112 U.S. NATIONAL MUSEUM BULLETIN 227 



Family Syllidae 



Body of small size. Prostomium with 4 eyes (sometimes with an 

 additional minute anterior pair), 2 palps (may be reduced and fused), 

 3 antennae. Tentacular segment achaetous, with 1 or 2 pairs tentacular 

 cirri. Parapodia uniramous (may be biramous in sexual forms), with 

 dorsal and ventral cirri (latter may be absent). Anal cirri 2-3. Setae 

 mostly compound (may be secondarily fused), sometimes with addi- 

 tional simple setae. Proboscis eversible, armed or not with one to 

 several chitinous teeth. Carnivorous, living on sponges, hydroids, 

 ascidians, etc. 



The modes of reproduction are extremely varied in the group and 

 may be rather complex and thus cause difficulties in their identifi- 

 cation. They may be summarized as follows: 



A. Reproduction direct (epigamy) : The mature males and females 

 become transformed into reproductive individuals or epitokes in 

 which the whole animal becomes modified. The eyes become enlarged, 

 long swimming setae develop in newly formed notopodia on a number 

 of segments, and the body is filled with sex products, often becoming 

 luminescent. They may leave the bottom and swarm in surface waters. 



(1) Pelagic larvae: Eggs and sperm are given off into the water, 

 developing into pelagic larvae (as in Eusyllis (fig. 33), Odontosyllis, 

 Syllides, Streptosyllis, and Amblyosyllis). 



(2) Gestation : Large yolky eggs become attached to the dorsal or 

 ventral surface of the female where they are fertilized and develop 

 into advanced nonciliated young of 5-6 segments (as in Exogone, 

 Brania, Sphaerosyllis, and Parapionosyllis). 



B. Reproduction indirect, by asexually formed stolons : A variable 

 number of posterior segments become modified to form a sexual 

 stolon, in which the segments become massed with sex products, long 

 swimming setae develop in newly formed notopodia and a newly 

 formed head develops on the anterior part, with four large eyes and 

 various appendages. Wlien more or less completely modified, the 

 stolon breaks off from the stem form, the latter then regenerates a 

 new posterior end. The stem form may form: 



(1) Similar male and female stolons (chaetosyllis stage) : Head 

 appendages poorly developed, usually two antennae (2-3) and few 

 small tentacular cirri (0-3 pairs); develop into pelagic larvae (as in 

 Sylb's, fig. 32,d,e). 



(2) Sexually dimorphic male (polybostrichus stage) and female 

 (sacconereis stage) stolons: Head appendages well developed, three 

 antennae, 1-3 pairs tentacular cu-ri; female with large yolky eggs 

 carried in a large ventral sac where the embryos pass through their 

 early stages of development (as in Autolytus, figs. 37-40). 



