Mantle Lobe Research Articles

New camaenid genus and species from Zhejiang, East China (Eupulmonata, Helicoidea).

We report a new land snail species representing a new genus from the mountainous area of Zhejiang, China. The snail has a depressed shell with granules all over the surface. The soft part of the new taxon is characterized by the presence of a mantle lobe whose form is reviewed herein across a wide range of helicoid snails, the presence of a developed epiphallic papilla, and the absence of a penial sheath, a dart sac apparatus and a flagellum. As indicated by a molecular-based phylogeny (16S + ITS2), the new taxon is deeply nested in the eastern Asian camaenid genera and shows a close relationship with the camaenids distributed in Central China.

A new lineage of fresh‐ and brackish‐water mussels (Bivalvia, Mytilidae) from Southeast Asia

AbstractThree species of mussels collected from fresh‐ and low salinity (10 psu or lower) brackish‐water environments in southern Thailand, Singapore, northern Borneo and south Sulawesi formed a new, well‐supported and distinct mytilid clade based on molecular phylogeny. All are small (< 30 mm) species with either radially ribbed or smooth shells. Internally, the upper edges of the ascending lamellae of the outer and inner demibranchs are, respectively, fused to the mantle lobes and visceral mass. A new genus Parabrachidontes is proposed to accommodate the three species. Of the species in the new genus, one is described as new (Parabrachidontes amnicus sp. n.), and the other two poorly known species (P. leucostictus and P. cochinensis) are re‐described. The Parabrachidontes clade is closely related to Mytella, Perna and Arcuatula. Together, they formed a well‐supported clade, most members of which have ctenidial edges attached to the mantle and/or visceral mass. These genera are clearly distinct phylogenetically from two other mytilid clades containing brackish‐ and fresh‐water species with ctenidia free of the mantle: one comprising the genera Limnoperna and Sinomytilus (together constituting the Limnoperninae), and the other Xenostrobus and Vignadula (forming the Xenostrobinae). We therefore suggest the existence of at least three lineages of mytilids living in rivers and estuaries of East Asia and Australasia.

Systematic revision of the limestone karst-restricted land snail genus Aenigmatoconcha (Eupulmonata: Helicarionidae), with description of a new species

Thai limestone karsts are known to contain a rich biodiversity of animals, especially terrestrial snails, but still require further intensive exploration to evaluate their biodiversity. To date, only a few studies on the limestone karst-inhabiting land snail genera have been published. The present work focuses on the species diversity and phylogenetic relationships of the limestone karst-restricted land snail genus Aenigmatoconcha from Thailand, based on comparative morphology and molecular evidence. The results yielded three known species (A. clivicola Tumpeesuwan & Tumpeesuwan, 2017, A. sumonthai Tumpeesuwan & Tumpeesuwan, 2018, and A. mitis (Pfeiffer, 1863) comb. nov.), plus a new species (A. eunetis Pholyotha & Panha sp. nov). The phylogenetic analyses of partial fragments of the mitochondrial cytochrome oxidase c subunit I (COI) gene confirmed the monophyly of all recognized species and congruence with the traditional morphology-based species designations. Average uncorrected p-distances of COI sequences between species were 9.7–12.0% and within species were 0.2–4.2%. This study also provides the re-description of penial sculpture, penial sheath, flagellum, penial caecum, and mantle lobe morphology that were neglected from the type species description. The present discovery of a new species increases the known diversity of Thai land snails and will support the conservation planning to protect karst biodiversity.

When size matters: the first comprehensive anatomical study of a species of "Condylocardiidae", an extremely miniaturized bivalve.

