Onchidium Verruculatum Research Articles

Distribution Patterns of Key Gastropods (Mollusca) Species Along the Intertidal Zone of Adri Coast, Kathiawar Peninsula, India

Distribution patterns of key gastropod species were studied on a rocky-sandy intertidal zone of Adri coast of Kathiawar peninsula. The studied coast has an ideal habitat for intertidal ecological studies. It has rich marine faunal and floral diversity devoid of any anthropogenic pressure. The present study was focused on distribution pattern of dominating intertidal gastropods species that considered as the most communal inhabitants of the intertidal zone worldwide. The coast has both rocky and sandy intertidal area with rock crevices and small to large pools and puddles. Physico-chemical parameters of seawater and ecological attributes like density, abundance, and frequency of five gastropod species Astralium semicostatum, Cerithium caeruleum, Gyrenium natator, Nerita albicilla and Onchidium verruculatum have been studied. Result indicates that all the species have their distinct preference for intertidal microhabitats like rocks, puddles, crevices and different substrata. The species has different strategies for the selection of microhabitat for their survival particularly in extreme environment of low tide when desiccation is at maximum.

Opsins in the Cephalic and Extracephalic Photoreceptors in the Marine Gastropod Onchidium verruculatum.

AbstractThe marine gastropod Onchidium verruculatum has a pair of ocular photoreceptors, the stalk eyes, on the tip of its stalk near the head, as well as several extracephalic photosensory organs. The retinas of the stalk eye consist of two morphologically distinct visual cells, namely, the type I cells equipped with well-developed microvilli and the type II cells with less developed microvilli. The extracephalic photosensors comprise the dorsal eye, dermal photoreceptor, and brain photosensitive neurons. The characteristics of these cephalic and extracephalic photosensory organs have been studied from morphological and electrophysiological perspectives. However, little is known about the visual pigment molecules responsible for light detection in these organs. In the present study, we searched for opsin molecules that are expressed in the neural tissues of Onchidium and identified six putative signaling-competent opsin species, including Xenopsin1, Xenopsin2, Gq-coupled rhodopsin1, Gq-coupled rhodopsin2, Opsin-5B, and Gq-coupled rhodopsin-like. Immunohistochemical staining of four of the six opsins revealed that Xenopsin1, Gq-coupled rhodopsin1, and Gq-coupled rhodopsin2 are expressed in the rhabdomere of the stalk eye and in the dermal photoreceptor. Xenopsin2 was expressed in the type II photoreceptors of the stalk eye and in the ciliary photoreceptors of the dorsal eye. These immunohistochemical data were consistent with the results of the expression analysis, revealed by quantitative reverse transcription polymerase chain reaction. This study clarified the identities of opsins expressed in the extracephalic photosensory organs of Onchidium and the distinct molecular compositions among the photoreceptors.

Systematic revision of the genus Peronia Fleming, 1822 (Gastropoda, Euthyneura, Pulmonata, Onchidiidae).

The genus Peronia Fleming, 1822 includes all the onchidiid slugs with dorsal gills. Its taxonomy is revised for the first time based on a large collection of fresh material from the entire Indo-West Pacific, from South Africa to Hawaii. Nine species are supported by mitochondrial (COI and 16S) and nuclear (ITS2 and 28S) sequences as well as comparative anatomy. All types available were examined and the nomenclatural status of each existing name in the genus is addressed. Of 31 Peronia species-group names available, 27 are regarded as invalid (twenty-one synonyms, sixteen of which are new, five nomina dubia, and one homonym), and four as valid: Peronia peronii (Cuvier, 1804), Peronia verruculata (Cuvier, 1830), Peronia platei (Hoffmann, 1928), and Peronia madagascariensis (Labbé, 1934a). Five new species names are created: P. griffithsi Dayrat & Goulding, sp. nov., P. okinawensis Dayrat & Goulding, sp. nov., P. setoensis Dayrat & Goulding, sp. nov., P. sydneyensis Dayrat & Goulding, sp. nov., and P. willani Dayrat & Goulding, sp. nov.Peronia species are cryptic externally but can be distinguished using internal characters, with the exception of P. platei and P. setoensis. The anatomy of most species is described in detail here for the first time. All the secondary literature is commented on and historical specimens from museum collections were also examined to better establish species distributions. The genus Peronia includes two species that are widespread across the Indo-West Pacific (P. verruculata and P. peronii) as well as endemic species: P. okinawensis and P. setoensis are endemic to Japan, and P. willani is endemic to Northern Territory, Australia. Many new geographical records are provided, as well as a key to the species using morphological traits.

