ANNULATA.
(Worms, Tube- Worms, Nereids.) Char.—Body soft, symmetrical, vermiform, annulated, with suckers, or sets, or setigerous tube-feet ; blood of a red colour in most.
The peculiar markings on the surface of the old Cambrian slate rocks, conjectured to afford the earliest indications of the existence of marine worms, are not without suspicion as to their origin. The so-called " Nereites " bear considerable resemblance to other equally ancient impressions which have been described as Zoophytes, under the name of Protovirgu laria (fig. 3, 1). No such doubt attaches to the worm-tracks which abound in the thin-bedded sandy strata of the forest marble ; and the " Cololites" of the lithographic limestone are most probably the castings of worms. Long calcareous tubes occur in the upper Silurian and carboniferous strata, which have received the name of Serpaites. The Microconchus of the carboniferous period is now regarded as an Anellide ; and in all the later formations, tubicolar Anellides, especially of the genera Serpula, Spirorbis, and Vermilia abound. Some of
these, although attached and gregarious, are so regular in their growth as to have been usually called V ermeti, but are now placed in the genus Vermicularia. Spiroglyphus, and some other shell-excavators, are indicated in the tertiaries. Amongst the problematic fossils of the palwozoic strata, two are supposed to be anellidous, viz., the Tentaculites (fig. 10, which was apparently free, and almost always regular in its growth, so as more to resemble one of the gregarious Pteropods ; and the Conudite (fig. 10, s), which is attached when young, singly or in groups, to Silurian shells and corals : the structure of its shell is vesicular, and the cavity resembles a series of inverted cones. The unattached and gregarious Ditrupa appears in the upper chalk, and abounds in the London clay and crag.