‘Miniaturization’ is a widespread phenomenon among the Metazoa. In the molluscan class Bivalvia, records of miniaturization are numerous. Among the Archiheterodonta, Warrana besnardi (Klappenbach, 1963) has attracted attention for its tiny size, which does not exceed 1.5 mm in shell length, and because it belongs to a group with limited anatomical information and often-debated status, the “Condylocardiidae” (which recent molecular studies place deeply nested within the family Carditidae). All species of Warrana Laseron, 1953 are small-bodied, and so miniaturization presumably occurred from a large-bodied ancestor within the Carditidae sensu lato. South American W. besnardi is here studied in detail. Its small size and the enlargement of the anterodorsal region during growth, reflects (and likely led) to infaunal habit, living as a burrowing bivalve that passively feeds on deposit particles entering the pallial cavity anteriorly. Mantle glands, previously reported as a common feature of other archiheterodonts, are missing in W. besnardi, but spongiform tissue in the antero-ventral portion of the mantle lobes presumably represents a blood sinus that might compensate for the great reduction of the ctenidia. Lecithotrophy is reported, with yolky oocytes bearing a thick non-cellular capsule layer; brooding was not observed, and it is here hypothesized that the extreme miniaturization, with the great reduction of ctenidia, is responsible for a shift in the reproductive mode of condylocardiids, contrasting with the commonly reported ovoviviparity of the carditids.

Mechanics unlocks the morphogenetic puzzle of interlocking bivalved shells

Brachiopods and mollusks are 2 shell-bearing phyla that diverged from a common shell-less ancestor more than 540 million years ago. Brachiopods and bivalve mollusks have also convergently evolved a bivalved shell that displays an apparently mundane, yet striking feature from a developmental point of view: When the shell is closed, the 2 valve edges meet each other in a commissure that forms a continuum with no gaps or overlaps despite the fact that each valve, secreted by 2 mantle lobes, may present antisymmetric ornamental patterns of varying regularity and size. Interlocking is maintained throughout the entirety of development, even when the shell edge exhibits significant irregularity due to injury or other environmental influences, which suggests a dynamic physical process of pattern formation that cannot be genetically specified. Here, we derive a mathematical framework, based on the physics of shell growth, to explain how this interlocking pattern is created and regulated by mechanical instabilities. By close consideration of the geometry and mechanics of 2 lobes of the mantle, constrained both by the rigid shell that they secrete and by each other, we uncover the mechanistic basis for the interlocking pattern. Our modeling framework recovers and explains a large diversity of shell forms and highlights how parametric variations in the growth process result in morphological variation. Beyond the basic interlocking mechanism, we also consider the intricate and striking multiscale-patterned edge in certain brachiopods. We show that this pattern can be explained as a secondary instability that matches morphological trends and data.

Jawless land snail Sinorachis, a new bradybaenine genus from China (Eupulmonata, Camaenidae).

A new land snail species that represents a new genus is reported from Hubei, China. The snail has a conical shell with pits and/or granules on embryonic whorls and a smooth teleoconch with straight peristome. The head of the animal has a developed wart. The mantle lobe is only developed on the left side. At the front of the buccal mass there is no chitinous jaw that is without exception seen in Chinese camaenids. Its radular teeth are usually slender and tongue-shaped, not typical in bradybaenine snails. The genital system is typical of Bradybaeninae and is characterized by the absence of a membranous sac surrounding the terminal genitalia, penial caecum or flagellum; a well-developed penis sheath; a symmetrical dart sac apparatus; and one distally branched mucous gland. The new species Sinorachis baihu Wu & Chen, gen. and sp. nov., is assigned to the type species of the new genus, in which all the known Chinese Rachis species are included. Thereby, the new genus is composed of three species, namely Sinorachis onychinus (Heude), comb. nov., Sinorachis aureus (Heude), comb. nov. and the new species.

The controlling mechanism of mid- to late Holocene carbon isotopic variations of Tridacnidae in the South China Sea

The carbon isotopic fractionation process in biogenic carbonate is very complex, and the mechanism for seasonal and long-term variations in biogenic carbonate δ13C remains a matter of debate. In this study, 5 Tridacnidae samples were collected from the South China Sea and analyzed in detail to study seasonal variations. The high-resolution δ13C records exhibited cyclic variations, likely related to seasonality in environmental parameters (e.g., Chl-a concentration, salinity, SST, rainfall). 57 Tridacnidae were collected and analyzed to study the millennium-scale changes of Tridacnidae δ13C during the mid- to late Holocene and the controlling mechanism. The Tridacnidae δ13C over the period 500–5500 BP is statistically significantly correlated with solar activity (TSI and sunspot number), likely attributed to the presence of symbiotic zooxanthellae within Tridacnidae's mantle lobes. Solar activity could significantly affect the metabolic activity of zooxanthellae, Tridacnidae's microenvironment, and thus Tridacnidae's δ13C composition. The decoupling between the Tridacnidae δ13C and solar activity over the past 200 years is most likely due to increased amount of anthropogenic CO2 and the oceanic δ13C Suess effect. This study improves our understanding about the seasonal and long-term variations of δ13C in Tridacnidae.

