Tentacles Of Sea Anemones Research Articles

N-acetylneuraminic acid (NANA) stimulates in situ cyclic AMP production in tentacles of sea anemone (Aiptasia pallida): possible role in chemosensitization of nematocyst discharge.

Cnidocytes, the stinging cells of cnidarians, optimally discharge nematocysts in response to combined physical contact and stimulation of specific chemoreceptors. In the tentacles of certain sea anemones, the primary chemoreceptors bind N-acetylated sugars, such as N-acetylneuraminic acid (NANA). Sensitization with NANA predisposes contact-sensitive mechanoreceptors (CSMs) to trigger discharge in response to physical contact. In the ectoderm of sea anemone tentacles, cnidocyte/supporting cell complexes (CSCCs) control and trigger nematocyst discharge. Previous findings have implicated cyclic AMP (cAMP) as a second messenger in NANA-sensitized nematocyst discharge. However, no reports have directly demonstrated that the cAMP content of tentacles changes in response to NANA stimulation. We now show that NANA elevates in situ cAMP levels in a dose-dependent manner in the ectoderm of tentacles from the sea anemone Aiptasia pallida. However, the endoderm of tentacles shows no detectable cAMP response to NANA. The effect of NANA on the cAMP content of the ectoderm is biphasic. Micromolar NANA increases the in situ cAMP level, with a maximal response occurring at 1.8x10(-5)mol x l(-1) NANA. At higher NANA concentrations, the cAMP content decreases to that of controls. Because the cAMP dose/response curve to NANA coincides precisely with the dose/response curves of NANA-sensitized nematocyst discharge and nematocyst-mediated adhesive force, a second-messenger role for cAMP in NANA-sensitized nematocyst discharge is strongly suggested. The addition of isobutyl-1-methylxanthine (IBMX) to the medium with sea anemones increases tissue cAMP levels both in the absence and in the presence of NANA. However, anesthetizing anemones in sea water containing high levels of Mg(2+) blocks the NANA-stimulated cAMP response of the ectoderm. In addition, our results suggest that NANA-stimulated cAMP may activate endogenous cAMP-dependent protein kinase (PKA) in broken cell preparations of tentacles. Thus, NANA-stimulated cAMP may function as a second messenger in the NANA chemosensory signaling pathway controlling nematocyst discharge.

Reorganization of actin during repair of hair bundle mechanoreceptors.

Hair bundle mechanoreceptors can be damaged by over-stimulation or by exposure to calcium-free buffers. Provided the trauma is slight, hair bundles recover, although the subcellular mechanisms for such recovery are poorly understood. Hair bundle mechanoreceptors on tentacles of sea anemones are especially resilient, recovering from severe trauma within several hours. During the recovery period, large protein complexes are secreted called "repair proteins" containing replacement linkages for those lost during trauma. In the present study, we find that recovery requires reorganization of the actin-based cytoskeleton in hair bundles. F-actin is first partially depolymerized and then repolymerized in hair bundles based on confocal microscopy. Furthermore, stereocilia show considerable motility during repair based on field emission scanning electron microscopy of hair bundles fixed at 1 min intervals after exposure to exogenously supplied repair protein complexes. Recovery of vibration sensitivity occurs at the organismal level within 8 min. Paradoxically, a full recovery of morphology of hair bundles requires approximately 45 min and a recovery of F-actin levels requires approximately 40 min. Similarly, a full recovery of mechanoelectric responses of hair cells requires approximately 45 min. Thus, it appears that the recovery of responsiveness at the organismal level precedes a full recovery of hair bundles.

