308 U.S. NATIONAL MUSEUM BULLETIN 227 



Family Trochochaetidae, new name 

 ( = Disomidae and Disomididae) 



Type genus: Trochochaeta heYmsen, 1883; =Disoma Oersted, 1843, 

 preoccupied; see p. 309. 



The family, as defined by Mesnil, included Disoma Oersted and 

 Poecilochaetus Clapar^de. I am following Hannerz (1956) by con- 

 sidering Poecilochaetidae as a separate family. Although they show 

 similarities, both genera differ sufficiently to regard them as belonging 

 to separate families. Both families show relationships to the Spi- 

 onidae, the 3 families, then, forming a well-defined group among the 

 spioniform polychaetes. 



Body long, slender, cylindrical or somewhat flattened anteriorly, 

 fragile (posterior end often missing in collections) . Prostomium sim- 

 ple, elongate oval, wedged between or more or less encased in first 2 

 setigerous segments, usually with a median crest extending back on 

 first setiger, with or without a small median occipital antenna, with 

 or without 2-4 small eyespots, with a pair of very long, extensible 

 tentacular palps which are longitudinally grooved along sides facing 

 the mouth. Tentacular palps attached at base of prostomium, break 

 off very easily and often missing, of various lengths, probably in 

 different stages of regeneration (fig. 82,a-c). 



Body divided into 2-3 more or less distinct regions, changing 

 gradually and with transitional segments: 



(1) Anterior or thoracic region (of about 9-20 segments, figs. 82,a-c; 

 83, a^) with biramous parapodia. First 4 setigers modified. First 

 tentacular or buccal segment with biramous parapodia projecting 

 anteriorly, with bundles of long capillary notosetae and neurosetae, 

 with triangular postsetal lobes (sometimes referred to as tentacular 

 cirri) ; segment enlarged ventrally forming lips around large triangular 

 mouth. Second segment with similar notopodial and neuropodial 

 postsetal lobes, with or without notosetae. Neurosetae in form of 

 slender capillary setae and heavy acicular setae or the neurosetae may 

 not be specialized. Ventrally second segment forms lower lip of mouth. 

 Third segment with neuropodia with dark heavy acicular spines and 

 few capillary setae in vertical series. Notopodia with capillary setae. 

 Postsetal lobes short, broad, oval or flattened, with border entire or 

 serrated. Thus setiger 3 and sometimes setiger 2 with specialized 

 heavy projecting acicular spines. Rest of thoracic segments with 

 fan-shaped bundles of slender, pointed notosetae and neurosetae which 

 may be spiny or hairy (fig. 83e). With additional stouter lanceolate 

 neurosetae with hairy sheaths (fig. 83j,g) or curved neurosetae with 



