Hair Cell Interactions in the Statocyst of Hermissenda

Hair cells in the statocyst of Hermissenda crassicornis respond to mechanical stimulation with a short latency (<2 ms) depolarizing generator potential that is followed by hyperpolarization and inhibition of spike activity. Mechanically evoked hyperpolarization and spike inhibition were abolished by cutting the static nerve, repetitive mechanical stimulation, tetrodotoxin (TTX), and Co⁺⁺. Since none of these procedures markedly altered the generator potential it was concluded that the hyperpolarization is an inhibitory synaptic potential and not a component of the mechanotransduction process. Intracellular recordings from pairs of hair cells in the same statocyst and in statocysts on opposite sides of the brain revealed that hair cells are connected by chemical and/or electrical synapses. All chemical interactions were inhibitory. Hyperpolarization and spike inhibition result from inhibitory interactions between hair cells in the same and in opposite statocysts.     

Fine structural study of the statocysts in the veliger larva of the nudibranch,Rostanga pulchra

Summary The two statocysts of the veliger larva of Rostanga pulchra are positioned within the base of the foot. They are spherical, fluid-filled capsule that contain a large, calcareous statolith and several smaller concretions. The epithelium of the statocyst is composed of 10 ciliated sensory cells (hair cells) and 11 accessory cells. The latter group stains darkly and includes 2 microvillous cells, 7 supporting cells, and 2 glial cells. The hair cells stain lightly and each gives rise to an axon; two types can be distinguished. The first type, in which a minimum of 3 cilia are randomly positioned on the apical cell membrane, is restricted to the upper portion of the statocyst. The second type, in which 9 to 11 cilia are arranged in a slightly curved row, is found exclusively around the base of the statocyst. Each statocyst is connected dorso-laterally to the ipsilateral cerebral ganglion by a short static nerve, formed by axons arising from the hair cells. Ganglionic neurons synapse with these axons as the static nerve enters the cerebral ganglion. The lumen of the statocyst is continuous with a blind constricted canal located beneath the static nerve.A diagram showing the structure of the statocyst and its association with the nervous system is presented. Possible functions of the statocyst in relation to larval behavior are discussed.     

Mosaic arrangement of SCPb-, FMRFamide-, and histamine-like immunoreactive sensory hair cells in the statocyst of the gastropod mollusc Pleurobranchaea japonica

A pair of statocysts are located in the periganglionic connective tissue of the pedal ganglia of the opisthobranch mollusc Pleurobranchaea japonica. Light- and electron-microscopic observations show that the sensory epithelium of the statocyst consists of 13 disk-shaped hair cells. Each hair cell sends a single axon to the cerebral ganglion through the static nerve. Neurotransmitters in the hair cells were examined by means of immunocytochemistry. Our results show that the 13 sensory hair cells include two SCPB-, three FMRFamide-, and eight histamine-like immunoreactive cells. One hair cell contains a transmitter substance other than SCPB-, FMRFamide, histamine, serotonin, or GABA. One of the two SCPB-like immunoreactive cells, located in the ventral region of the statocyst, is the largest cell in the statocyst. The other, located in the anterodorsal region, shows co-immunoreactivity to both SCPB and FMRFamide antisera. Among the three FMRFamide-like immunoreactive hair cells, one is located in the posteroventral region, separated from the other two, which are adjacent to each other in the anterodorsal region. All the eight histamine-like immunoreactive hair cells are adjacent to one another, occupying the remainder of a triangular pyramid-shaped region. These immunoreactive cells are symmetrically placed in the right and left statocysts. This mosaic arrangement was identical among specimens. Thus the static nerve may code information about position or movement of the statoliths, with the use of different transmitters in the mosaic arrangement of the hair cells.     