Cropping of sea anemone tentacles by a symbiotic barnacle

As sessile animals, barnacles (Cirripedia: Thoracica) are generally suspension feeders, extending their cirri into the surrounding water to collect food particles (1). Although it has been suggested that some symbiotic barnacles obtain nutrients directly from their hosts, either by absorbing body fluids (2-4) or by rasping the host's tissue (4-6), most of these cases are inferred from their morphology. Direct evidence, such as gut content analysis, has been limited (for an exception, see ref. 5), and no actual feeding on their hosts has been observed. Koleolepas avis (Hiro, 1931) is a pedunculate barnacle symbiotic with the sea anemone Calliactis japonica, which lives on gastropod shells occupied by large hermit crabs (7), mainly Dardanus arrosor. Symbiotic relationships between various hermit crabs and sea anemones have been well documented (8), but the relationship between the barnacle and its host sea anemone has been virtually unknown. From February to April 1996, we collected living individuals of K. avis from lobster nets landed at Minabe Fishery Port, southwestern Japan (33{deg} 44' N, 135{deg} 20' E). On the basis of behavioral observations in the laboratory and analyses offecalpellets and gut contents, we concluded that this barnacle feeds actively on its host's tentacles.

Efferent Mechanisms of Discharging Cnidae: II. A Nematocyst Release Response in the Sea Anemone Tentacle.

Feeding behavior in cnidarians is a sequence of coordinated responses beginning with nematocyst discharge. The nematocyst response produces prey capture by envenomating prey and attaching prey to the tentacle. The strength of attachment of discharged nematocysts to the tentacle is termed intrinsic adherence and is calculated from measurements of adhesive force. Following prey capture, the feeding response involves movement of the tentacles toward the mouth and mouth opening. For ingestion to occur, nematocysts attaching the prey to the tentacles must be released from the tentacle. A nematocyst release response has been proposed, but never documented nor measured. Our criterion for a nematocyst release response is that the intrinsic adherence of discharged nematocysts must decrease to zero. The unit of nematocyst discharge in sea anemone tentacles is the cnidocyte/ supporting cell complex (CSCC). The nematocyst response includes nematocysts discharged from Type C CSCCs by physical contact alone and nematocysts discharged from the more numerous Type B CSCCs that require both chemosensitization and physical contact. We identify two prey-derived substances, N-acetylneuraminic acid (NANA) and glycine, both of which chemosensitize nematocyst discharge from Type B CSCCs at low concentrations. At higher concentrations NANA stimulates the release response of Type Cs, and glycine stimulates the release response of Type Bs.

Frequency specificity of vibration dependent discharge of nematocysts in sea anemones

Hair bundles on tentacles of sea anemones are similar to vertebrate hair bundles in terms of structure and function. Anemone hair bundles are involved in regulating discharge of nematocysts, "stinging capsules," used to capture prey. N-acetylated sugars from the prey including N-acetylneuraminic acid (NANA) induce hair bundles to elongate while shifting vibration dependent discharge of nematocysts to lower frequencies matching prey movements. In the present study, we find that vibration dependent discharge of nematocysts exhibits sharp frequency discrimination to within one Hz. Testing at one-Hz intervals over the range of frequencies spanning 1-75 Hz, we find that seven of these are stimulatory in seawater alone. A total of twenty-six frequencies are stimulatory in the presence of NANA. Stimulatory frequencies in NANA are lower than those in seawater alone. We find that antagonists of ryanodine receptors including ryanodine, procaine and tetracaine shift discharge to lower frequencies. Fluorescently tagged ryanodine labels numerous small loci in the apical cytoplasm of supporting cells. We propose that calcium induced calcium release (CICR) via ryanodine receptors may sharpen frequency specificity and/or cause shortening of hair bundles to shift frequency specificity to higher frequencies.

Ultrastructure of neurons and synapses in the tentacle epidermis of the sea anemone Calliactis parasitica.

