Mesogloea

noun

1. The mesodermal intercellular substance, or ground-substance, of some animals, as sponges and other cœlenterates.
2. [capitalized] A genus of gelatinous seaweeds, typical of the Mesoglæaceæ, with olive-brown branching filiform fronds.
3. A thin gelatinous tissue separating the ectoderm and endoderm in certain cœlenterates.