The animal feeds upon very minute organisms which are conveyed to the mouth by the action of the cilia lining the brachial grooves. The mouth in C. rosacea is sub-central, but in some Comatulids (Actinometra) it is quite excentric; while the anus is usually supported on a tubular projection and situated on one side. According to the researches of Dr W. B. Carpenter, the nervous system of Comatula consists of a fibrillar sheath surrounding a central quinquelocular vascular organ, and giving off a series of radial branches which differ from the radial nerve-cords of the other Echinoderms in not running along the ventral surface of the arms, but in occupying a median canal in the centre of each arm. While the principal nerve-cords have this position, and have a motor function, it has also been shown that there exists, as before remarked, a fibrillar band below the epithelial lining of the ventral furrow of each arm, and these bands are supposed to be of the nature of sensitive nerves. They spring from a circular band, which is placed round the gullet, above the ambulacral and blood-vascular rings. It has also been shown by modern researches, that there exists in Comatula a complicated blood-vascular system.

As regards the vascular system of the Crinoids generally, there is found in Comatula, occupying the dorso-ventral axis of the body, a largish lobated structure homologous with the heart of the Asteroids, and, like it, consisting of numerous closely-packed vessels. Dorsally, these resolve themselves into a central group (of one or more) and five peripheral vessels, the latter of which expand in the calyx into the five chambers of the "chambered organ," the chambers and axis alike giving branches to the dorsal cirri. In the pedunculate Crinoids in which there are no cirri, the chambers narrow again, and the group of vessels is continued down the central canal of the column. In Pentacrinus, which has cirri at regular intervals, the five peripheral vessels expand in each cirrus-bearing joint into five dilatations, which thus give rise to a miniature "chambered organ," each chamber of which gives off a single vessel to a cirrus. In the body, the vascular axis is connected with (1) a large network of vessels round the alimentary canal, (2) an extensive plexus beneath the ventral surface of the disc, in which vessels arise that run out into the arms and enclose the genital glands, and (3) a plexus of convoluted tubes depending from the oral blood-vascular ring in which the radial vessels of the arms originate (P. H. Carpenter).

The reproductive organs of Comatula are situated beneath the soft skin of the arms, and their ducts open into the pinnulae, by the rupture of the ventral integument of which the generative elements are set free into the surrounding water.

As regards the development of Comatula, the larva is at first cylindrical, with four transverse bands of cilia, a hinder tuft of cilia, and an alimentary canal furnished with a lateral aperture, its general aspect closely resembling that of the embryos of certain Annelides. The skeleton of the calyx is developed anteriorly, that of the column posteriorly, the former being the first to appear. In its early condition (fig. 106) the calycine skeleton consists of a row of five "basal" plates, which rest below upon the so-called " centro-dorsal plate," and are succeeded above by a cycle of five "oral" plates, in the centre of which the permanent mouth is finally developed. Five "radial" plates are next developed as a cycle between the oral and basal plates; and to the radials are rapidly added the plates of the arms proper (the "brachial" plates). Inferiorly, the centro-dorsal plate rests upon a short, jointed column (fig. 106, c), the lowest plate of which is expanded to form a disc of attachment; and the larva now passes into what is known as its "Pentacrinus stage." In the further progress of growth the arms increase in length, and the oral plates diminish in size and ultimately disappear. At the same time the centro-dorsal plate increases in size, so as to enclose the radial plates, which in turn become fused with one another, and remain only as the so-called "rosette" on the upper surface of the centro-dorsal. The latter also develops jointed cirri from its outer surface, and finally becomes detached from the next joint of the column below, when the animal enters upon its free stage of life.

Fig. 106.   Larva of Comatula (Antedon) rosacea, enlarged (after Sir Wyville Thomson). o o Oral plates; r r Radial plates ; b b Basal plates ; c d Centro dorsal plate ; c Column ; d Disc of attachment.

Fig. 106. - Larva of Comatula (Antedon) rosacea, enlarged (after Sir Wyville Thomson). o o Oral plates; r r Radial plates ; b b Basal plates ; c d Centro-dorsal plate ; c Column ; d Disc of attachment.

Numerous living forms of Comatula are known, and have been described under various subordinate types (Antedon, Actinometra, Comaster, and Phanogenia); and the group seems to be cosmopolitan in its distribution.