Regulation of the length of the snail tentacle by the concentration-dependent contraction

The tentacle of terrestrial snail with olfactory organs on the tips display complex behavior when snail investigates the new environment. We reconstructed the trajectory of the tentacle in three dimensions from two simultaneous video recordings in freely moving snail without odor and after odor application. We found that without oder the snail displayed continuous environment scanning with elongated tentacles. Odor application elicited startle-like short-term flexions of the tentacle which were independent from odor concentration and concentration-dependent gradual tentacle contraction. Identified central motoneuron MtC3 is known to produce the most part of the central tentacle retraction to the noxious stimuli. In nose-brain preparation the MtC3 responded to odors in concentration-dependent manner similar by dynamics and duration to the concentration-dependent gradual tentacle contraction in intact snail. It suggests that the MtC3 provides the central control of the extent of the scanning area by limiting the tentacle length. The MtC3-related gradual contraction of the tentacle can be aimed to tune the olfactory behavior of the terrestrial snail to the particular odor environment.     

Comparative ultrastructure of catch tentacles and feeding tentacles in the sea anemone Haliplanella

TEM observations of catch tentacles revealed that the tentacle tip epidermis is filled with two size classes of mature holotrich nematocysts and a gland cell filled with electron-dense vesicles. Vesicle production is restricted to upper-middle and tentacle tip regions, whereas holotrich development occurs in the lower-middle and tentacle base regions. Thus, catch tentacles have a maturity gradient along their length, with mature tissues concentrated at the tentacle tip. Occasional feeding tentacle cnidae (microbasic p-mastigophores and basitrichs) and mucus gland cells occur in proximal portions of catch tentacles, but are phagocytized by amoeboid granulocytes and transported to the gastrodermis for further degradation. No feeding tentacle cnidae or mucus cells occur distally in catch tentacles. Unlike catch tentacles, feeding tentacles are homogeneous in structure along their length with enidocytes containing mature spirocysts, microbasic p-mastigophore or basitrich nematocysts distributed along the epithelial surface. Cnidoblasts are recessed beneath cnidocytes, occurring along the nerve plexus. Mucus gland cells and gland cells filled with electron-dense vesicles are present in feeding tentacles, distributed at the epithelial surface. Granular phagocytes are rare in the feeding tentacle tip, but common in the tentacle base.     

Suspension-feeding mechanisms of the armoured sea cucumber Psolus chitinoides Clark

The armoured sea cucumber Psolus chitinoides Clark feeds on suspended particulate matter by means of tentacle ensnarement and the adhesive papillae of the tentacle buds. The latter provide the only ‘sticky’ surface on the feeding tentacles. Electron microscope preparations of the tentacle tips show the adhesive papillae to be comprised of both stout, warty papillary cells which appear to secrete the adhesive material used in the capture of food, and slender, uniciliated cells which may function to disengage food from the tentacle papillae during ingestion. Tentacular response to olfactory and mechanical stimuli together with ultrastructural evidence indicate that the papular cells may also function in a sensory capacity.     

Tentacular and oral-disc regeneration in the sea anemone,Aiptasia diaphana. I. Sequential morphological events in distal-end restitution

The complete regeneration of a new oral-disc and tentacles has been observed and described for Aiptasia diaphana. These structures are regenerated quite rapidly: seven to ten days at 20°C. At three days post-amputation, the new primary, secondary, and tertiary tentacle buds begin to develop in direct association with the underlying primary, secondary, and tertiary septae (respectively) of the column, suggesting that the latter organize the form of the regenerating oral-disc. Two days after amputation, the zooxanthellae of the presumptive oral disc arrange themselves into a ring which quite precisely delimits the area from which the tentacle buds will form. In spite of its suggestive proximity, this accumulation of algae plays no role in the induction of tentacle buds as was shown by studying regeneration in anemones which essentially lacked large quantities of these symbiotic algae. Cuts perpendicular to the longitudinal axis of the column result in an equal rate of tentacular regeneration around the entire circumference of the presumptive oral disc. Oblique amputations foster an asynchronous regeneration: the tentacle buds of the distal-most area of the severed column are larger and regenerate much sooner than those of the proximal region. Similar results were obtained by studying anemones which were cut perpendicular to their longitudinal axes at different levels along the column. The data suggest that an oral-aboral gradient exists concerning the time required for the initiation of tentacle budding and the rate of tentacle regeneration.     

