Abstract
Members of the Cryptochiridae are small gall-crabs that live as obligate symbionts of scleractinian corals. Only two species have so far been recorded in the western Atlantic Ocean. Herein a new Cryptochiridae genus and species is described, and new information is added on the life history of cryptochirids. The new genus is characterized by having the carapace with the lowest deflection angle among the genera, and also shows the following features: thoracic sternite 4 with setules and constriction smaller than half of the width of the basis, anterior margin curved with apical row of granules; third maxilliped with subcircular exopod reaching medially the lateral margin of the ischium; pereiopod 2 with prominent distomesial and anterolateral expansion on the merus, propodus almost twice larger than dactylus; thoracic sternite 7 with complete medial suture, female pleopod 3 uniramous with longitudinal opening. Male first pleopod straight with subdistal curvature of approximately 90°. Individuals belonging to the new genus are found in galls in massive corals although this structure is cited as being characteristic of ramified corals. The long plumose setae of the maxilliped 3 suggest a filter-feeding function, but the toothless chelae suggest that they are used to gather mucus.
Highlights
The Cryptochiridae Paul’son 1875 constitutes a group of small, sexually dimorphic, cryptic crabs, commonly referred to as “gall-crabs” as they are all obligate symbionts of scleractinian corals
While the galls have been mostly attributed to ramose colonies enclosing water-filtering crabs, the pits have been related to massive corals that usually shelter individuals adapted to feed on living and nonliving particles deposited on the border of the cavities (Potts 1915, Carricart-Ganivet et al 2004)
Identification of the coral host was at genus level due to the impossibility of differentiating S. stellata and S. radians in the field
Summary
The Cryptochiridae Paul’son 1875 constitutes a group of small, sexually dimorphic, cryptic crabs, commonly referred to as “gall-crabs” as they are all obligate symbionts of scleractinian corals.Described from shallow tropical waters to depths of 140 m approximately, the family is so far represented by 20 genera and 46 species (Kropp and Manning 1995, Ng et al 2008).Sexual partners may inhabit distinct, adjoining cavities on the coral surface with contact occurring during breeding periods (Kropp and Manning 1987, Johnsson et al 2006). Males usually may move from one colony to another to mate, and are occasionally found outside the cavities as free-living, benthic individuals (Potts 1915, Edmondson 1933, Fize and Serene 1957, Castro 1976, McCain and Coles 1979). Because of their small size, males have been observed sharing a single gall with conspecific females, eventually attached to the females’ abdomen (Henderson 1906, Warner 1977). Circumstantial differentiation among gall and “pit” dwellers has apparently provided a base for the correlation among the different feeding mechanisms of crabs, and the effectiveness of the morphological spatial arrays (branching vs. massive) of coral hosts (Abelson et al 1993, Carricart-Ganivet et al 2004)
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