Slime Stars

Pteraster militaroides Clark

Pteraster caribbaeus [part] Perrier, 1884:216.–Verrill, 1915:82, pl. 7: fig. 4.–H. L. Clark, 1941:60.

Non Pteraster caribbaeus.–Perrier, 1881a.

Pteraster militaroides H. L. Clark, 1941:61.

The form of this species is plump and stellato-pentagonal, with the interradii slightly indented. The five arms are recurved at the tip, so the end of the ambulacral groove is on the abactinal surface. The supradorsal membrane is heavily encrusted with numerous small calcareous deposits, and has a lacy appearance due to the many small spiraculae. The membrane rests loosely on the underlying paxillar spines, so the dorsal surface is rugose, but the spines do not protrude through the membrane nor lift it in tent-like peaks above the general surface. The lobes of the abactinal plates are short, broad, and flat, and the pedicel is thick, columnar, and short; it bears 6–12 long, slender, glassy spines, not acute. Usually, there is one central spine and about nine peripheral spines, all about of equal length. The central osculum is of moderate size and surrounded by a continuous ring of numerous, close-set spines about the same length as the paxillar spines.

The actinal membrane is mostly without deposits; it is supported by 20–25 short, ridged, blunt-tipped actinolateral spines which neither reach the ambitus nor support a marginal fringe; the supradorsal membrane extends well onto the actinal surface interradially. There are a few small, supplementary actinolateral spines, either near the base of the large actinolaterals or between a pair of them. There are seven adambulacral furrow spines (six distally; on the smallest specimens, there are 6 or 5 spines) webbed together in a curved series and graded from shortest at the inner (or groove) end of the series to longest at the outer end. The mouth plates have a prominent central ridge along the suture. Each plate bears a long, stout, hyaline suboral spine and a marginal series of about eight spines (6–10), four at the side of the plate and, at right angles to these, four along the front margin. The four spines on the side are short and subequal; the four on the front margin are longer and grade upward to longest at the apex. All are slender and blunt tipped, and none are nearly as long as the suborals.

Clark reported this species as occurring only in northwestern Cuba; this collection contains specimens from off the Leeward Islands and from the western Caribbean, between the Caymen Islands and Panama. The depth range is 250–355 fathoms.

MATERIAL EXAMINED.—Oregon Stations: 1917 (2) [R=23 mm, r=11 mm, Rr=1:2]; 1885 (1) [R=17 mm, r=9 mm, Rr=1:9]; 1929 (1) [R=22 mm, r=13 mm, Rr=1:1.8]; 5929 (1) [R=19 mm, r=11 mm, Rr=1:1.7].

Since the publication of my brief paper on Marsipaster acicula Downey, 1970c, I have had the opportunity to examine many more specimens of Pterasteridae and have concluded that Marsipaster Sladen (1882) is not a good genus; it is practically indistinguishable from Pteraster. The characters on which Sladen based Marsipaster are minor and subject to variation even within a species. The nature of the supradorsal membrane in Marsipaster is certainly distinctive, but scarcely of generic significance when one considers how this feature may vary between species of Pteraster. The web connecting the suboral spine to the other mouth plate spines is certainly not of sufficient importance to be a generic character, while the placement of the adambulacral spines (Sladen says high in the furrow and horizontal in position) does not hold true for both of the species described by Sladen in his paper (true for M. spinissimus, not true for M. hirsutus). In light of these conclusions, it is thought appropriate to include here a more thorough description of the species I described as Marsipaster acicula.

Pteraster is a genus of sea stars in the family Pterasteridae.

Known from seamounts and knolls

The status of the subgenera proposed by Fisher (1940) needs reassessment. A.M. Clark (1989: 205) treats the absence of webbing on the oral spines as of supraspecific weight but Downey (1992) does not agree and treats Pteraster stoibe H.L. Clark (1941) without webbing, as a subspecies of P. militaroides, which does have webs linking the oral spines of each plate. Downey notes that the absence of webbing in the holotype of stoibe might be an artefact of preservation but in other species of Apterodon, this appears to be the natural condition. As a compromise, rather then segregate the species listed as Pteraster (Retaster) and Pteraster (Apterodon) by Fisher (1940) or subsequently referred to these subgenera, all are included under the heading of Pteraster.