Ultrastructure of the Statocysts in the Apodous Sea Cucumber Leptosynapta inhaerens (Holothuroidea, Echinodermata)

The burrowing sea cucumber Leptosynapta inhaerens possesses five pairs of statocysts, one pair on either side of each radial nerve cord where it arises from the circumoral nerve ring. The nerve cords exhibit only ectoneural components at the level of the statocysts. A sinus-like epineural canal lies superjacent to each cord. This canal is lined by a robust monociliated neuroepithelium which lacks any special support cells. Beneath the neuroepithelium, the somata of the ectoneural neurons form a perikaryal layer whereas the axons are located within the proximal parts of the cords. Glial cells have not been found. Each statocyst is a hollow sense organ. Its central cavity is lined by a monolayer of monociliated parietal cells. Axons of these parietal cells extend towards the statocyst nerve which connects each statocyst with the ectoneural pathways of the cord. A single lithocyte floats within each central statocyst cavity. This unciliated cell contains a voluminous vacuole with the statolith and several smaller vacuoles. It is concluded that statocysts do not belong to the basic organization of the Holothuroidea but have been evolved within this group. The statement, that the statocysts of apodous sea cucumbers and that of the enigmatic Xenoturbella bocki are homologous organs, is rejected.     

Ultrastructural aspects of nervous-system and statocyst morphogenesis during embryonic development of Convoluta psammophila (Turbellaria,Acoela)

The notion that statocysts originated from an infolding of ectoderm lined by ciliated sensory cells has been challenged with evidence of capsule-limited, non-ciliary statocysts in several independent phyla. Statocysts in turbellarians primitively lack cilia and are embedded within or closely adjoined to the cerebral ganglion; they are likely to be derived from nervous tissue. We investigated the development of the simple statocyst in an acoel turbellarian, a statocyst consisting of three cells. Observations of serial TEM sections of embryos at different stages of development support the hypothesis of an inner (non-epithelial) origin of the statocyst. First, a three-cell complex is delimited by a basal lamina; it then undergoes cavitation by swelling, autophagy, and fluid secretion. The statocyst becomes discernible within the precursor ganglion cells while they still contain yolk inclusions. The two outer (parietal) cells, enclosed together by a 10-nm-thick basal lamina, arrange themselves in an ovoid of about 10 µm diameter and surround the inner statolith-forming cell. The statolith is formed later within vacuoles of the statolith-forming cell.     

The neuron of the fast conducting system in hirudo medicinalis: identification and synaptic connections with primary afferent neurons.

A single neuron, located in the center of each segmental ganglion of H. medicinalis is antidromically activated by electrical stimulation of the ventral cord anteriorly and posteriorly to the ganglion, at the same threshold as the fast conducting system (FCS) and with a latency equal to the FCS conduction time. This neuron is activated trans-synaptically by tactile and photic stimulation of the skin and by stimulation of high-threshold fibres running along the cord. A spike evoked by intracellular stimulation of this neuron propagates along the FCS. Intracellular staining shows that this neuron sends two axonal branches in the anterior and posterior median connectives. Direct electrical stimulation of touch cells (T cells), as well as mechanical stimulation of the skin, lowers the threshold of and may eventually fire, the FCS neurons, not only at the level of the ganglion to which they belong, but also at the level of the neighbouring ganglia. This effect is mediated by bilateral pathwasy located in the lateral connectives. It is concluded that the FCS consists of a chain of single neurons, located in each ganglion and electrotonically coupled to each other. Touch cells project with excitatory synapses on the FCS neurons.     

Structure and function of the Nautilus statocyst.

The two equilibrium receptor organs (statocysts) of Nautilus are avoid 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.     

Influence of Microgravity on Cellular Differentiation of Root Apical Meristematic Cap in Rice Seedling

Three groups of experimental treatment of rice seeds were designed: (1) As control,the seeds were germinated(1–3 days after imbibition) and sprouted (4–7 days after imbibition) at static state, (2) Seeds were germinated under microgravity simulated by the horizontal clinostat,and (3) Seeds were germinated at the static state and sprouted under microgravity. The differentiation of the apical meristematic cap of the seedling was observed. 1. Germination and sprouting in the static state (CK), the root apical meristematic cap cells could differentiate into statocysts which could sense the least irritation of the gravity. The amyloplasts of statocysts deposited in the distal region,later changed into secretory cells ,and finally resulted in exocytosis which led the root tip cells to fall off during the cap growth. 2. The rice seedlings germinating and sprouting under microgravity,the apical meristematic cap cells differentiated into statocysts but the amyloplasts in the statocyst were distributed throughout the cell and a central vacuole was formed. The statocysts could form nonsecretory cells similar to the cells in the dividing and elongating area without exocytosis. The number of the root cap cell layers increased and root cap elongated. 3. The rice seedlings germinating in the static state and sprouting under micro-gravity,the amyloplasts of the statocyst were scattered in the cell. The statocysts became vacuolized quickly but remaind on the root cap.     

