Himasthla, Dietz, 1909

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 : 474-475

Himasthla sp. B

(7. Hisb; Figs. 1 , 27–29 )

Diagnosis: Parthenitae. Colony comprised of active rediae, densely concentrated in snail gonad with dispersion into basal visceral mass regions. Rediae translucent orange to colorless; ~ 750–2000 µm long, oblong to elongate (length:width up to ~5:1), with posterior appendages that are often not pronounced.

Cercaria . Body opaque white; non-oculate; with oral and ventral sucker; with main excretory ducts forming a broad “v”; with basal portions of main excretory ducts being particularly inflated and filled with large, distinct granules; collar with 25 collar spines in a single row, and 4 in a second row (2 pairs of “corner spines”); body ~ 550 µm long, ~equal in length to tail; tail dorso-ventrally finned.

Cercaria behavior: Fresh, emerged cercariae remain in water column, swim ~continuously, body ventrally flexed (~forming an overall spheroidal shape), lashing tail back and forth.

Similar species: Hisb is most readily distinguished from all the echinostomatoids by having a tail fin.

Remarks: The rediae and cercariae of this species have not been thoroughly described. However, Hechinger et al. (2011b) present several aspects of redia morphology.

This species corresponds to the ‘fin-tailed echinostome” of Martin (1955) and the “ Echinoparyphium sp.” of Martin (1972), but it has been considered to be a species of Himasthla since Huspeni’s unpublished thesis (2000).

Based on observations of natural infections at various stages of development, it appears that the initial mother sporocyst frequently invades the snail heart lumen (first pointed out to me by TC Huspeni; pers. observations).

Mature, ripe colonies comprise ~24% the soft-tissue weight of an infected snail (summer-time estimate derived from information in [ Hechinger et al. 2009]).

Hisb infection causes (stolen) snail bodies to grow ~ 2x faster than uninfected snails ( Hechinger 2010).

Hisb has a caste of soldier rediae ( Hechinger et al. 2011b). In fact, it is first trematode species for which it was documented that trematodes can have a reproductive division of labor and a soldier caste.

Nadakal (1960b) presents information on the pigments of the rediae and cercariae of this species (as his “fintailed 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 of this species (as Molinella sp.).

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 27–29. Himasthla sp. B (Hisb). 27, 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 and part of the basal visceral mass. Scale bar = 1 cm. Base photo credit: Todd Huspeni. 28, Reproductive redia, live, with developing cercariae, under coverslip pressure, with an adjacent soldier redia indicated by the black arrow. Scale bar = 100 µm. 29, Cercariae, live, under coverslip pressure. Scale bar = 100 µm.