40 
is interesting to see, how Lamellibranchs such as Abra are able to a certain 
extent to sort out the detritus entering through their siphon; this will certainly 
hold good for all Lamellibranchs. 
In the animal community the Gastropods and ÅAsterias must be regar- 
ded as predatory animals; but though it may be very easy to capture the whelks 
on pieces of cod, (Buccinum and Nassa), it is just as difficult on the other hand 
to ascertain what they eat under normal conditions; their stomachs are almost 
always empty or contain a slime, the origin of which it has not been possible to 
determine. 
In the above-mentioned aquarium I have had the apportunity to see, how 
Fusus antiquus was able to open Mytilus edulis of almost the same length as the 
whelk and then eat up the soft parts. The whole method of the opening of the 
Lamellibranch however requires to be further investigated; I am inclined to 
believe, that a secretion from the whelk has in some way a paralysing influence 
on the mussel. If this whelk can open Lamellibranchs, then it is certain that 
Buccinum and Nassa can also do so. 
That AÅsterias rubens feeds on Lamellibranchs, I consider as beyond all 
doubt; on the one hand I have found, for example, Abra in its stomach and on 
the other I have seen it devouring Mytilus edulis both in nature and in the 
aquarium.  Opluoglypha often takes only fine food, I have seen detritus with 
bottom-diatoms in its stomach. The occasional occurrence of shells of small 
molluscs in its stomach may perhaps be regarded as due to chance. The species 
occurring in Thisted Bredning is O. texturata, but the individuals are fairly small. 
The investigations of both Eichelbaum and Rauschenplat agree with mine in 
the fact, that Ophioglypha contains much bottom-material in its stomach.  R. 
seems to regard it as in half part a plankton feeder, but I do not quite under- 
stand his statement (p. 149), and E. regards it as a predatory animal, which 
specially seeks after Polychaeta; he has found the remains of worms among the 
contents of its stomach. I have sometimes found comparatively pure quantities 
of bottom-diatoms in its stomach; one would almost think that it knew how to 
select them in one or other way. In the aquarium I have seen it standing up in 
the soft mud on all 5 arms, so that the dise was raised just above the bottom; 
im this way perhaps the cavity formed with its 5 small exits may help in one 
way or another to collect the bottom-diatoms just under the mouth. In the aqua- 
rium I have seen 0. albida ihrow itself with great rapidity on cut pieces of the 
soft parts of Molluscs, which shows that the Ophiurids are not always content 
with detritus-food; but I have never seen them attack living Abra in the aqua- 
Tium. I am inclined with Eichelbaum to consider them as worm-feeders: but 
the whole matter must be more closely investigated. 
On the detritus-bottom in Thisted-Bredning we thus have a detritus-eating, 
Lamellibranch-worm community with its predatory animals. This animal commu- 
nity forms the basis for a great part of the fish-life there, but this subject will be 
dealt with in a later section. 
When we come closer in towards the land, into depths of ca. 5 meters 
and less, we meet with the Zostera belt as a rule and its fauna; for 
