Cainocreadium gulella ( Linton, 1910 ) Durio & Manter, 1968

Martin, Storm B., Cutmore, Scott C., Ward, Selina & Cribb, Thomas H., 2017, An updated concept and revised composition for Hamacreadium Linton, 1910 (Opecoelidae: Plagioporinae) clarifies a previously obscured pattern of host-specificity among species, Zootaxa 4254 (2), pp. 151-187 : 171

Cainocreadium gulella ( Linton, 1910) Durio & Manter, 1968

Synonyms: Hamacreadium gulella Linton, 1910 .

Records. From Lutjanus griseus , off the Dry Tortugas, Florida, Gulf of Mexico, by Linton (1910). From L. griseus off Matecumbe Key, Florida by Schroeder (1970). From Gymnocranius griseus in the South China Sea, by Shen (1985). From southern red snapper, Lutjanus purpureus (Poey) and the lane snapper, L. synagris , off Columbia, Caribbean Sea by Velez (1978).

Remarks. This species was described from two specimens among the original collection of H. mutabile . Linton (1910) described a Y-shaped excretory vesicle with lateral protrusions extending to the pharynx but McCoy (1930) found this to be a mistake; the excretory vesicle is simple and reaches only to the ovary. McCoy (1930) determined the life-cycle of C. gulella and found it and H. mutabile share the same first intermediate host, a turbinid snail, Lithopoma americanum (Gmelin) [as Astraea americana (Gmelin) ].

Linton (1910) reported only two specimens of C. gulella from 69 L. griseus, but 66 of those same fish were infected with H. mutabile (prevalence 95.7%) with densities of up to 50 worms per fish. McCoy (1930) confirmed that natural infections of C. gulella in L. griseus are both less prevalent and less intense than those of H. mutabile . Through experimentation, McCoy (1930) also showed that, when infected with high densities of C. gulella , L. griseus appeared to be able to rapidly lose most or even all of the parasites, and that fish previously infected with a heavy load of C. gulella were more resistant to subsequent infection of that species; fewer worms established and those which did were smaller. Neither of these observations appeared to be true of H. mutabile for the same host ( McCoy 1930). The combined evidence of Linton (1910) and McCoy (1930) might suggest that L. griseus is only an occasional or incidental host for C. gulella . Although his experiments focussed on L. griseus, McCoy (1930) experimentally demonstrated that C. gulella could establish in two other lutjanids ( L. apodus and O. chrysurus ) but failed to establish in a carangid, kyphosid, pomacanthid, serranid and a sparid.

The record of Shen (1985) is dubious because of the geographical separation from the type-locality.