COE: NEMERTEANS OF WEST AND NORTHWEST COASTS. 213 



44. Zygonemertes thalassina Coe. 



Proc. Wash. Acad. Sci., 3, p. 29, PI. 2, fig. 5 ; PL 7, fig.l ; PI. 13, 

 fig. 2, 1901 ; Harriman Alaska Expedition, 11, |.. 29, 1904. 



Text-figs. 17, 34, 35. 



The very active and restless worms belonging to this species and 

 the closely related Z. virescens may be easily recognized by their 

 olive green color, and by the ocelli 

 which are very numerous on each 

 side of the head, and which extend 

 posteriorly along the lateral nerve 

 cords far behind the brain. 



Mature individuals are very slen- 

 der, and are usually from 80-60 mm. 

 in length. 



The proboscis sheath reaches to 

 the posterior end of the body, but 

 the proboscis itself is but little more 

 than half as long. The central stylet 

 of the proboscis is remarkably short 

 and blunt ; its basis is at least twice 

 and often three times as long as the 

 stylet itself, and is massive in pro- 

 portions (Text-fig. 84). The basis is 

 sharply truncated posteriorly, with 

 serrated edges. Each of the two 

 lateral pouches usually contains five 

 remarkably stubby accessory stylets 

 (Text-fig. 35). There are 12 probos- 

 cidial nerves. In Z. virescens the 



stylets are more slender, commonly but 2 or 3 in each lateral pouch, 

 and the proboscis has but 10 or 11 nerves. 



Habitat. — This species has been found only at Sitka, Alaska, 

 where it is not uncommon among hydroids, broken shells, etc., in 

 clear water (Coe, :01). 



The only decided differences that I have been able to determine 

 between this species and the closely related Z. virescens of the Cali- 



FiG. 34. — Zygonemertes thalassina. 

 Outline of st.vlet apparatus of pro- 

 boscis. 