Ultrastructural studies of the commensal suctorian,Choanophrya infundibulifera hartog

Summary The feeding tentacles of Choanophrya contain a central canal lined by microtubules. Only one tentacle develops during metamorphosis of the embryo into the adult, but others develop at intervals throughout adult life. Each tentacle forms adjacent to a solitary, subcortical kinetosome which lies parallel to the body surface, lacks accessory elements and never develops a cilium. Small condensations of electron-dense material and short bundles of microtubules form adjacent to the cartwheel region of the kinetosome. Initially these bundles are orientated randomly but later they become radially arranged and curved into prolamellae around a disc-shaped condensation centre, to form a paddlewheel-like tentacle primordium 0.8–1.1 m in diameter. The condensation centre consists of alternating concentric electron-dense and electron-transparent zones, and lies with its axis perpendicular to both the kinetosome and the cortex. The microtubules in each prolamella increase in number and pairs of short tip microtubules develop between adjacent prolamellae. Subsequently the developing lamellae become enclosed by a cylinder of ring microtubules. Once all the microtubule components of the tentacle primordium are established it increases in length by addition of material to the basal ends of the microtubules to form a short microtubule canal. As the canal elongates the epiplasm above it disappears and the pellicle membranes become uplifted around the protruding tentacle. An epiplasmic collar differentiates around the growing tentacle whilst spheroid vesicles and solenocysts begin to accumulate in the surrounding cytoplasm.This investigation was supported by the J.S. Dunkerley Fellowship in Protozoology, awarded by the University of Manchester.     

Correlation between membrane potential responses and tentacle movement in the dinoflagellate Noctiluca miliaris

Membrane potential responses and tentacle movement of the marine dinoflagellate Noctiluca miliaris were recorded simultaneously and their time relationships were examined. The food-gathering tentacle of Noctiluca exhibited slow extension-flexion movements in association with the spontaneously recurring membrane potential responses termed the tentacle regulating potentials (TRPs). The flexion of the tentacle began during the slow depolarization of the TRPs. The rate of the flexion increased after the hyperpolarizing (negative) spike following the slow depolarization. The tentacle then extended slowly during the hyperpolarized level of the TRPs. A TRPs-associated flexion did not occur when the external Ca(2+) ions were removed. On the contrary, the tentacle showed conspicuous flexion (coiling) when the external Ca(2+) concentration was raised. In association with the stimulus-evoked action potential, which triggers bioluminescent flash (flash-triggering action potential; FTP), the tentacle coiled quickly. The FTP-associated coiling took place even in the Ca(2+)-deprived condition. The coupling mechanisms of the TRPs-associated and FTP-associated tentacle movements were compared, and their biological significance was discussed.     

Tentacle development in dermophis mexicanus (amphibia,gymnophiona) with an hypothesis of tentacle origin

The development of the tentacle, a chemosensory and perhaps tactile structure unique among vertebrates to gymnophione amphibians is described in Dermophis mexicanus and Gymnopis multiplicata. The tentacle is associated with the vomeronasal organ and its glands, and utilizes several structures usually associated with the eye, such as the Harderian gland, the retractor and levator muscles, and their nerves. Innervation of the tentacle itself is from the trigeminal nerve. We present an hypothesis that the tentacle originated from modified eye components.     

The fine structure and function of the tentacle in Tokophrya infusionum

The feeding apparatus of Suctoria consists of long, thin, stiff tubes called tentacles. When a swimming prey attaches to the tip of the tentacle a number of events follow in rapid succession. The tentacle broadens, a stream of tiny granules starts to move upward at its periphery to the tip, the prey becomes immobilized and shortly thereafter the cytoplasm of the still living prey begins to flow through the center of the tentacle to the body of the predator. An electron microscope study of the tentacle in Tokophrya infusionum, a protozoan of the subclass Suctoria, has disclosed a number of structural details which help to clarify some of the mechanisms involved in this unusual way of feeding. Each tentacle is composed of two concentric tubes. The lumen of the inner tube is surrounded by 49 tubular fibrils most probably of contractile nature. In the inner tube the cytoplasm of the prey is present during feeding, and in the outer tube are small dense bodies. It was found that the dense bodies originate in the cytoplasm of Tokophrya. They have an elongate, missile-like appearance, pointed at one end, rounded at the other, and are composed of several distinct segments. At the tip of the tentacle they penetrate the plasma membrane, with their pointed ends sticking out. It is assumed that the missile-like bodies play a major role in the feeding process. Their composite structure suggests that they might contain a number of enzymes which most probably are responsible for the various events preceding the actual food intake.     