Hox gene expression in postmetamorphic juveniles of the brachiopod Terebratalia transversa

BackgroundHox genes encode a family of homeodomain containing transcription factors that are clustered together on chromosomes of many Bilateria. Some bilaterian lineages express these genes during embryogenesis in spatial and/or temporal order according to their arrangement in the cluster, a phenomenon referred to as collinearity. Expression of Hox genes is well studied during embryonic and larval development of numerous species; however, relatively few studies focus on the comparison of pre- and postmetamorphic expression of Hox genes in animals with biphasic life cycle. Recently, the expression of Hox genes was described for embryos and larvae of Terebratalia transversa, a rhynchonelliformean brachiopod, which possesses distinct metamorphosis from planktonic larvae to sessile juveniles. During premetamorphic development, T. transversa does not exhibit spatial collinearity and several of its Hox genes are recruited for the morphogenesis of novel structures. In our study, we determined the expression of Hox genes in postmetamorphic juveniles of T. transversa in order to examine metamorphosis-related changes of expression patterns and to test whether Hox genes are expressed in the spatially collinear way in the postmetamorphic juveniles.ResultsHox genes are expressed in a spatially non-collinear manner in juveniles, generally showing similar patterns as ones observed in competent larvae: genes labial and post1 are expressed in chaetae-related structures, sex combs reduced in the shell-forming epithelium, whereas lox5 and lox4 in dorso-posterior epidermis. After metamorphosis, expression of genes proboscipedia, hox3, deformed and antennapedia becomes restricted to, respectively, shell musculature, prospective hinge rudiments and pedicle musculature and epidermis.ConclusionsAll developmental stages of T. transversa, including postmetamorphic juveniles, exhibit a spatial non-collinear Hox genes expression with only minor changes observed between pre- and postmetamorphic stages. Our results are concordant with morphological observation that metamorphosis in rhynchonelliformean brachiopods, despite being rapid, is rather gradual. The most drastic changes in Hox gene expression patterns observed during metamorphosis could be explained by the inversion of the mantle lobe, which relocates some of the more posterior larval structures into the anterior edge of the juveniles. Co-option of Hox genes for the morphogenesis of novel structures is even more pronounced in postmetamorphic brachiopods when compared to larvae.

Palaeoecology of Macaronichnus segregatis degiberti: Reconstructing the infaunal lives of the travisiid polychaetes

Macaronichnus segregatis degiberti, a relatively large ichnosubspecies of Macaronichnus segregatis, is an almost straight to gently curved, cylindrical, fossilized burrow, oriented horizontal to oblique to the bedding plane. It is interpreted as a pascichnial trace fossil formed through selective sand feeding and excretion of a free-living polychaete, such as a relatively large travisiid (formerly classified as opheliid or scalibregmatid) polychaete Travisia. While the other ichnosubspecies, i.e., M. s. segregatis, M. s. lineiformins, M. s. meandriformis, and M. s. spiriformis, are commonly 2–5 mm in diameter and occur exclusively in foreshore deposits, M. s. degiberti attains a diameter of up to 15 mm and shows wide environmental distribution, ranging from tidal channels, tidal sand bars, tidal sandridges, tidal flats, upper to lower shorefaces, bioturbated sandy shelves, shelf storm-sheets, to shelf sand ridges. The core of M. s. degiberti, consisting mainly of light mineral-rich sand grains, is composed of alternating lamellae of light mineral-rich and heavy mineral-rich sands, arranged oblique to the bedding plane. On the other hand, the mantle, composed mainly of heavy mineral-rich sands, has a smooth outline, or evenly spaced lobes flanked on both sides. The morphology of the mantle lobes and core lamellae suggests repeated pulses of sediment probing and excreting behaviour of the tracemaker. Two or more burrows of this ichnosubspecies tend to occur adjacently, sometimes intertwining. As Travisia develops directly, lacking any planktic larval stages, aggregations of the burrows can be interpreted to reflect the burrowers' interindividual exploratory behaviour with the aim of copulation. Travisia, also known as a “stink worm”, secretes volatile chemical substances that might act as sex pheromones to attract other individuals for reproduction within the substrate. Therefore, a new category of ethological classification of trace fossils “sequorichnia” (sequor, follow; and ichnia, traces), for exploration of other individuals, is proposed here. This is the first record of interindividual exploratory behaviour of infaunae.