Molecular and anatomical analyses reveal that Peronia verruculata (Gastropoda: Onchidiidae) is a cryptic species complex

Recent years have seen an increase in the number of studies that use DNA sequence information in addition to morphological methods, as the latter alone can be inadequate for morphologically similar, cryptic species. Marine onchidiid slugs (Mollusca: Gastropoda: Onchidiidae), which commonly inhabit intertidal environments and have a near-global distribution, comprise 11 genera and 86 described species. Singapore has 19 recorded species of onchidiids with Peronia verruculata (Cuvier, 1830) being the most abundant. Here we present mitochondrial DNA sequence data from 63 P. verruculata-like specimens to show that they constitute two closely-related clades with distinct sequence signatures and a clear barcode gap. Intraclade distances are 0–1.8% while interclade distances range from 4.7 to 6.0%. Scanning electron microscopy of internal copulation organs reveals that the two clades have distinct penial and accessory gland spine structures, which also differ in size. Using an integrative taxonomic approach, we propose that what was initially thought to be P. verruculata in Singapore, actually are two different species of Peronia.

Phylogenetic analysis of euthyneuran gastropods from sea to land mainly based on comparative mitogenomic of four species of Onchidiidae (Mollusca: Gastropoda: Pulmonata)

We generated complete mitochondrial genome sequences data for 4 genera (Onchidium, Platevindex, Paraoncidium and Peronia) in Onchidiidae to construct a phylogenetic tree in conjunction with other 9 existing data among gastropods. The topology showed that the taxa clustered into two main groups of four species, one of which included Onchidium struma and the Platevindex mortoni, the other Paraoncidium reevesii and Peronia verruculata. The process in Pulmonata from sea to land in accordance with the evolution of respiratory organs from branchial gills to pulmonary cavity has been shown. This will also constitute a framework for phylogeny evolution analysis, systematic classfication of Onchidiidae and other euthyneurans (pulmonates and opisthobranchs).

Species diversity of Onchidiidae (Eupulmonata: Heterobranchia) on the mainland of China based on molecular data

The identification of members of the Onchidiidae is based on morphological characters; this is often time-consuming and can be inconclusive. In order to explore the species diversity of onchidiids in China, we provide a phylogeny constructed using partial sequences of two mitochondrial genes (16S rRNA and COI) and one nuclear ribosomal RNA gene (28S rRNA) from 32 samples comprising five genera. The topology, using both Bayesian and Maximum Likelihood inference methods, showed that the taxa clustered in two main groups of six species, one of which included Platevindex mortoni, Platevindex sp. and Onchidium ‘struma’; the other included Paraoncidium reevesii, Onchidella sp. and Peronia verruculata. It is clear that COI will be useful in discriminating onchidiid species-group taxa.

