The larval characters ofDorhynchus thomsoniThomson (Crustacea, Brachyura, Majoidea) and their evolution

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Abstract
Each of the 2 zoeal stages of D. thomsoni has a total of 24 carapace spines and 2 pairs of spines on each abdominal somite 2-5. The carapace and legs of the megalopa are also very spiny. The armature of the zoeal carapace and abdomen resembles that in the late zoeal stages of Homola (Homoloidea), but the characters of the zoeal telson and appendages are those of the Inachidae (Majoidea). The characters of the adult are entirely those of the Inachidae. The similarity between the zoeal spines of Dorhynchus and Homola can not be explained as due to inheritance from a common ancestral group. The zoeal spines of Homola probably evolved by a direct route, but those of Dorhynchus were acquired by loss, redevelopment and the reversal of evolutionary trends. The wider implications of this departure from evolutionary parsimony are discussed and observations are made on the use of larval characters in phylogenetic studies.