3499. Body sacciform, mostly gelatinous, without head and eyes; species androgynous. They are destitute of independent locomotion, most of them being quite stationary or fixed, and surrounded frequently by a shell; some few float about passively in the sea.
Fam. 1. Infusorial Kracken—Salpæ.
The Salpæ are gelatinous, freely natant cylinders, perforated by an open tube, within which are situated the branchiæ, heart, mouth, intestine, and liver, without any tentacula. They continue to hang for a long time to each other, as though they were in the ovary.
They undergo a remarkable metamorphosis, which traverses two generations, the young meanwhile not resembling the mother but the grandmother.
Body within a sacciform mantle, with two opposite respiratory apertures.
Fam. 2. Polypary Kracken—Ascidiæ.
The Ascidiæ have a sacciform body with two co-approximate respiratory apertures; branchiæ internal and trellis-shaped.
These gelatinous or cartilaginous animals adhere firmly to rocks, with the respiratory apertures directed upwards as in the Mussels, but the branchiæ are not foliiform; the internal cavity is lined with a membranous sac, upon which the branchial vessels are dispersed in a trellis-like manner. At the bottom of and within the sac is the mouth, which is destitute of tentacula. Intestine, liver, and a heart that is simple or undivided. Mode of propagation unknown.
They are frequently connato-sessile, like the Polyps.
Fam. 3. Acalephan Kracken—Cirripedia.