Pallial Gland Research Articles

Review of the Genus Habeas from Brazil, with Description of Four New Species and in Which Anatomical Features Revealed That They Belong to Urocoptidae (Eupulmonata, Stylommatophora)

South American land snails are relatively poorly known, but their taxonomic relationships can be illuminated with the help of detailed anatomical descriptions and comparisons. The genus Habeas Simone, 2013, species of which are associated with caves, was tentatively described in the prosobranch family Diplommatinidae. Recently collected samples that permitted anatomical investigation, revealed that Habeas actually belongs to the eupulmonate family Urocoptidae. The genus is thus reviewed, including the three so far known species: H. corpus, H. data and H. priscus, all Simone, 2013. Four new species collected in Brazil are described: Habeas lekolus (from Cônego Marinho, Minas Gerais), H. peruassus (from Januária, Minas Gerais), H. lapensis (from Bom Jesus da Lapa, Bahia) and H. claudus (from Cocos, Bahia). Anatomical description is based on H. lekolus, revealing in its most interesting features, the absence of the ureter, presence of a pallial gland, lack of anterior duct to digestive gland, small penis and epiphallus, and absence of bursa copulatrix. Species in this genus usually inhabit cave habitats and are only found in Bahia (BA) and Minas Gerais (MG) Brazilian states, in areas close to São Francisco River. A brief discussion of the family attribution to Habeas is also performed. The present seven species in a genus recently discovered in a relatively small area demonstrate how weak the knowledge on the Brazilian malacofauna is.

Alidation of reference genes for quantitative expression analysis by qPCR in various tissues of date mussel (Lithophagalithophaga)

qPCR is a very popular method for identifying nucleotide sequences as a result of its sensitivity and relatively low cost and technical simplicity. Normalization is one of the most important steps in analyzing qPCR data and the use of reference genes is the most common normalization strategy. In the present study five commonly used reference genes (18S, 28S, ef1a, ß-act, and ?-tub) were evaluated for their stability in the mantle, gill, foot, and pallial gland of date mussel (L. lithophaga) in different seasons. Four different software packages were used for evaluation: geNorm, NormFinder, BestKeeper, and RefFinder. Although these programs contain different algorithms and analytical procedures, their ranking of the candidate reference genes was similar. Of the five selected reference genes 18S, 28S, and ef1a were determined as the three most stable in different tissues and seasons. A-tub was evaluated as the least stable reference gene and therefore inappropriate for normalization of quantitative gene expression data. The results will help improve the accuracy of gene expression analysis in samples of date mussel and at the same time provide guidance for selection of reference genes in future qPCR studies in the species.

Candidate Calcium-Binding Genes for Chemical Boring in the Date Mussel Lithophaga lithophaga

The date mussel Lithophaga lithophaga is a chemical borer that uses pallial gland secretions to bore holes in the substrate. Calcium-binding proteins are generally considered to be responsible for the chemical dissolution of the calcareous substrate. The aim of this study was to investigate the relative expression of five candidate genes – ANXB9, SCP, CALR, PLA2 and V-ATPase – in four different tissues, with the hypothesis that the expression profile of the candidate genes in the pallial gland would differ from the rest. The results from gene expression analysis revealed that CALR, PLA2 and SCP were up-regulated in the pallial gland. Two of the candidate genes (ANXB9 and V-ATPase) had the same expression profile in all four investigated tissues, indicating that they are not directly involved in the chemical boring mechanism. The results of this study shed light on the genetic background of the chemical boring mechanism in date mussel. This set of candidate genes could be used in future research studies of chemical boring in the date mussel and other marine or freshwater borers.