Preliminary classification and phylogenetic relationship among Onchidiidae in China inferred from 18S rRNA partial sequence

As a nutritious mollusk living in the intertidal zone, Onchidiidae has a significant value for biological research. Nine populations were collected from the costal areas such as Chongming (Shanghai), Ningde (Fujian), Haikou (Hainan) in this study. Through the study of anatomy and other methods to investigate the major category characteristics, the nine populations were preliminary classified. By sequencing segments of 18S rRNA gene and constructing phylogenetic trees using these nine populations and four other 18S rRNA gene sequences from GenBank, with Siphonaria as an outgroup, we analyzed the phylogeny of Onchidiidae in mainland China. The trees were used for discussing the relationship between the populations of the Onchidiidae in this study. The results showed that the southern coast has more populations than the northern coast in China. Besides two known species, Onchidium struma (JZH) and O. verruculatum (FJZ & HNZ), five new recorded species may exist: Onchidium(1), Platevindex(2), one Peronia(1) and Paraoncidium(1). The phylogenetic trees indicated that the nine populations can be divided into four subgroups, Peronia, Onchidium, Platevindex and Paraoncidium, and Peronia has the highest confidence level in clustering. Onchidium verruculatum (FJZ & HNZ) should be Peronia verruculata.

A new role for photoresponsive neurons called simple photoreceptors in the sea slug Onchidium verruculatum: Potentiation of synaptic transmission and motor response

The simple photoreceptors Ip-1 and Ip-2 are intrinsically light-sensitive neurons that exist in the abdominal ganglion of the sea slug Onchidium verruculatum. Using isolated ganglia and semi-intact or intact animal preparations, the present studies examined the light-sensing and physiological roles of Ip-1 and Ip-2 cells, which respond jointly to light by inducing a slow hyperpolarizing receptor potential. First, the synaptic inputs received by Ip-1 and Ip-2 and the axonal branches arising from their cell bodies were investigated. We found that these cells are not only first-order photosensory neurons, but also second-order neurons (interneurons), relaying inhibitory synaptic inputs such as water pressure and/or tactile senses. The amphibian Onchidium opens a pneumostome at low tide in order to aero-breathe. This pneumostome opening; i.e., aero-breathing behavior, was produced by spike discharges of Ip-1 and Ip-2 cells. Furthermore, the present results suggested that the hyperpolarizing photoresponse of Ip-1 and Ip-2 cells operates in the potentiation of inhibitory sensory synaptic transmission. Thus, we conclude that the simple photoreceptors of Onchidium play a role in the long-lasting potentiation of synaptic transmission and the subsequent behavioral response and so may be involved in a new photosensory modality, non-image-forming vision.

A comparison of two onchidiid species (Mollusca, Pulmonata)

Two externally similar species of Onchidiidae (Superfamily Onchidioidea), Onchidium verruculatum and Onchidina australis, occur together at Careel Bay in Sydney, NSW. These species were identified in a study of both external and internal morphology. The alimentary system and reproductive structures were examined and are illustrated. The most obvious external character separating the two species is the position of the pneumostome, which is located posteriorly in the midline in Onchidium verruculatum and to the right of the midline in Onchidina australis. In addition, differences in shape and colour distinguish the two species, as does presence or absence of accessory eyes. Important anatomical differences are the length of the penis and the presence or absence of an accessory penial gland, the number of lobes of the ovotestis and the presence or absence of a crop.

Fine structure of the dioptric apparatus in the stalk eye of Onchidium verruculatum (Gastropoda, Stylommatophora): a distinct lamellar substructure of the lens

The dioptric apparatus of the stalk eye in Onchidium verruculatum, including a tentacular epidermis, a cornea, and a lens, was examined using transmission electron microscopy. The tentacular epidermis was formed by columnar epidermal cells, sensory dendrites, and glandular cells. The cornea was an anterior part of the eye vesicle and consisted of corneal cells which contained abundant glycogen particles but no dark pigment granules in their cytoplasm. An acellular, transparent, ellipsoidal lens was located in the center of the eye vesicle. The lens showed a marginal zone, an outer zone, a transitional zone, an inner zone, and a central region arranged concentrically. The outer zone was the most intense electron-dense region and was finely granular in structure. The marginal zone was also finely granular and surrounded the outer zone with many hair-like slender strands on the retinal side. Toward the center of the lens this homogeneous fine granularity gradually changed into globular or rod-like substructures, about 30 nm in diameter, and then abruptly transformed into a lamellar substructure of about 30 nm in thickness. The inner zone contained a mosaic of lamellar substructures which were arranged in a fingerprint pattern that was particularly enhanced with periodic acid methenamine silver proteinate staining. The center itself consisted of deformed lamellar substructures. The concentric arrangement of substructures inside the lens of the O. ver-ruculatum stalk eye is probably responsible for the concentration and/or refraction of light.