Über Bau und Funktion der Statocyste bei der Schnecke Aplysia limacina

Zusammenfassung Die Statocyste von Aplysia limacina zeigt in ihrem Bau keine wesentliche Abweichung vom durchschnittlichen Gastropoden-Typ. Besondere statolithfreie Räume oder Sinneshaare, wie sie von Tieren mit echtem Rotationssinn bekannt sind, wurden nicht angetroffen.Frei schwimmende, aus ihrer Normallage gebrachte Aplysien zeigen Lagekorrekturbewegungen, bei denen der Kopfteil führt. Auch fixierte und im Wasser hochgehobene Aplysien zeigen nach Drehung um horizontale Achsen kompensatorische Kopfstellreflexe. Auf Drehung um die Vertikalachse wird nicht reagiert. Einseitige Entstatung (Durchschneidung des N. staticus) ruft keinen, beiderseitige Entstatung einen vollständigen Ausfall der statischen Lagekorrektur- und Reflex-bewegungen hervor; die schwimmende Aplysia vollführt dann Purzelbäume. Taktile Reize vom Untergrund unterstützen die Lageorientierung. Ein orientierender Lichteinfluß machte sich nicht geltend.Nach einseitiger Durchschneidung des Cerebro-Pedal-Konnektivs reagiert eine fixierte Aplysia nur mehr in ipsilateraler Seitenlage mit der kompensatorischen Kopfdrehung zur intakten Seite hin; in kontralateraler Seitenlage wird nicht mehr reagiert. Das Ergebnis der Ausschaltversnche (Tabelle, S. 49) führt zu Schluß-folgerungen über den Verlauf der statischen Reflexbahnen, die in einem Diagramm (Abb. 7, S. 53) zusammengefaßt sind.Diese und andere Befunde werden in Zusammenhang mit den Ergebnissen früherer Autoren diskutiert. Bezüglich des Reizvorganges wird angenommen, daß auch in der Schneckenstatocyste Scherung der Cilien den effektiven, physiologisch adäquaten Reiz darstellt.

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Structure and functioning of the statocyst in the gastropod Aplysia limacina

Summary The statocyst of Aplysia limacina is a rounded vesicle with a diameter of 200–250 . Its wall is composed of two kinds of cells. The outer supporting cells are separate cells in fresh tissue; only under the influence of pressure or fixing agents their walls burst and artificial syncytia are created. The inner sense or giant cells are on their inner surface covered with motile cilia. Each statocyst of Aplysia contains 13 sense cells; their nervous offshoots constitute the statocyst nerve which runs towards the cerebral ganglion. The statolith is a cluster of about 1000 loosely aggregated chalk particles (statoconia). It fills the greater part of the statocyst lumen and is lightly moved by the cilia. Special statolith-free cavities or sense hairs, such as are known from animals with a true rotation sense, were not found in the statocyst of Aplysia.Freely swimming Aplysiae perform correction movements with their head leading, when they are brought out of their normal position in space. Likewise, fixed Aplysiae, when lifted up in the water and rolled or tilted about horizontal axes, show compensatory static head reflexes. Rotation around a vertical axis causes no response. Unilateral section of the statocyst nerve causes neither a loss of the position reflexes nor any asymmetry of posture or movement. Bilateral section of this nerve, however, abolishes all correction movements and compensatory reflexes; swimming animals perform somersaults. Tactile stimuli from the underground support the animal's spatial orientation. An orienting influence of light was not observed.After unilateral section of the cerebro-pedal connective a fixed Aplysia only responds when rolled the towards ipsilateral side (with a compensatory turn of the head towards the contralateral side); when rolled 90° towards the controlateral side no reaction occurs. The results of the elimination experiments (Table, p. 49) lead to the following conclusions: 1) from each statocyst two reflex pathways originate, one of which is activated after a roll around the long axis to the left side and causes a head turn to the right, whereas the other one comes into action after a roll to the right side and causes a head turn to the left; 2) the pathways of both statocysts which turn the head to the left run from the cerebral ganglion through the left cerebro-pedal connective towards the left pedal ganglion; both pathways which turn the head to the right run through the right cerebropedal connective towards the right pedal ganglion (diagram, Fig. 7, p. 53).These and other results are discussed in relation to data of earlier investigations. The course of the static nerve as shown morphologically to occur in other gastropods resembles closely the pathways postulated for Aplysia on physiological grounds. With regard to the process involved in stimulation it is assumed that in the statocyst of gastropods, like in other static organs, a shearing force exerted on the cilia represents the effective, physiologically adequate stimulus. Recent findings about the submicroscopical structure of the cilia in the statocyst of gastropods as well as about the mechanical sensitivity of motile cilia give this assumption strong support.