Possible co-option of engrailed during brachiopod and mollusc shell development.

In molluscs, two homeobox genes, engrailed (en) and distal-less (dlx), are transcription factors that are expressed in correlation with shell development. They are expressed in the regions between shell-forming and non-shell-forming cells, likely defining the boundaries of shell-forming fields. Here we investigate the expression of two transcription factors in the brachiopod Lingula anatina We find that en is expressed in larval mantle lobes, whereas dlx is expressed in larval tentacles. We also demonstrate that the embryonic shell marker mantle peroxidase (mpox) is specifically expressed in mantle lobes. Our results suggest that en and mpox are possibly involved in brachiopod embryonic shell development. We discuss the evolutionary developmental origin of lophotrochozoan biomineralization through independent gene co-option.

Size at first maturity of Brachidontes rodriguezii (d'Orbigny, 1846) from the South-western Atlantic Ocean

The size at first maturity of the bivalve Brachidontes rodriguezii was estimated in a population located in the northernmost limit of its distribution along Argentinean coast. Specimens were collected in two consecutive reproductive seasons from December 2011 to February 2012 and from December 2012 to February 2013. Individuals were evaluated using biometric and histological analyses of the gonads. This study intended to provide important information about the development of gonadal tissue according to shell length increase. Our results showed immature specimens lack gonads or exhibited groups of cells undergoing mitosis adjacent to the epithelium of the mantle and the tubules of the digestive gland. Male and female gonad development extended to mantle lobes and visceral mass as long as maturation occurred to reach sexual maturity. Using a logistic model our results showed that the size at which 50% of females were mature at a gonadal level was 7.05 mm in shell length; in males, 50% of the population were mature at 8.13 mm in shell length. The minimum shell length at which maturity was observed was 6.99 mm in shell length in females and 6.00 mm in shell length for males.

Larval development of Brachiopod Coptothyris grayi (Davidson, 1852) (Brachiopoda, Rhynchonelliformea).

The larval development of the Brachiopod Coptothyris grayi (Davidson, 1852) from the Sea of Japan is described for the first time. Ciliated blastula proved to represent the first free-swimming stage. The blastopore is initially formed as a rounded hole stretching later along the anteroposterior axis. The larva is first divided into two lobes (the apical lobe and the trunk); the mantle lobe is formed later as two lateral folds. Two pairs of seta bundles appear in the late stage larvae. The apical larval lobe in brachiopods is supposed to match the pre-oral lobe and anterior part of the trunk with tentacles in phoronids.

Morphology and taxonomy of Isognomon spathulatus (Reeve, 1858), a cryptic bivalve from the mangroves of Thailand.

Isognomon spathulatus (Reeve, 1858) is redescribed based on type material and original collections from Kungkrabaen Bay, Thailand. The species agrees with previously described isognomonids in most conchological and anatomical features, but possesses a suite of diagnostic characters, including a comma-shaped outline of the nacreous border, an uncoiled ventral diverticulum of the stomach, and the thickened mantle lobes with granulated cells. This study is the most comprehensive morphological analysis to date for any species of Isognomonidae Woodring, 1925 (1828). It describes and illustrates a number of previously unrecognized or underutilized anatomical characters of potential phylogenetic significance: the morphology of the byssal threads (cross-sectional shape, plumate rootlets, and the shape of adhesive disks), the presence and extent of the interdemibranchial buttresses, the presence of secretory cells in the central zone of the mantle, the shape of the ventral diverticulum of the gastric chamber, the presence of the typhlosolar guard ridge, and the position of the renal pore. A comparison is made between I. spathulatus and morphologically similar Isognomon ephippium (Linnaeus, 1758) with which it has been previously synonymized. Pearls of both species are described and illustrated. Individuals of I. spathulatus inhabit mangroves, where they attach by byssus to prop roots, typically in parapatry with individuals of I. ephippium that occupy adjacent mudflats. The spacial distribution and diverging adaptive strategies (pertaining to physical stabilization and response to predation) displayed by the two isognomonid species are considered in the light of the ecological speciation theory.

