Definition.—Phæodaria without lattice-shell, either without any skeleton, or with an incomplete skeleton, composed of numerous single pieces, which are scattered in the calymma without connection. Central capsule placed in the centre of the spherical calymma.
Family LXXI. Phæodinida, Haeckel (Pl. [101], figs. 1, 2).
Phæodinida, Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 4.
Definition.—Phæodaria without skeleton. Central capsule with one to three (or more) openings, placed in the centre of the spherical naked calymma.
The family Phæodinida is the simplest and most primitive of the Phæodaria, and differs from all the other families of this legion in the complete absence of a skeleton. It bears, therefore, the same relation to the latter as the Thalassicollida do to the other Spumellaria. The soft body is only composed of the central capsule with the nucleus, and the calymma with the phæodium.
Of course it is quite possible that the skeletonless Phæodaria, which we regard here as the ancestral family of that legion, may be either members of other families which have lost their skeleton accidentally, or young Phæodaria which have not yet developed a skeleton. But in some preparations of the Challenger certain large, well-preserved Phæodaria, without any trace of skeleton, are not rare; and since I myself have observed a complete living Phæodina, I have no doubt that they are independent, primordial forms (like Actissa, Thalassicolla, Cystidium, Nassella, &c.). Probably also two skeletonless Phæodaria belong to this family which are figured by R. Hertwig, in 1879, in his Organismus d. Radiol. (Taf. x. fig. 1, 11); this author, however, supposed that they had lost their original skeleton.
The three species of Phæodinida which are described in the sequel represent two different genera, Phæodina and Phæocolla, already distinguished in my first note on the Phæodaria (Sitzungsb. med.-nat. Gesellsch. Jena, 1879, Dec. 12, p. 4). Phæodina is a true Tripylea, and has the usual three openings which occur in the majority of Phæodaria, a large astropyle or main-opening on the oral pole of the main axis, and a pair of lateral accessory openings, or parapylæ, on the aboral pole. Phæocolla, however, has only a single opening, the astropyle, and agrees therefore with those Phæodaria which possess no parapylæ (Challengerida, Medusettida, Castanellida, &c.).
The complete body is in all observed Phæodinida a small jelly sphere of 1 to 3 mm. in diameter, with a transparent cortical layer and an opaque dark central part. This latter is the phæodium, in which the central capsule is hidden, surrounded on all sides by the gelatinous spherical calymma; the smooth surface of the latter is spherical.
The central capsule of the Phæodinida (Pl. [101], figs. 1, 2), is either spherical or spheroidal, somewhat lenticular, slightly depressed in the direction of the main axis. Its diameter is between 0.15 and 0.25. Its double membrane exhibits the same structure as in the other Phæodaria. The thick, double-contoured outer membrane is separated from the thin and delicate inner membrane by a clear space, filled up by jelly or by a fluid; the two are connected in Phæocolla (fig. 1) only at the astropyle, in Phæodina (fig. 2), they are also connected at the two parapylæ. The radiate operculum of the astropyle opens by a tubular prolongation or proboscis, which is very long in the former, shorter in the latter. The two parapylæ of the latter also bear short tubules. The protoplasm, enclosed in the inner membrane, contains numerous small circular vacuoles. The large central nucleus is sometimes spherical or ellipsoidal, at other times spheroidal or lenticular; it always contains numerous nucleoli. One specimen observed, with two nuclei, was apparently engaged in self-division (fig. 2).
The spherical gelatinous calymma, in the centre of which the central capsule is placed, has a diameter of 1 to 2 mm. In the specimen of Phæodina tripylea, which I observed living, it exhibited exactly the same shape as the figure of Dictyocha stapedia in Pl. [101], fig. 10; the only distinction in this latter being indicated by the pileated pieces of the skeleton on the surface. The jelly-sphere contained numerous roundish or globular alveoles of very different sizes, and between them an areolated network of protoplasm; the latter has arisen from the outer surface of the calymma in the form of very numerous, radiating, partly branched and anastomosing pseudopodia. The dark and opaque centre of the jelly-sphere is filled up by the granular, blackish-brown phæodium, which envelops the oral half of the central capsule completely; it exhibits the same characters as in all the other Phæodaria.