mesogloea

from The Century Dictionary.

• noun The mesodermal intercellular substance, or ground-substance, of some animals, as sponges and other cœlenterates.
• noun [capitalized] A genus of gelatinous seaweeds, typical of the Mesoglæaceæ, with olive-brown branching filiform fronds.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) A thin gelatinous tissue separating the ectoderm and endoderm in certain cœlenterates.