Crinoids, or Anthometra adriani, are comprised of three basic sections; the stem, the calyx, and the arms. The stem is composed of highly porous ossicles which are connected by ligamentary tissue. The calyx contains the crinoid's digestive and reproductive organs, and the mouth is located at the top of the dorsal cup, while the anus is located peripheral to it. The arms display pentamerism or pentaradial symmetry and comprise smaller ossicles than the stem and are equipped with cilia which facilitate feeding by moving the organic media down the arm and into the mouth.
The crinoid nervous system is divided into three parts, with numerous connections between them. The uppermost portion is the only one homologous with the nervous systems of other echinoderms. It consists of a central nerve ring surrounding the mouth, and radial nerves branching into the arms. Below this lies a second nerve ring, giving off two brachial nerves into each arm. Both of these sets of nerves are sensory in nature, with the lower set supplying the pinnules and tube feet. The third portion of the nervous system lies below the other two, and is responsible for motor action. This is centred on a mass of neural tissue near the base of the calyx, and provides a single nerve to each arm and a number of nerves to the stalk.
There are three interconnected nervous subsystems:
1. The oral/superficial/ectoneural system: comprises a neural band beneath the ambulacral grooves of the arms and cirri, immediately beneath the epidermis, and innervates the podia. The five main bands converge to the mouth and form a nerve sheath along the wall of the digestive tract.
2. The deeper oral or hyponeural system: comprises a pentagon in the connective tissue of the tegmen, lateral to the water-vascular ring canal. It gives out nerves to the tegmen podia, the anal cone, the internal organs and ten radial nerves to the arms. These ten nerves fork to give two nerves per arm. These innervate the water-vessels, pinnules and podia.
3. The aboral or entoneural system: the main part of the nervous system in crinoids. (The oral system dominates in other echinoderms). It forms a cup-shaped mass in the apex of the calyx cavity and gives out nerves to the cirri (in comatulids) or to the column and hence also to the cirri at the nodes (in sea lilies). It gives out 5 brachial nerves to the arms. These contain ganglia that innervate the flexor muscles. The aboral nerve mass also gives out 5 lateral trunks, which fork into ten and are united by a pentagonal commissure (concentric with the main nerve mass) in the radial plates of the calyx.
The crinoid nervous system is divided into three parts, with numerous connections between them. The uppermost portion is the only one homologous with the nervous systems of other echinoderms. It consists of a central nerve ring surrounding the mouth, and radial nerves branching into the arms. Below this lies a second nerve ring, giving off two brachial nerves into each arm. Both of these sets of nerves are sensory in nature, with the lower set supplying the pinnules and tube feet. The third portion of the nervous system lies below the other two, and is responsible for motor action. This is centred on a mass of neural tissue near the base of the calyx, and provides a single nerve to each arm and a number of nerves to the stalk.
There are three interconnected nervous subsystems:
1. The oral/superficial/ectoneural system: comprises a neural band beneath the ambulacral grooves of the arms and cirri, immediately beneath the epidermis, and innervates the podia. The five main bands converge to the mouth and form a nerve sheath along the wall of the digestive tract.
2. The deeper oral or hyponeural system: comprises a pentagon in the connective tissue of the tegmen, lateral to the water-vascular ring canal. It gives out nerves to the tegmen podia, the anal cone, the internal organs and ten radial nerves to the arms. These ten nerves fork to give two nerves per arm. These innervate the water-vessels, pinnules and podia.
3. The aboral or entoneural system: the main part of the nervous system in crinoids. (The oral system dominates in other echinoderms). It forms a cup-shaped mass in the apex of the calyx cavity and gives out nerves to the cirri (in comatulids) or to the column and hence also to the cirri at the nodes (in sea lilies). It gives out 5 brachial nerves to the arms. These contain ganglia that innervate the flexor muscles. The aboral nerve mass also gives out 5 lateral trunks, which fork into ten and are united by a pentagonal commissure (concentric with the main nerve mass) in the radial plates of the calyx.