An improbable opportunistic predator: the functional morphology ofPinna nobilis(Bivalvia: Pterioida: Pinnidae)

The functional morphology ofPinna nobilisis described, with special reference to the uniquely pinnid pallial organ, the similarly unique buccal (formerly pallial) gland, the stomach and its contents. The pallial gland produces sulphuric acid which as well as functioning as a shell cleaning swab may be involved in prey capture. The buccal gland discharging into the oesophagus has proteolytic digestive functions while the stomach is adapted for the reception and digestion of captured, mucous-bound, mesozooplanktonic and epi- and endo-benthic, prey items.Pinna nobilisis thus not simply either an accidental or incidental predator of such species but is opportunistic. The buccal glands and stomachs of other Pinnidae are not so specialized as inP. nobilis,possibly indicating that in the particular, oligotrophic, environment of the Mediterranean and Adriatic Seas, and in which it is endemic,P. nobilishas, in addition to being a typical ctenidial suspension feeder, become an opportunistic predator. Although the deep sea representatives of the Septibranchia (Anomalodesmata) and Propeamussidae are obligate predators, this is the first record of any bivalve functioning as an opportunistic predator with unique morphological adaptations to facilitate this.

De novo transcriptome of the pallial gland of the date mussel (Lithophaga lithophaga)

Lithophaga lithophaga is a rock-boring bivalve with an ability to dissolve carbonate substrata with its siphonal and pallial gland secretions. However, the molecular mechanism that enables this species to bore into calcareous rocks is not yet known. In order to identify genes potentially involved in chemical boring we performed transcriptome sequencing of pallial-gland tissue samples of L. lithophaga. Transcriptome sequencing using an Ion Torrent platform generated 60.563 million clean reads with an average read length of 96 bp. De novo assembly of clean reads produced 62,490 contigs with a mean length of 408 bp. Since the boring mechanism is attributed to calcium-binding proteins, the search focused on transcripts capable of binding this element. In all, 178 genes with calcium-binding ability were found to be expressed in the pallial gland of L. lithophaga. Annexins, calreticulin, phospholipase A2 and V-type proton-ATPases were considered as possible candidate chemical-boring genes due to their known function and involvement in various other biological processes: e.g. ion transport, cellular catabolic process, protein folding. Transcriptome analysis of L. lithophaga revealed a set of candidate genes putatively associated with chemical boring. The selected set of genes will be studied further to verify their expression patterns and their possible involvement in the rate of chemical boring in L. lithophaga.

Micro-spatial distribution of two sibling periwinkle species across the intertidal indicates hybrdization

Populations of periwinkles Littorina saxatilis (Olivi 1792) and L. arcana Hannaford Ellis, 1978 are well suited for microevolutionary studies, being at the same time closely related and intraspecifically diverse. The divergence between these two sibling species, sympatric over large parts of their distribution areas, is small, the only morphological difference being the pallial gland complex structure in females. Molecular identification is possible with the use of a RAPD nuclear marker (cloned A2.8 DNA fragment) typical for L. arcana. However, in some individuals from sympatric populations molecular and morphological criteria suggest conflicting species affiliation, which may be explained either by hybridization or by shared ancestral polymorphism. We tested the hybridization hypotheses examining the micro-spatial distribution of these two species across the intertidal zone in two distant sites at the Barents Sea. We found that (a) the frequency of putative hybrids in sympatric populations was proportional to the frequency of L. arcana; (b) L. saxatilis bearing A2.8 DNA fragment were almost absent in the lower part of the intertidal zone, where L. arcana was absent too; (c) there was a close positive correlation between the distribution of potential parent molluscs and putative hybrids. Moreover, logistic regression models showed a good agreement between the distribution of putative hybrid frequencies and that of parental species frequencies. All our observations taken together support the hypothesis of hybridization between L. saxatilis and L. arcana. Elucidating the mechanisms that support the species status of these sympatric populations is necessary.

Taxonomic review of the Spixia pyriformis species complex (Gastropoda: Pulmonata: Odontostominae)

The genus Spixia (Pilsbry & Vanatta, 1898) is endemic from southern South America. Information about this group is scarce, particularly referring to its anatomy and shell ultrastructure. According to current classification the Spixia pyriformis complex includes the following species, S. doellojuradoi (Parodiz 1941), S. martensii (Doering 1874), S. pyriformis (Pilsbry 1901) and S. tucumanensis (Parodiz 1941). In the present study a complete redescription of the species component of this complex, as well as new information on shell ultrastructure and anatomy of the different organ systems is provided. The Spixia pyriformis complex has a pyriform-subpyriform shell shape that distinguishes it from the rest of the species of the genus. Three of the four species studied have a similar periostracum structure consisting of spiral striae and triangular lamellae. Radular morphology is similar in all species. Jaw structure is diagnostic for each species. The inner morphology of the penis is divided into five areas marked by differential pattern of sculpture. Four new anatomical characters, the presence of a pallial gland in the distal portion of the pulmonary roof, the presence of a penial gland in the penial complex, the position of the insertion of the penial retractor muscle in either penial area I or area II and the sculpture of penis inner wall, are identified as the most informative for species diagnosis.