A Neural Mechanism for Processing Colour Information in Molluscan Extra-Ocular Photoreceptors

ABSTRACT This study was conducted to clarify the electrical and spectral properties of the combined photoresponses of two extra-ocular photoreceptor neurones, A-P-l and Es-1, in the abdominal ganglion of the marine mollusc Onchidium verruculatum. The depolarizing receptor potential or inward receptor current of Es-1 appeared to result from a decrease in K+ conductance, in the same way as in A-P-l. The direct photoresponse of Es-1 had a peak at 580 nm, while A-P-l had its peak at 490nm. Under normal conditions, Es-1 was hyperpolarized by blue-green light (490nm) and was depolarized by yellow light (580nm), indicating that its responses were wavelength-dependent. Slow inhibitory synaptic potentials in Es-1 occurred during a sustained depolarization of A-P-l, suggesting that Es-1 received some inhibitory synaptic input from A-P-l. The amplitude of these slow synaptic hyperpolarizations was dependent on graded changes in the depolarization of A-P-l. However, presynaptic spikes in A-P-l were not followed by discrete synaptic potentials in Es-1. These results suggest that graded photoresponses of A-P-l could produce the slow hyperpolarization of Es-1 and that the photore-sponse of A-P-l is thereby transmitted to Es-1 with reversed polarity. The differing responses of Es-1 to light of different wavelengths may have a role in colour discrimination.

High-Voltage Electron Microscopic Study on the Axon of the Dermal Photoreceptor Cell in the Dorsal Mantle of Onchidium verruculatum

Axons of the dermal photoreceptor (DP) cell in the papilla of the dorsal mantle of Onchidium verruculatum were examined with a high-voltage electron microscope through 700 serial sections of an osmicated specimen. A single axon extending from the boundary area between the distal and proximal parts of the DP cell was confirmed in 14 out of 19 DP cells in a group. The course of the axon varied from cell to cell, and the diameter and fine structure also varied from region to region of the same axon. The axon traveled along the apical surface of the cell in the initial part, subsequently took a meandering course through the intracellular connective tissue, and frequently ran in close association with muscle fibers along its course. It finally joined a small papillar nerve (SPN) bundle which consisted of several axons derived from other DP cells in the group. No synaptic structure was found on the DP cell body or on the axon. Supporting cells covered the surface of the DP cell, including the initial part of the axon. Sheath cells which were located separately in the connective tissue between the DP cells continuousloy ensheathed the SPN bundle and the axon of the DP cell. The present study suggests that photic information is conducted from the DP cell to the central nervous system via the axon

Three types of chemical modification-effects induced by various chemical reagents on the glutamate receptors in molluscan neurons.

