The first zoea, megalopa, and first crab stage of the hydrothermal vent crab Xenograpsus testudinatus (Decapoda: Brachyura: Grapsoidea) and the systematic implications for the varunidae

Abstract

The first stage zoea and megalopa of the hydrothermal vent crab Xenograpsus testudinatus Ng, Huang, and Ho, 2000, are described, figured, and compared with a typical varunid, Brachynotus sexdentatus (Risso, 1827). Further comparisons are made between the first stage zoea of X. testudinatus and those representing the remaining current families of the Grapsoidea, namely Gecarcinidae, Glytograpsidae, Grapsidae, Plagusiidae, and Sesarmidae. A number of zoeal characters, including (1) the absence of the antennal exopod, (2) the setal formula [0,4] for the maxillular endopod, (3) the presence of a spine on both the distal coxal and proximal basal lobes of the maxilla, and (4) the presence of a minute spine on the lateral margin of the telson fork, appear to distinguish X. testudinatus first stage xoea from all the other grapsoids examined for this study. The zoeal evidence suggests that Xenograpsus is significantly different from known grapsoid larvae and the genus should eventually be removed from the Varunidae. Although Xenograpsus has similarities with known Scopimera (Ocypoidea) first stage zoea descriptions, including two of the above characters (1,2) and the setation of the maxillary endopod [2,3], these are not considered significant. A new family may need to be established to accommodate Xenograpsus within the Grapsoidea.