Geoduck clam (Panopea generosa): Anatomy, Histology, Development, Pathology, Parasites and Symbionts
Turbellaria of Geoduck Clams
Turbellaria are free living, commensal flatworms (phylum Platyhelminthes, class Turbellaria, order Rhabdocoel, and family Graffillidae) (Figs. 1 to 3) of less than 3 mm in length that were found in close association with the gills of geoduck clams. In all cases, there was no evidence of pathology (Figures 4a and 4b). They were found in geoduck clams from all Fisheries Management Areas sampled except in the fifteen clams sampled from Fisheries Management Area 23. They occurred more frequently and in higher intensity in the clams from Fisheries Management Areas 7 and 8 on the central coast of B.C.
Figure 1. Unstained wet mount of a commensal turbellarian obtained from the gill of a geoduck clam collected from the central coast of British Columbia. The two eye spots (ocelli) are evident at the anterior end (A).
Figure 2. Histological section through a turbellarian showing a testis (ts) full of basophilic spermatozoa, an ovary (ov) with a few developing ova, a nerve ganglion (ng) and the ciliated epidermus (ce).
Figure 3. The edge of the turbellarian with rhabdite forming gland cells (rh, that provide a mucous coating around the animal) within the mesenchyme (me) and the ciliated epithelium (ce) separated from the underlying tissue as an artifact of fixation.
Figures 4a and 4b. Histological sections showing the close association with minimal pathology between a commensal turbellarians (T) and the gills of geoduck clams. Haematoxylin and eosin stain.
Figure 4a. Histological sections showing the close association with minimal pathology between a commensal turbellarians (T) and the gills of a geoduck clam.
Figure 4b. Histological sections showing the close association with minimal pathology between a commensal turbellarians (T) and the gills of a geoduck clam.
Cáceres-Martínez et al. (2015) also observed unidentified turbellaria in the gills and mantle of P. generosa with no evidence of direct physical damage. Similar turbellarians have been described from numerous species of clams and other bivalves including oysters and scallops in European and North American coastal waters (Bower et al. 1992, Bower 2004). The distribution of these turbellarians is probably global although each species may be confined to certain areas or host species. There are no known adverse affect on hosts. Most of these trubellarians are thought to pass freely between the mantle cavity and alimentary canal. As a group they are considered to be midway between being endocommensal and parasitic.
References
Bower, S.M. 2004. Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Turbellaria in clams.
Bower, S.M., J. Blackbourn and G.R. Meyer. 1992. Parasite and symbiont fauna of Japanese littlenecks, Tapes philippinarum (Adams and Reeve, 1850), in British Columbia. Journal of Shellfish Research 11: 13-19.
Cáceres-Martínez, J., R. Vásquez-Yeomans and R. Cruz-Flores. 2015. First Description of symbionts, parasites, and diseases of the Pacific geoduck Panopea generosa from the Pacific coast of Baja California, Mexico. Journal of Shellfish Research 34: 751-756.
Lauckner, G. 1983. Diseases of Mollusca: Bivalvia. In: O. Kinne (ed.). Diseases of Marine Animals. Volume II: Introduction, Bivalvia to Scaphopoda. Biologische Anstalt Helgoland, Hamburg, p. 630-632.
Citation Information
Bower, S.M. and Blackbourn, J. (2003): Geoduck clam (Panopea generosa): Anatomy, Histology, Development, Pathology, Parasites and Symbionts: Turbellaria of Geoduck Clams.
Date last revised: August 2020
Comments to: Susan Bower
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