Phocitremoides ovale Martin

(12. Phov; Figs. 1, 49–52)

Diagnosis: Parthenitae. Colony comprised of active rediae, densely concentrated in snail gonad region. Rediae translucent white, grey, weak yellow, to colorless; ~ 500–1000 µm long, elongate (length:width ~4:1 to 10:1), sausage-shaped.

Cercaria . Body posterior 2/3 opaque white; oculate; with oral sucker and no ventral sucker; body ~ 200 µm long, much shorter than tail (<1/2 length); tail dorso-ventrally finned.

Cercaria behavior: Fresh, emerged cercariae remain in water column, swim intermittently in short bursts, with periods of resting and slow sinking.

Similar species: Phov is readily distinguished from the other two heterophyids with tail fins by only having a dorso-ventral fin (lacking the proximal lateral fins). Additionally, the penetration gland distribution imparts a distinctive coloration pattern to the body, with the anterior 1/3 being translucent and the posterior 2/3 being more homogeneously white (with reflected light) or dark (with transmitted light).

Remarks: Martin (1950c) described Phov and documented its life cycle; he described the rediae and cercariae from natural infections, and metacercariae and adults from experimentally infected second intermediate and final hosts. I suspect that cercariae of this species were accidentally pooled with Acha to comprise Maxon & Pequegnat’s (1949) Pleurolophocercous II.

Mature, ripe colonies comprise ~16% the soft-tissue weight of an infected snail (summer-time estimate derived from information in [Hechinger et al. 2009]).

Garcia-Vedrenne et al. (2017) presents several lines of evidence indicating that this species has a caste of soldier rediae. However, the in vitro attack trials had limited success.