The effects of specific protein modifying reagents on the dose (Glu)-response (delta G) relationship of the glutamate-hyperpolarizing (Glu-H) receptors in molluscan neurons (Onchidium verruculatum) were analyzed. The effects could be classified into three types. Type I, parallel shift of the dose-response curve towards higher concentration by modification of COO- groups by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). The double reciprocal plots of the dose-response curves before and after the treatment indicated competitive inhibition type modification. Type II, a decrease in the slope of the dose-response curve through modification of -SH by N-ethylmaleimide and -NH3 groups by trinitrobenzenesulfonic acid. The double reciprocal plots indicated non-competitive inhibition type modification. The combined effects of Type I and Type II, after modification of arginyl residues with diacetyl trimer. The modification was most effective when applied during an activated state of receptors and channels by Glu. EEDQ had an irreversible after-effect on Glu-H type Onchidium neurons to activate an additional Na+ permeability increase in Glu induced hyperpolarizing response. Pretreatment of N-acetylimidazole (NAI), Glu-H (including weak D) receptors in Helix aspersa produced no significant difference in Glu response. However, simultaneous application of NAI and Glu induced an additional Na+ permeability increase, probably by modification of tyrosyl residues. This indicates the greatest effectiveness of the NAI modification during the activated state of the receptors and the channels by Glu. It is suggested that the Glu-H receptor protein possesses both negatively and positively charged residues, containing COO- and arginyl+ in the receptive site, and that several amino acid resides (SH, -NH, arginyl, and tyrosyl) act in the Glu-activated receptors and channels as their subsites. The role of the subsites in the receptors and channels is discussed.

Seasonal changes in the biochemical composition of the chiton Chiton iatricus (Polyplacophora: Mollusca) and the marine pulmonate Onchidium verruculatum (Gastropoda: Mollusca) in relation to their reproductive cycles

Seasonal changes in the biochemical composition of two molluses, gonochoric Chiton iatricus and a marine pulmonate, Ochnidium verruculatum inhabiting the same tropical area, but having different modes of reproduction, were studied. Protein is the major biochemical component stored in C. iatricus, whereas lipid is predominantly stored in O. verruculatum. The correlation between these quantifications and the annual reproductive cycles of the two species investigated suggest that nutrients stored in the somatic body parts are channeled towards the gonad during the gametogenesis. In C. iatricus sexual differences efrist in the biochemical needs of the ovary and the testis. The ovary always has a higher protein content than the testis. In the hermaphrodite pulmonate O. verruculatum, biochemical expenditure on gamete production is relatively low because this species has to spend energy on the reproductive propagation viz. copulation and egg-laying. On the contrary, in C. iatricus the biochemical energy is mainly utilized for the production of gametes which have to be produced in great numbers in order to counter-balance the loss of gametes caused by external fertilization. The collected data are discussed in the light of comparative physiology of reproduction.

Hormonal control of egg-laying in the marine pulmonate, Onchidium verruculatum

Extirpation of the pleurovisceral ganglia (PV) blocked egg-laying whereas reimplantation of PV or injection of a PV homogenate into PV-less animals restored the egg-laying capacity of the marine pulomonate, O. verruculatum. Injection of PV homogenate induced egg-laying in intact, mature individuals within 15–45 minutes. Boiling of the homogenate for 15 minutes did not abolish its egg-laying efficacy. However, after incubation with trypsin, a PV homogenate lost its potency. Homogenates of PV from colchicinized animals could not induce egg-laying in intact Onchidium. Similarly, colchicinized animals did not respond to a PV ectract from intact Onchidium. It is hypothesized that egg-laying in O. verruculatum is under the control of a heat-stable, trypsin sensitive hormone secreted by the PV ganglia.

In the intertidal homing gastropod onchidium verruculatum (Cuv.) the outward and homeward trails have a different information content

At low tide Onchidium verruculatum (Cuv.) emerge from holes or crevices in rocks to graze. They can find home again by retracing a trail laid down during the outward journey. When animals going to or from home are placed at 90° to the outward trail they usually turn and follow it towards the origin (i.e. towards home). Homeward-bound animals are more responsive to the trail than are outward-bound animals. Trails contain directional information because tested animals still turn mostly towards the origin of trails rotated 180° (i.e. they turn away from home). Animals heading home show few positive responses to their inward path, whether or not this is rotated. Similarly, when they are shifted to sand, animals that were outward-bound when moved show more positive responses to their trails than animals that were inward-bound. Directional information may be strongly present only in the outward trail: on the return path the polarized trail is either switched off or its information content is reduced. Trails are individual-specific. Faeces are produced throughout the feeding excursion but they are probably not the source of trail information.

