268 f^-S- NATIONAL MUSEUM BULLETIN 2 27 



Rhode Island, Long Island Sound, Gulf of Mexico, low water to 640 

 fathoms. 



Distribution.- — ^Gulf of St. La^^Tence to Florida, Gulf of Mexico, 

 off northwest Spain, Chile, Antarctic (off South America). Low water 

 to 640 fathoms. 



Family Arabellidae 



Body elongate, cylindrical, of nearly uniform width, attenuated 

 slightly anteriorly and more so posteriorly. Prostomium (figs. 71a, 

 72,a,b) reduced to a simple, conical or flattened spatulate lobe, 

 without appendages, with or without eyespots on posterior margin, 

 without buccal cushions or palps visible ventrally. First 2 segments 

 apodous, distinct (not fused ventrally forming a lower lip). Para- 

 podia (figs. 71,6,/; 72,c,d) essentially uniramous. Notopodia may be 

 represented by minute papillar lobe (sometimes referred to as reduced 

 dorsal cirrus) with embedded notoacicula. Neuropodia with simple 

 limbate setae, with or without projecting thick acicular setae or acicula 

 (without hooded hooks as in Lmnbrineridae) . Without dorsal and 

 ventral cirri. Without branchiae. Pygidium with 2-4 short anal 

 cirri. 



Proboscis eversible, with elaborate dark chitinized jaw pieces, con- 

 sisting of a pair of ventral flat plates, the mandibles (may be absent) 

 and 4-5 pairs of more dorsal maxillae disposed in parallel rows, with 

 pair of long slender maxillary carriers as well as a shorter median 

 unpaired piece (figs. 71,d,e,g; 72, g,h). 



The arabellids are essentially burrowing, predaceous, carnivorous. 

 They burrow readily but rather slowly in sand or mud. They secrete 

 a good deal of mucus, which serves probably to lubricate the burrow. 

 Some are endoparasitic in other worms — eunicids, onuphids, syllids, 

 terebellids, echiuroids (Bonellia). They appear to be parasitic from 

 a very young stage up to advanced stages, apparently becoming 

 sexually mature after leaving the host. Although maintaming a 

 marked similarity to their free-living relatives, they may show modi- 

 fications associated with their parasitic existence, such as reduction 

 m setae, jaw parts, pigmentation, and mucous glands (Pettibone, 

 1957b). 



Key to the New England Genera of ArabelUdae 



1. Free living 2 



Endoparasitic in other polychaetes. With stout acicula or acicular setae 

 which sometimes project from parapodial lobes (fig. 71/) 4 



2. Parapodia without heavy projecting acicular setae (fig. 716). Prostomium 



usually with 4 eyes on posterior margin (fig. 71a). Maxillae I and II 

 asymmetrical (fig. 71e); mandibles well developed, wing shaped (fig. 71d). 



Arabella (p. 269) 



Parapodia provided with heavy projecting acicular setae or acicula (figs. 



72,c,d; 736) 3 



