Structure and function of the Nautilus statocyst

Abstract

SUMMARYThe two equilibrium receptor organs (statocysts) of Nautilus are ovoid sacks, half-filled with numerous small, free-moving statoconia and half with endolymph. The inner surface of each statocyst is lined with 130 000-150 000 primary sensory hair cells. The hair cells are of two morphological types. Type A hair cells carry 10-15 kinocilia arranged in a single ciliary row; they are present in the ventral half of the statocyst. Type B hair cells carry 8-10 irregularly arranged kinocilia; they are present in the dorsal half of the statocyst. Both type of hair cells are morphologically polarized. To test whether these features allow the Nautilus statocyst to sense angular accelerations, behavioural experiments were performed to measure statocyst-dependent funnel movements during sinusoidal oscillations of restrained Nautilus around a vertical body axis. Such dynamic rotatory stimulation caused horizontal phase-locked movements of the funnel. The funnel movements were either in the same direction (compensatory funnel response), or in the opposite direction (funnel follow response) to that of the applied rotation. Compensatory funnel movements were also seen during optokinetic stimulation (with a black and white stripe pattern) and during stimulations in which optokinetic and statocyst stimulations were combined.These morphological and behavioural findings show that the statocysts of Nautilus, in addition to their function as gravity receptor organs, are able to detect rotatory movements (angular accelerations) without the specialized receptor systems (crista/cupula systems) that are found in the statocysts of coleoid cephalopods. The findings further indicate that both statocyst and visual inputs control compensatory funnel movements.

Guidelines for the Care and Welfare of Cephalopods in Research –A consensus based on an initiative by CephRes, FELASA and the Boyd Group

“…In Nautilus the shell should be vertical; however, air bubbles can become trapped in the eyes and under the hood, leading to adverse health effects. 221,222 Information on treatments related to poor health conditions is available in Barord et al 223 Trapped air can be released by slowly turning the animal, laterally from side to side. All cephalopods have well-developed statocyst systems to maintain body posture and coordinate body position with eye orientation 224 so an abnormal body posture may indicate a nervous system problem or a physical defect that the animal cannot compensate for (e.g.…”

“…In Nautilus the shell should be vertical; however, air bubbles can become trapped in the eyes and under the hood, leading to adverse health effects. 221,222 Information on treatments related to poor health conditions is available in Barord et al. 223 Trapped air can be released by slowly turning the animal, laterally from side to side.…”

Comparative and functional anatomy of the mantle margin in ark clams and their relatives (Bivalvia: Arcoidea) supports association between morphology and life habits

“…Alternatively, these ciliated cells might perform sensory functions. Sensory cells with a single or few cilia were described for other mollusks as well, such as the mechanoreceptor cells in the statocyst of Nautilus pompilius (Neumeister & Budelmann, 1997).…”

New Eocene Coleoid (Cephalopoda) Diversity from Statolith Remains: Taxonomic Assignation, Fossil Record Analysis, and New Data for Calibrating Molecular Phylogenies

“…Two statocysts, one on the left part, the other on the right, occur in the cartilaginous skull of all coleoid species [ 17 ]. Nautiloids have tiny statoliths named statoconia [ 19 , 20 ]. They are ovoid and about 10 μm in size [ 21 ].…”