Systematics of Ophicardelus (Gastropoda: Heterobranchia: Ellobiidae)

Ophicardelus is currently used for a small group of estuarine ellobiid snails found in Australia and New Zealand, but a previous study (Hyman et al. 2004) suggested that it may not be monophyletic. In the present study, morphological data are used in a cladistic analysis to test the monophyly of Ophicardelus. Taxa included are the three Australian species (Ophicardelus ornatus, O. quoyi and O. sulcatus), the New Zealand Ophicardelus costellaris, nine other Australasian Ellobiidae and outgroup Salinator solida (Amphibolidae). The results show that Ophicardelus is not monophyletic and a new genus, Pleuroloba, is introduced for quoyi and costellaris. Ophicardelus is distinguished from Pleuroloba by the presence of a pallial gland and the absence of a muscular vagina. The cladistic analysis indicated that Ophicardelus and Pleuroloba both belong in Pythiinae, but did not support Cassidulinae as recognised by Martins in 1998.

Ophicardelus (Mollusca, Pulmonata) in eastern Australia: how many taxa?

The common south-eastern Australian estuarine ellobiid snails belonging to Ophicardelus have been considered to be one variable taxon by some authors, and three largely sympatric species by others. This study was undertaken to determine the number of taxa present. Different types of data collected included shell shape, allozyme electrophoresis, shell and radular morphology, anatomy and geographic range. These data sets were then examined for consistent discontinuities, and the results showed that the nominal species could be distinguished by a combination of shell shape and sculpture. Individuals from each nominal species also grouped together using allozyme data, although one taxon (Ophicardelus quoyi) is sometimes paraphyletic based on these data. There are several differences in the anatomy and radular morphology that separate the three taxa. These included marked differences in the penial complex, vagina, and presence or absence of a pallial gland. The three taxa also have different geographic ranges, albeit with most of their ranges in sympatry. Based on these differences, Ophicardelus ornatus, O. quoyi and O. sulcatus should be regarded as valid species.

Early development and morphogenesis of the intracapsular veliger of Haminaea navicula (Gastropoda: Opisthobranchia: Bullomorpha)

Summary The development of Haminaea navicula was studied by anatomical and histological methods. This species shows typical spiral cleavage, which leads to a stereoblastula. Gastrulation is reached by epiboly. A fully developed veliger larva is reached within the egg capsule that is not only capable of swimming when artificially hatched but is also provided with the same larval organs (larval shell, velum, operculum, larval cephalic sensory organ, anal cells, anal gland, nephrocyst-protonephridial complex, epipodial and pallial gland cells) that are present in pelagic larvae of related species. Aspects of the development of H. navicula are compared with observations of the pelagic larvae of H. exigua and H. vesicula. Additional data from the literature are discussed.

The biology and functional morphology of Minnivola pyxidatus (Bivalvia: Pectinoidea)

