STYLASTERIDAE 



*3 



The fan-shaped colonies are in general branched in one plane and not recurved; they display 

 a marked difference between small branches, main branches and stem. The cyclosystems are placed 

 laterally and alternately on the small branches; their main axis forms an angle of 45 or more with 

 the longitudinal axis of the branch. The cyclosystems are circular except on the thick main branches, 

 where they have a more oval form. The cyclosystem shows from 8 to 17, in general 9— 11 quite 

 separate dactylopores, each provided with an almost rudimentary dactylostyle. The wall of the 

 gasteropore has quite a small incision towards the dactylopores. The gasterostyle is almost spherical 

 with the same height as breadth. The gasterozooid has four very small tentacles. - The male am- 

 pullae generally contain 4 to 6 gonophores and are scarcely seen on the surface of the colony. The female 

 ampullae appear like hemispheres on the surface of the colony; they are smooth, without spines. 

 The surface of the colony is smooth and faintly reticulate. 



Colour: rose with lighter stem and main branches. 



Occurrence: Atlantic Ocean in depths from 230 to 1400m. 



Material : 



"Ingolf" St. 7 63°i3' N., i5°4i' W 



- 15 66°i8' - 2 5 °59' - 



- 17 62*49' - 2 6°55' - 



- 52 6 3 °57' - i3°32' - 



- 94 6 4 ° 5 6' - 3 6°i 9 ' - 

 "Thor" 1904 65°5o' - 26°53' - 

 East Greenland Expedition. Off Angmagsalik 



At first glance Stylaster roseus is confusingly like the preceding species; it may especially be 

 easily confounded with such colonies of the latter as are represented in figs. 5 and 6 of PI. I. Closer 

 examination however shows that there are great and constant differences between the colonies, so that 

 they must be taken as representatives of different species. The first mark of distinction apparent on com- 

 paring larger colonies is the form of colony itself. In Stylaster roseus there is a greater difference 

 between the main branches and the small branchlets than in the preceding species and the colony is 

 more robust; in addition, the branching of the colony in Stylaster roseus normally proceeds in a single 

 plane and it seldom shows a slight tendency to curve inwards towards the front surface. When the 

 colonies are in full process of reproduction they are often so swollen also in the outermost 

 small branches (PI. II, fig. n) that there is danger of confusing the species with Stylaster (Allopora) 

 norvegica. The position of the cyclosystems in relation to each other on the outermost small branches 

 however shows that the species here dealt with belongs to the subgenus Eustylaslcr. The main axis 

 of a cyclosystem is at right angles to the axes in the inner-lying and the succeeding cyclosystems and 

 this is more obvious than in Stylaster gemmascens, where the cyclosystems owing to the smaller angle with 

 the branch axis do not give the small branches such a distinct zigzag form as in Stylaster roseus. In 

 addition the number of the dactylopores is on the whole less in Stylaster roseus, their number varying 

 between 8 and 17 but in general lying about 9 to n. Further, the communication of the dactylopores 

 with the central gasteropore takes place through a smaller incision in the gasteropore wall than in 

 Stylaster gem mascens. 