     

Modification of statocyst input to local interneurons by behavioral condition in the crayfish brain

Posture control by statocysts is affected by leg condition in decapod crustaceans. We investigated how, in the crayfish brain, the synaptic response of local interneurons to statocyst stimulation was affected by leg movements on and off a substratum. The magnetic field stimulation method permitted sustained stimulation of statocyst receptors by mimicking body rolling. The statocyst-driven local interneurons were classified into four morphological groups (Type-I–IV). All interneurons except Type-IV projected their dendritic branches to the parolfactory lobe of the deutocerebrum where statocyst afferents project directly. Type-I interneurons having somata in the ventral-paired lateral cluster responded invariably to statocyst stimulation regardless of the leg condition, whereas others having somata in the ventral-unpaired posterior cluster showed response enhancement or suppression, depending on the cell, during leg movements on a substratum, but no response change during free leg movements off the substratum. The synaptic responses of Type-II and IV interneurons were also affected differently by leg movements depending on the substratum condition, whereas those of Type-III remained unaffected. These findings suggest that the statocyst pathway in the crayfish brain is organized in parallel with local circuits that are affected by leg condition and those not affected.     

Morphological characteristics of chemosensory,visual, and statocyst pathways in the snailHelix lucorum

The following structural characteristics of the chemosensory, visual, and vestibular pathways of the snail (Helix lucorum) were demonstrated by using a variety of histological techniques. Large and small neurons of the tentacle ganglion, the bipolar cells of the olfactory nerve, and a proportion of optic tentacle bulb chemoreceptors within the olfactory nerve all send their processes to the CNS of the mollusk. Here they are divided up into numerous bundles of fibers in the neuropil of the ipsilateral cerebral ganglion. They are joined by processes from the central nervous system put out by all neurons of the protocerebrum and the cluster of cells of the commissural section of the metacerebrum. Ocular receptors do not send processes down below the enlargement of the upper optic nerve. This enlargement is also the site where processes from cells within the CNS and the nerve itself terminate. An area of arborization of processes from the visual pathway cells is located in the neuropil of the pleural portion of the metacerebrum. Hair cells of statocysts put out processes to the cerebral ganglion, whence axons of small metacerebral neurons extend towards the organ of balance. Some processes from vestibular pathway cells form an arborization zone at the ipsilateral cerebral ganglion, while others pass through the cerebral commissure to form their area of arborization in the contralateral ganglion. Processes from vestibular and visual pathway cells arborize in exactly the same area.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 7–16, January–February, 1986.     