The anatomical organization of neutrons and synaptic pathways in tentacles of sea anemones is poorly understood. Transmission electron microscopy of serial thin sections was carried out on various regions of tentacles of the sea anemone Calliactis parasitica in order to locate and characterize typical epidermal neutrons and synapses. Both surface-oriented sensory cells with ciliary cones and basally located ganglion cells lacking a cilium have Golgi-derived granular or faintly cored vesicles. Similar vesicles are present at synaptic loci on some ganglion and muscle cells. The synaptic contacts on the longitudinal muscle cells are generally en passant rather than terminal. They vary from single neuromuscular synapses to pairs of neurites innervating the same muscle cell or one neurite innervating two or more muscle cells. Both two-way and one-way interneuronal synapses with vesicles aligned at paired synaptic membranes with dense material in a 14-20-nm-wide cleft are present in the epidermal nerve plexus. The vesicles average from 50 to 80 nm in diameter and vary from electron lucent to faintly cored. The results of this study demonstrate the presence of a complex system of epidermal neuronal pathways with specific synaptic loci in this modern representative of a first-evolved nervous system.

Ultrastructure of neurons and synapses in the tentacle gastrodermis of the sea anemone Calliactis parasitica.

Little is known about gastrodermal neurons and synapses in the tentacles of sea anemones. Using transmission electron microscopy of serial thin sections of Calliactis parasitica, we have identified both a sensory cell and a ganglion cell with granular vesicles originating from the Golgi complex and have identified four types of synapses in the tentacular gastrodermal nerve plexus. The sensory cell has a recessed apical cilium with a basal body and a perpendicularly oriented centriole, below which are several strands of striated rootlets surrounded by mitochondria. The ganglion cell lacks a cilium and resembles a bipolar neuron, with oppositely directed processes lying parallel to the basally located circular smooth muscle. Both one-way and two-way interneuronal synapses are present with 60- to 90-nm granular vesicles of various densities aligned at the paired electron-dense membranes and fine cross filaments in the intervening 13-nm cleft. Two types of neuroeffector synapses have been located. Dense granular vesicles are present at neuromuscular synapses, whereas less dense vesicles are present at neuroglandular synapses. Most of the synaptic vesicles range from 60 to 120 nm in diameter. Two types of nerve cells and a variety of synaptic loci provide morphological substrates for the spontaneous SS2 conduction pulses in the tentacular gastrodermis of C. parasitica. J Morphol 231:217-223, 1997. © 1997 Wiley-Liss, Inc.

Ontogenetic and interspecific variation in the protection of anemonefishes from sea anemones

Anemonefishes are well known for their ability to live unharmed among the stinging tentacles of sea anemones. This study examined whether there is ontogenetic and interspecific variation in the protection of anemonefishes from being stung by symbiotic anemones. Ontogenetic variation in protection was studied by determining if the tentacles of anemones would adhere to the eggs, larvae (0–5 days old), and recently metamorphosed anemonefish juveniles (7–14 days old). Interspecific variation in protection was examined by forcing juveniles of 10 species of anemonefishes to contact the tentacles of up to 9 anemone species. The tentacle adhesive forces of the anemone species were also measured. The eggs of anemonefishes were protected from all species of symbiotic anemones tested. Larval fishes were captured and killed by anemones, but recently metamorphosed juvenile fishes were protected from certain host species. Thus, the anemonefishes developed some form of protection during metamorphosis from a pelagic larva to a benthic juvenile. The juveniles of only one anemonefish species ( Amphiprion percula) were protected from all the symbiotic anemone species tested, while most other anemonefish species were stung by at least one anemone species. The extreme host specialist, Premnas biaculeatus, was only protected from its natural host species ( Entacmaea quadricolor) and was stung by 6 other symbiotic anemone species. The juveniles of all anemonefish species were protected from E. quadricolor, but only a few fish species were able to contact Stichodactyla gigantea without being stung. Fish that were stung by anemone species with strongly adhesive tentacles (e.g., S. gigantea, S. haddoni), were generally captured and killed. However, there was no correlation between the tentacle adhesive force of an anemone species and the number of anemonefish species that it stung.