The shallow subtidal scallop Minnivola pyxidutus occurs in the relatively clean oceanic, southern, and south‐eastern waters of Hong Kong and elsewhere in the Western Pacific and is highly polymorphic in terms of shell patterning of the left, upper valve. Locally, because of sea‐bed perturbations, numbers are declining. The species can probably live for ∼ 3 years, with reproduction occurring in winter. M. pyxidatus is monoecious.Shell form and anatomy are described. Normally, the species lives attached by a fragile byssus to sand grains or stones, but can swim, albeit weakly, in response to predation risks.In most respects, Minnivola pyxidatus is a typical scallop, with a bowl‐shaped, right lower valve and a concave, disc‐like, left upper valve. The mantle has pallial eyes and a complex array of tentacles which possess small, ciliary‐based sensory cells. There is also a cleansing tract on the outer surface of the middle mantle fold and a muscular velum formed from the inner fold. The latter is developed into a simple exhalant aperture posteriorly. Both mantle lobes possess extensive posterior pallial glands and an abdominal sense organ on the right lobe only, anterior to the single posterior adductor muscle. Ciliary currents of the mantle cavity are for cleansing and are powerful, particularly on the visceral mass and right mantle lobe but not the left.The ctenidia and their ciliary currents are typical of the Pectinidae except that the ascending lamellae of all demibranchs are greatly reduced and, it is suggested, previse the situation seen in the Propeamussiidae where they are lost and the ventral margins of the inner and outer descending lamellae fuse to create an ‘inside out’ gill. Unusually, the labial palps of Minnivola pyxidatus are fused to the mantle and visceral mass, preventing their collapse in the mantle cavity and thus maintaining particle selection efficiency. The gut is simple. Left and right statocysts are unusually equal and the pericardium is located dorsal to the adductor muscle. Minnivola pyxidatus is adapted to an epibenthic life on subtidal sands and muds. Powerful cleansing currents and an ability to swim have allowed this species to survive in dredged and trawled waters with high levels of settling and resuspended silt.

The biology and functional morphology of the coral‐boring Jouannetia cumingii (Bivalvia: Pholadacea)

The coral‐boring bivalve Jouannetia cumingii (Pholadacea) has been investigated from Phuket, Thailand. It only bores dead heads of Porites lutea and the siphons open, not on to the general coral surface, but into galleries created by other borers and inhabited by cryptobion. The bivalve may thus have a relationship not with the coral, except as a substratum, but with these other gallery occupants.The juvenile shell is anteroposteriorly reduced, the anterior face represented only by dorsally reflected shields between which extends the anterior adductor muscle. A considerable area of the anterior mantle is thus exposed to the burrow heading and there is a small pedal gape through which can be extended a large foot. This is absent, however, in the adult. The large posterior adductor is located between shell buttresses, one on the posterior face of each valve to reduce shear. Also attached here are small posterior pedal retractors. Anterior retractors are located on condyles projecting downwards from the hinge plate which is sunken and covered by the umbones and reflected anterior shell shields. The ligament is small, inequilateral, and covered by periostracum. A normal complement of mantle cavity organs is present but is reduced and posteroventrally‐anterodorsally aligned. Gill ciliation is of type C(1) and the labial palps are large.Mechanical boring, despite anterior shell teeth, is impossible and a chemical boring process is proposed from a large gland located internal to, and discharging via, the pedal gape. Secretion cannot be from the outer surface of the exposed mantle as this, because of extensive mantle fusion, is covered by periostracum.In the adult, a callum is formed over the exposed anterior regions of the mantle. Callum formation and sexual maturity occur over a wide size range and is related, as in other pholads, to an inability to bore further. The callum is not an extension of the true shell and is thought to be secreted from pallial glands located on the internal surface of the mantle and discharging via the pedal gape. As with boring, secretion cannot be from the exposed general mantle surface. The callum of the left valve is much larger and external to that of the right. Left callum formation must take place first, against the heading of the boring. Right callum formation must take place subsequently, largely against the left. Dorsally, the callum covers the anterior shields and all areas of exposed mantle. The unequal callum is a consequence of the mode of shell adduction in which the valves rock about dorsal and ventral fulcra: an equal callum would not permit this, the unequal form does, the right callum sliding beneath that of the left. Adult J. cumingii are almost perfectly spherical except for a spiked siphonoplax developed on the posterior face of the right valve only, by enhanced growth of shell lamellae.The spherical shell form in Jouannetia may be a consequence of this animal's more intimate association with the coral community which, in providing protection, obviates the need for deeper burrowing and thus an elongate shell form.

Larval development and metamorphosis in the marine pulmonate Amphibola crenata (Mollusca: Pulmonata)

The development of the free‐swimming veliger of Amphibola is followed from hatching to settlement, and the larval structures compared with those of post‐metamorphic juveniles and adult snails. Observations of living specimens and light‐microscope sections were combined with scanning electron microscopy to build up a composite picture of veliger structure.Four stages in the development of veligers are recognized, each being characterized by the appearance of organ systems such as the mantle cavity, larval heart, adult heart and kidney, and larval pallial gland. At or after metamorphosis, the larval systems (heart, kidney and pallial gland) disappear, and the developing adult organs move to the positions characteristic of adult snails.Organogenesis in Amphibola veligers is compared with that of prosobranch and opisthobranch larvae, and with that of pulmonate larvae with direct development. The closest similarity is seen to be with opisthobranch veligers.

