The ecology and functional morphology of Trigonothracia jinxingae (Bivalvia: Anomalodesmata: Thracioidea) from Xiamen, China

All anomalodesmatans are 'rare' but Trigonothrucia jinxingae is relatively common in Xiamen Harbour, Fujian Province, China. This is because the species has a life span of approximately one year and is a simultaneous hermaphrodite, probably with either a short or absent planktonic larval stage. That is, success results from rapid maturation, self-fertilization, direct development and within-habitat recruitment over an extended period in early summer.
Trigonothracia jinxingae is interesting in another way, however. The Thraciidae is the Mesozoic stem group of the Thracioidea which also contains the more modern (Caenozoic) Laternulidae and Periplomatidae. Features of the anatomy of T. jinxingae , such as the method of hydraulically moving the foot by the pumping of blood into a capacious pallial haemocoel, and the structure of the stomach, are reminiscent of the earliest (Palaeozoic) anomalodesmaans, i.e. the Pholadomyoidea, represented today by Pholadomya candida. The thraciid Asthenothaerus sp. (Pelseneer, 1911) even has, like P. cundida , an opisthopodium on its visceral mass. P. candida , however, fed on sub-surface deposits using its foot. T. jinxingae is also a deposit feeder, but on surface deposits using the inhalant siphon.
Modern periplomatids resemble thraciids in their separate siphons, but both representatives of this family and the Laternulidae are suspension feeders with extensive sorting areas on the wall of the stomach to process such material. The Thraciidae thus form a link between the oldest, pedal feeding, pholadomyoidean anomalodesmatan and the most advanced, suspension feeding, laternulids and periplomatids.     

Within- and among-lake variation in shell morphology of the freshwater clam Elliptio complanata (Bivalvia: Unionidae) from south-central Ontario lakes

To compare the relative magnitude of variation in shell morphology within and among lakes, Elliptio complanata were collected from low and high exposure areas in each of four small lakes in south-central Ontario. Nested ANOVA's on shell length, height, width and weight revealed that shell morphology varied much more between sites of differing exposure within a lake than among lakes of differing alkalinity. Canonical variates analysis showed that clams from high exposure areas had larger and proportionately taller and heavier shells than those from low exposure areas. There was no relationship between alkalinity of lakes and shell morphology. These results suggest that the use of unionid shell morphology to predict long-term whole lake water chemistry (e.g. alkalinity) requires sampling designs which take into account within-lake variation in shell morphology.     

The biology and functional morphology of Arca noae (Bivalvia: Arcidae) from the Adriatic Sea, Croatia, with a discussion on the evolution of the bivalve mantle margin

In the Croatian Adriatic, Arca noae occurs from the low intertidal to a depth of 60 m; it can live for > 15 years and is either solitary or forms byssally attached clumps with Modiolus barbatus. The shell is anteriorly foreshortened and posteriorly elongate. The major inhalant flow is from the posterior although a remnant anterior stream is retained. There are no anterior but huge posterior byssal retractor muscles and both anterior and posterior pedal retractors. The ctenidia are of Type B(1a) and the ctenidial–labial palp junction is Category 3. The ctenidia collect, filter and undertake the primary sorting of potential food in the inhalant water. The labial palps are small with simple re‐sorting tracks on the ridges of their inner surfaces. The ciliary currents of the mantle cavity appear largely concerned with the rejection of particulate material. The mantle margin comprises an outer and an (either) inner or middle fold. The outer fold is divided into outer and inner components that secrete the shell and are photo‐sensory, respectively. The latter bears a large number of pallial eyes, especially posteriorly. The inner/middle mantle fold of A. noae, possibly representative of simpler, more primitive conditions, may have differentiated into distinct folds in other recent representatives of the Bivalvia.     

Arenophilic mantle glands in the Laternulidae (Bivalvia: Anomalodesmata) and their evolutionary significance

The mantle margins of several anomalodesmatans bear multicellular arenophilic glands, the mucoid secretions of which attach sand grains and other foreign particles to the outer surface of the periostracum. These glands have been recorded for many of the anomalodesmatan families and are used as a key morphological character in recent attempts to unravel the evolutionary relationships within the Anomalodesmata. The glands occur in Laternula elliptica, L. truncata, L. boschasina and L. marilina, discharging from the top of muscular papillae at the distal tip of the siphons. The secretions are laid down as threads organized in longitudinal lines along the length of the periostracum that covers the siphonal walls. This is the first record of arenophilic mantle glands in members of the Laternulidae, a finding that not only broadens our current knowledge of the family's morphology, but assists in the reconstruction of anomalodesmatan evolutionary history.     

