DO I.I.KT1X 76, UNITED STATES NATIONAL MUSEUM 



POLABIS SECTION 

 LEPTASTEKIAS POLARIS (Muller anil Troschel) 



p; ures 1, la-lc, 2, 2a-2d; Plate 32, Figures 3, 3a; Plate 35 



-., ■ d Troschel, System der Asteriden, 1842, p. 16. 



Stimpson, Proc. Boston Soc Nat. Hist., vol, 8, 1862, p. 271. 



her, \in. and Man. Nat. Hist., ser. 8, vol. 12, 1923, p. 599. 



On the Atlantic side of North America Leptasterias polaris ranges from Disco 

 Island, on the wesl coasl of Greenland, south to the Gulf of St. Lawrence (Anticosti 

 Island and Gaspe" Peninsula), and the fishing: hanks oil' Nova Scotia. It extends into 

 Hudson Bay. Although no specimens have been taken between Hudson Bay and a 

 point east of Cape Lisburne, Alaska, there can he little doubt regarding the continuity 

 of its range. 



In the Antic Ocean north of Bering Strait, in Bering Sea, and in the north Pacific 

 just south of the Alaska Peninsula, a polymorphic race of polaris is in an extreme 

 state of flux. It is represented l>.\ at least three well-marked forms, two of which have 

 been described as distinct species. This race is L. polaris acervata, which takes its 

 name from the earliest described of its formae. We appear to have here three species 

 in the process of (volution. L. katherinae Gray, from the mouth of the Columbia 

 and Straits of Georgia, is a more stabilized form apparently derived from the an- 

 cestors of the Bering Sea complex. It greatly resembles L. polaris borealis (Perrier) 

 of Labrador. These two races are not genetically so close as their similarity would 

 indicate, if they are each marginal differentiations, geographically widely separated, 

 of an arctic and sub-arctic species (polurix-acerrata). A possible alternative expla- 

 nation would be that L. polaris Tcatlierinae and L. polaris borealis represent isolated 

 segments of a preglacial species having a continuous distribution by way of a formerly 

 warmer Arctic Ocean. With the advent of a colder era the arctic segment of the 

 species became changed, leaving less modified and nearer the ancestral form that 

 port ion of the species which dwells in the warmer waters of either side of the continent. 



L. Jcaiherincu i- apparently nearest to forma aphelonota, the only one of the three 

 phases of L. polaris acervata to be found at the south of the Alaska Peninsula. Else- 

 where 1 have mentioned the possible duplicate origin of the specimens classified in 

 this forma. Typical aphelonota may represent a geographic race, an offshoot of 

 acervata to the south of the Alaskan Peninsula. 



L. coei Verrill is probably an ancient derivative of polaris stock. Indeed, one may 

 go further and assign a common origin to all the North Pacific 6-rayed species of 

 Leptasterias. 



Since the type specimen of Asieracanthion j'olaris Muller and Troschel came from 

 Greenland, the Greenland race is naturally the substructure for taxonomic elaboration. 

 There arc two fairly well-marked formae of this race: One, forma polaris, has the 

 spinelets fairly uniform in length, without evident aggregation into convex groups. 

 Sometimes the spinelets are fairly well spaced; sometimes crowded. In the other 

 and apparently less common variety, forma subacervata, new forma, there are a vari- 

 able number of convex groups of somewhat enlarged spines. This is the biological 

 equivalent, in polaris, of forma acervata in L. acervata. Similarly forma polaris is 

 an equivalent of aphelonota. Both subacervata and polaris are present among Disco 

 Island specimens. 



