A NEW POLYCHAETOUS ANNELID OF THE GENUS 

 PHYLLODOCE FROM THE WEST COAST OF COSTA 

 RICA 



By Aaron L. Treadwell 



Of the Department of Zoology, Vassar College, Fouyhkeepsie, N. Y. 



In August, 1927, a small collection of invertebrates from the Gulf 

 of Nicoya was sent to the United States National Museum by Pro- 

 fessor Manuel Valerio of the Lyceum of Costa Rica, for identiiication. 

 Included in this material was a polychaetous annelid, here described, 

 which appears to be new to science. 



PHYLLODOCE NICOYENSIS. new species 



Of the three specimens in the collection, only one is not badly 

 coiled. This is 90 mm. long, about 0.5 mm. wide at the prostomium, 

 and 1.5 mm. wide in the region of the fifteenth somite. So far as 

 can be determined in their coiled condition the others are approxi- 

 mately the same length. None is entire posteriorly, but all show a 

 gradual tapering in width behind the fifteenth somite. In preserved 

 material the body color is an iridescent purple, the parapodia, pros- 

 tomium, peristomium, and tentacular cirri light brown. 



The anterior margin of the prostomium (fig. 1) is only very 

 slightly I'ounded and from the bases of the tentacles each lateral 

 margin slopes latero-posteriorly at an angle of about 45° as far as 

 the level of the eyes. Here it bends forming the rounded latero- 

 posterior prostominl angle. The posterior prostomial margin has the 

 usual median incision, in which is a very small and inconspicuous 

 papilla. The eyes are small and black, situated at about one quarter 

 of the length of the prostomium from its posterior border. The 

 tentacles are short and stout, about as long as the distance between 

 those of opposite sides. The first tentacular cirrus and the ventral 

 one on somite 2 are about equal in size and extend as far posteriorly 

 as somite 5. The dorsal one on somite 2 extends to somite 8 and the 

 one on somite 3 to somite 12. 



In two of the three individuals the proboscis is protruded. The 

 proximal portion of the proboscis, extending rather more than one- 

 No. 2757.— Proceedings U. S. National Museum. Vol. 74. Art. 12. 



5924—28 



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