SEGMENTED WORMS OR ANNELIDA. 



having been compared to the notochord of Ve-rtebrates. The sexes are 

 usually separate, the reproductive organs simple and devoid of accessory 

 structures. The nephridia function as genital ducts. There is a 

 metamorphosis in development. 



(a) Some of these marine Polychcetes lead a free and more or less 

 active life, crawling between tidemarks or on the sea bottom, burrowing 

 in the sand, or swimming in the open water. These Errantia have well- 

 developed appendages, and a large pre-oral segment, and are generally 

 furnished with eyes and well-developed antennre. Gills are usually 

 associated with the dorsal parts of the parapodia. Most of them feed 

 on other animals, and have sharp "horny jaws," while the anterior part 

 of the gut is protrusible as a 



proboscis. 



Nereis and Nephthys are 

 two common genera, species 

 of which may be unearthed 

 by digging in the sand close 

 to rocks, though at times 

 these or other species are 

 seen swimming freely. The 

 sea mouse, Aphrodite, has 

 irridescent bristles, a feltwork 

 of matted hair covering large 

 gill plates which lie along its 

 back, a very large muscular 

 pharynx, and a gut with 

 numerous irregular branches 

 extending throughout the 

 body. A very common 

 shore form, a little like a 

 small Aphrodite, is Polynoe. 

 As an actively errant worm, 

 with well developed eyes, 

 Alciope may be noted, and 

 the family of Syllicke is re- 

 markable for the unusually 

 prolific asexual budding, 

 which sometimes results in 

 a chain or even an irregular 

 branched aggregate of individuals. As the cuticle is often irridescent, 

 and as the red blood may shine through the skin, these marine worms 

 are frequently beautiful. The list of nymphs and goddesses has been the 

 source of such titles as Nereis, Aphrodite, Eunice, and Hermione, and 

 one can almost believe the legend, according to which a specialist on 

 Errantia christened his daughters after his seven favourites. 



(b] Other marine Polycheeta, however, lead a more sluggish life within 

 various kinds of tubes, limy, sandy, papery, or gelatinous. As one would 

 expect, their parapodia are minute, apt to degenerate, and often used 

 solely for clambering within the tube. The pre-oral region is small, but 

 the anterior rings usually bear gills, cirri, and tentacles, often in rich 

 profusion. These Sedentaria rarely have a protrusible pharynx, and 



FIG. 69. Parapodium of a Marine 

 Polychrete, Heteronereis. (From 



QUATREFAGES. ) 



A, Notopodium ; B, neuropodium ; a, 

 notopodial cirrus ; f, neuropodial cirrus ; 

 b, c, g; gill plates ; e, i, tufts of bristles. 



