116 U.S. NATIONAL MUSEUM BULLETIN 227 



Syllis gracilis Grube, 1840 



Figure 32 



Syllis {Syllis) gracilis Webster, 1879, p. 217; 1886, p. 137.— Fauvel, 1923, p. 259. 



fig. 96,/-r; 1953, p. 147, fig. 73,jr-z; 1955, p. 6; 1957b, p. 214.— Miner, 1950. 



p. 292, pi. 96.— Day, 1953, p. 412; 1957, p. 73; 1960, p. 309.— Tebble, 1955, 



p. 89.— Reish, 1959, p. 80.— Banse, 1959, p. 428.— Fauvel and Rullier, 1959, 



p. 514. 

 Synsyllis longigularis Hartman, 1942b, p. 48, figs. 76-82; 1945, p. 15, pi. 2, fig. 



8; 1951, p. 42. 



Description, — ^Length up to 50 mm., width up to 1 mm. Pro- 

 stomium with 4 eyes in trapezoidal arrangement, with 3 antennae 

 rather short, scarcely surpassing the palps, subequal. Dorsal cirri 

 rather short, with about 10 articles (7-16). Parapodia of anterior 

 and posterior regions with compound setae, with terminal blades 

 rather short, hooked and fringed; middle segments with few (2-3), 

 stout, bifurcated or Y-shaped simple setae formed by the fusion of 

 the short blade to the stem or shaft (fig. 32c). Body colorless or 

 transversely banded with light brown dots; eyes orange-red. 



Sexual stolons or chaetosyllis stage formed from posterior ends 

 of adults. Some posterior segments (12-37) become massed with 

 developing eggs or sperm and drop off. After brealdng off from the 

 more anterior region of the body, a head region develops on the an- 

 terior part of the first segment of the stolon. One may find all stages 

 as: (1) Small bilobed structure on anterior part of first setigerous 

 segment; sex products massed in all segments except the first, no 

 sign of modified setae; (2) oval head with 4 small eyes in trapezoidal 

 arrangement, with a pair of short bulbous palps and 3 short antennae; 

 sex products massed in body from second segment on, without modi- 

 fied segments; (3) completely modified stolons (fig. 32, d, e), with 

 suboval head and 2 pairs of large orange eyes with lenses, 1 pair 

 dorsal, 1 larger pair lateroventral, a pair of short bulbous palps ven- 

 trally, 3 beaded antennae; with or without tentacular cirri between 

 the head and first setigerous segment (0-3 pau's). Anterior unmodi- 

 fied segments 1 to 3. Middle modified segments (19-35) with long 

 capillary swimming setae between nem-opodia and dorsal cirri. 

 Posterior unmodified segments 1 to 3. The dorsal, ventral, and anal 

 cirri and the nem'osetae resemble those of the posterior end of the 

 stem form, since the stolons are but modified tails which were dropped 

 off from the adult worms ; thus they lack the modified fused Y-shaped 

 setae, except sometimes in the anterior few segments. Female stolons 

 filled with large yolky, closely packed, coral pink or deep violet eggs. 

 Male stolons massed with whitish or pale pink sperm masses. An 

 abnormal stolon had 2 pairs of extra small eyes between segments 

 5 and 6, with long swimming setae beginning on segment 6. 



