The Biological Bulletin, Vol 195, Issue 3 260-263, Copyright © 1998 by Marine Biological Laboratory

RESEARCH NOTES

Coelomic Cavities May Function as a Vascular System in Amphioxus Larvae

T. Stach
Lehrstuhl fur Spezielle Zoologie der Universitat Tubingen, Auf der Morgenstelle 28/E, D-72076 Tubingen, Germany

At the level of light microscopy, Branchiostoma lanceolatum may be the best studied species of the Cephalochordata-the probable sister taxon of the craniates (1, 2, 3, 4). The blood vascular system of adult lancelets was studied by Rahr (5) and the detailed anatomical similarities of the major vessels prompted him to propose their homology with the vascular anatomy of craniates. He also showed that, in contrast to those of the craniates, most of the vessels in B. lanceolatum are not lined by an endothelium (6). In addition, there are rarely any hemocytes in the blood of cephalochordates. Nevertheless, certain parts of the circulatory system-endostylar artery, bulbilli, glomus, hepatic portal vein, hepatic vein, sinus venosus, subintestinal vein, and others-are reported to be contractile. Ruppert (7) proposed that the myoepithelial lining of adjacent coelomic cavities may provide the driving force for such contractions. On the basis of an extensive study by transmission electron microscopy as well as light microscopical observations of living larvae, I propose that Ruppert's hypothesis also holds true for larval stages. Moreover, the observations reported here suggest that the coelomic canal system is the functional circulatory system at a stage when the blood vessels are rudimentary.

This article has been cited by other articles:

				A Schmitz, M Gemmel, and S. Perry Morphometric partitioning of respiratory surfaces in amphioxus (Branchiostoma lanceolatum Pallas) J. Exp. Biol., January 11, 2000; 203(22): 3381 - 3390. [Abstract] [PDF]