, and bear a single, thick, upright, thorny-tipped spine, the spines of the superomarginals being slightly larger than those of the other plates. The spines are all surrounded, about halfway up, by a wreath of small, crossed pedicellariae. The inferomarginals bear two thicker, blunter spines. The small, crowded adambulacral plates bear either one or two spines, alternately; they are usually chisel shaped and often grooved. Between the spines, over the entire surface, and on many of the adambulacral spines are straight, flat, oval or cordiform pedicellariae, larger than the crossed pedicellariae which wreath the spines. The papulae between the plates are small and numerous.

The long, narrow mouth plates consist of 3–7 adambulacral plates which meet across the interradius; each bears a long, straight, slender, somewhat flattened spine. The madreporite is large, irregularly round, raised, and wartlike, covered with many fine gyri.

This species ranges from Maine to the Gulf of Mexico, in shallow water. It is the southern form of Asterias vulgaris, which ranges from Labrador to the Carolinas (and, rarely, to Florida). It is sometimes difficult for even a specialist to distinguish these two species, and hybridization is not uncommon, particularly in the Cape Cod area. This is one of the many cases among marine invertebrates which compels us to realize how very unsatisfactory are any of the proposed definitions of “species.”

MATERIAL EXAMINED.–Oregon Stations: 5894 (1) [R=83 mm, r=21 mm, Rr=1:4]; 6300 (12) [R=45 mm, r=11 mm, Rr=1:4]; 5882 (1) [R=22 mm, r=6 mm, Rr=1:4], Silver Bay Stations: 1564 (1) [R=20 mm, r=5 mm, Rr=1:4]; 1710 (1, with four arms) [R=42 mm, r=10 mm, Rr=1:4]; 1952 (4, two with four arms) [R=80 mm, r=18, Rr=1:4].

Coscinasterias Verrill

Cosinasterias Verrill, 1867:248. [Type, by original designation, C. muricata Verrill.]

Stolasterias (subgenus) Sladen, 1889:583. [Type, by subsequent designation, Asterias tenuispina Lamarck, 1816 (Fisher, 1923:128).]

Lytaster Perrier, 1894:09. [Type, by original designation, L. inaequalis Perrier (=Asterias tenuispina Lamarck, 1816).]

Polyasterias Perrier, 1894:108. [Type, by original designation, Asterias tenuispina Lamarck, 1816.]

Disc small; variable number (5–12) of moderately long, angular rays; single series of spiniferous actinal plates; adambulacral plates monacanthid throughout; only outer of two inferomarginal spines carries cluster of crossed pedicellariae; fissiparous.

Only one species is known from the western Atlantic.