The marine podocopid Ostracoda of Easter Island: a paradox in zoogeographyand evolution

From a total of 20 samples, of which 8 were collected in the eulittoral and 12 by SCUBA diving in the sublittoral, more than 11,000 ostracods were rec overed. These comprise 30 species belonging to 20 genera. Of the 30 species , one is a cladocopid, one a platycopid and the remainder podocopids, of wh ich three are bairdiids, three cyprids and the remainder (22) are cytherids . Twenty-one of the species are both new and endemic as are two new subspec ies. Only four species have been described from elsewhere (Peripontocypris magnafurcata, Neonesidea tenera, Triebelina bradyi, Dentibythere dentata), although two others (Cytherelloidea keiji, and Loxoconchella honoluluensis) are represented at the island by new subspecies. However, an additional th ree species are known elsewhere only in manuscript; two of these are only k nown from the nearest inhabited land, the Pitcairn/Henderson group some 140 0 miles to the west. The remaining 22 are endemic to Easter Island and are monographed elsewhere. There are no species common with the Galapagos Islan ds nor with the South or Central American coast or Clipperton Island. The t hree described species and the four known, but as yet undescribed species, all occur to the west and it is in the Indo-Pacific and Australasia that th e closest relatives of the endemic species are encountered. The Easter Isla nd fauna seems clearly to be the product of a migration or series of migrat ions from the west. However, that this or these events were not simple is a ttested to by the fact that, although the seven species known at Easter Isl and and elsewhere are all from tropical environments, none of the pan-tropi cal Tethyan taxa are recorded there. Three of this group occur at Pitcairn/ Henderson, however, although none are among the four species common to Pitc airn/Henderson and Easter islands. Easter Island and the other volcanic isl ands to the west and west-northwest are all situated on a submarine ridge t ogether with numerous guyots. Many of these today have relatively shallow s ummits and all flat-topped seamounts must have been emergent at times in th eir history. It is suggested that the eastwards migration (migrations) took place at those times of lowest sea level and greatest emergence of the sum mits by normal island-hopping sweepstakes routes. (C) 1999 Elsevier Science B.V. All rights reserved.