rhagon
/ˈreɪɡɒn/Zoology
noun
1Originally: a hypothetical stage in the development of sponges, having a simple pyramidal form with an apical osculum and rounded flagellated chambers like those of a mature leuconoid sponge. In later use: a young sponge at a stage of development in which the larva has settled to form a flattened pyramid with a functional system of water canals (irrespective of its internal organization).
2The most complex type of sponge structure, characterized by small rounded flagellated chambers and a high degree of folding; a sponge of this type. Also called leucon. Usually attributive.
Origin
Late 19th century; earliest use found in William Sollas (1849–1936), geologist and anthropologist. From ancient Greek ῥαγ-, ῥάξ grape, of uncertain origin (probably a loanword from another language of the Mediterranean) + -on; so called on account of its shape: see quot. 1887 at sense 1.