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This study asked whether reductive traits in cave organisms evolve at a slower pace (suggesting neutral evolution under relaxed selection) than constructive changes, which are likely to evolve under directional selection. We investigated 11 subterranean and seven surface populations of Sundathelphusa freshwater crabs on Bohol Island, Philippines, and examined constructive traits associated with improved food finding in darkness (increased leg and setae length) and reductive traits (reduced cornea size and eyestalk length). All changes occurred rapidly, given that the age of the most recent common ancestor was estimated to be 722-271 ka based on three mitochondrial markers. In order to quantify the speed of character change, we correlated the degree of morphological change with genetic distances between surface and subterranean individuals. The temporal pattern of character change following the transition to subterranean life was indistinguishable for constructive and reductive traits, characterized by an immediate onset and rapid evolutionary change. We propose that the evolution of these reductive traits-just like constructive traits-is most likely driven by strong directional selection.

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The identity of the rare xanthid crab, Pilumnoplax acanthomerus Rathbun, 1911, originally described from the AmiranteIslands in the western Indian Ocean, is elucidated. Števčić (2005) transferred the species from Pilumnoplax Stimpson,1858, to a new genus, Linnaeoxantho. This monotypic genus is re-diagnosed and new morphological characters are high-lighted. New records from Ryukyu and Line Islands, in the western and central Pacific, respectively, are reported. Linnae-oxantho is compared with the morphologically similar Melybia Stimpson, 1871, from the western Atlantic, and theiraffinities are discussed. Linnaeoxanthinae Števčić, 2005, is here recognised as a valid xanthid subfamily for Linnaeoxantho and Melybia, and is considered to have priority over Melybiidae Števčić, 2005.

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Relatively few studies have been done to define or assess rarity in the marine environment. Published studies have focused on shallow-water and intertidal habitats, and the available information appears to reflect the same pattern observed in terrestrial environments, i.e., that there are many rare species and few common species in any one given area. However, our studies of the abundance of new and/or supposedly rare taxa of decapod crustaceans from the deep, steep slopes of the island of Balicasag, in the central Philippines, have raised questions on how rarity should be defined in marine invertebrates. Examples of such supposedly rare species of crabs and lobsters (Crustacea: Decapoda) are presented here. That these animals come from deep, steep slopes, a relatively under-studied habitat, highlights the major gaps in current knowledge of marine biodiversity that are in part due to the inadequacy of both traditional and high technology sampling methodologies and the limited habitat types that the former can target. Low-technology, artisanal tangle nets have proved to be an optimal capture technique for deep-water decapod crustaceans on deep, steep slopes; many new taxa have been discovered and, in other cases, perceptions of rarity and endemicity have been corrected.

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Examination of the holotype and other specimens of the type species of Garthiella Titgen, 1986, G. aberrans (Rathbun,1906), reveals that this genus must be excluded from Chlorodiellinae Ng & Holthuis, 2007, due to the absence of thediagnostic morphological features of the subfamily such as spoon-tipped chelae, prominent dactylo-propodal locks on theambulatory legs, and subdistal teeth on the ambulatory dactyli. Garthiellinae subfam. nov. is therefore established for thisgenus, as molecular and morphological evidence show that it cannot be classified in any other subfamily of XanthidaeMacLeay, 1838. A new species of Garthiella from the Bohol Sea, central Philippines, is also described. Garthiellasikatuna sp. nov. can be distinguished from G. aberrans by its relatively flatter and less granular carapace, more pronounced and curved anterolateral teeth, longer and more slender pereopods and by the form of the male first gonopods.