A Hemocoel is a cavity or series of spaces between the organs of organisms with open circulatory systems like most arthropods and mollusks. A combination of blood, lymph, and interstitial fluid called hemolymph circulates through the hemocoel. An open circulatory system is an arrangement of internal transport in which blood bathes the organs directly and there is no distinction between blood and interstitial fluid. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders, scorpions, etc. ... Classes Caudofoveata Aplacophora Polyplacophora Monoplacophora Bivalvia Scaphopoda Gastropoda Cephalopoda † Rostroconchia The molluscs or mollusks are the large and diverse phylum Mollusca, which includes a variety of familiar creatures well-known for their decorative shells or as seafood. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... In mammals including humans, the lymphatic vessels (or lymphatics) are a network of thin tubes that branch, like blood vessels, into tissues throughout the body. ... Interstitial fluid is one of the two components of extracellular fluid, the other being plasma. ... Hemolymph (or haemolymph) is the blood analogue used by all arthropods and most mollusks that have an open circulatory system. ...

A Hemocoel is also the space in the connective tissue compartment derived from the embryonic blastocoel with contributions from mesoderm, filled with blood. A blastocoel(e) or blastocele or cleavage cavity or segmentation cavity is the central region of a blastula (or blastosphere). ... It has been suggested that organogenesis be merged into this article or section. ...