Occurrence and characterization of pearls from oysters of the genus Crassostrea

The occurrence of pearls in the ‘true’ oysters, the Ostreioidea, is poorly documented despite being the most produced mollusc species in the world. Oysters of the Crassostrea genus were collected in two different sites in southern Portugal where both Crassostrea angulata and C. gigas are present, namely in: (1) the Ria Formosa lagoon where pearls were not observed (N = 446); and (2) the Guadiana estuary where pearls were found in 12 out of the 798 oysters analysed. The pearls were located mainly at the edge of the right mantle lobe in the inhalant chamber and their maximum length ranged from 0.9 to 5.5 mm. Almost all the pearls had a white-cream colouration with the exception of two pearls that had a black-brown colour. X-ray diffraction analysis of one pearl showed that it was entirely calcitic with no traces of either aragonite or vaterite. The pearls observed were therefore non-nacreous pearls. Scanning electron microscopy (SEM) revealed a diversity of microstructures including prismatic, foliae-like sheets and blocky textures, i.e. highly reminiscent of the host oyster shell microstructures. Parasites (e.g. parasitic copepods, Haplosporidium-like plasmodia) and signs of diseases (e.g. foot disease) were observed in some of the oysters analysed, but they were not associated with the occurrence of pearls. The present work is one of the few studies on the occurrence of natural pearls in ‘true’ oysters and to our knowledge the first description of their microstructure by SEM.

Accumulation of Enterococcus faecalis and variation of SOD and ACP activities in scallop Pactinopecten yessoensis tissues

Enterococcus faecalis is a common bacterium found in aquatic environment and intestines of warm-blooded animals and human.In summer,it can reach high level in sewage-polluted seawater and be accumulated by scallops.Large numbers of bacteria may constitute significant health risk to cultured animals at high temperature or in other specific conditions.However,the retention of E.faecalis in scallop remains unclear,and information about hosts' growth performance,innate immunity and disease outbreak after a long-term exposure to non-pathogenic fecal bacteria is limited.The present study aims to investigate the relationship between retention of an opportunistic bacterium and variation in immune enzyme activity in the scallop,Pactinopecten yessoensis.The findings of this study will be useful for developing aquaculture probiotics and will provide scientific basis for sustainable aquaculture of bivalves. By bath exposure,the accumulation and distribution of E.faecalis in scallop tissues were analyzed,and the variation in activities of two immunity-related enzymes in haemolymph were also detected.After exposure to seawater inoculum of 5 lg(CFU/mL) E.faecalis for two weeks,the uptake of bacteria at day 1,3,5,7 and 14 and their distribution in scallop tissues were detected by plate counting method respectively.The activity of acid phosphatase(ACP) and superoxide dismutase(SOD) were also determined both in haemocytes and in serum of P.yessoensis.The uptake results showed that at 7 d top level of E.faecalis[5.20 lg(CFU/g)]were tested in scallop tissues,but at 14 d it decreased to the level of 3 d after treatment.However,the rate of bacterial accumulation(RA) was the highest at 1 d,and then significantly decreased(P0.05).It indicated that the bacterial accumulation rate in scallops decreased with exposure time.The top level of E.faecalis,over ten times higher than the average density of total tissues,was observed in digestive tract,mantle lobes and gills,but the lowest was detected in haemolymph,over 100 times lower than the average.SOD and ACP activities in cell-free haemolymph significantly increased to the maximum at 7 d,and then decreased.It can be deduced that there was a positive correlation between enzyme activities in serum and the bacterial accumulation in scallop(P0.05).Soluble factors in serum were more sensitive to bacterial accumulation than those in haemocytes,therefore,the serum may be a chief part of innate immune system of bivalves to digest and kill invading bacteria.Bivalves have an open circulatory and innate immune system.Haemocytes and soluble factors operate in a coordinated way to provide protection from invading microorganisms,and different types of haemocytes play various roles in innate immunity.Understanding the immune response in bivalves to invasive infections at cellular and molecular levels offers a theoretical base for exploring molluscan probiotics.Further study on variations in activities and gene expression in haemocytes and the roles of different scallop tissues in immune system is required.

