Phocitremoides ovale Martin, 1950

Hechinger, Ryan F., 2019, Guide to the trematodes (Platyhelminthes) that infect the California horn snail (Cerithideopsis californica: Potamididae: Gastropoda) as first intermediate host, Zootaxa 4711 (3), pp. 459-494 : 481

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.

Figures

FIGURE 1. General characteristics of the parthenitae and cercariae of the trematodes infecting Cerithideopsis californica as first intermediate host. Species numbers and codes follow Table 1 and species accounts. Cercariae are all to scale, with additional magnified views of six small species (indicated by dashed lines). Note the oral stylets (presented in right lateral view) for Pruc and Smmi. Parthenitae are not to scale. Scale bars consistently indicate 100 µm.

FIGURES 49–52. Phocitremoides ovale (Phov). 49, Overview of a colony in a freshly deshelled, infected horn snail in sea water. Arrow indicates the colony, which is localized in the gonadal region. Scale bar = 1 cm. Base photo credit: Andrew Turner. 50, Reproductive rediae, live, with developing cercariae, under coverslip pressure. Scale bar = 100 µm. 51, Soldier redia, live, under coverslip pressure. Scale bar = 50 µm. Base photo credit: Ana Garcia-Vedrenne. 52, Cercariae, live, under coverslip pressure. Scale bar = 100 µm. Photo credit: Todd Huspeni.