Acanthoparyphium spinulosum Johnston

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 : 471-472

Acanthoparyphium spinulosum Johnston

(5. Acsp; Figs. 1 , 19–22 )

Diagnosis: Parthenitae. Colony comprised of active rediae, densely concentrated in snail gonad region. Rediae translucent orange, yellow, or colorless; redial gut often yellow; ~ 400–900 µm long, ovoid to oblong (length:width typically <3.5:1), with collar and posterior appendages that are often not pronounced.

Cercaria . Body translucent colorless, often with opaque and refringent white granules in distinctive, pinnately branched excretory system; non-oculate; with oral and ventral sucker; with two lateral pinnately branched excretory ducts; body ~ 320 µm long, ~equal in length to tail; tail simple.

Cercaria behavior: Fresh, emerged cercariae remain in water column, swim ~continuously, lashing tail back and forth.

Similar species: The Acsp cercaria is readily separated from the other himasthlids by its pronounced pinnatelybranched excretory system. It is readily distinguished from Hisb [7] by lacking a tail fin; Acsp is also often smaller than Hisb, but there is overlap, so this is not a consistently reliable distinguishing trait. Acsp’s collar spine count of 23 is also diagnostic, but seeing this requires mounting at the compound scope.

Remarks: Martin and Adams (1961) document the life cycle. They described miracidia, rediae, cercariae, and metacercariae from experimentally infected horn snails, and adults from experimentally infected young domestic chickens. They identified the adults as Acanthoparyphium spinulosum , which was originally described from adults naturally occurring in Australian birds, indicating A. spinulosum likely represents a broadly distributed species complex.

There are almost certainly at least two cryptic species subsumed within A. spinulosum of California horn snails, but we have not yet determined clear morphological traits to distinguish them. Martin (1972) included two Acanthoparyphium species in his key: A. spinulosum and “ Acanthoparyphium sp.”, which he reported as having smaller cercaria than A. spinulosum and as forming metacercariae within polychaetes and snail feces. Similarly, we have regularly noted natural and experimental infections of Acanthoparyphium metacercariae in both bivalves, horn snails, and polychaetes (but never in feces) ( Hechinger et al. 2007; Nguyen et al. 2015; Hechinger, unpublished data). This disparate host use may reflect one or more cryptic species, each of which would have more restricted host use. Additionally, DNA sequence data indicates the existence of cryptic Acanthoparyphium spp. in California horn snails ( Nguyen et al. 2015; Miura, Torchin, & Hechinger, unpublished data). However, the sequence data has not been connected to specimens suitable for morphological examination, and results of experimental infections have been ambiguous ( Nguyen et al. 2015; Hechinger, unpublished data). Hence, research is called for to resolve the existence of, morphological differences of, and host use by cryptic species of A. spinulosum .

This species almost certainly corresponds to the “small echinostome” of Martin (1955).

Mature, ripe colonies comprise ~20% the soft-tissue weight of an infected snail (summer-time estimate derived from information in [ Hechinger et al. 2009]).

Acsp infection causes (stolen) snail bodies to grow over 1.5x faster than uninfected snails ( Hechinger 2010).

This species has a caste of soldier rediae ( Garcia-Vedrenne et al. 2016).

Nadakal (1960b) presents information on the pigments of the rediae and cercariae of this species (as his “small echinostome”).

As part of one of the first studies documenting the syncytial nature of trematode integuments, Bils and Martin (1966) examined the fine structure and development of the tegument for the rediae and cercariae (and metacercariae and adults) of this species.

Koprivnikar et al. (2010) performed laboratory experiments to examine the effects of salinity, temperature, and pH on survivorship and activity of Acsp cercariae from Bolinas Lagoon (central California).

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 19–22. Acanthoparyphium spinulosum (Acsp). 19, Overview of a colony in a freshly deshelled, infected horn snail in sea water. The arrow indicates the colony, which is localized in the gonadal region. Note the prominent white areas, which are masses of cercariae that have left the orange rediae. Scale bar = 1 cm. Base photo credit: Todd Huspeni. 20, Reproductive rediae, live, with developing cercariae, under coverslip pressure. Scale bar = 100 µm. 21, Soldier redia, live. Scale bar = 100 µm. Base photo credit: Ana Garcia-Vedrenne. 22, Cercariae, live, under coverslip pressure. Scale bar = 100 µm. Base photo credit: Todd Huspeni.