188 U.S. NATIONAL MUSEUM BULLETIN 2 27 



row beginning on the outside of the base of the branchia, continuing 

 around the tip of the branchia, and on the inner side and extending on 

 the body wall between the rami to the base of the neuropodium. The 

 effective beat of the cilia is from the head end toward the tail end. 

 A current of water flows on each side of the worm posteriorly in the 

 groove between the parapodial rami. The metachronal wave of cilia 

 is at right angles to their effective beat. This wave passes from dorsal 

 to ventral on the right side of the worm and from ventral to dorsal on 

 the left side. The metachronal wave of cilia shows a rhythmic move- 

 ment. The beating of the cilia on the branchiae and body wall 

 produces a current which carries liquids and other materials posteriorly 

 along the body. This ciliary movement is independent of the nervous 

 system. 



In studies of the nervous system, Clark (1955, 1956c, 1957, 1958a-c) 

 found that, in contrast to the relative uniformity of external 

 morphology in the Nephtyidae, the nervous systems in the different 

 species show many differences and may very well prove to be of im- 

 portant diagnostic value. The early planktonic stages of Nephtys sp. 

 in Rhode Island were followed in part by Fewkes (1883, p. 180, pi. 4). 



Key to the Known Genera of Nephtyidae 



1. Parapodial lobes with lamellae lacking or rudimentary (fig. 47,6, c). 



Micronephthys (p. 188) 

 Parapodial lobes with lamellae 2 



2. Branchiae involute, curved or rolled in spiral inwardly toward lateral side of 



body (fig. 4i8,a,b,d) Aglaophaxnus (p. 190) 



Branchiae recurved, cirriform or foliaceous, with convex side toward lateral 

 side of body (fig. 51) Nephtys (p. 193) 



Genus Micronephthys Friedrich, 1939 



Type (monotypy): Micronephthys minuta (Theel, 1879). Contains 

 only one New England species. 



Micronephthys minuta (Theel, 1879) 



Figure 47,6,c 



Nephthys minuta Th^el, 1879, p. 28, pi. 2, fig. 18.— Annenkova, 1937, p. 164; 



1938, p. 162.— Gorbunov, 1946, p. 38.— Uschakov, 1955, p. 217, fig. 68. 

 Micronephthys minuta Friedrich, 1939, p. 123, figs. 3-4. 



Description. — Length up to 16 mm., width up to 3 mm., segments 

 up to 30. Antennae subequal. Tentacular segment with prominent 

 neuropodial conical setigerous lobes, with ventral tentacular cirri 

 subequal to antennae. Notopodial setigerous lobes less prominent, 

 without dorsal tentacular cirri. Parapodia (fig. 47,6,c) with rami 

 widely separated, subequal, with rather sharply conical acicular lobes, 

 without lamellae, with preacicular setae barred, longer than the rami. 



