The sesarmid crab Parasesarma erythodactyla consumes large amounts of mangrove leaf litter but its biochemical capacity for cellulose digestion is poorly known. We demonstrate the presence of endo-β-1,4-glucanase, β-glucosidase and total cellulase activities in the digestive juice of this crab. The highest total cellulase activity was observed at mildly acidic pH (5 to 6) and temperature between 30 and 50 °C. A 1752 bp cDNA containing an open reading frame of 1386 bp encoding a putative endo-β-1,4-glucanase (EG) of 461 amino acids was identified in the crab's hepatopancreas using polymerase chain reaction (PCR), cloning and sequencing techniques. P. erythodactyla endo-β-1,4-glucanase (PeEG) contains a glycosyl hydrolase family 9 (GHF9) catalytic domain with all catalytically important residues conserved, and shows high sequence identity to GHF9 EGs reported from other arthropods. The endogenous origin of PeEG was confirmed by PCR amplification of a ~ 1.5 kb DNA fragment, containing a phase 1 intron flanked by two exon sequences identical to the cDNA, from genomic DNA isolated from the crab's muscle tissue. PeEG encoding cDNA is the first endogenous EG sequence reported from the brachyuran crabs. Using degenerate primers, we also isolated 204 bp cDNA fragments with sequences affiliated to EG from the hepatopancreas of eight other mangrove crabs of the Sesarmidae (Neosarmatium trispinosum and Sesarmoides borneensis), Macrophthalmidae (Ilyograpsus daviei, Australoplax tridentata, and Macrophthalmus setosus), Varunidae (Pseudohelice subquadrata), Heloeciidae (Heloecius cordiformis), and Ocypodidae (Uca perplexa) families, suggesting that endogenous cellulase production may be a common characteristic among the detritivorous mangrove crabs.