mesotheca
/ˌmɛsə(ʊ)ˈθiːkə/Zoology and Palaeontology
noun
Originally: the middle layer of the sac enclosing the gonophore in certain hydrozoans. Later also: the median lamina on which the individuals of a bifoliate bryozoan colony are supported.
Origin
Late 19th century; earliest use found in George Allman (1812–1898), naturalist. From meso- + theca.