Healing and regeneration of the freshwater pearl mussel Hyriopsis cumingii Lea after donating mantle saibos

After excision of mantle tissue from Hyriopsis cumingii Lea, survival rates, specific growth rate, healing and regeneration were observed and quantified for three months. High survival rates (94.7%, 92%, 95.3% and 94.7%, respectively) of mussels with small (8–12mm×8–12mm) (S-group)excision taken from the front, middle and back of the ventral mantle margin, and control mussels were observed, and no significant difference was observed among the four groups. The specific growth rates, SGR (length), SGR (thickness) and SGR (weight) of H. cumingii with different excision locations did not differ significantly but the SGR (height) of the group with the front excision was significantly lower than that of the other excised groups and controls. Mussels were excised with small, medium (8–12mm×28–32mm) (M-group) or large (8–12mm×48–52mm) (L-group) from the middle ventral mantle margin. The survival rates of mussels with S-, M- and L-group and controls were, respectively, 92%, 90%, 90.7% and 94.7%. The survival rate of the L-group was significantly lower than that of the other three groups. The trends in SGR (length), SGR (height), SGR (thickness) and SGR (weight) among the four groups were similar: controls>S-group>M-group>L-group. Macroscopic observation of mantle tissue showed that the wound area became reduced since 12th d after the excision. To grow to the same level as the surrounding normal tissue, the regenerated tissue needed 40d, 75d and 90d, respectively, in the S-, M-, and L-group. Histological observation of wound tissues showed that haemocytes aggregated at the wound site soon after excision and completely sealed the wound after 12h. Epithelialization sealed the wound completely after 72h. The three mantle lobes began to form at 15d. The regenerated lobes were morphologically different from normal tissues after 25d but were identical to the normal mantle lobes, in both morphological structure and function, by 90d. This is the first report on the survival rate, growth rate, wound healing, and regeneration in the freshwater pearl mussel after excision of its mantle tissue. The study demonstrates that donor mussels, without being killed, may donate mantle pieces (saibos) for evaluating the effect of donor mussel on pearl quality. Donor mussels contributing to pearl quality, this provides support for selective breeding of donor mussels in the future.

Development of the larval anterior neurogenic domains of Terebratalia transversa (Brachiopoda) provides insights into the diversification of larval apical organs and the spiralian nervous system.

