EGG STRINGS IN EUCHIRELLA-PSEUDOPULCHRA (AETIDEIDAE) AND COMMENTS ON CONSTRAINTS ON EGG BROODING IN PLANKTONIC MARINE COPEPODS

Adult female Euchirella pseudopulchra Park, 1976 from the California C urrent System bear a pair of unusual linear ovisacs or ''egg strings.' ' Each membrane-bound, single file row of eggs contains 11-14 relative ly large ova. Calculations suggest that the geometric arrangement of s ingle file rows of eggs could facilitate oxygen diffusion in O-2-defic ient waters. The presence of ventrally carried egg masses in E. pseudo pulchra and other members of the Calanoida appears to be associated wi th evolutionary loss of the fifth swimming legs (P5) in the adult fema le. We hypothesize that loss of the female P5 would improve hydrodynam ic thrust during escape responses and reduce the probability of loss o f ventrally brooded ova. We re-examine the relationship between egg si ze and body size for planktonic marine calanoid and cyclopoid copepods from the mesopelagic and epipelagic zones and compare the advantages of brooding versus broadcast-spawning life histories. The size distrib ution of adult females of 43 egg-brooding copepod species is bimodal, comprising a number of small-bodied species and large-bodied species, with only one intermediate-sized species (between 10-100 mu g C). The size distribution of 75 broadcast spawners includes a large number (41 ) of intermediate-sized species. The interrupted size distribution of the egg-brooding species probably reflects enhanced predation risk to intermediate-sized copepods of carrying attached egg masses in the epi pelagic zone. (C) 1998 Elsevier Science B.V. All rights reserved.