Formation of pattern in regenerating tissue pieces of Hydra attenuata: II. Degree of proportion regulation is less in the hypostome and tentacle zone than in the tentacles and basal disc

The relative sizes of the various structures in Hydra attenuata were compared over a broad range of animal sizes to determine in detail the ability to regulate proportions during regeneration. The three components of the head, namely hypostome, tentacles, and tentacle zone from which the tentacles emerge, the body column, and the basal disc were all measured separately. Ectodermal cell number was used as the measure of size. The results showed that the basal disc proportioned exactly over a 40-fold size range, and the tentacle tissue proportioned exactly over a 20-fold size range. In contrast, the hypostome and tentacle zone proportioned allometrically. With decreasing size, the hypostome and tentacle zone became an increasing fraction of the animal at the expense of body tissue, and in the very smallest regenerates at the expense of tentacle tissue. In their current form, the reaction-diffusion models proposed for pattern regulation in hydra are not consistent with the data.     

Les Tentacules d'Ephelota; Etude au Microscope Electronique.

SUMMARY. The central canal of the suctorial tentacle of Ephelota is limited by a fine pellicle composed of numerous longitudinal fibrils and bearing 16–18 membrano-fibrillar ridges arranged radially in the lumen of the canal. This structure resembles that of the myonemes in the heterotrichous ciliate Stentor.
The prehensile tentacle of Ephelota contains 4–6 axial protein fibers each consisting of a lamello-fibrillar bundle and isolated from one another by thin intracytoplasmic membranes.
In both types of tentacle the cytoplasmic portion is immediately limited by a very thin pellicle which is continuous with the "epiplasmic membrane" and covered by the alveolar cuticle which envelops the entire body of the ciliate.     

Feeding and wounding responses in Hydra suggest functional and structural polarization of the tentacle nervous system

The nervous system of Hydra, a freshwater cnidaria, occurs as dispersed, or diffuse, nerve net throughout the animal. It is widely accepted that in a diffuse nervous system an external stimulus is conducted in all directions over the net. Here I report observations that hydra tentacles respond to feeding and wounding stimuli in a unidirectional manner. Upon contact of a tentacle with a brine shrimp larva during feeding, tissue on the proximal side of the point of contact contracted strongly, whereas tissue on the distal side contracted only very weakly. Feeding a tentacle to which a second tentacle was grafted to the proximal end in the reversed orientation showed that unidirectional conduction, once initiated, was blocked by the reversal of polarity, demonstrating that the distal to proximal polarity of tissue is crucial for unidirectional conduction. Unidirectional conduction was obtained also by mechanically pinching the tissue. The response of tentacles devoid of neurons examined was bidirectional, demonstrating that the nervous system is responsible for the unidirectional responses. These observations suggest that polarized property of the nerve net in hydra tentacles is responsible for the unidirectional tentacle contraction.     

Novel triplet of flexor muscles in the posterior tentacles of the snail, Helix pomatia

The anatomy of three novel flexor muscles in the posterior tentacles of Helix pomatia is described. The muscles originate from the ventral side of the sensory pad and are anchored at different sites in the base of the tentacle stem. The muscles span the tentacle and always take the length of the stem which depends on the rate of tentacle protrusion indicating that the muscles are both contractile and extremely stretchable. The three anchoring points at the base of the stem determine three space axes along which the contraction of a muscle or the synchronous contraction of the muscles can move the tentacle in space.     

Ultrastructure of tentacles in the sipunculid worm <Emphasis Type="Italic">Thysanocardia nigra</Emphasis> Ikeda, 1904 (Sipuncula)

The ultrastructure of the tentacles was studied in the sipunculid worm Thysanocardia nigra. Flexible digitate tentacles are arranged into the dorsal and ventral tentacular crowns at the anterior end of the introvert of Th. nigra. The tentacle bears oral, lateral, and aboral rows of cilia; on the oral side, there is a longitudinal groove. Each tentacle contains two oral tentacular canals and an aboral tentacular canal. The oral side of the tentacle is covered by a simple columnar epithelium, which contains large glandular cells that secrete their products onto the apical surface of the epithelium. The lateral and aboral epithelia are composed of cuboidal and flattened cells. The tentacular canals are lined with a flattened coelomic epithelium that consists of podocytes with their processes and multiciliated cells. The tentacular canals are continuous with the radial coelomic canals of the head and constitute the terminal parts of the tentacular coelom, which shows a highly complex morphology. Five tentacular nerves and circular and longitudinal muscle bands lie in the connective tissue of the tentacle wall. Similarities and differences in the tentacle morphology between Th. nigra and other sipunculan species are discussed.Original Russian Text Copyright © 2005 by Biologiya Morya, Maiorova, Adrianov.     

