On a new genus of MILLEPORIDAE.
By the Rev. J. E. TENISON-WOODS, F.G.S., F.L.S., Cor. Mem. Lin. Soc., N.S.W., &c.
The family of Milleporidoe were formerly included by zoologists amongst the Zoantharia in an entirely different class from the
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Acalephs, to which they are now referred. They are solid and stony corals, as much so in fact as any of the reef-building class. They generally have a smooth surface, and are always without any prominent calices, there being only very minute rounded punctures over the surface from which the animals show themselves. Some of the principal reefs on the Carribean Sea are mainly composed of Millepore corals. The cells in the zoothome are divided parallel to the surface by very thin plates or tables, as in the Pocilliporoe and Favosites, and they were formerly classed therefore with the other tabulate corals. The following was the arrangement proposed by Messrs. Edwards and Haime.
MADREPORARIA TABULATA.
Corallum essentially composed of a highly developed mural system, and having the visceral chambers divided into a series of stages by a complete diaphragm or transverse dissepiment. Septa rudimentary, either uniting or at most represented by processes extending more or less into the visceral chamber. There are four families in this section. A. coenenchyma abundant. 1. Cellules or tubulae foliaceous or massive Milleporidoe. 2. Seriatoporidoe: compact in arborescent tufts. B. Little or no coenenchyma, the walls uniting with one another. 1. Favositidoe: walls lamellar. 2. Thecidoe: wall thick and compact.
1st Family MILLEPORIDAE.
Corallum composed of an abundant tubular or cellular coenenchyma, distinct from the walls of the corallites. Septa, few; dessepiments well developed and numerous.
M. Agasiz has proved that these animals aro not corals, properly speaking, but an intermediate form of Acalephs between the embryo and adult state of Medusae. The Millepores afford, therefore, examples of coral-making by species of the class Acalephs. The corals are solid and stony, with a smooth surface without any prominent calices, there being only very minute rounded punctures over the surface from which the animals show themselves. They have no resemblance to true
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polyps. There is simply a fleshy tube with a mouth at the top, and a few small rounded prominences in place of tentacles, four of them sometimes the largest.
ARACHNOPORA. New Genus.
Zoothome parasitic spreading like a small thin web over other corals.
ARACHNOPORA ARGENTEA. n.s.
Zoothome spreading in a small extremely thin web, silvery white, and in parts quite transparent, which are sparsely covered with small silvery granules. The calices are all small very slightly raised, rounded, on which septa protrude as three or six broadly triangular teeth; calices irregular, but with a tendency to a quincuncial arrangement. Length of zoothome 7, breadth 3 mil. Calices like minute dots, barely discernable to the unassisted eye.
In this species the substance of the zoothome seems a quite transparent membrance, on which there is generally a very close arrangement of small silvery granules. It occurs parasitic on corals, filling up half of the calice and spreading from opposite septa just like a spider's web. It also spreads over the sides of the costae, where it appears just like a snail's track on which some very fine white dust had been sparsely scattered. There are no calices on the outside.