Fam. 6. Fungiidae.—Fungia is an unattached solitary coral of a flat disc-like shape with very numerous exsert imperforate septa. It is frequently of considerable size (six to twelve inches in diameter). On many of the coral reefs of the old world it is extremely abundant, and consequently it is one of the commonest corals of our collections. When alive the corallum is almost hidden by the disc, which is studded all over with very numerous long tentacles.[[420]] The colour varies in different species, but is usually brown. One species on the Australian barrier reef, F. crassitentaculata, is of a dark olive green colour, the tentacles terminating in white knobs.
The free adult Fungias are derived from a fixed stock called the trophozooid, from which the young Fungias are detached by transverse fission (see p. [388]). The thecal wall of the young Fungia when detached from the trophozooid is perforated, but the pores become largely filled up during the later growth of the coral.
There are several genera of colonial Fungiidae of less frequent occurrence, such as Halomitra, Herpetolitha, and Cryptabacia.
Fam. 7. Cycloseridae.—These are solitary or colonial Fungacea with an imperforate theca. Bathyactis occurs at great depths. Diaseris, shallow water on coral reefs.
Fam. 8. Plesioporitidae.—The septa in this family are trabeculate and perforate, resembling in this respect the septa of Poritidae. Leptophyllia, Microsolena, extinct.
Fam. 9. Eupsammiidae.—This family of perforate corals is usually placed with the Madreporidae and Poritidae in the old group Perforata. The researches of Fowler and Gardiner have shown that the arrangement of the mesenteries is that of the Cyclocnemaria, and the presence of synapticula connecting the septa suggests affinities with the Fungacea. The synapticula of the Eupsammiidae, however, are peculiar in being arranged, not in a vertical series, but alternately with one another or quite irregularly in position. The members of this family are solitary or colonial in habit.
Stephanophyllia is a flattened disc-shaped coral, with perforate and dentate septa, found in the Pacific Ocean and as a fossil in various strata since Cretaceous times.
In Leptopenus, from depths of about 1500 fathoms, the perforations are much larger than in the last-named genus, and the skeleton is reduced to a system of slender trabeculae.
Rhodopsammia has a conical shape, and gives rise by gemmation to a number of young zooids, which remain attached for some time to the parent form before becoming free.
Among the colonial genera are Dendrophyllia, Coenopsammia, and the well-known Mediterranean genus Astroides.