STYLASTBRIDAE 



Material: 



"Ingolf" St, 15 66i8'N. 2.559'W. 620 m. -^0.75 C. 



Hjeltefjord ca. 150 m. 



Gidsko (Sondmore) ? 



Sondmore ? 



Trondhjeni Fjord 5040010. 6.5 8.5 C. 



West coast of Norwav 



The form and appearance of the colonies are subject to such great variations in Stylastcr 

 gcmmascens, that we may often be in doubt as to whether one and the same species is before us. The 

 available material was very large, especially from the Trondhjeni Fjord, where the species is fairly common 

 and more luxuriantly developed than from any other locality hitherto known; further, I was able to examine 

 a number of colonies from the west coast of Norway and lastly a couple of small fragments from 

 "Ingolf St. 15. Examination of this very large material shows the relationship of all the many 

 different kinds of variants, partly owing to series of chain-forming variants, partly on account of 

 apparently quite different growth-types being present in different branches of single colonies. Hickson 

 in several of his works has divided up some of the species into a series of different "fades". As the 

 most illustrating examples I may mention his treatment of Stylaster eximius Duchassaing et Michelotti 

 (1905) and Errina nova-zelandiac Hickson (1912). The deeper meaning of these "facies" is not apparent from 

 his method of treatment; they seem only to illustrate the varying growth modifications of the species; nor 

 do we obtain any information as to the biological conditions under which they appear. In dealing with 

 the present species, therefore, I discard the subdivision into "facies", which only serves to give the misleading 

 impression that the species is divided into distinctly separated growth forms or types. 



There is always a distinct difference present between the front and hind surfaces of the colony 

 in Stylaster gemmascens and the more or less composite, fan-shaped colony is almost always bent some- 

 what inwards, so that the front surface becomes more or less concave. To give any explanation of 

 the biological significance of these structural features cannot be done with certainty at present, least 

 of all for our northern species, which only live in great depths. A conclusion by analogy from tropical 

 species is excluded, since, as Hickson and England (1905 p. 4) point out, we lack all knowledge of 

 the biology of these animals. - There is a gradual increase in thickness from the outermost small 

 branches and inwards towards the thick main branches and main stem; the last are almost entirely- 

 free of cyclosystems. The small branches may sometimes show coalescences, but this is seldom. 



On the outermost, fine branches we see how the cyclosystems arise alternately on the lateral 

 sides of the branch; this is the primary condition in the species. The larger cyclosystems however 

 are not restricted to the lateral part of the branch; they also extend far in over the front surface of 

 this, as can be seen regularly a few millimetres inside the tip of the branch. The increase in thickness 

 of the branch proceeds most rapidly on the hind surface; in this we may have one of the causes of 

 the colony's tendency to bend in towards the front surface. It has the further effect, that the cyclo- 

 systems are secondarily moved more and more forwards towards the front of the branches, the nearer 

 we come to their origin; at the same time a few irregularly situated, new cyclosystems arise between 

 the old. Here and there we also find, that cyclosystems appear quite singly on the back of the colony 

 but their number here is always very small. 



The Ingolf-Expedition. V. ;. 2 