Shell and hinge morphology of juvenile Limopsis (Bivalvia: Arcoida) - implications for limopsid evolution

Early ontogenetic shells of Limopsis angusta, L. aurita, L. cristata, L. friedbergi and L. minuta are described in detail and their morphogenetic traits discussed in a phylogenetic context. Prodissoconch length is found to range from 170-370 µm discounting the so-called prodissoconch 2 stage of authors. Reports of such a stage refer to the early postlarval 'interdissoconch'. Prodissoconch sizes are indicative of lecithotrophy but not of brooding. Limopsid-like prodissoconchs are rather common among pteriomorphs and at present of little use for phylogenetic interpretations, therefore. The early postlarval hinge is characterized by two tooth generations: an early one, (G1), representing the postlarval continuation of provincular teeth, and a late one, (G2), representing the independent adult dentition. This is a plesiomorphic trait for Pteriomorphia. The postlarval ligament is continuous with the larval resilium; it is neither co-functional with nor is it substituted by the typical duplivincular ligament as in other arcoids. Occasionally developed ridges, gutters or multiplication of ligament sublayers remain restricted to the primordial resilifer. It is concluded that the limopsid adult ligament represents a fusion of adult sublayer repetition within a retained larval resilium, a phenomenon best described as a heterochronic process. Comparisons with homologous characters of other arcoids support the view that Limopsidae evolved from parallelodontid arcoids and that they gave rise to Philobryidae but not to Glycymerididae.     

Growth and shell morphology of three mytilidae (Bivalvia) species from the Sea of Japan

The growth and shell morphology of bivalve mollusks Crenomytilus grayanus, Mytilus coruscus, and Modiolus modiolus from the Sea of Japan are examined. The changes in body proportions and shell form in the ontogenesis of C. grayanus, M. coruscus, and M. modiolus are different even in the cases when the mussels develop in similar environmental conditions. Rapid growth shapes a well-streamlined and flat form of shell; slow growth leads to the formation of a massive and convex form. The parameters of the Bertalanffy growth curve for each species are calculated. The differences are discussed from the standpoint of functional morphology and spatial distribution patterns of mytilids in the coastal areas of the sea.     

Larval development of the shell and the shell gland inMytilus (Bivalvia)

Summary In the newly hatched larva ofMytilus galloprovincialis the larval shell field almost totally invaginates to form a shell gland. Only very few cells remain outside and they meet at one point. Only these cells secrete the pellicle, which in the beginning is protected by the glycocalyx and the microvilli of the surrounding cells. The invaginated cells do not participate in pellicle secretion. The secretion partly passes through infoldings of the apical cell membrane. Mineralization of each valve begins along the hinge line, continues to the valve margins and includes the valve centre.     

Feeding behavior and related functional morphology of the mayflyEphemerella needhami (Ephemeroptera: Ephemerellidae)

The feeding behavior and functional morphology associated with feeding in Ephemerella needhamiMcDunnough larvae were studied using videomacroscopic techniques, gut content analysis, and scanning electron microscopy. Two stereotypic feeding cycles were employed by the larvae. In the maxillary brushing cycle, the maxillae are the primary food-gathering organs, with the main food being detritus deposited on the filamentous alga Cladophora.In the mandibular biting cycle, the mandibles are the primary food-gathering organs used to bite Cladophora filaments.Epiphytic diatoms on Cladophorawere another important part of the diet. Behavioral similarities are apparent in the choreography and synchronization of mouthpart movements among mayflies from several families. Functional morphological comparisons are drawn with hypognathous E. needhami, Cloeon dipterum, Baetis rhodani,and Siphlonurus aestivalis, aswell as the prognathous Heptageniidae. Differences in mouthpart usage and structure are related to the relative development of setal fields and combs and the feeding microhabitat.