184 



7. Note on the Occurrence of Phoronis larvae (Actinotrochai at Monterey 



Bay, California. 



By M. H. Spaulding, Stanford University, California. 



eingeg. 6. März 1906. 



The occurrence of Phoronis on the Western Coast of the United 

 States was first recorded by Torrey' who described Phoronis jJacifiea, 

 in 1901, from specimens taken at Humboldt Bay, California and Puget 

 Sound, Washington. 



This past summer, during a long continued calm spell in June, some 

 remarkably rich plankton was collected by the students of the Hopkins 

 Seaside Laboratory, Monterey Bay, California, and on two days June 15 

 and 16 — a few Actinotrocha were taken. 



In external appearence these were similar to those figured by 

 Masterman^, Boule^ and Ikeda*, representing several stages of 

 development. The youngest larva, 0,5 mm in length, had a well deve- 

 loped preoral hood, 6 pairs of short larval tentacles, a comparatively 

 large j^erianal band, and a short invagination of the rudimentary stalk. 

 Some of the older larvae showed this invagination at a more advanced 

 stage. The largest of the typical larvae was 1,75 mm in length, with 

 11 pairs of larval tentacles and was more robust in the trunk region, 

 while the body cavity was crowded with the intestine and the coiled, 

 invaginated stalk. A still older larva appeared to be nearly through the 

 free swimming period ; the stalk had evaginated and was filled with the 

 coiled intestine, while the remains of the hood and the j)erianal band 

 appeared as irregular lobes beside the tentacles, which were more slender 

 and appeared to be massed into the beginnings of a lophophore. 



With the exception of the very oldest, all the larvae when alive 

 carried the preoral hood at right angles to the long axis of the body, -i. 

 e. , in the position described and figured by Ikeda and not that men- 

 tioned by Masterman. In killing, nearly all retained the hood in this 

 position, although one specimen raised the hood until its long was 

 parallel to that of the body. 



While as yet no adults have been found, the presence of the larvae 

 indicates their occurrence and forms a valuable addition to the rich fauna 



1 Torrey, H. B.. On Phorotiis pacifica. Biol. Bull. n. 1901. p. 283-288. 



- Masterman. A. T., On the Diplochorda. I. The structure of Actinotrocha. 

 Quart. Joum. Micr. Sci. XL. 1897. p. 281-338. 



3 Roule, L., Etude sur le développement embrvonnaire dos Phoronidiens. 

 Ann. Sci. Nat. ser. 8. XI. 1900. p. 51-230. 



* Ikeda, I., Observations on the Development, Structure and Metamorphosis 

 of Actinotrocha. Joum. coll. Japan. XIII. 1901. p. .507—582. 



