Life‐history studies on New Zealand Brachyura

Abstract

Pre‐zoea and first stage zoea larvae of the New Zealand grapsid crabs Leptograpsus variegatus (Fabricius), Planes marinus Rathbun, Hemigrapsus crenulatus (H. Milne Edwards), H. edwardsi (Hilgendorf), Cyclograpsus lavauxi H. Milne Edwards, C. insularum Campbell and Griffin, Helice crassa Dana, and Plagusia chabrus (Linnaeus) are described, and a key is given for their separation. On the basis of larval characters known grapsid zoeae fall into four groups, and these support the arrangement of adult genera into subfamilies except for a division among larvae of the subfamilies Varuninae and Sesarminae. The four groups are defined in a key and this arrangement is compared with an earlier system of larval classification. Grapsid zoeae show close affinities with those of genera in the families Ocypodidae and Gecarcinidae. Except Hemigrapsus edwardsi which breeds in late autumn and winter, all New Zealand species breed during late spring or summer. Where Cyclograpsus lavauxi and the recently rediscovered C. insularum occur together, their breeding periods do not coincide. All species have five zoeal stages and a megalopa larva, and planktonic larval life may last up to seven weeks. The length of larval life is apparently unrelated to the absence of grapsid crabs (or to the presence of certain other species) in the Chatham Islands.