Morphological re-description of Aplysia depilans (Gastropoda: Anaspidea): new insights into the anatomy of the anaspideans

Although Aplysia depilans is a widely known European species and the type species of the genus, the distinctions that separate it from other related congeners are not entirely clear. Aimed at improving this scenario, a detailed morphological description is performed herein, showing some unprecedented and useful features. Based on our anatomical examination, this study has found the opaline gland to be dark in colour, as well as a metapodium with an indistinctly delimited pedal sucker, a crop divided into two equal chambers of similar volume by a circular muscle, gizzard plates arranged in groups, and a peculiar penial sheath structure. All of these characters appear to be significantly different from the other species, based on a review of the anatomical literature and several examined samples of ongoing studies. Our central objective is to provide new data on the anatomy of the type species of Aplysiidae; and, based on topological evidence, to propose a new terminology and possible homologies to some important characters, such as parapodia lobation, cephalic tentacles, crop, penial sheath, gizzard plates and visceral ganglion in anaspideans, for future phylogenetic analysis. The subgenus Subaplysia Medina, Collins & Walsh, 2005 is regarded as a junior synonym of subgenus Aplysia Linnaeus, 1767.

The elevation of cAMP levels by a putative diuretic hormone in the osmoregulatory organs of the freshwater snail Helisoma duryi

In the freshwater snail Helisoma duryi, the kidney and mantle are major organs for osmoregulation and the visceral ganglion is the putative source of diuretic hormone. The role of cAMP as a second messenger in hormonal regulation of these organs has been studied. Hypo-osmotic treatment of snails raised the levels of intracellular cAMP in their kidney and mantle tissues. Forskolin, isobutylmethylxanthine, and theophylline also increased the levels of intracellular cAMP in these tissues. In addition, when these tissues from snails that were acclimated in isosmotic medium were treated in vitro with extracts of visceral ganglion of snails that were acclimated in hypo-osmotic medium, elevated levels of cAMP were observed, 12-fold for the kidney tissue and 4-fold for the mantle tissue. The stimulatory substance from the visceral ganglion was heat stable but labile to proteolytic digestion. In similar in vitro experimental conditions, hemolymph taken from hypo-osmotically treated snails also raised levels of cAMP. It is suggested that in H. duryi cAMP is involved as a second messenger for hormonal osmoregulation by kidney and mantle, and that the putative diuretic hormone is a neuropeptide.

Neural Control of Heart Beat in the African Giant Snail, Achatina Fulica Ferussac: II. Interconnections Among the Heart Regulatory Neurones

The synaptic connections between identified heart regulatory neurones were examined in the central nervous system of the African giant snail, Achatina fulica Férussac. Two cerebral ganglion cells, the dorsal right and left cerebral distinct neurones (d-RCDN and d-LCDN), were found to have excitatory connections with several neurones in the suboesophageal ganglia (the periodically oscillating neurone, PON, the tonically autoactive neurones, TAN, TAN-2 and TAN-3, and the visceral intermittent firing neurone, VIN) and the connections are probably monosynaptic. VIN had a weak electrical coupling with PON. VIN inhibited TAN, TAN-2 and TAN-3, and the connections were considered to be monosynaptic. At the same time, TAN, TAN-2, TAN-3 and the visceral ganglion neurone (VG1) inhibited PON and VIN although the connections are unlikely to be monosynaptic. Another neurone in the pedal ganglia, the dorsal left pedal large neurone (d-LPeLN), was found to excite PON, VIN, TAN, TAN-2 and TAN-3. These connections were not monosynaptic. These results are interpreted in relation to heart regulation in Achatina.

Neural Control of Heart Beat in the African Giant Snail, Achatina Fulica Férussac: I. Identification of the Heart Regulatory Neurones

Seven heart regulatory neurones (PON, TAN, TAN-2, TAN-3, d-RCDN, d-LCDN and VG1) were identified in the central nervous system of the African giant snail, Achatina fulica Férussac. Among these neurones, the periodically oscillating neurone (PON) was the most effective heart excitor, producing heart excitation at rather low firing frequencies. The tonically autoactive neurones (TAN, TAN-2 and TAN-3) were tonically firing neurones and their spontaneous activity was found to produce tonic heart excitation which supplemented the myogenic heart activity. There was some evidence that two cerebral ganglion cells (the dorsal right and left cerebral distinct neurones, d-RCDN and d-LCDN) were also likely to be heart excitors although the direct connection to the heart was somewhat doubtful in some specimens. No direct inhibitory neurone was found, but the high firing frequency of the visceral ganglion neurone (VG1) usually produced heart inhibition.