Polynoë.[[370]]—The body is short; none or only a few segments at the end of the body are uncovered by the elytra, except in the long body of P. johnstoni.
A. With twelve pairs of elytra.—In P. squamata Linn. the elytra entirely cover the body and conceal the head, each elytron overlapping the next posterior one, and those of the two sides overlapping. General colour sandy-brown, speckled, lighter or darker. The fringed elytra are very firmly fixed to the body. The notopodial chaetae scarcely project from below the elytra. The worm is common between tide-marks and in the coralline region, is about one to one and a half inches in length, and about one-third of an inch in width. Atlantic. P. clava Montagu, may attain a larger size, though it is generally smaller. The elytra are dark, usually grey, mottled with white or light grey, unfringed, and do not overlap to so great an extent as in P. squamata, so that the middle of the back and the hinder part of the body is more or less exposed. This is never the case in the preceding species, but even here it is subject to variation in extent, depending on the amount of food contained by the worm or on the ripeness of the genital products. It occurs in the Mediterranean.[[371]]
Fig. 162.—Elytra, A, of Polynoë squamata L.; B, of P. clava Mont. × 10. a, Area of attachment; e, external margin; f, fringe (the letter is at the posterior side of the elytron); i, internal margin. (From Bourne.)
B. With fifteen pairs of elytra.—P. imbricata L. is probably the commonest species of the genus, occurring nearly everywhere under stones at low tide. It is about an inch in length; the elytra are deciduous, and are very variously coloured and marked; sometimes uniformly grey or even black, sometimes mottled with brown: in other specimens each elytron has its outer half pale or white, while its inner half is darker, usually some tint of brown or olive green, so that the worm appears to have a dark band along the middle of its back. Other patterns occur. The body is entirely covered by the elytra. The chaetae project considerably, and are nearly as long as half the width of the body; those of the notopodium are brown and are directed upwards, being nearly as long as the golden neuropodial chaetae. This species has a very wide range, occurring on both sides of the Atlantic, even on the shores of Nova Zembla, and reappearing again at Japan. P. semisculptus Leach is rather larger than the foregoing. The elytra are very readily detached: they are light in colour, without a fringe, but with large papillae near the margin. The notopodial chaetae are thicker than those of the neuropodium. Several other species are also common, but P. johnstoni v. Marenz.[[372]] differs from the rest in having an elongated body of some seventy segments, so that the posterior half is uncovered by the elytra, which are small, greenish-grey, speckled, and have no fringe. It is common and widely distributed, but appears to be only found in the tubes of Terebella nebulosa.
Fig. 163.—Elytron of Polynoë imbricata. a, Area of attachment to body; e, outer border; i, inner border.
C. With eighteen pairs of elytra.—P. gelatinosa Sars, may attain a length of 2 inches. The elytra are very faintly coloured, transparent and soft, attached by rather long peduncles. In spirit they become swollen and folded, giving the worm a very untidy appearance. The prostomium is partly overlapped by a peculiar collar-like fold of the peristomium.
D. With numerous pairs of elytra.—Lepidasthenia has a very long body, consisting of more than eighty segments. The elytra are quite small, and occur throughout the body on the usual segments. There are no notopodial chaetae. L. elegans Gr. is a very elegantly marked worm, which, however, has not been recorded from the British area; it occurs in the Mediterranean (see Fig. 156, p. [293]).
Sub-Fam. 2. Hermionina.—The body is short, oval and depressed; the particularly strong notopodial chaetae are directed upwards and backwards so as to protect the elytra. The neuropodial chaetae are also strong. The prostomium carries a single tentacle and two long palps; the prostomial ridge may be well developed. The peristomium is chaetigerous, with long cirri. The jaws are represented merely by thickened prominences.