FAM. 5. _Tomopteridae._[379]—This includes but one genus, _Tomopteris_, which is pelagic. The transparent, colourless body consists of only a few (eighteen to twenty) segments; the parapodia are as long as the body is wide, and carry no chaetae; each is bilobed, and fringed with a membrane; each of these lobes contains a yellow rosette-shaped photogenic organ. The only chaetae present in the worm are on the "head." The prostomium is hammer-shaped, and appears to carry a pair of short filaments ventrally (Fig. 167, _x_) each with a single chaeta within it; and a longer filament laterally (_y_), supported by a long, very delicate chaeta. The mouth is behind these, and they probably are the first pair of parapodia which have shifted forwards. _T. onisciformis_ Eschscholtz is not unfrequently obtained off our shores in the tow-net. [Illustration: FIG. 167.—_Tomopteris rolasi_ Grf. × 10. From Guinea Isles. _pr_, Hammer-shaped prostomium; _x_, first chaetigerous process; _y_, second chaetigerous process; _c_, rosette (photogenic) organ on first two parapodia; _b_, similar organ in the lobes of the following parapodia; _d_, pigment spots; _f_, parapodium. (From Greef.)] FAM. 6. _Nereidae (Lycoridae)._—This family contains a very large number of species, differing from one another in small and not readily recognisable characters, such as the relative lengths {316}of the various processes of the head, of the lobes of the feet, the arrangement of the "paragnaths" (see Fig. 125, _d_) and so forth. The general features of the family have been already described. The genus _Nereis_ is represented by six fairly common species on our coast, which are almost world-wide in distribution. _N. diversicolor_ Müll. is about 3 to 4 inches in length, of a general fleshy-red colour, though tending in some cases to yellowish-brown or even greenish. It may be distinguished by two diverging brown bands, which start on the peristomium and pass backward one along each side of the body for several segments. The prostomium is broader than it is long. The worm burrows in mud or sand, all round our coast between tide-marks. It has a very wide distribution, being met with on this side of the Atlantic, and off the coast of Greenland, and off Japan. It is even found in brackish water at Bembridge, Isle of Wight. _N. cultrifera_ Gr. is green or greenish-grey, with a series of small rectangular light spots along the mid-dorsal surface, and oblique light lines at the sides of each segment. Posteriorly the greenish pigment becomes less and less till the hinder segments are flesh-coloured. The prostomium is as long as it is broad. This species attains a length of 6 inches. Southern coasts: locally known as "Red Cat."