Chemoreceptor‐mediated polymerization and depolymerization of actin in hair bundles of sea anemones

Hair bundles located on tentacles of sea anemones are morphodynamic mechanoreceptors employed to regulate discharge of nematocysts into swimming prey. Activation of chemoreceptors for N-acetylated sugars is known to induce anemone hair bundles to elongate while shifting discharge to lower frequencies matching those produced by calmly swimming prey. In the continued presence of N-acetylated sugars, activation of proline receptors is known to induce hair bundles to shorten while shifting nematocyst discharge to higher frequencies presumed to correspond to movements produced by wounded, struggling prey. In the present study, N-acetylneuraminic acid (NANA) causes stereocilia to become more intensely fluorescent in confocal optical sections of phalloidin-stained specimens, suggesting that receptors for N-acetylated sugars initiate processes to increase the density of F-actin within stereocilia. Computer analysis of electron micrographs is consistent with this interpretation for large diameter stereocilia but not for small diameter stereocilia. In the continued presence of NANA, proline causes fluorescence intensity of phalloidin to decrease to or below control levels. DNaseI uniformly stains large diameter stereocilia, suggesting that these stereocilia contain a pool of G-actin. Fluorescence intensity of DNaseI in stereocilia is significantly less bright in specimens exposed to NANA alone than in specimens exposed to proline in the continued presence of NANA. It appears that whereas activated receptors for NANA induce G-actin to polymerize in large diameter stereocilia, activated receptors for proline induce F-actin to depolymerize, restoring G-actin pools.

Morphodynamic hair bundles arising from sensory cell/supporting cell complexes frequency‐tune nematocyst discharge in sea anemones

Discharge of nematocysts from cnidocytes occurs in response to appropriate chemical and mechanical stimulation. In sea anemone tentacles, activating chemoreceptors for N-acetylated sugars shifts maximal discharge into vibrating targets to low frequencies corresponding to prey movements and induces hair bundles to elongate by approximately 1-2 microns. Until now, only indirect, correlative evidence linked these two events. Using cytochalasin D, we provide evidence that bundle elongation is necessary for the frequency shift. Moreover, we find that only bundles associated with sensory cell/supporting cell complexes elongate with chemosensitization, and not bundles associated with cnidocyte/supporting cell complexes as was previously thought. Cytochemical labeling of sensory cells, purported to be bipolar neurons connected to the nerve net, suggests that sensory cells may interconnect with each other and with cnidocytes. Taken together, these findings are incompatible with the classical view that cnidocytes are independent effectors of nematocyst discharge and, furthermore, implicate the involvement of morphodynamic neurons in fine-tuning vibration-dependent discharge of nematocysts into swimming prey.

Evidence for calcium channels involved in regulating nematocyst discharge

In the tentacles of sea anemones, nematocyst discharge is regulated by cnidocyte/supporting cell complexes (CSCCs) of which three functional types have been identified: A, B and C. Type A CSCCs respond to contact by vibrating targets. Types B and C CSCCs respond to contact by static targets. Whereas type C CSCCs respond to contact alone, type B CSCCs require that surface chemoreceptors bind ligands before becoming responsive. Reducing Ca 2+ levels in artificial seawater to below 1 mM inhibits discharge from each type of CSCC. The calcium channel inhibitors, nifedipine or verapamil, selectively inhibit discharge from type B CSCCs. The calcium channel activator, Bay K-8644, mimics the biphasic dose response of type B CSCCs to natural chemosensitizers such as N-acetylated sugars. Discharge from type A CSCCs is unaffected by inhibitors of L-type calcium channels, but is selectively inhibited by the aminoglycoside antibiotics, gentamicin and streptomycin. While each type of CSCC requires extracellular calcium, the calcium channels employed may vary according to CSCC type.

