Morphology of the Larval And First Juvenile Stages of Two Jamaican Endemic Crab Species with Abbreviated Development, Sesarma windsor And Metopaulias depressus (Decapoda: Brachyura: Sesarmidae)

Abstract

The complete larval development and the morphology of the first juvenile stages of two freshwater-breeding crab species endemic to Jamaica are described and illustrated in detail in the present paper. One of these species, Sesarma windsor, lives in and near caves in the karst regions of central western Jamaica, whereas the second species, Metopaulias depressus, occurs sympatrically but with a wider range in western and central Jamaica in water-filled leaf axils of bromeliads. Even if these species are placed in separate genera, they are extant representatives of the same adaptive radiation that resulted in at least ten Jamaican endemic crab species thriving in different land-locked habitats. Consequently, larval morphologies of the two species are very similar, but conspicuously different from the developmental patterns in their marine relatives. Both species display an abbreviated mode of development, showing morphological reductions in some features and pre-displacement in the expression of several others. Both species pass through two non-feeding zoeal stages, after which S. windsor moults to a facultatively lecithotrophic megalopa. In contrast, M. depressus directly moults from the zoea II to a juvenile stage (also facultatively lecithotrophic) that shows a mixture of juvenile and vestigial larval characters, such as a partly folded pleon, but no longer larval traits such as natatory pleopods. This represents the first record of larval development with no megalopal stage for Sesarmidae. A closely related species from mangroves in the Caribbean and northeastern South America, Sesarma curacaoense, shows a reduction in larval development, but with different morphological characteristics. We here discuss whether this could be a shared ontogenetic character or the consequence of convergent evolution.