Preliminary evidence for the hormonal control of urea concentration in the marine pulmonate, Onchidium verruculatum

Changes in blood, hepatopancreas and kidney urea concentrations in O. verruculatum have been assessed in response to endocrinological provocations. Two hr after pleurovisceral (PV) ganglion removal blood and nephridial urea levels were found to be significantly lowered and elevated respectively, whereas the hepatopancreas urea value remained unaltered, over the sham control. Unboiled and boiled macerates of PV (2 gn/animal) ganglion were effective in significantly inhibiting urea levels in blood and kidney of normal intact individuals. The possibility of a neurohormone from the PV, influencing tissue urea levels is discussed.

Involvement of neurohormone in regulation of oxygen consumption in the marine gastropod, Onchidium verruculatum

Ablation of whole central nervous system (CNS) or pleurovisceral (PV) ganglia significantly inhibited O2 uptake, after 4 hr through 24 hr of the operation over sham controls. Replacement of PV in PV-less animals restored their metabolic rates to the normal level. O2 consumption of normal animals is significantly augmented by the macerates of CNS and PV, but not by cerebral and pleural ganglia, and body muscles. Reserpine was ineffective in lowering the O2 uptake of PV-removed animals unlike in normal, intact individuals. The possible implication of a neurohormone originating from PV ganglia controlling whole body O2 consumption, is discussed.

Excitatory and inhibitory effects of histamine on molluscan neurons

Histamine elicited depolarization (excitation) in some neurons and hyperpolarization (inhibition) in other neurons of the central nervous system of the marine mollusc, Onchidium verruculatum. The histamine sensitive region was along the axon at some distance from the soma. H 1-receptor blockers (SA-97 and mepyramine) suppressed the excitatory (H 1) response without affecting the inhibitory (H 2) response, while H 2-receptor blockers (burimamide and metiamide) suppressed the H 2-response without affecting the H 1-response. The H 1-response was associated with a marked increase in membrane conductance and was blocked by removal of the external Na. The H 2-response consisted of a hyperpolarization without much change in conductance, compared with the hyperpolarization of same amplitude produced by glutamate in the same neuron. Passive polarization of the membrane and reduction of Cl concentrations to 15−125 caused to significant change in H 2-response. The H 2-response was slightly suppressed in K-free saline. Thus, it seems difficult to account for the hyperpolarization only by an increase in K or Cl conductance. Complete removal of Na and addition of ouabain blocked the H 2-response, suggesting a contribution of an electrogenic Na-pump to the hyperpolarization. However, in 20 mM Na saline with or without K, histamine still caused clear hyperpolarization. In this solution, the histamine response was not affected by ouabain. Although it is difficult to exclude the possibility that an increase in K conductance may be responsible for the hyperpolarization, it is tentatively proposed as a hypothesis that the H 2-response involved some active transport mechanism, different from a ouabain-sensitive electrogenic Na-pump.

Regulation of ammonia (NH3-N) metabolism in the marine pulmonate, onchidium verruculatum. I. effects of a neuroendocrine centre on tissue ammonia levels

Effect of ganglionic extirpations and replacement on the ammonia levels in the blood and various tissues of the marine pulmonate, O. verruculatum was studied. Three hrs after extirpation of the pleurovisceral (PV) complex only and not any other ganglia, revealed a significant (P < 0.001) decline in the blood and foot ammonia levels and significant (P < 0.001) increment in the hepatopancreatic ammonia level. However, no change was observed in the mantle and nephridial ammonia levels. Replacement of the PV complex, either via implantation of intact ganglia or boiled and unboiled homogenate administration (1 gn/animal) into the ganglionectomised group, restored ammonia levels in the blood and foot and showed significant (P < 0.005) decrease in hepatopancreatic ammonia levels. The results are discussed in the light of hormonal regulation of the nitrogen metabolism.