The ultrastructure of the statocysts in the pediveliger larvae of Pecten maximus (L.) (Bivalvia)

The pediveliger of Pecten maximus (L.) has a pair of statocysts situated at the base of the foot on either side of a bilobed pedal ganglion. The statocysts consist of a spherical sac connected to the mantle cavity by a cylindrical ciliated canal. Within the sac there are statoconia which are variable both in shape and structure. The cells of the sac are joined by septate desmosomes. There is a non-ciliated cell in each sac containing a variety of granules some of which resemble certain of the statoconia. The remainder of the sac is composed of hair cells, which bear a circular array of radiating cilia. The basal bodies and horizontal striated roots of these cilia are directed radially. The hair cells give rise to thin processes which probably join together to form the static nerve. This nerve runs from the static canal to the pleural ganglion.     

Central neuronal pathways of the cardioinhibitory reflex in the isopod crustacean Bathynomus doederleini

We have already identified central neurons for cardioinhibition and cardioacceleration in Bathynomus, an isopod crustacean. The 1st thoracic ganglion (TG1) has cardioinhibitory neurons, which we call CIs, while the 2nd and 3rd thoracic ganglia (TG2 and TG3) have cardioacceleratory neurons, which we call CA1s and CA2s. We examined neuronal pathways for cardioinhibitory reflexes in whole animal preparations, using intracellular and extracellular recording methods. Cardiac inhibition in response to a variety of external stimuli was mediated by activation of CIs and inhibition of both CAs. When preparations had the ventral nerve cord intact, CIs were activated by excitatory postsynaptic potentials and CAs were inhibited by inhibitory postsynaptic potentials in response to tactile stimuli applied to sensilla setae on appendages and afferent stimuli applied to ganglionic roots of the thoracic ganglia. However, stimulation of ganglionic nerve roots of TG2 and TG3, or tactile stimulation of the body surface, failed to evoke inhibition of CAs in preparations in which both the cerebral ganglion and TG1 had been excised. These results suggest that TG1 is an indispensable central region for the excitation of CI and for inhibition of CA neurons, induced by tactile stimuli and by stimuli applied to nerve roots of TG2 and TG3.     

Single neurone responses to tactile stimulation of the heart in the snail,Helix pomatia L.

Summary The electrical activity of the heart nerve and of single neurons in the suboesophageal ganglia were recorded during tactile stimulation of the heart. 15 neurons were identified which responded to heart stimulation by inhibiting or accelerating activity. Cells influenced by heart afferents are scattered in the visceral and in the right and left parietal ganglia.In most of the cases both decrease and increase of cell activity are caused by synaptic potentials, in some cases, however, the neuron is assumed to have a sensory character.The activity of three neurons influenced by heart stimulation was conducted into the heart nerve. These cells are central neurons of a heart-CNS-heart reflex.Some of the neurons located in the right parietal and visceral ganglia have no connection with the mechanoreceptors of the heart. Since their spikes propagate into the heart nerve, they probably take part in the extracardial regulation of heart activity.One of the neurons located in the visceral ganglion (cell V12) sends its axon into the heart nerve. The response of this neuron to heart stimulation was an increase in activity and an inhibition of the heart rate. This is an inhibitory neuron of the extracardial heart regulatory system.     

Information processing at a central synapse suggests a noise filter in the auditory pathway of the noctuid moth

1. The central projections of the A1 afferent were confirmed via intracellular recording and staining with Lucifer Yellow in the pterothoracic ganglion of the noctuid moths, Agrotis infusa and Apamea amputatrix (Fig. 1). Simultaneous recordings of the A1 afferent in the tympanal nerve (extracellularly) and in the pterothoracic ganglion (intracellularly) confirm the identity of the stained receptor as being the A1 cell. 2. The major postsynaptic arborizations of interneurone 501 in the pterothoracic ganglion were also demonstrated via intracellular recording and staining (Fig. 2). Simultaneous recordings of the A1 afferent (extracellularly) and neurone 501 (intracellularly) revealed that each A1 spike evokes a constant short latency EPSP in the interneurone (Fig. 2Bi). Neurone 501 receives only monaural input from the A1 afferent on its soma side as demonstrated by electrical stimulation of each afferent nerve (Fig. 2Bii). EPSPs evoked in neurone 501 by high frequency (100 Hz) electrical stimulation of the afferent nerve did not decrement (Fig. 2Biii). These data are consistent with a monosynaptic input to neurone 501 from the A1 afferent. 3. The response of neurone 501 to a sound stimulus presented at an intensity near the upper limit of its linear response range (30 ms, 16 kHz, 80 dB SPL) was a plateau-like depolarization, with tonic spiking activity which continued beyond the end of the tone. The instantaneous spike frequency of the response was as high as 800 Hz, and was maintained at above 600 Hz for the duration of the tone (Fig. 3). 4. The relationship between the instantaneous spike frequency in the A1 afferent and that recorded simultaneously in neurone 501 is linear over the entire range of A1 spike frequencies evoked by white noise sound stimuli (Fig. 4). Similarly, the relationship between instantaneous spike frequency in the A1 afferent and the mean depolarization evoked in neurone 501 is also linear for all A1 spike frequencies tested (Fig. 5). No summation of EPSPs occurred for A1 spike frequencies below 100 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interaction between hair cells in the statocyst ofHelix lucorum

