Cirri of the stalked crinoidMetacrinus rotundus: neural elements and the effect of cholinergic agonists on mechanical properties

Abstract

Sea lilies are enigmatic animals due to their scarcity and their biology is comparatively neglected. Cirri, arranged in whorls of five along the sea lily stalk, anchor and support the animal. They consist of ossicles interconnected by collagenous ligaments and by a central canal. Cirri have a well-developed nervous system but lack muscular cells. A light and electron microscopic study was performed to clarify the morphology of the nervous system of the cirri. Two cellular networks were found, one of neuron-like cells and one of cells filled with bullet-shaped organelles. Both networks ramify throughout the cirral ossicles up to the interossicle ligaments. Mechanical tests were performed to analyse the influence of cholinergic agonists on the mechanical properties of these ligaments. In the tests, the cirral ligaments softened after the application of acetylcholine, muscarinic agonists and nicotinic agonists. The reaction time to muscarinic agonists was much slower than to acetylcholine and nicotinic agonists. At low concentrations, muscarinic agonists caused active development of force. No reaction to stimuli was observed in anaesthetized cirri. The data clearly establish the existence of catch connective tissue which can change its mechanical properties under nervous control mediated via nerves with cholinergic receptors. The possible sources of the observed force production are discussed and it is concluded that active contraction of collagenous ligaments causes movement of cirri.

Physiological and immunocytochemical evidence that glutamatergic neurotransmission is involved in the activation of arm autotomy in the featherstarAntedon mediterranea(Echinodermata: Crinoidea)

“…These caused diarthrial flexion that was succeeded by syzygial fracture only rarely (particularly after large-magnitude diarthrial flexions that might have caused tissue damage and secondarily initiated the autotomy response). Both a muscarinic agonist (acetyl--methylcholine) and a nicotinic agonist (nicotine) produced diarthrial flexion, which is compatible with reports that acetylcholine, muscarinic agonists and nicotinic agonists cause destiffening of the aboral arm ligaments and cirral ligaments of a stalked crinoid (Birenheide et al, 2000;Motokawa et al, 2004) and suggests that both muscarinic and nicotinic acetylcholine receptors are involved. This would not be peculiar to echinoderm ligaments as muscarinic and nicotinic cholinoceptors co-exist in echinoderm muscles (Devlin, 2001).…”

Tensilin-like stiffening protein fromHolothuria leucospilotadoes not induce the stiffest state of catch connective tissue

“…These unique tissues include catch connective tissue (mutable connective tissue) and contractile connective tissue. Catch connective tissue changes its passive mechanical properties but is not contractile in the physiological condition, unlike the contractile connective tissue of crinoids (Birenheide and Motokawa, 1996;Birenheide et al, 2000;Motokawa et al, 2004). Catch connective tissue was regarded as one of the main characteristics of members of the phylum Echinodermata and was believed to have played a key role in the success of this phylum (Motokawa, 1988).…”

Regrowth of the stalk of the Sea lily, Metacrinus rotundus (Echinodermata: Crinoidea)

“…Fortunately, the isocrinid sea lily Metacrinus rotundus lives at relatively shallow depths of just 100 to 150 m in Suruga Bay and Sagami Bay in Japan, making it easier for biologists to obtain a variety of information on living stalked crinoids, for example, information about their crown regeneration, physiology, and embryology (Amemiya and Oji, '92;Birenheide and Motokawa, '94;Birenheide et al, 2000;Nakano et al, 2002Nakano et al, , 2003.…”