ENOPLA

McDermott, John J., 2011, Parasites of shore crabs in the genus Hemigrapsus (Decapoda: Brachyura: Varunidae) and their status in crabs geographically displaced: a review, Journal of Natural History 45 (39 - 40), pp. 2419-2441 : 2428

Class ENOPLA

Ribbon worms within the family Carcinonemertidae and belonging primarily to the genus Carcinonemertes are associated particularly with brachyuran crabs but are also known from some anomurans, astacideans and palinurans ( Kuris 1993; McDermott and Gibson 1993; Jensen and Sadeghian 2005). Adult worms encyst on the gills, walls of the gill chamber or other external parts of mainly female hosts. They attach egg strings or egg sacs to the pleopods of ovigerous hosts where embryos of host and symbiont develop and hatch simultaneously. Predation of the host’s embryos may severely interfere with its reproductive potential ( Jensen and Sadeghian 2005).

Carcinonemertes epialti parasitizes the sympatric, northeastern Pacific species H. nudus and H. oregonensis ( Kuris 1978, 1993; Roe 1979) ( Table 2). Juvenile worms are enclosed in mucous sheaths attached primarily on the ventral exoskeleton. These worms anticipate moulting of the host and move out of their sheaths onto the new exoskeleton. Maturation of juveniles occurs upon host oviposition, and they move onto the newly deposited brood to feed on the developing embryos. The worm’s embryos, enclosed in mucous sheaths, are attached to the host’s pleopods, where they develop and hatch into larvae in synchrony with the host’s embryos. Parthenogenesis in Carcinonemertes epialti occurs in the laboratory, and Roe (1986) suggested that it might have functional significance in locations where worm intensities are low.

Besides the two species of Hemigrapsus , Carcinonemertes epialti infests several other species of Brachyura living along the western coast of the USA and Canada ( Wickham and Kuris 1985). Its life cycle and host–parasite relationships in these hosts are probably similar to those in H. oregonensis , the most extensively studied. These additional brachyurans include another grapsid crab Pachygrapsus crassipes Randall, 1840 ; five members of the Cancridae , Cancer productus Randall, 1840 , Glebocarcinus oregonensis (Dana, 1852) , Metacarcinus anthonyi (Rathbun, 1897) , Romalean antennarius (Stimpson, 1856) and Romalean jordani (Rathbun, 1900); Epialtidae , Pugettia producta (Randall, 1840) ; Leucosiidae , Randallia ornata (Randall, 1840) ; Portunidae , Euphylax dovii Stimpson, 1860 . In addition, Carcinus maenas , recently introduced to the west coast of the USA, is now a host of Carcinonemertes epialti ( Torchin et al. 1996) .