The biology and functional morphology of Eufistulana mumia (Bivalvia: Gastrochaenacea)

Eufistulana mumia Spengler 1783 (Gastrochaenidae) is one of the rarest of all bivalves, a preserved specimen only once having been previously reported upon (Fischer, 1866). Eufistulana lies buried in subtidal sediments, entombed, except for a siphonal orifice, in an adventitious tube of its own construction. The tube comprises four layers secreted in stages by an equal number of pallial glands, housed in the reflected middle folds anteriorly, the reflected inner folds further posteriorly and the siphons. The process of tube formation is discussed. The larva probably settles on a calcareous substrate, possibly an empty shell, and then proceeds to construct a vertical tube when the initial site of settlement has been penetrated. Periodic dissolution of the original tube basally, possibly by a gland in the foot, is followed by growth downwards with a concomitant secretion of new tube material. At the end of a phase of growth a new base to the tube is secreted.The true shell of Eufistulana is modified with the anterior face very reduced, laterally expanded and, in life. covered by reflected middle folds. The posterior face is elongate and covered by reflected inner folds. The ventral margin is widely emarginate. The pedal gape is small and the foot reduced, the sole acting as a sucker attaching the animal to the tube and leaving a characteristic impression. There is a tiny, papilla‐like anterior pedal projection to the foot. A septum in the tube separates tissues contained within the shell from the siphonal region, possibly restricting entry into the basal region of sediment and small, shelter‐seeking, invertebrates. Similarly, the tips of the siphons possess glands that produce a secretion which probably deters would be inhabitants of the siphonal region of the tube.The major specializations of Eufistulana to its mode of life are pallial. In other respects it is a typical bivalve with little reduction of the pedal apparatus and few modifications to the organs of the mantle cavity. The labial palps are small implying little food selection in the mantle cavity. The intestine is adapted for handling large amounts of sediment.Soft deposits have been colonized in a number of ways by a number of bivalve lineages. Eufistulana is an example of another way in which this habitat has been exploited, albeit from an ancestor that was probably a borer.

Functional morphology ofBathyarca pectunculoides(Bivalvia: Arcacea) from a deep Norwegian fjord with a discussion of the mantle margin in the Arcoida

Abstract Bathyarca pectunculoides (Scacchi, 1834), a small Atlantic species, most noticeably possesses posterior extensions of the inner mantle folds which serve as simple siphons channelling inhalant and exhalant currents, discharging pseudofaeces, and permitting exchange with the water above even if the shell is covered by silt. The ctenidia are large, of the typical arcoid plan and ciliation, with the labial palps small. The ciliary currents of the mantle and visceral mass are powerful. A pallial gland, with a structure similar to that of the primitive bivalve hypobranchial gland, occurs on the posterior region of each mantle lobe and probably consolidates waste material to be expelled into the exhalant stream. The mantle margin comprises three folds as in the typical bivalve. The suggestion of Waller that the Arcoida possess an arrangement of pallial folds different from all other bivalves is discussed and it is concluded that in essence the same three folds occur, but that in the shallow-water Arcoida a special photosensory sub-fold of the outer fold has evolved, whereas in other bivalves this sensory function is typically an attribute of the middle fold. Bathyarca is modioliform, with a reduced anterior shell face and anterior adductor muscle. Shell form is typical of nestling species. Probably Bathyarca has evolved from an infaunal endobyssate shallow-water ancestor and the trend towards hetero-myarianism has resulted from, because of functional conservatism in the Arcoida, residence on the surface of the sediment, byssal attachment to sediment particles permitting this. This rare example of a deep-water suspension feeder (most other deep water bivalves being either deposit feeders or predators), is interesting in revealing how a primitive lineage has evolved mechanisms permitting colonization of soft deposits. Though normally placed in the Arcidae, B. pectunculoides possesses an arrangement of hinge teeth that more properly ally it with the extinct Palaeozoic Cyrtodontidae or Mesozoic Parallelodontidae. The question is posed: is Bathyarca a living remnant of an otherwise extinct primitive arcacean and pteriomorph stock?

