The range of larval sizes noted in the samples agrees fairly well 

 with the literature. With regard to My a , Thorson (19U6) gives the sizs 

 at metamorphosis in shallow water as 210 microns. Sullivan gives the 

 range of size as 10 5 microns, earliest straight-hinge stage, to 250 microns 

 metamorphosing larva. Loosanoff's photomicrographs show the earliest 

 shelled larvae to be 93 microns long. Larvae taken i n Wickford Harbor and 

 Greenwich Bay range from 90 to 100 microns, earliest shelled larvae, to 225 

 microns, when they disappear from the plankton, evidently as metamorphosing 

 larvae. 



Loosanoff and Davis (1950) give the range o f Venus larvae as 105 microns, 

 earliest straight -hinge stage, to 22? microns, ready-to-set larvae. Loosanoff, 

 Miller and Smith (195l) give the length at which metamorphosis takes place as 

 ranging from 175 to 236, with metamorphosis occurring most commonly between 

 200 and 210 microns. Sizes taken in our samples ranged from 110, earliest 

 straight-hinge larvae, to 200 to 225, when they disappear from the plankton. 



SUMMARY 



1. The literature concerning Mya arenaria and Venus mercenaria early life- 

 history was reviewed, and quantitative data on seasonal abundance were 

 found to be lacking. 



2. Identification of the larvae was made by a combination of two or more 

 of the following methods: Use of photomicrographs of field-obtained or 

 artificially reared larvae; use of diagnostic features such as color and 

 transparency not apparent in photographs; and rearing of field-collected 

 late umbone stage larvae to a post-setting size for positive identifica- 

 tion. 



3. Samples of larvae were collected with a rotary pump and strained through 

 a plankton net. Counts were made with a Sedgewick -Rafter cell. 



h. In Wickford Harbor, larvae of Mya arenaria are most abundant in May and 

 June, those of Venus mercenaria in June and July. In the western half 

 of Greenwich Bay, Venus is present in some abundance from June to 

 September. 



5. Variations in spawning patterns at the two locations are similar and 

 are probably c aused by variations in water temperature. 



6. The range of size of Mya arenaria larvae is 90 to 100 microns in length 

 as earliest straight-hinge stage to approximately 225 when late umbone 

 stage is reached. Venus mercenaria larval size range is 110 microns 



to 225 microns. 



27 



