Fate of the second maxilla during embryogenesis in some Anomopoda Crustacea (Branchiopoda) ALEXEY KOTOV Institute of Animal Evolutionary M orphology and Ecology, Russian Academy of Sciences, Leninsky Prospect 33, M oscow 117071, Russia Received January 1995, accepted for publication M arch 1995 The maxilla II, normally present in crustaceans, is absent in most adult anomopods although it was found to occur in embryos of six species of this group. The appendage is reduced in representatives of families that lack it in the adult. The disappearance of the second maxilla is accomplished in a different way in the Chydoridae and Bosminidae as compared with the Daphniidae. A biramous structure of this appendage was observed in some stages of development in the largest species of Anomopoda. This feature of morphology is similar to the situation in other Branchiopoda. ©1996 The Linnean Society of London ADDITIONAL KEY WORDS:— Head appendages – maxilla II – later embryogenesis – Anomopoda. CONTENTS Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 393 Material and methods . . . . . . . . . . . . . . . . . . . . . . . 394 Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . 395 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396 The periodization of Anomopoda embryogenesis . . . . . . . . . . . . 396 The development of the second maxilla in Eurycercus lamellatus . . . . . . . . 398 The development of the second maxilla in Bosmina . . . . . . . . . . . . 400 The second maxilla in the embryogenesis of Daphnia . . . . . . . . . . . 400 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 404 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 404 INTRODUCTION The maxilla II, normally present in crustaceans, is absent in most adult anomopods. Another peculiar feature of these animals is the considerable morphological difference of the first trunk limb compared with the other thoracic appendages (Cannon, 1933). There is a special lobe near the basis of the first limb of the Chydoridae and Macrothricidae (‘inner lobe’ of Fryer (1963)) which is similar in some respects to the maxilla (maxilla II) of some of those branchiopods that have Z oological Journal of the Linnean Society (1996), 116: 393–405. With 6 figures 393 0024–4082/ 96/ 040393 + 13 $18.00/ 0 ©1996 The Linnean Society of London