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Show 1 9 0 5 . ] CAPE VERDE MARTNE FAUNA. isr also during the life of the animal, but Pecten remains free. The upper coils of Gastropoda are generally bored, but a large white Murex escapes. The sponge seems to have a selective action in the case of living organisms-e. g., a dead oyster-shell was dredged which had been riddled with sponge : on one side was growing nullipore and on the other a thick soft crust of Polyzoa, both of which were free. The small irregular cavities enclosed by the growth of encrusting species of nullipore are a great aid to the spread of the sponge through the mass. The more solid Astraeid Corals are far less rapidly attacked. Hemispherical lumps, apparently long dead, are frequently dredged, which are quite white and clean inside except for a tinge of red near the surface, or one or two layers of the same concentric with this. Some of these lumps have as nuclei a nullipore nodule, which is absolutely rotten. (2) Polychceta.-Lysidice, Nicidion, two species of Sabellidae, Dodecaceria concharum and Eunice siciliensis are ubiquitous in the same places and generally in company with the sponge. Of these the Eunicidae are the most important, but the one large species, E. siciliensis, the great borer of the Indo-Pacific Corals, is rare. The Sabellidae, which are not so conspicuous as borers in East Africa, here occupy an important place. Dodecaceria, the well-known shell-borer of European seas, here occupies a subordinate position. Wherever found it occurs in numbers together, but it does not occur with anything like the frequency of the Eunicidae and Sabellidae. A favourite habitat for this and other species is the base of coral-colonies. Splitting an encrusting Astraeid from the lava rock usually lays bare a number of galleries and their occupants. The small Eunicidae Lysidice and Nicidion are especially characteristic borers of the encrusting nullipore of exposed positions, the Sabellidae of dredged Lithothamnion nodules, but either may occur in any position. Although in all cases sponge seems to be the first of the attacking host, yet in the case of the Astraeid Corals, whose pores are too minute for the purpose, the rapid spread of the sponge is dependent on the presence of unoccupied worm-burrows, around which are seen extensions of the red tint from the surface, or other zones, into the white and as yet unattacked portions of the mass. The final state of a nullipore nodule is a grey mud enclosed in a thin shell of still growing Alga. The Sponge and boring Polychaeta have now disappeared, the sole inhabitant being a large but remarkably fragile Capitellid worm. (3) The Lamellibranch Lithophagus is abundant in Corals; nullipores are nearly always infested and very often are quite full of it. This species is notable as being the only borer to attack the Serpulid and nullipore compound when the proportion of the latter is low. Lithophagus lines its burrows with a hard enamel-like secretion which is not attacked by sponge until after the death of the mollusc. (4) Sipunculoidea: Aspidosiphon is common in both nullipore and Coral. |
