Bioacoustics of Glyptoxanthus vermiculatus

Remarks. In G. vermiculatus the afferent opening at the base of the cheliped is protected by dense setae ( Fig. 33B, F ), so that the water entering the branchial chamber via the afferent aperture is “filtered” and freed from excess of particles in suspension and propagules of fouling organisms. The pleonal-holding system ( Guinot & Bouchard 1998 ), well-developed in young females, is preserved in mature females (both press-button and socket), even though folding of the pleon beneath the thorax is made impossible by the egg-mass carried by the ovigerous female of G. vermiculatus . Generally, the pleonal and thoracic sternal margins closely fit each other in males, so much that the outline of the pleon is not always clearly distinguishable. The male locking system is well-developed and effective but only releases the distal half of the pleon when disengaged. The press-button system is complemented by a sterno-pleonal locking system (very rare in Eubrachyura, v. Guinot & Bouchard 1998 ). The sterno-pleonal cavity is protruded into an edge at the level of the sternite 7 that overhangs the corresponding margin of the pleonal somite 3, whose role is preventing the pleon from being lifted.Additionally, the margin of the pleonal somite 3 is provided with a hollowed, curved forward spur that closely fits the rounded posterior edge of the thoracic sternite 7 from behind and beneath. Both systems work together to prevent the proximal half of the pleon from being lifted. The proximal half of the pleon is released only when moved backwards and then upwards. No mention has been made in the literature of the presence of sound producing apparatus in G. vermiculatus . However, stridulation is obtained by rubbing the heavily granulated mesial lower surface of the P1 propodi against the also heavily granulated mesial surface of P1 meri, which can be considered the pars stridens. Sound production as a result of friction of the cheliped against itself has been reported in a few numbers of crab species ( Guinot-Dumortier & Dumortier 1960 , and references therein).