Pseudohemal System

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Pseudohemal System

 

(also perihemal, or sinus, system), in echinoderms, a series of canals surrounding the blood vessels that develops from isolated portions of the secondary body cavity, or coelom. The pseudohemal system includes an annular circumoral canal, which is situated between the ambulacral and nerve rings. There also are axial canals, annular aboral canals, and five radial canals—all of which extend into the ambulacra and run between the radial nerves and ambulacral canals. The fluid of the pseudohemal system, which is similar in composition to that of the body cavity, contains amoebocytes and apparently serves to nourish the nerve cords and prevent them from being compressed. The pseudohemal system is not equally developed in all echinoderms; for example, crinoids have only radial canals. The axial canal in some echinoderms is capable of contracting rhythmically.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.