exotheca

from The Century Dictionary.

• noun The aggregate of hard structures which are developed upon the exterior of the wall, or the proper investment of the visceral chamber, of a coral: distinguished from endotheca, and also from epitheca.

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

• noun (Zoöl.) The tissue which fills the interspaces between the costæ of many madreporarian corals, usually consisting of small transverse or oblique septa.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun zoology The tissue that fills the interspaces between the costae of many madreporarian corals, usually consisting of small transverse or oblique septa.