N-arachidonoyl dopamine is a possible factor of the rate of tentacle formation in freshwater hydra

The effect of N-arachidonoyl dopamine, haloperidol, and their mixture on the rate of tentacle formation was studied during regeneration of the gastral and basal fragments of freshwater hydra. Some concentrations of haloperidol inhibited the tentacle formation, which was more pronounced in the basal fragment. N-arachidonoyl dopamine accelerated the tentacle formation in both fragments, particularly, in the basal one (an inversion of the natural difference in the rate of tentacle formation between the gastral and basal fragments). After the exposure to the mixture of these drugs, the effects of each of them were observed. Mass spectrometry assay has demonstrated endogenous N-arachidonoyl dopamine in the intact hydra homogenate. The possible involvement of this acyl-neurotransmitter in the regulation of the rate of tentacle formation in regenerating hydra is discussed.     

An IQGAP-related gene is activated during tentacle formation in the simple metazoan Hydra

Differentiation of body column epithelial cells into tentacle epithelial cells in Hydra is accompanied by changes in both cell shape and cell-cell contact. The molecular mechanism by which epithelial cells acquire tentacle cell characteristics is unknown. Here we report that expression of a Hydra homologue of the mammalian IQGAP1 protein is strongly upregulated during tentacle formation. Like mammalian IQGAP, Hydra IQGAP1 contains an N-terminal calponin-homology domain, IQ repeats and a conserved C terminus. In adult polyps a high level of Hydra IQGAP1 mRNA is detected at the basis of tentacles. Consistent with a role in tentacle formation, IQGAP1 expression is activated during head regeneration and budding at a time when tentacles are emerging. The observations support the previous hypothesis that IQGAP proteins are involved in cytoskeletal as well as cell-cell contact rearrangements. Received: 25 January 2000 / Accepted: 2 May 2000     

The eversible tentacle organs of Polyommatus caterpillars (Lepidoptera,Lycaenidae): Morphology,fine structure,sensory supply and functional aspects

In their late (3rd and 4th) larval stages, caterpillars of the myrmecophilous lycaenid (Lepidoptera) species Polyommatus coridon and Polyommatus icarus, possess on their 8th abdominal segment two eversible so called tentacle organs (TOs). Previous histological and behavioural results have proposed that the TOs may release a volatile substance that elicits “excited runs” in attendant ants. In our study we investigated for the first time the temporal in- and eversion pattern of TOs. Using nerve tracing, Micro-CT, light- and electron microscopy techniques we studied (i) the histology of the 8th abdominal segment, (ii) the fine structure of the cuticular and cellular apparatus of the TOs, (iii) the attachment sites of the retractor muscle of each TO and (iv) the fine structure of the long slender tentacle hairs which are exposed to the outside, when the TOs are everted and fold back into the TO-sac during inversion. Our data show that the tentacle hairs are typical insect mechanoreceptors, each innervated by a small bipolar sensory cell with a tubular body in the tip of the outer dendritic segment. The latter is enclosed by a cuticular sheath previously called the “internal cuticular duct” and misinterpreted in earlier studies as the space, where the tentacle hairs actively secrete fluids. However, we found no glandular structures nearby or in the wall of the TO-sac. Also we did not reveal any conspicuous signs of secretory activity in one of the enveloping cells belonging to a tentacle hair. Although highly unusual features for an insect mechanoreceptor are: (a) the hair-shaft lumen of tentacle hairs contains flocculent material as well small vesicles and (b) the thin cuticular wall of the hair-shaft and its spines possess few tiny pores. Our data do not support the assumption of previous studies that volatile substances are released via the tentacle organs during their interactions with ants which in turn are supposed to cause excited runs in ants.     