Frequency and amplitude tuning of nematocyst discharge by proline

AbstractIn sea anemone tentacles, discharge of nematocysts into vibrating targets is regulated by hair bundles. N‐acetylated sugars are known to induce hair bundles to elongate while tuning nematocyst discharge to low frequencies and small amplitudes corresponding to movements produced by calmly swimming prey. Proline is known to induce hair bundles to shorten while tuning nematocyst discharge to higher frequencies. In this report, we provide evidence suggesting that proline linearly tunes nematocyst discharge. Nematocyst discharge is tuned by increases of 10−18 M proline above background levels ranging from 10−12 M to 10−8 M proline, but only after anemones adapt to the background levels of proline. Anemones adapt more rapidly to 10−12 M proline than to 10−10 M, followed by 10−8 M proline. L‐proline and D‐proline comparably tune nematocyst discharge. Proline tunes discharge to higher frequencies and/or to larger amplitudes at the same lower frequencies produced by prey. We propose that N‐acetylated sugars tune nematocyst discharge to the movements of calmly swimming prey. After the prey is wounded by nematocysts, it releases proline into the seawater. This proline tunes nematocyst discharge to higher frequencies and/or larger amplitudes at low frequencies corresponding to movements produced by struggling, wounded prey. Thus, the greatest numbers of nematocysts may be discharged into calmly swimming, fresh prey and into vigorously struggling, wounded prey. © 1994 Wiley‐Liss, Inc.

Direct Monitoring of Intracellular Calcium Ions in Sea Anemone Tentacles Suggests Regulation of Nematocyst Discharge by Remote, Rare Epidermal Cells.

In tentacles of sea anemones, cnidocytes and adjacent supporting cells are believed to be independent receptor-effector complexes that regulate nematocyst discharge in response to exogenous N-acetylated sugars. When sugar chemoreceptors on supporting cells are activated, nematocyst discharge is two- to threefold greater than discharge without chemosensitization. To examine the role of Ca2+ as a second messenger in chemodetection of sugars, we used fluo-3 to monitor Ca2+ levels in epidermal cells of intact anemone tentacles. Certain epidermal cells exhibit relatively high Ca2+ both with and without chemosensitization. With chemosensitization, a two-to threefold increase occurs in the abundance of relatively rare cells exhibiting the highest Ca2+ levels. Timecourses depicting abundances of these rare cells in chemosensitized specimens show positive correlations to timecourses for nematocyst discharge from chemosensitized specimens and for labeling of chemoreceptors. Cnidocyte/supporting-cell complexes discharging nematocysts are about three times more abundant than the rare cells exhibiting the highest intracellular Ca2+ levels. One interpretation of these data is that the Ca2+-dependent regulation of nematocyst discharge occurring with chemosensitization involves intense Ca2+ signaling by remote, rare cells. This interpretation is inconsistent with the current model that portrays cnidocyte/supporting-cell complexes as independent effectors of nematocyst discharge.

Receptors for N-acetylated sugars may stimulate adenylate cyclase to sensitize and tune mechanoreceptors involved in triggering nematocyst discharge