BackgroundLarval features such as the apical organ, apical ciliary tuft, and ciliated bands often complicate the evaluation of hypotheses regarding the origin of the adult bilaterian nervous system. Understanding how neurogenic domains form within the bilaterian head and larval apical organ requires expression data from animals that exhibit aspects of both centralized and diffuse nervous systems at different life history stages. Here, we describe the expression of eight neural-related genes during the larval development of the brachiopod, Terebratalia transversa.ResultsRadially symmetric gastrulae broadly express Tt-Six3/6 and Tt-hbn in the animal cap ectoderm. Tt-NK2.1 and Tt-otp are restricted to a central subset of these cells, and Tt-fez and Tt-FoxQ2 expression domains are already asymmetric at this stage. As gastrulation proceeds, the spatial expression of these genes is split between two anterior ectodermal domains, a more dorsal region comprised of Tt-Six3/6, Tt-fez, Tt-FoxQ2, and Tt-otp expression domains, and an anterior ventral domain demarcated by Tt-hbn and Tt-NK2.1 expression. More posteriorly, the latter domains are bordered by Tt-FoxG expression in the region of the transverse ciliated band. Tt-synaptotagmin 1 is expressed throughout the anterior neural ectoderm. All genes are expressed late into larval development. The basiepithelial larval nervous system includes three neurogenic domains comprised of the more dorsal apical organ and a ventral cell cluster in the apical lobe as well as a mid-ventral band of neurons in the mantle lobe. Tt-otp is the only gene expressed in numerous flask-shaped cells of the apical organ and in a subset of neurons in the mantle lobe.ConclusionsOur expression data for Tt-Six3/6, Tt-FoxQ2, and Tt-otp confirm some aspects of bilaterian-wide conservation of spatial partitioning within anterior neurogenic domains and also suggest a common origin for central otp-positive cell types within the larval apical organs of spiralians. However, the field of sensory neurons within the larval apical organ of Terebratalia is broader and composed of more cells relative to those of other spiralian larvae. These cellular differences are mirrored in the broader spatial and temporal expression patterns of Tt-FoxQ2 and Tt-otp. Corresponding differences in the expression of Tt-hbn, Tt-NK2.1, and Tt-FoxG are also observed relative to their respective domains within the cerebral ganglia of spiralians. Based on these data we argue that the anterior region of the bilaterian stem species included Six3/6, NK2.1, otp, hbn, fez, and FoxQ2 expression domains that were subsequently modified within larval and adult neural tissues of protostome and deuterostome animals.

Homeobox gene expression in Brachiopoda: The role of Not and Cdx in bodyplan patterning, neurogenesis, and germ layer specification

The molecular control that underlies brachiopod ontogeny is largely unknown. In order to contribute to this issue we analyzed the expression pattern of two homeobox containing genes, Not and Cdx, during development of the rhynchonelliform (i.e., articulate) brachiopod Terebratalia transversa. Not is a homeobox containing gene that regulates the formation of the notochord in chordates, while Cdx ( caudal) is a ParaHox gene involved in the formation of posterior tissues of various animal phyla. The T. transversa homolog, TtrNot, is expressed in the ectoderm from the beginning of gastrulation until completion of larval development, which is marked by a three-lobed body with larval setae. Expression starts at gastrulation in two areas lateral to the blastopore and subsequently extends over the animal pole of the gastrula. With elongation of the gastrula, expression at the animal pole narrows to a small band, whereas the areas lateral to the blastopore shift slightly towards the future anterior region of the larva. Upon formation of the three larval body lobes, TtrNot expressing cells are present only in the posterior part of the apical lobe. Expression ceases entirely at the onset of larval setae formation. TtrNot expression is absent in unfertilized eggs, in embryos prior to gastrulation, and in settled individuals during and after metamorphosis. Comparison with the expression patterns of Not genes in other metazoan phyla suggests an ancestral role for this gene in gastrulation and germ layer (ectoderm) specification with co-opted functions in notochord formation in chordates and left/right determination in ambulacrarians and vertebrates. The caudal ortholog, TtrCdx, is first expressed in the ectoderm of the gastrulating embryo in the posterior region of the blastopore. Its expression stays stable in that domain until the blastopore is closed. Thereafter, the expression is confined to the ventral portion of the mantle lobe in the fully developed larva. No TtrCdx expression is detectable in the juvenile after metamorphosis. This expression of TtrCdx is congruent with findings in other metazoans, where genes belonging to the Cdx/caudal family are predominantly localized in posterior domains during gastrulation. Later in development this gene will play a fundamental role in the formation of posterior tissues.

Earliest ontogeny of Early Palaeozoic Craniiformea: implications for brachiopod phylogeny

