Physiology

The perivisceral coelom or body cavity is the main circulatory system within the central disc, arms and pinnules in crinoids (Ruppert et al 2004). The perivisceral coelom mainly occupies the central disc where it surrounds the gut and axial organ which is a large blood vessel that holds a collection of blind-ended epithelial,membranous tissue, tubes that have an unknown function (Ruppert et al 2004). The perivisceral coelom then branches into the arms and pinnules where the arms have a bilateral pair of oral coelomic cavities and unpaired aboral cavity (Ruppert et al 2004). Branches from the oral and aboral cavities are connected to the pinnule where it joins the arm, and are coupled via canals along the length of the pinnule (Ruppert et al 2004). These aboral and oral cavities play roles similar to veins and arteries in the human body in regards to the flow of fluid, with the aboral cavity carrying outbound ciliary flow from the disc (arteries) while the oral cavities carry an inbound flow (veins). These coelomic cavities throughout the crinoid body are also subdivided by mesenteries, folds in the membrane, to create a network of communicating spaces (Ruppert et al 2004).

Respiration and Excretion

There are no specialized respiratory or excretory organs within the crinoid body plan but the tube feet play a principle role in respiration by being the key site for gas exchange (Ruppert et al 2004). The large surface area created by the numerous arms containing tube feet means that a special respiratory surface or organ would be unnecessary (Ruppert et al 2004). In regards to excretion it is a possibility that crinoids are ammonotelic, an organism that excretes soluble ammonia (Ruppert et al 2004).

Nervous System

There are three interconnected neural divisions within the crinoid nervous system (Ruppert et al 2004). The first division is mostly sensory and is called the oral ectoneural system, and consists of an oral nerve (intra-epidermal) ring around the mouth, with five rays (radial nerves) branching out onto each arm (Ruppert et al 2004). This system also supplies nerves to the sensory cells within the epidermis and tubefeet (Ruppert et al 2004). The other two divisions, the hyponeural and entoneural systems, are related to motor function and are found in the connective tissues of the body (Ruppert et al 2004). The hyponeural system resembles the oral ectoneural system in regards to an oral ring as the center,with branching rays (radial nerves) extending down the lengths of the arms and pinnules to supply nerves to the musculature of the tube feet and other structures (Ruppert et al 2004). The last division the entoneural system is the principle motor system and is centered in a large, cup-shaped mass in the apex of the calyx, with branching nerves extending to the flexor muscles within the arms and pinnules (Ruppert et al 2004).

Chemical Defense

Comatulid crinoids, such as C. glebosus, use a number of polyketide compounds as chemical defenses which include a number of chemicals such as sulphuric acids, esters and derivatives as well as undefined water-soluble components that breakdown into polyketides (Rideout et al 1979). These chemicals may provide a chemical defense mechanism for crinoids by rendering them inedible to likely predators, as previous studies have found that several species of fish are deterred from eating food that include chemicals like those found in crinoids (Rideout et al 1979).

During observational and experimental studies of the C. glebosus individuals collected from Stradbroke Island’s Amity Point, the water it was housed in during movement between the aquaria and laboratory was tainted by a substance that turned the water and human skin yellow. It is believed that this was release of chemicals from the individuals during a stressful situation as there was no trace of these chemicals within the tank it resided in within the aquaria.

Autonomy and Regeneration

Autonomy and Regeneration, the separation and regrowth of body parts, is common in many echinoderms (Emson and Wilkie 1980) with many crinoid comatulids, like C. glebosus, discarding arm parts, such as pinnules, arms and cirri, (Oji and Okamoto 1994) and then regenerated them later on (Hyman 1955). Autonomy can occur in comatulids due to breakage from wave action, entanglement in seaweed, physical disturbances, intense sunlight, high temperatures, or other unfavorable conditions (Perrier 1873, Hyman 1955). The rate of regeneration of crinoid arms varies on the number of other regenerating arms, the length of the remain arm part, the species and the reason for autonomy (e.g. bad environmental conditions would slow rate of regeneration) but overall it seems that the rate of regeneration per arm decreases slightly with the more arms that are amputated ,while the total rate of formation of new arm tissue per individual increases (Mladenov 1983).

A number of pinnules and arms were lost during the observational and experimental studies of the C. glebosus individuals collected off Stradbroke Island’s Amity Point due to manual handling and stressful conditions, but regeneration of these arm parts were seen over the course of the observational studies.