Crrtstacenr/‘r 37 121, 1979. li. J. Brill, Leideii OBSERVATIONS ON THE RELATIONSHIP BETWEEN OCTOLASMZS GRAYZZ (DARWIN, 1851) (CIRRIPEDIA, THORACICA) AND CERTAIN MARINE SNAKES (HYDROPHIIDAE) BY WILLIAM B. JEFFRIES Department of Biology,, Dickinson College, Carlisle, Pa. 1701 3, U.S.A and HAROLD K. VORIS Division of Amphibians and Reptiles, Field Museum of Natural History, Chicago, Illinois, 60605, U.S.A. INTRODUCTION This paper concerns a species of small, stalked (goose) barnacle which attaches to the skin of marine snakes. Most species of the genus 0rtolasmi.s Gray, 1825, attach themselves to hard-shelled crustaceans. However, Annandale ( 1909) reported “...at least two [species] have been found on the shells of echinoids, and that one LO. warzuiikii Grayj sometimes fixes itself to the shells of living molluscs, to the skin of sea snakes and even to that of fish.” 0rtolusmi.r grayii (Darwin, 1851) alone has been reported exclusively on sea snakes. Snakes from the Indian Ocean, Bay of Bengal, and the Arabian Sea, reported by Annandale (1909) to have 0. grayii on them were Enhydrina srhistosa Daudin, Mirro- cephalophis gracilis Shaw, Hydro phis fusiiatus Schneider, H. spiralis Shaw, and Pelamis platurus L. Those having 0. grayii var. pernzida were Enhydrina .rihistosri. Hydrophis sp., and Tbalassoph’i iiperina Schmidt. The study of this obligate epizoite barnacle and its vertebrate hosts was under- taken with the purpose of exploring the nature, extent, and importance of their interrelationships. The numbers and distribution of 0. grayii found on seventeen species of marine snakes collected at several locations in the Straits of Malacca and the South China Sea are reported. A detailed description of the numbers, size, distribution, and the attachment sites of 0. grdyii found on Lapemis hnrdzoickii Gray collected over a nine-month period is also presented. MATERIALS AND METHODS In late 1974 and 1975, marine snakes were collected along the coast of the Malay Peninsula. Three localities were sampled in the Straits of Malacca (Sungai Buloh, 3’15’45”N 101°18’10”E; Muar, 2’3’20’” 102”4’20”E; Parit Botak, 1’41’45’” 103’6’15”E) and one locality in the South China Sea (Endau, 2’40’O’’N 103”38’0”E). A general survey of epizoite organisms was made on over 1300 of the 2900 snakes collected. Detailed work on the goose barnacle, 0rtolasmi.s