Vol. VI. April, 1904. No. 



BIOLOGICAL BULLETIN 



ON THE HABITS AND REACTIONS OF SAGARTIA 



DAVISI. 



HARRY BEAL TORREY. 



Sagartia davisi 1 is the Pacific representative of the 5. luciic of 

 the Atlantic coast of the United States. The two species appear 

 to differ only in the absence, in 5. davisi, of the narrow yellow 

 stripes on the column which are so characteristic of the eastern 

 form. Both species commonly reproduce by fission, and it is 

 probable that the following descriptions of some of the other 

 habits of 5. davisi may be applicable to J>. lucicc also. 



5. davisi was first discovered clustered on the valves of a spe- 

 cies of the bivalve Chione, common in the harbor of San Pedro, 

 Cal. 2 The clam dwells near or on the surface of the sand. As 

 it plows its way along, the uppermost regions of the shell are 

 about the hinge and the siphons. To these regions, invariably, the 

 polyps cling. The deeper the clam goes the more do their small, 

 thin-walled bodies lengthen, supported by the surrounding sand, 

 to a degree I have never seen in an erect and unsupported form. 

 vS. davisi is not, however, a burrower, nor is the association with 

 Chione a case of commensalism, as might be concluded at first 

 sight. It fastens readily to any object which can give it a foot- 

 hold and keep it out of the sand. On the sand flats at San Pedro 



1 Description. Column of largest polyps about I cm. in diameter; spread of ten- 

 tacles about 2. cm. Foot disk very extensible ; body wall everywhere quite thin and 

 semitransparent ; a distinct capitulum above a well-defined collar as in Metridium ; 

 oral disk almost circular, mouth small, oval, lips with about twelve lobes, not prom- 

 inent ; one or two, occasionally three siphonoglyphs. Tentacles tapering, slender, 

 pointed, variable in number, most often 45-50 in perfect individuals. Color of column 

 dark brown, tentacles and disk green. Many individuals with light longitudinal stripe 

 of variable width on column (zone of regeneration after fission). Mesenteries unusu- 

 ally variable in number and arrangement. Reproduction sexual and non-sexual ; latter 

 the cause of irregularities in number and arrangement of tentacles and mesenteries. 



2 It has since been found in San Diego Bay, Cal. 



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