The apical end of the rotifer usually narrows suddenly beyond the curve of the gut and the cloacal aperture to form the foot of pseudopodium which ends in an organ of attachment, a pair of movable toes, each with the opening of a cement-gland (gl) at its tip. Thus for orientation we place the rotifer like the cuttle-fish, head downwards: the ciliated disk is basal or oral, proximal to the rest of the animal, the foot is apical, and the brain and cloacal aperture are anterodorsal.
As a rule, the wall of the ovary is continued into a uterine tube opening into the cloaca; but in Philodinaceae this is absent, and the young are free in the body cavity and escape by perforating the cloacal walls.
Un like the molluscs and annelids, however, the cloacal invagination lies outside this region, and the foot is formed by an elongation of the end of the body between the two apertures.
Open into a cloacal slit on the surface of the body.
Cl, Cloacal or pallial chamber of Neomeniae and Chaetoderma.
Into the groove open mucous glands, a large one anteriorly and another opening into a posteriorly cloacal, branchial cavity.
- In Neomeniidae and most of the Parameniidae there is a circlet of gills on the inner walls of the cloacal chamber.
Slender, tapering behind, with subventral cloacal orifice; thin cuticle without papillae; flattened spicules; no gills.
Short, truncate in front and behind; cloacal orifice transverse; gills present; rather thin cuticle; no radula.
- Aplacophora without distinct ventral groove, with single median unisexual gonad, with differentiated hepatic sac, and with cloacal chamber furnished with two bipectinate gills.
Little thicker than the an terior; the posterior ex tremity forms the enlarged funnel-like branchial or cloacal chamber.
The other pair lies just within the lips of the cloacal opening.
The mouth and cloacal aperture are generally at opposite ends of the ventral surface.
Into this same cloacal chamber open ventrally a pair of ciliated tubes communicating by funnels with the coelom (Nansen and Wheeler); these are possibly nephridia, and excretory in function.
A, Cloacal aperture.