KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 51. N:o Il. 17 
The Colony and its Substratum. 
In Alcyonium, as well as in Gersemia (sensu MOLANDER), we find, in the case of 
certain species, a somewhat widely deviating construction with regard to the form of the 
colony, for the colony often assumes a creeping form, due to the substratum to which 
it has attached itself. If this consists of a worm tube, a stem of a gorgonid, or something 
similar, of a rounded or longitudinal form, the colony extends parallel to, or around, 
this object, and the trunk and branches are often greatly reduced. As early as 1890, 
V. KocH showed something similar in regard to Alcyonium coralloides (PALLAS), and 
during the course of my own investigations I have found many such cases. BROCH 
showed quite recently (1912) that the same phenomenon may be found in the case of a 
gorgonid, Anthothelia grandiflora, a fact I have had the opportunity of confirming. Such 
transformations have generally given rise to accounts of »new» species and have caused 
a number of mistakes as regards systematization. 
Within the genus Gersemia, we find distinct changes from the normal colony for- 
mation to different varieties of shortened and reduced trunk. In the case of a couple 
of species (Gersemia clavata and Gersemia fruticosa), the colony seems to become con- 
stantly less and more weakly developed, as soon as it is attached to a worm tube, a minor 
branch of algae, or the like. This is the case with Gersemia clavata in particular, where 
we can plainly perceive the difference in size and form between colonies attached to stones 
and large shells, and these attached to worm tubes and small shells. These latter colonies 
also show a stronger extension of the membranous basal portion of the trunk, which at 
times grows around a tube, or extends along it. The colonies are then usually devoid 
of branches, and a small number of large polyps assemble on a reduced trunk. A number 
of species of Gersemia (sensu KUKENTHAL), such as Gersemia arctica (DAN.), Gersemia 
loricata (MAR.), etc., exemplify this (Pl. I, fig. 6, 13). A further development is denoted 
by an additional reduction of the trunk and the number of polyps, in addition to which 
many minor trunks or, here and there, small groups of polyps are often developed from 
the membranous part. By degrees the trunks become fewer and fewer, and often the 
term »trunk» cannot really be employed, for there then exists only a collection of a small 
number of large polyps, situated very near to each other. The membranous portion does 
not always grow around the substratum, but spreads only on the upper side, here and 
there with interruptions and openings. In the case of a continued simplification, all trunks 
and branches become reduced, and the polyps extend more or less evenly over the mem- 
brane too. Such is the case, for instance, with Gersemia fruticosa forma membranea (= 
Synopodium hyalinum, GRIEG) (Fig. 7), Gersemia clavata var. truncata, etc. Such speci- 
mens show little similarity to the large, branched colonies, and it is fully explainable 
why they have been considered Cornulariidae, etc. 
The examples now given have been taken from the genus Gersemia, but in the genus 
Alcyonium, too, there are similar examples. v. KocH shows that Alcyonium coralloides 
(PALLAS) on another substratum assumes the typical form of Alcyonium, a fact which I 
have had the opportunity of ascertaining. Alcyomum digitatum var. norvegicum (= Ery- 
K. Sv. Vet. Akad. Handl. Band 31. N:o 11. 3 
