STVLASTERIDAE 



The Stylasteridae of the North Atlantic. 



Pliobothrus Pourtales 



The colonies are branched fan-shaped, often with dichotomonsly divided brandies and branchlets. 

 The gasteropores and dactylopores open irregularly over the surface of the colony and are not collected 

 into cyclic systems. The dactylopores open out on the top of lower or higher tubular projections. 

 The gasteropores are of varying depth, sometimes closed below by one or more tabulae; both the 

 gasteropores and dactylopores sometimes open without distinct ending into the large, irregular, central 

 longitudinal canals of the colony. The gasteropores and the dactylopores have no styles. 



With this diagnosis the genus agrees fairly closely with the Pliobothrus of Moseley (1881 p. 94). 

 There are a few changes however which require further mention. Moseley included as a generic 

 character in his diagnosis the absence of tentacles in the gasterozooid, in spite of the fact, that his 

 own investigations indicated that Pliobothrus tubulatus Pourtales has 5 — 6 tentacles on the gasterozooids. 

 When we remember the great variation to which the number of tentacles is subject in other genera, 

 where they have been studied, this character is of extremely problematic value as generic character. 

 The same applies to the form of the polyps, which more than anything else is dependent on the state 

 of contraction and preservation. So long as we are unable to demonstrate more constant peculiarities 

 in the form of the polyps than hitherto, it has no great value even as specific characteristic. The 

 number of the gonophores in the ampullae must also be referred to the specific characteristics and 

 may even here be of subordinate importance. 



A close study of Pliobothrus symmetricus shows, that the pores of the zooids vary greatly in 

 length and often stand in open communication with the large central canals which appear irregularly 

 in the branches. This blots out the boundaries between Pliobothrus and the genus Steganopora recently 

 described by Hick son and England (1905 p. 26). Open communications between the gasteropores 

 and the dactylopores may also exceptionally be found in Pliobothrus symmetricus. Steganopora must 

 therefore be included under Pliobothrus. The species Steganopora spinosa Hickson and England, the 

 only known species of this genus, stands very near to Pliobothrus tubulatus Pourtales and will possibly 

 on closer examination prove to be identical with the latter. 



Pliobothrus symmetricus Pourtales. 



187 1 Pliobothrus symmetricus, Pourtales, Deep-Sea Corals p. 57, Plate IV, figs. 7 and 8. 



1874 , P. M. Duncan, Madreporaria .... "Porcupine" p. 336, Plate 49, fig. 7. 



1879 — — , Pourtales, Corals .... "Blake" p. 211. 



1881 — , Moseley, Stylasteridae "Challenger" pp. 48, 80 and 84, Plate VIII, fig. 2. 



The fan-shaped colonies are normally branched in one plane; sometimes a portion of the colony 

 may develop to a new fan, which forms an angle with the primary plane. There is no distinct or 

 prominent main stem. The gasteropores are evenly distributed throughout the colony, somewhat more 

 numerous on the front than on the back. The dactylopores, which open out on low, broadly conical 



