title: A crab with three eyes, two rostra, and a dorsal antenna-like structure.
abstract: We describe a malformed specimen of the freshwater crab Amarinus lacustris from New Zealand. With three eyes in a horizontal row, two rostra, and a dorsal antenna-like structure, the pattern of malformation of this animal is unique and has not been described before. A careful inspection and description of external and internal structures, in particular the central nervous system, were carried out. These revealed, in addition to the external abnormalities, a retarded brain with a hypertrophied and backwards bent protocerebrum connected with all three eyes and putatively with the dorsal antenna-like structure. Based on these data, a variety of hypotheses about the causes for this kind of malformation are discussed. A scenario combining a conjoined twin (Duplicitas anterior) based on the duplication of the embryonic anterior head lobes and a regeneration event leading to the replacement of an eye by an antenna shows the best fit to the observed patterns.
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Biologie/Vergleichende Zoologie, Philippstrasse 13, D-10115 Berlin, Germany. Electronic address: gerhard.scholtz@rz.hu-berlin.de.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Scholtz
authors.affiliation: Raffles Museum of Biodiversity Research, Department of Biological Sciences, Faculty of Science, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore. Electronic address: peterng@nus.edu.sg.
authors.forename: Peter K L
authors.initials: PK
authors.lastname: Ng
authors.affiliation: Landcare Research, 231 Morrin Rd, Tamaki Campus, University of Auckland, Private Bag 92170, Auckland, New Zealand. Electronic address: moores@landcareresearch.co.nz.
authors.forename: Stephen
authors.initials: S
authors.lastname: Moore
mesh_terms: D000818:Animals; D003386:Brachyura / Q000033:anatomy & histology*; D002490:Central Nervous System / Q000002:abnormalities*; D005123:Eye
keywords: Brain; Crustacea Decapoda; Development; Regeneration; Siamese twins