In fishing tentacles of sea anemones, cnidocyte/supporting cell complexes (CSCCs) trigger the discharge of nematocysts following stimulation by swimming prey of specific mechanoreceptors and chemoreceptors located on the supporting cells. Two types of mechanoreceptors have been identified: a contact-sensitive mechanoreceptor (CSM), and a vibration-sensitive mechanoreceptor (VSM). The CSMs become predisposed to initiate nematocyst discharge into static (i.e., nonvibrating) test probes in the presence of submicromolar free and conjugated N-acetylated sugars, a process referred to as sensitization. In seawater, the VSMs cause maximal discharge in response to test probes vibrating at 30, 50–55, and 75 Hz, whereas in the presence of submicromolar N-acetylated sugars the VSMs cause maximal discharge into test probes vibrating at 5, 15, 30, and 40 Hz, a process referred to as tuning. Tuning of the VSMs is accompanied by elongation of the stereocilium bundles comprising the VSMs. We report that dibutyryl cyclic-AMP sensitizes CSMs and tunes VSMs to the lower frequencies of 5, 15, 30, and 40 Hz, while cyclic-AMP has no such effects. Endogenous adenylate cyclase activity at the apical plasma membrane of the supporting cells is detectable by cytochemical methods in the presence of N-acetylated sugars but not in seawater alone. By activating adenylate cyclase with L858051, an analogue of forskolin, or by activating the stimulatory form of G proteins (G s) with cholera toxin, CSCCs are induced to sensitize CSMs and to tune VSMs to the lower frequencies of 5, 15, 30, and 40 Hz. Caged GTP-γS also sensitizes CSMs but tunes VSMs to 5, 15, 30, 40, 55, 65, and 75 Hz, suggesting that VSM tuning may be regulated both by G s and inhibitory G-proteins. Together, these results implicate cAMP as the second messenger for activated supporting cell chemoreceptors involved in sensitizing the CSMs and tuning the VSMs to lower frequencies.

The acclimation of anemone fishes to sea anemones: Protection by changes in the fish's mucous coat

The anemone fish Amphiprion clarkii (Bennett) lives unharmed among the tentacles of sea anemones following acclimation. What occurs during this process is unknown; however, two hypotheses have been formulated recently. One suggests that the fish coats itself with anemone mucus to mask its chemical stimulus for cnida discharge. The second suggests that the fish is protected by some alteration in its own mucous coating. In order to test these alternative hypotheses, a surrogate anemone was constructed and an Amphiprion allowed to associate with it prior to being placed with a real anemone. If the subsequent acclimation times to a real anemone are reduced significantly after exposure to the surrogate anemone, one would conclude that the fish does not need to coat itself with anemone mucus to become protected. After association with a surrogate anemone, it was found that the acclimation times of isolated A. clarkii to the sea anemone Macrodactyla doreensis (Quoy & Gaimard) decreased seven-fold. These results support the hypothesis that the fish is responsible for manufacturing its own protection from sea anemones, presumably by independently altering its own mucous coat during acclimation.

Inhibition of Coral and Algal Photosynthesis by Ca2+-Antagonist Phenothiazine Drugs

The effects of various calcium ion antagonists and ion transport inhibitors on photosynthetic O(2) evolution of corals, isolated zooxanthellae, sea anemone tentacles, and Chlorococcum oleofaciens were measured. Only the phenothiazine drugs were effective at inhibiting photosynthesis. Trifluoperazine, a calcium ion antagonist drug, inhibited at low concentrations, with 10(-4) molar and 8 x 10(-6) molar completely abolishing photosynthesis in the intact corals and isolated zooxanthellae, respectively. Net photosynthetic O(2) evolution of C. oleofaciens was eliminated by concentrations of trifluoperazine as low as 2.8 x 10(-5) molar.

The cellular basis of the aggressive acrorhagial response of sea anemones.

Some sea anemones possess structures called acrorhagi at the base of the tentacles. The acrorhagi are utilized solely for aggression. Acrorhagial aggression involves very exquisite intra- and interspecific recognition. This study examined acrorhagi and putative acrorhagial analogues or homologues in four species of sea anemone. The morphology and ultrastructure of tentacles, pseudoacrorhagi, column vesicles, and verrucae (adhesive column vesicles) differed from that of acrorhagi. Coral capitate tentacles and acrorhagi have different surface morphology, nematocysts, and functions. Besed on morphology, acrorhagi seem more likely to be homologous to tentacles than to verrucae. Acrorhagial nematocyst discharge and ectodermal peeling, the culmination of the response, were shown to require prior acrorhagial expansion in Anthopleura krebsi and Bunodosoma cavernata. A mechanical mechanism is suggested where- by distention of the acrorhagus opens a ciliary pit on the nematocyte surface and exposes the pit wall and microvilli, which may contain the chemoreceptors for the peeling process, including nematocyst discharge. A similar system may also be responsible for changing the threshold of nematocyst discharge in sea anemone tentacles. A case of possible neurosecretion in an anthozoan was also shown in this study.