An electrophysiological study of interactions between hair cells within the statocyst ofHelix lucorum was undertaken by intracellular and extracellular recording. Analysis of the results led to the following conclusions. First, some hair cells, subtending on angle on the arc of the statocyst sphere of not more than 90°, were electrically connected; electrical synapses, moreover, possessed polar properties; the coefficient of coupling in one direction was about 10 times greater than the other. Second, some connections between hair cells which subtended an angle of not more than 90° were mixed electrochemical in character. The excitatory chemical component in this case was directed in a direction opposite to effective electrical conduction. Third, inhibitory connections were observed between statocyst receptors: monosynaptic chemical (subtending an angle of about 180°, evidently, between the hair cells) and polysynaptic weak inhibitory interactions (subtending an angle in this case of not less than 90–100° between the test neurons). Fourth, all types of connection between hair cells were observed in CNS preparations with the vestibular nerve divided close to the cerebral ganglion. This means that zones of synaptic contacts between these receptors are located not in the CNS, but close to the statocyst.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 2, pp. 230–239, March–April, 1985.     

A crustacean statocyst with only three hairs: Light and scanning electron microscopy

Standard histological and SEM techniques have been used to examine the pair of statocyst organs located in the telson of the isopod, Cyathara polita. Each organ is formed as an invagination of the dorsal cuticle of the telson. The invagination narrows to form a stalk between the statocyst and dorsal surface. A canal courses longitudinally through this stalk and forms a continuous channel between the lumen of the cyst and the external environment. On the luminal floor of each statocyst, there are three pits; each correlates with a nodule protruding from the ventro-medial wall. From each pit, a single, bifurcating hair projects dorsally to contact the single concretion within the statocyst lumen. No other static organs have been found in this animal. Thus, maintenance of equilibrium in this species appears to be under the control of but six hairs, three in each statocyst. Innervation of each statocyst is provided by a branch of a nerve which connects anteriorly with the last abdominal ganglion.     

Carbonic anhydrase is required for statoconia homeostasis in organ cultures of statocysts from Aplysia californica

A novel organ culture system has been developed to study the regulation of statoconia production in the gravity sensing organ in Aplysia californica. Statocysts were cultured in Leibovitz (L15) medium supplemented with salts and Aplysia haemolymph for four days at 17°C. The viability of the system was evaluated by examining four parameters: statocyst morphology, the activity of the mechanosensory cilia in the statocyst, production of new statoconia during culture and change in statoconia volume after culture. There were no morphological differences in statocysts before and after culture when ciliary beating was maintained. There was a 29% increase in the number of statoconia after four days in culture. Mean statocyst, statolith and statoconia volumes were not affected by culture conditions. The presence of carbonic anhydrase in the statocysts was shown using immunohistochemistry. When statocysts were cultured in the presence of 4.0 × 10^–4 M acetazolamide to inhibit the enzyme activity, there was a decrease in statoconia production and statoconia volume, indicating a role for this enzyme in statoconia homeostasis, potentially via pH regulation. These studies are the first to report a novel system for the culture of statocysts and show that carbonic anhydrase is involved in the regulation of statoconia volume and production.