Geoduck clam (Panopea generosa): Anatomy, Histology, Development, Pathology, Parasites and Symbionts

Normal Histology - Overview

The histological morphology of geoduck clams was established from cultured juveniles and both normal and abnormal wild adults. The cultured geoduck clams (6 - 25 mm in shell length) were collected from ocean nursery sites in Georgia Strait, B.C. Adult clams were gathered from the east and west coast of Vancouver Island and the central coast of British Columbia during the course of the 1997/1998 fishery (supplied by Underwater Harvesters Association and Fan Seafoods). Histological examination was conducted on whole geoduck clam seed (up to 10 mm in valve length), whole shucked juveniles (10 - 25 mm in valve length), and portions of organs dissected from adult geoduck clams. Tissues were fixed in Davidson's solution (Shaw and Battle 1957), processed, embedded in paraffin wax, sectioned at 5 to 6 µm, stained with haematoxylin and eosin stain and examined under a compound microscope at 100 to 1000 times magnification.

The following histological sections through the longitudinal plane of a one year old geoduck clam illustrate the orientation and histological appearance of the major organs. The orientation of this specimen is similar to the orientation of the sketch presented near the bottom of the anatomy page.

Figures 1a and 1b: Photomicrographs of two sagittal histological sections through the same cultured juvenile geoduck clam (valve length about 6 mm) revealing the spatial relationships of the major organs. The siphon (si) is posterior and the top of the image is the dorsal surface. Labels are as follows: am - anterior adductor muscle, b - byssal gland at "heel" of the foot, d - digestive gland, f - foot, g - gills, h - heart, hc - hinge complex, i - intestine, ib - infrabranchial chamber, k - kidney, lp - labial palps, mm - cut surface of muscular mantle, pa - pedal aperture, pm - posterior adductor muscle, s - stomach, sb - suprabranchial chamber, si - siphon, ss - style sac.

Two dorsal muscles, called adductors, extend transversely between the valves, one at the anterior end and the other at the posterior end. The labial palps and anterior portion of the gills are located adjacent to the anterior adductor muscle. The gills are attached on each side of the visceral mass and extend from the attachment site of the labial palps to the anterior edge of the siphon septum. They divide the mantle cavity into two regions, the suprabranchial chamber and the infrabranchial chamber. The visceral mass contains the digestive system including the digestive gland, stomach, style sac, gonad, and loops of the intestine. In sexually mature animals, the visceral mass also contains the reproductive system (not evident in the sections of the immature geoduck clam above). The foot is attached to the anterio-ventral surface of the visceral mass and can extend forward to the labial palps and mouth (Fig. 1b above) or through the pedal aperture in the fused mantle into the external environment (as illustrated in anatomy sketch). Between the visceral mass and the dorsal surface lies a structure that appears to be associated with the secretion of the hinge ligament (hinge complex). The heart and excretory system lies posterior to the stomach. The excretory system includes the kidney tissue (nephridia) which has fused to form a single structure lying posterior to and extending slightly ventral to the heart. The posterior adductor muscle is posterior to the kidney. Details of various organs are available by clicking on the highlighted words.

References

Morse, M.P. and Zardus, J.D. 1997. Bivalva. Microscopic Anatomy of Invertebrates Vol. 6A Mollusca II. F.W. Harrison and A.J. Kohn. Wiley-Liss. pp. 7-118.

Simkiss, K. 1988. Molluscan Skin (excluding Cephalopods). The Mollusca Vol. 11 Form and Function. E.T. Truman and M.R. Clarke. Academic Press Inc. pp. 11 - 35.

Shaw, B. L., and Battle, H.I. 1957. The gross and microscopic anatomy of the digestive tract of the oyster Crassostrea virginica (Gmelin). Can. J. Zool. 35: 325-347.

Citation Information

Bower, S.M. and Blackbourn, J. (2003): Geoduck clam (Panopea generosa): Anatomy, Histology, Development, Pathology, Parasites and Symbionts: Normal Histology - Overview.

Date last revised: August 2020
Comments to: Susan Bower