Marine invertebrates with larvae having long planktonic lives and consequent wide dispersal are predicted to have greater genetic homogeneity and less highly differentiated populations than ones with internal brood protection or encapsulated eggs. This idea is tested with 2 species of sympatric brittle stars Ophioplocus esmarki and Ophionereis annulata collected at 3 closely located intertidal sites near San Diego and analysed electrophoretically for genetic variation at 13 gene loci.  Ophioplocus esmarki broods its embryos, while Ophionereis annulata produces lecithotrophic pelagic larvae.  Surprisingly, similar levels of genetic variation are found in both species despite their different reproductive modes.  Although O. annulata does produce a pelagic larva, its life-span of only 4d may be too short to lead to wide dispersal. Both species display substantial differentiation on a microgeographic scale, tentatively attributed by the authors to genetic drift and population subdivision.  Gaarde & McClenaghan 1982 The Southwestern Nat 27: 255. Photo of O. annulata courtesy Peter Bryant, UC Irvine; photo of O. esmarki courtesy Bill Austin, Khoyotan Marine Laboratory, Victoria.

NOTE  the sites are located within 20m of one another

NOTE  it is a vitellaria type (i.e., lots of yolk) that metamorphoses within 4d