Two new septate junctions in the phylum Coelenterata.

Freeze-fracture of fixed and unfixed tissue, lanthanum tracer and conventional thin-section studies have revealed 2 new types of septate junction in the class Anthozoa, phylum Coelenterata. These new junctions have the 15-18-nm intercellular spacing of all other described septate junctions and are found around the apical circumference of cells lining a lumen or outside edge. However, in freeze-fracture replicas and tangential views of lanthanum-impregnated tissue, they are seen to be quite different from other known septate junction types. One of the new junctions is found in endothelial tissue such as that lining the gut or the inside of the tentacles. In tangential view it is seen to consist of relatively short, straight, double septa, again with lateral projections. In feeeze-fracture of unfixed tissue, the junction consists of double rows of particles on the P face, the particles of one row being rounded, those of the other being elongated at right angles to the line of the septum. This dichotomy in particle size is unexpected, as the 2 halves of the septa as seen in tangential view are symmetrical. In freeze-fracture of fixed material the particle arrays remain on the P face and appear similar to those of unfixed material, but never as clear. In fixed tissue, some distortion had occurred and in extreme cases septa appear as a single broad jumbled row of particles. In this double septa junction, the rows of particles seen in freeze-fracture are occasionally seen to anastomose with a septum dividing into 2 and a third row of particles aligning with the 2 new septa to form their double particle rows. In both fixed and unfixed tissues, the E face of the junction consists of wide, shallow grooves. The second of the new junctions occurs in epithelial tissue, such as around the outer edge of sea-anemone tentacles, and consists of long wavy septa with lateral projections. In views where these projections appear longest, they arise predominantly from one side of the septa. In freeze-fracture of both fixed and unfixed tissue, this junction appears as rows of closely spaced particles on the P face. Occasionally rows of particles are seen on the E face, but usually this face is characterized by shallow grooves. In some aspects these 2 new junctions have features in common with the Hydra type junction also found in the Coelenterata. In all 3 types septa are relatively straight, rather than pleated, and there are lateral projections on the septa.

Scanning electron microscopy of the sensory surface of the tentacles of sea anemones and corals.

Examination of the sensory surface of the tentacles of sea anemones and corals prepared by the Freon critical-point method has revealed three primary structures: ciliary cones consisting of a cilium surrounded by a cluster of shorter stereocilia, single long cilia, and microvilli. The ciliary cones occur on, and the single cilia and microvilli occur both on and between, the nematocyst- and spirocyst-bearing regions of the tentacles. The similarity of the anthozoan ciliary cones to the ciliary sensory structures in the lateral line, and the auditory and vestibular organs of vertebrates is noted and the possible functional significance of the coelenterate structures is discussed.

HISTOCHEMICAL LOCALIZATION OF AMINES IN HYDRA AND THE SEA ANEMONE.

SEVERAL investigators utilizing chemical techniques have identified neuropharmacological substances within coelenterates. Welsh1,2 has presented evidence for the presence of 5-hydroxytryptamine (5-HT) and a number of quaternary ammonium compounds in the sea anemone and Hydra; 5-HT occurring in greatest concentration within the tentacles and acontia. Methias et al.3,4 identified 5-HT, histamine and other amines in the sea anemone as well as in Physalia. This worker found the highest concentration of 5-HT in the cœelenteric tissues, including the acontia, with relatively low concentration in the tentacles. These compounds were discussed as possible agents responsible for the toxicity within nematocysts of sea anemone tentacles; however, the exact histological localization of the substances was not presented. The present investigation concerns the histochemical localization of epinephrine, norepinephrine, and 5-HT in Hydra and the sea anemone.