Usefulness of the size of dark spots on the body surface as a diagnostic character distinguishing two morphologically similar <i>Hemigrapsus</i> species (Decapoda: Brachyura: Varunidae)

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  • Usefulness of the size of dark spots on the body surface as a diagnostic character distinguishing two morphologically similar Hemigrapsus species (Decapoda: Brachyura: Varunidae)

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Abstract

The size of dark spots on the body surface was evaluated quantitatively as a diagnostic character to distinguish two species of varunid crabs of similar morphology: Hemigrapsus penicillatus and H. takanoi, common estuarine species in eastern Asia. From 37 Japanese localities, 171 H. penicillatus (106 males, 65 females) and 185 H. takanoi (113 males, 72 females) were collected and identified to species level by a molecular method. Spot size (the longest diameter of the largest dark spot) on the ventral face of the cephalothorax and on the outer faces of chelae were measured, with carapace width as an index of body size. Although the spot sizes at both loci increased with increases in carapace width, the spot sizes were significantly larger in H. penicillatus than H. takanoi. In both sexes, the ranges of variation in spot size partially overlapped between the species but the extent of such interspecific overlap was smaller for spot sizes on the ventral face of the cephalothorax in both sexes. Based on the spot size on the ventral face of the cephalothorax and carapace width, 92% and 82% of males and females were identified correctly into species via quadratic discriminant analyses. The spot size measured from the ventral face of the cephalothorax was therefore judged to be a useful diagnostic character to distinguish H. penicillatus and H. takanoi.

Journal

  • Plankton and Benthos Research

    Plankton and Benthos Research 10 (1), 45-54, 2015

    The Plankton Society of Japan, The Japanese Association of Benthology

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