N-arachidonoyl dopamine is a possible factor of the rate of tentacle formation in freshwater hydra regeneration

The effect of N-arachidonoyl dopamine, haloperidol, and their mixture on the rate of tentacle formation was studied during regeneration of the gastral and basal fragments of freshwater hydra. Some concentrations of haloperidol inhibited the tentacle formation, which was more pronounced in the basal fragment. N-arachidonoyl dopamine accelerated the tentacle formation in both fragments, particularly, in the basal one (an inversion of the natural difference in the rate of tentacle formation between the gastral and basal fragments). After the exposure to the mixture of these drugs, the effects of each of them were observed. Mass spectrometry assay has demonstrated endogenous N-arachidonoyl dopamine in the intact hydra homogenate. The possible involvement of this acyl-neurotransmitter in the regulation of the rate of tentacle formation in regenerating hydra is discussed.     

Evaluation of tentacle regeneration as a biological assay inHydra

Summary Tentacle number in non-buddingHydra attenuata, randomly selected from mass culture varies <0.5 tentacles over a 3 month period. Replicate samples of untreated regenerates (n=50–60), however, show some variability in mean tentacle number regenerated (S _x0.13–0.15). The variability is similar whether experiments are performed using randomly selected animals or animals with identical tentacle numbers. The variability is, further, not the result of profound differences in the time of tentacle initiation in individual animals.Addition of 10^–5 M glutamate or a methanol extract to the assay medium results in both an earlier appearance of tentacles and in more tentacles being regenerated during early time periods. The mean tentacle number of methanol extract-treated animals is significantly higher than the mean tentacle number of either control or glutamate-treated animals at all time periods examined.The distribution of tentacle number classes among regenerates is normal in control and glutamate-treated animals but nonparametric in methanol extract-treated animals, making statistical analysis of the data using Student'st-test in-appropriate. The usefulness of the Mann WhitneyU and Kruskal-Wallis tests is discussed, as is the appropriateness of tentacle regeneration as an assay forhydra morphogens.     

Putative sensory structures in marine bryozoans

Abstract. SEM studies of 21 species of marine bryozoans demonstrated that the abfrontal side of the tentacles bears a row of mono- or multiciliated cells, which are presumably sensory. In stenolaemates, the abfrontal cells, as well as the cells at the tentacle tips and the laterofrontal cells, are monociliated. In the 17 gymnolaemate species studied, each tentacle tip bears at least 3 multiciliated cells, each with a tuft of 5–7 stiff cilia of various lengths. On the abfrontal tentacle surface, mono- and multiciliated cells alternate, but all species studied have multiciliated cells at the base and the tip of each tentacle. In live animals, single cilia perform occasional flicks, whereas the tufts of 7–15 cilia on the multiciliated cells are immotile. Length and number of abfrontal cilia vary between species. Two types of multiciliated, putative sensory organs were found on the introvert of some gymnolaemates. One has an apical knob surrounded by a ring of cilia; the other has an apical tuft of cilia. The ultrastructure of the sensory cells of tentacles and introvert was studied in Rhamphostomella ovata . Our observations on both fixed and living material all suggest that these cells are primitive mechanoreceptors. The few species lacking ciliary structures on the introvert have long proximal ciliary tufts on the abfrontal tentacle surface.     

Electrically induced tentacle contraction in the suctorian protozoonTrichophrya collini

Summary Extracellular electrical stimulation ofTrichophrya collini induces tentacle contraction. There is an inverse relationship between stimulus duration and voltage in producing a threshold response, and at a set voltage the response is graded depending upon duration of stimulus. With a threshold stimulus (6.3 V, 1,000 ms) the response is restricted to the anodal tentacles, and with increasing stimulus intensity or duration the response spreads to the cathodal and finally the intermediate tentacles. With a stimulus of 15 V, 1,000 ms the mean tentacle length is reduced to 28% of the control within 1.2 s. Recordings using intracellular microelectrodes give resting membrane potentials between –10mV and –40mV. Intracellular hyperpolarizing currents of 1nA and 2nA induce tentacle contraction to 50% and 25% of the control length respectively, but depolarizing currents do not induce contraction. SEM studies show that in the initial stages of contraction, only the central region of the tentacle shaft becomes shortened, but on full contraction shortening involves the whole of the shaft. TEM studies show that on contraction no depolymerization of tentacle axoneme microtubules occurs, but that the entire axoneme passes down into the body cytoplasm. These observations are discussed in relation to the possible mechanisms of tentacle contraction.Abbreviations Ax axoneme - C cortex - EDB elongate dense body - SEM scanning electron microscopy - TEM transmission electron microscopy