Popov, L.E., Bassett, M.G., Holmer, L.E., Skovsted, C.B. & Zuykov, M.A. 2010: Earliest ontogeny of Early Palaeozoic Craniiformea: implications for brachiopod phylogeny. Lethaia, Vol. 43, pp. 323–333. Well preserved specimens of the Early Palaeozoic craniiform brachiopods Orthisocrania and Craniops retain clear evidence of a lecithotrophic larval stage, indicating the loss of planktotrophy early in their phylogeny. The size of the earliest mineralized dorsal shell was <100 μm across, and the well preserved shell structure in these fossil craniiforms allows their earliest ontogeny to be compared directly with that of living Novocrania, in which the first mineralized dorsal shell (metamorphic shell) is secreted only after settlement of the lecithotrophic larvae. Immediately outside this earliest shell (early post-metamorphic or brephic shell) and in the rest of the dorsal valve the primary layer in both fossil and living craniiforms has characteristic radially arranged laths, which are invariably lacking in the earliest dorsal shell. The ventral valve of the fossil specimens commonly preserves traces of an early attachment scar (cicatrix), which is equal in size to the dorsal metamorphic shell, and the brephic post-metamorphic ventral valve also has a primary shell with radially arranged laths. However, a primary shell with radial laths is completely lacking in the ventral valve of living Novocrania, indicating that heterochrony may have been involved in the origin of the encrusting mode of life in living craniids; the entire ventral valve of Recent craniids (with the possible exception of Neoancistrocrania) may correspond to the earliest attachment scar of some fossil taxa such as Orthisocrania. It is also probable that the unique absence of an inner mantle lobe as well as the absence of lobate cells in Novocrania could be the result of heterochronic changes. The dorsal valve of both fossil and living craniiforms has a marked outer growth ring, around 500 μm across, marking the transition to the adult, and a significant change in regime of shell secretion. The earliest craniiform attachment is considered to be homologous to the unique attachment structures described recently in polytoechioids (e.g. Antigonambonites) and other members of the strophomenate clade. However, unlike the craniiforms, polytoechioids and strophomenates all have planktotrophic larvae, and planktotrophy is most probably a plesiomorphic character for all Brachiopoda. □Brachiopoda, Craniiformea, Early Palaeozoic, ontogeny, phylogeny.

Regeneration of excised mantle tissue by the silver-lip pearl oyster, Pinctada maxima (Jameson)

This study investigated the capacity for mantle regeneration in the pearl oyster Pinctada maxima. Oysters were anaesthetised with 2.5 mL L −1 prophylene phenoxetol prior to a piece of tissue (approximately 10 × 30 mm 2) being excised from the ventral region of the mantle. In the first experiment, 56 oysters with mean (±SD) dorso–ventral measurement (DVM) of 125.5 ± 8.9 mm had tissue excised from either the right mantle lobe, left mantle lobe or both mantle lobes. Following a further three month period in suspended culture, oyster survival was recorded and two oysters were selected arbitrarily from each group to be sacrificed for histological examination of healed mantle. In the second experiment 36 oysters with mean (±SD) DVM of 151.6 ± 13.4 mm were used for excision of the distal part of the ventral region of the left mantle lobe. Two oysters were sampled at 1, 3, 6, 12, 24, 36, 48, 72 and 120 h (5 days) after mantle excision, and then at 12, 24, 45, 72 and 90 d after mantle excision for histological and histochemical analysis of mantle regeneration. There was almost 100 percent survival in both experiments. Healing and regeneration of mantle tissue in oysters subject to excision from the left, right or both mantle lobes was evident, with regenerated mantle appearing similar to non-regenerated mantle. All external and internal components of non-regenerated mantle were present in regenerated mantle tissue. Epithelization signifying wound healing occurred within 36–72 h and was characterised by a reduced wound area, haemocyte infiltration and accumulation, and cell dedifferentiation. Within 48 h of mantle excision, the latero-ventral edges of the wound flexed dorsally and attached to the dorsal edge of the wound reducing the wound area. Between five and twelve days after excision, the distal part of the mantle had divided into three small lobes which developed into the outer, middle and inner mantle folds two weeks later. Ninety days after excision the mantle had completely regenerated with histological observations indicating no difference in epithelial structure or in other internal mantle accessories when compared to non-regenerated mantle. Shell material began to be secreted onto the shell by regenerating mantle twelve days after excision. Initially this occurred in a position dorsal to the non-injured mantle edge. However, forty-five days after mantle excision, regenerated mantle had extended ventrally to a position similar to that of non-injured mantle. Nacre deposition by regenerated mantle had now reached the same position ventrally as that of non-injured mantle indicating full acquisition of nacre secreting abilities by regenerated mantle.