Morphological and functional specializations of the shell, musculature and pallial glands in the Lithophaginae (Mollusca: Bivalvia)

The structure of the pallial glands in limestone and coral boring species of Lithophaga (Bivalvia: Lithophaginae) is examined and related to evolutionary trends in habitat specialization. Boring glands of all species occur in the middle mantle fold but display a progressive degree of complexity from simple epithelial to ducted sub‐epithelial structures coinciding with increasing specialization of habitat from natural limestone to species specific live coral dwellers. The size of this gland is relatively reduced anteriorly and along the entire length of the mantle in live coral borers.

Histochemical and biochemical Research on the pallial Gland of Lithophaga (Lithodomus) lithophaga L.

Histomorphological staining demonstrated 2 types of cells in the pallial gland of the mantle of Lithodomus lithophaga: gland cells containing glycolipoprotein and interstitial cells, containing lipid droplets. Biochemical analysis aiming at separate and evaluate lipidic and peptidic components were carried out by lipid extraction, T.L.C. separation and colorimetric assays. Phospho- and sulfolipids were separated from non-polar lipids. Sialo-cerebrosides (gangliosides) are missing. Hydrophobic peptide component was extracted and aminoacid analysis was made. The presence of acid (phosphate) group in the gland secretion is discussed in relation to the function of the secretion (Ca uptake and rock boring). The prominent glycogen storage is considered as an important energy source to be used for osmotic work and to synthesize glycosidic stones for glycolipo-protein secretion.

Some aspects of feeding in thecosomatous pteropod molluscs

Various aspects of the feeding behavior of thecosomatous pteropods of the families Cavoliniidae and Cymbuliidae have been examined both in the field with SCUBA, and in the laboratory. It was found that the family Cavoliniidae employs a ciliary-mucus feeding mechanism in which the mantle cavity water current and pallial gland are of primary importance in food collection. The feeding mechanism is discussed, as well as related aspects including buoyancy control, particle size range of natural diets, oxygen consumption, and water filtration rates. It is concluded that Cavolinia must have a high efficiency of retention and assimilation of available carbon.

Reproductive systems and cyclic release of eggs in Littorina melanostoma from Malayan mangrove swamps (Mollusca: Gastropoda)

Littorina melanostoma, living high in the tidal range on mangrove vegetation, has reproductive systems similar to those of other littorinids but characterized especially by a closed, tubular prostate and simple penis in the male, and by complex, spiral pallial glands in the female. Eggs are released in simple pelagic capsules which hatch to release veliger larvae in seven days. Egg capsules are released almost entirely during the periods of spring tide associated with full moon. Such release occurs at all seasons of the year. Some females release eggs at successive full moons but it appears likely that many females more commonly release eggs at alternate full moons. There is no evidence of endogenous rhythms of egg release related to the times of high tide or the day/night cycle.

The Larval Shell of Some Prosobranch Gastropods

Growth of shells of larvae ofNassarius reticulatus(L.) andCrepidula fornicata(L.) reared in the laboratory under constant temperature (14 °C) and illumination (155 lx) occurs by the addition of successive strips secreted at the mantle edge. Growth lines on the embryonic teloconch also indicate intermittent growth; the protoconch secreted by the shell gland has no such lines. There is evidence that growth periods are short and pauses separating them prolonged. The diameter of the older whorls of the shells of these and six other species examined increase with the volume of the viscera. This change in diameter is made possible by the flexibility of the organic matrix, the funda-mental constituent of the shell. The matrix, secreted as fibres at the mantle edge, forms sheets, and provides sites for the deposition of calcareous concretions; at metamorphosis the concretions apparently initiate the formation of crystals. The concretions also sculpture the surface of the shell producing a pattern sufficiently conspicuous to allow identification of some species with the aid of only the stereomicroscope. For example, large concretions form longitudinal rows over the protoconch and teloconch ofLittorina neritoides(L.) and smaller ones combine to form a more decorative pattern inRissoa sarsiLoven. In other species details of the surface design require a scanning electron micro-scope. Interspecific differences in the arrangement of concretions may be traceable to differences in the pallial glands which secrete the matrix.