A large often greenish-appearing type of leptocephalus larva has been observed and photographed or filmed by divers at 4 different locations within the Indonesian Archipelago from 2008 to 2011, and this paper documents these sightings and evaluates what can be learned about this type of unusual eel larvae. These leptocephali (~300–400 mm long) appear to be exceptionally large metamorphosing larvae of some type of moray eel of the family Muraenidae. Because of the morphological similarities between these larvae and ribbon eels, Rhinomuraena quaesita, they are hypothesized to be their larvae, which have never been distinguished among leptocephali of the Muraenidae. These leptocephali were observed at Sangeang Island, in Lembeh Strait adjacent to north-eastern Sulawesi Island, in two different years at Ambon Island, and on two consecutive days at Bali, between December and June of 4 different years. All observations of the large leptocephali were at depths shallower than about 23 m in areas with mixed coral rubble or coarse sand and silt substrates during daylight hours. The larvae used various styles of anguilliform swimming and swam near the bottom or in the lower water column while being observed. One larva tried unsuccessfully several times to enter small crevices. They were all at the metamorphosing stage and may have been entering coastal habitats to find a hiding place where they could transform into juvenile eels. Further studies are needed to clearly identify these large leptocephali and to learn about their life history.

This paper reports the yellowline arrow crab, Stenorhynchus seticornis, acting as cleaner of longjaw squirrelfish, Holocentrus adscencionis moray eels Gymnothorax funebris, G. moringa, G. vicinus and squirrelfish Holocentrus adscencionis at two reefs in the Baía de Todos os Santos, Bahia State, eastern Brazil. We believe that other species of reef fish are potential ‘clients’ of yellowline arrow crab and that this activity occurs throughout its distribution.