This genus was first described by Koren and Danielssen as H. arctica. Two specimens were afterwards described by Horst as H. glacialis. Later Lankester described two other specimens; he was the first to find the male in the pharynx of the female. He is of the opinion that all three descriptions apply to the same species, and for this the original name H. arctica must be retained.
Hamingia arctica K. and D. Two hundred miles north of North Cape and in the Hardanger Fjord.
Saccosoma.—No proboscis. The body is flask-shaped. The mouth and anus are terminal. The ovary is anterior, and there is only one nephridium. No bristles.
Our knowledge of this remarkable Gephyrean is very incomplete, but such as it is, it is due to the careful investigations of Koren and Danielssen, who had only a single specimen at their disposition.
Saccosoma vitreum K. and D. North of the Faroe Islands.
Habits of the Echiuroidea.—As a rule the members of this group conceal their bodies in clefts and fissures of rocks and stones, keeping up communication with the outer world by means of their proboscis. Rietsch[[488]] describes a specimen of Bonellia minor, which he placed in an aquarium, exploring with its proboscis the nature of the bottom; when the animal had found a convenient crevice, it fixed its proboscis in it by means of the bifurcated end, and by its contraction drew the body up, and entered the hole, proboscis first. It then turned round, and during this operation doubtless the ventral hooks came into play; and then stretching out its proboscis, it began to explore the neighbourhood. The proboscis is evidently very sensitive, and in addition to being a locomotor organ, it is also used for the prehension of food. If cut off near the mouth, the animal does not long survive, but if a considerable portion is left the scar heals, and the lost part is probably regenerated. In captivity the animals frequently change their place of residence.
Eisig some years ago described the great extensibility of the proboscis of B. viridis when confined in the tanks of the Zoological Station at Naples. When contracted the proboscis was but a few inches long, but at times it was extended till it reached the length of 1½ metre, shining through the water as a transparent green thread. The body of the Bonellia was hidden under stones, but the proboscis could be seen seizing between its two ends the bodies of certain Ascidians which covered the inside of the tank, tearing them off the walls, and conveying them to the mouth along its grooved ventral surface.
The food of the Echiuroidea consists of organic matter, in the main of animal nature, but the group differs from the Sipunculoidea in not eating sand.
Rietsch describes Thalassema neptuni as being more active in its movements and less sedentary than B. minor. The proboscis is still the chief organ of locomotion, but the trunk plays a greater part in the movements of the animal than it does in the last-named species. Th. neptuni is found in cavities of stones or in the chambers worn out by the Mollusc Gastrochaena; when withdrawn from its house the body is found to be covered by a thick layer of tenacious viscid mucus.
