Life History & Behaviour

Reproduction

In the weeks leading up to reproduction crinoid start to produce excess amounts of mucus. The increase in production of mucus starts in September, just prior to the spawning season (Holland andGrimmer, 1975). This can be confirmed by in the in field observation of slimy crinoid during the month of September (Fig. 1). Spawning tends to occur late spring to summer when the plankton is most abundant (Boolootian,1966) (Fig. 2).

Figure 1. Collection of Comanthus gisleni out on the “pie crust” and coral rubble region on Heron Island Reef.

Crinoids congregate to spawn and the increase mucus required disperse pheromones. However, Holland and Grimmer (1975) did discuss the fact that male crinoids can spawn without forming congregation, leading to the conclusion the spawning events are based on environmental signals. Revision of this larval stages have now split into two stages: the first is a non-feeding auricularia stage with partly longitudinal ciliary bands and the second is a doliolaria larva with circumferential ciliary bands (Nakano etal., 2003).


Figure 2. A red Comanthus spawning. Adapted from Flickster.

Juvenile stage of comatulids (stalk-less crinoids) have a stage in which they are anchored to a hard surface like stalked crinoids. They attach and cement to a hard surface using a calcium carbonate compound and remain sessile until they're mature (Holland andGrimmer, 1975). The genera will determine the developmental period to maturity. Some genera take years to develop into a free-living form and other take less than a month. The length of development is relative to life-span; if they are long lived crinoids, development is also long.

At the end of development comatulids have a calyx (cup) and crown (arms). They cast off from their attachment site to begin a free-swimming existence. Once the young comatulids assume free life, it mode of attachment is via aboral organs called cirri. It is use to a projected object on the substrate and apart from the temporary swimming phases of short duration, assumes an essentially sedentary life on the sea floor or on some fixed or floating object (Boolootian,1966).

Most crinoids are nocturnal and shelter themselves on the under side of over-hanging or branching live coral, coral rubble or in cavities of sponges during the day. At night they move by their preferred mode of movement to a position for feeding. Interestingly, crinoids can attach facing down towards the sediments or any orientation. Meaning they aren't restricted to particular orientations in the marine environment.

Feeding

When feeding crinoids take up a position that projects their arms above their oral surface (“fishing” position) (fig. 3). With the expansion of the arms into the water column they either sit motionless or alternate the arms in a scooping action to sieve the water.

They are covered in a mucus that is used like a spiders web to capture prey. The mucus is excreted from specialized glands in the tube feet. The mucus can be ejected from the tube feet in a mechanical motion to entangle the organism (Holland andGrimmer, 1975). It contains toxins that are paralytic to plankton and small crustaceans. Once a prey is captured it is shifted down the ambulacral grooves that contains the tube feet. The groove diverges from the mouth and then divides on at each radiate, each arm and terminates at the end of each pinnule. Therefore, dependent on where a prey item is caught the food is filter down to the mouth in a wafting motion.

The preys in which crinoids consume are limited by the size of the ambulacral groove (its diameter), because of this often diatoms, algal fragments, plankton, small crustaceans and larva of larger organism can be found in the stomach of crinoids (Boolootian,1966). Tropical species are directly dependent upon water movements for renewing stocks of floating organisms to feed upon. However, in the summer months the density phyto- and zoo- plankton increases dramatically in which water flow is negligent.

Figure 3. Feeding using the scooping pattern. Plankton was placed in the tank to maintain vitality of crinoids in captivity. Please note all specimens were returned once experiments were completed.

Movement

The locomotion of crinoids varies significantly from stalked to stalkless species. Stalked crinoids are limited to the length of their stalk and circular region surround them. Stalkless individuals have complex modes of movement dependent on the sequence of arm movement.

There are two types of stalkless movements - Swimming and Creeping. Comanthus gisleni utilizes the creeping movement (Refer to video below). The genera Comanthusis one of the most active creepers found within the family of Comasteridae. This can be verified by the fast rate at which individual Comanthus gisleni specimens reacted in experiment 2 (Refer to “Ecology” for further information). Creeping involves the use of cirri (not always - not in this species), the centro-dorsal plate and aboral surface of the crown to move in the direction of interest.

Respiration and Gas Exchange

The small size and large surface area of Crinoids enable them to respire through their tube feet located across a significant proportion of the oral dermis (Ruppert etal., 2004).