Page:Scientific results HMS Challenger vol 18 part 2.djvu/22

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Definition.— with foamy calymma, containing numerous large extracapsular alveoles.

The genus Nassella differs from the preceding Cystidium, its probable ancestral form, in the development of numerous large alveoles in the extracapsular calymma, and therefore exhibits the same relation to it that Thalassicolla bears to Actissa among the. The foamy calymma is very voluminous, and includes numerous symbiotic xanthellæ.

1. Nassella thalassicolla, n. sp.

Central capsule spherical. Podoconus with simple circular porochora, half as long as the capsule. Nucleus spherical. Numerous oil-globules in the endoplasm. Calymma spherical, without pigment, with numerous xanthellæ and large alveoles.

Dimensions.—Diameter of the central capsule 0.12, nucleus 0.04, calymma 0.6.

Habitat.—South Pacific, Station 300 (off Juan Fernandez), surface.

2. Nassella nassiterna, n. sp.

Central capsule ovate. Podoconus two-thirds as long as the capsule, trifid, with three equal circular lobes (as in Cystidium inerme). Nucleus ovate. Three equal large oil-globules in the endoplasm, corresponding to the three lobes of the porochora. Calymma ovate, in the upper half much more voluminous than in the lower, including numerous large alveoli and xanthellæ, and around the mouth masses of black pigment.

Dimensions.—Diameter of the central capsule 0.1, nucleus 0.03, calymma 0.8.

Habitat.—Indian Ocean, Madagascar (Rabbe), surface. 



Plectoidea vel Plectida, Haeckel, 1881, Prodromus, p. 423. Plagiacanthida (sensu ampliori), R. Hertwig, 1879, Organismus d. Radiol., p. 72.

Definition.— with a rudimentary, originally tripodal skeleton, composed of radial spines, arising from one common central point or central rod; the spines are simple or branched, and the branches may form by concrescence of their meeting ends a loose wickerwork, but never a complete lattice-shell. Never a ring in the skeleton. 