Plumularia setacea. Plate XXI., figs. 1, 1a, 1b, 1c, 1d.
Corallina setacea, Ellis, Corall., 38 (an. 1755).
Sertularia pinnata, Lin. Syst., 1312.
Sertularia setacea: Ellis and Soland., Zooph., 47. Lister, Phil. Trans., 1534, 371.
Aglaophenia setacea, Lamour., Cor. Flex., 272.
Plumularia setacea: Lam., Anim. s. Vert., ii., 129. Hassall, Ann. Nat. Hist., vii., 285. Couch, Zooph. Cornw., 16; Corn. Faun., iii., 33. Johnston, 1867, Brit. Zooph., 97. Hincks, 1868, Hist. Brit. Hyd., 296. Bale, 1888, Proc. Linn. Soc. N.S.W. (ser. 2), iii., 778.
Plumularia tripartita, v. Lendenfeld, 1884, Proc. Linn. Soc. N.S.W., ix., 477.
Trophosome: Hydrocaulus attaining a height of 4 in., sometimes branched, pinnæ alternate, situated one at the top of each of the long internodes. The pinnæ are divided into alternate long and short internodes, of which only the long ones bear hydrothecæ. Hydrothecæ small, adnate almost to the thecostome, so that the aperture has its plane almost at right angles to the axis of the pinna. The character of the nematophores places P. setacea in the section Eleutheroplea, for they are narrow at the base and movable. One springs from below each hydrotheca, and a pair just above it, one from each short internode of the pinna, and one from the base of each internode on the stem.
Gonosome: The character of the gonangia places P. setacea in the still further division of the Eleutheroplean Plumularians—the Phyloctocarpa. The gonathecæ spring upward from the axils of the pinnæ, and, each being longer than the interval between two pinnæ, are densely crowded. They are slender, fusiform, with a rather long tubular neck.
Hab. Europe; Australia; Timaru; Dunedin.
This is the only Plumularian I have found, but it is extremely abundant, and gives excellent opportunities for the study of the Plumulariidœ as a whole. The nematophores are abundant, and the thread cells of large size. In the theca of the nematophore there is an intrathecal ridge, by which the cavity of the cup is divided into proximal and distal parts: this ridge does not occur in the hydrothecæ. The body of the hydranth is divided by a constriction into two parts, in both of which the enteric cavity is of considerable size. The ectoderm is composed of small cells, but those of the endoderm are of great relative size, and have scattered through them granular gland cells. Great masses of pigment are lodged in both proximal and distal divisions of the enteric cavity; they
are of many colours, varying through yellow, brown, and green. From their constancy these seem to be lodged in the endoderm cells, and have nothing to do with the presence of food. A strong core of endoderm cells runs through the axis of each tentacle, the ectoderm of which is loaded with irregularly distributed nematocysts. The mouth is placed on a conical hypostome, and the mosaic arrangement of the ectoderm cells is very apparent on the expanded parts of the zooid. Two varieties of this species have come under my own notice. In one the hydrocaulus attains the height of 4 in. or even 5 in., the oldest parts having taken on a light-horn colour. The other variety seems never to attain a height of more than ¾ in. or ½ in., has a milk-white appearance in the water, is really colourless, and occurs densely investing the seaweeds in rock-pools. The third variety is that described by von Lendenfeld under the name of Plumularia tripartita. This differs from P. setacea in the trilobation of the hydranth, and in a very different arrangement of the nematophores, the pairs of these structures occurring below instead of above the hydrothecæ. My variety, with its single constriction of the hydranth, is evidently intermediate between the European variety with no constriction and v. Lendenfeld's with two.