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Age, growth and mortality of Mactra chinensis were investigated during the period from October 2012 to September 2013 in Busan, South Korea. The monthly variation of the marginal index (MI) of the shell and chondrophore showed that the ring of this species was formed once a year during July. We estimated the age of M. chinensis by reading the external rings on the shell and the growth bands of the chondrophore to compare growth parameters between the two growth characters. The age of this species ranged from 0 to 8 years (shell-based age reading) and from 0 to 10 years (chondrophore-based age reading). Based on external rings and growth bands of chondrophore for the same period, the von Bertalanffy growth functions were expressed by the equation, Lt = 101.53[1-exp {-0.15(t + 0.75)}] and Lt = 90.03[1-exp {-0.20(t + 0.50)}], respectively. The likelihood test showed that there was a significant difference in L∞ (P < 0.001), K (P < 0.001), to (P < 0.001) estimated from non-linear regression between the two growth characters.

The age and growth of horse clams Tresus keenae from Seto Inland Sea (SIS) and Ise Bay, western Japan, were investigated using a water-based marking pen on the edge of sectioned shells, after which unstained translucent zones at the chondrophore could be clearly observed. The translucent zone was formed once per year during autumn. The ages of all the samples were determined. The most frequent shell length (SL) in SIS and Ise Bay populations were 100–120 mm and 120–140 mm, respectively and mainly consisted of 3-y-old and 4-y-old clams, respectively. Clams in the SIS were found to be younger by about 1 y and 20 mm smaller on average than the Ise Bay population. The age–SL relationships of clams from each area were analyzed, using the original von Bertalanffy growth function (VBGF), a VBGF with a biological intercept, and the Gompertz growth function. The original VBGF showed the best fit with the SIS dataset, whereas the Gompertz growth model showed the best fit with Ise Bay clams. The parameters for each growth model were significantly different between SIS and Ise Bay, which may be due to clams younger than 2 y and smaller than 80 mm SL that were present only in the samples from SIS. Faster growth rate of the VBGF in Ise Bay than that in SIS would be affected by higher water temperature during the season of rapid growth.

Thin sections of a compact, internal structure projecting from the hinge region of the bivalve Mya arenaria reveal the presence of tidal and seasonal patterns. This is the first demonstration that microgrowth increments are formed in a stucture not associated with the growing edge of the shell. The clarity and simple orientation of these extensive patterns, combined with the hinge region to disturbance and damage, suggests that detailed examinations of internal shell structures will prove valuable in ecological, archaeological, and paleoecological studies.

This study examines the morphological features of larval and postlarval shells of the paedomorphic bivalve Crenella decussata Montagu, 1808 from the Sea of Japan. During the early morphogenesis of the shell of C. decussata the following characteristics appear: prodissoconch I -the anterior and posterior provincular teeth, a broad primary ligament pit located on the chondrophore; nepioconch - the anterior and posterior juvenile teeth,primary lateral teeth, fine commarginal and radial sculpture. Larvae of C. decussata distinctly differ from other mytilid larvae by a D-shaped shell, absence of umbo, astraight hinge margin, and homogeneous fine-grained sculpture without co-marginal lines of growth. These shell characters indicate lecithotrophic development of this species. Some morphostructures are revealed which might be used in crenellin taxonomy.

Growth performance of the Antarctic bivalve Laternula elliptica was examined both by shell microstructural observation and by applying a fluorescent substance, tetracycline, as a shell growth marker. The shell was composed of two calcareous layers: the thick outer layer was homogeneous or granular in structure and the thin inner layer was nacreous. The architecture of Antarctic L. elliptica was different from that of temperate L. marilina, and the ratio of thickness between the outer and inner layers appeared to be different. The growth rate of the nacreous layer was analyzed to be very low. High correlations were found between the major axis of chondrophore and both shell length and shell dry weight, respectively. It is suggested that the chondrophore is an appropriate growth indicator, and combining the information of growth increments with the fluorescent method may be useful in estimating the bivalve growth performance in the Antarctic sea.

The Greenland smoothcockle (Serripes groenlandicus) has a circumpolar distribution in the northern hemisphere. Despite such a wide range and potential commercial importance, little is known about most aspects of the biology of this species. As part of studying the growth rate of this cockle species, we compared 3 methods that could be used to estimate the age of S. groenlandicus: (1) reading the external rings on the shell, (2) counting the growth rings on thin sections of the chondrophore, and (3) counting growth rings of whole shell sections. The chondrophore proved to be the best region to count the growth bands compared with the other regions in the cockle shell. Age bias plots and the coefficient of variation indicated that our ageing method represents a nonbiased and precise approach. This age method was validated by using Marginal increments Ratio method (MIR) to confirm that the growth bands are deposited annually. Marginal increments were significantly different between months (Kruskal-W...

[1] We analyzed shell cuts of five individuals of the Antarctic bivalve Laternula elliptica from three locations along the Antarctic Peninsula by means of Confocal Raman Microscopy (CRM) as well as Electron Microprobe (EMP). The shell of L. elliptica has been previously described as being composed of aragonite exclusively. Now, CRM mapping reveals that three polymorphs of calcium carbonate – aragonite, calcite, and vaterite – are present in the chondrophore region of the examined individuals. Annual shell growth layers continue through aragonite and vaterite, suggesting simultaneous mineralization of both polymorphs. Spatially congruent EMP scans showed that the calcium carbonate polymorph affects the distribution of magnesium and strontium within the chondrophore. This is, to our knowledge, the first report of the coexistence of these three calcium carbonate polymorphs within the mineralized structures of a marine calcifying organism. Particularly the presence of vaterite is unexpected, but shows striking similarities to some fish otoliths. The strong effect of the calcium carbonate polymorph on trace element incorporation restrict the suitability of magnesium and strontium based proxies for the chondrophore area of L. elliptica.

The ligament of the bivalve Mya arenaria was previously described as being composed of two layers: a fibrous and a lamellar one, the fibrous layer being more extensive. Other features described, such as the three-dimensional extent of the layers and their mode of attachment to the chondrophores, have been found to be inaccurate to a certain extent. The ligament is therefore redescribed here. It is conical in appearance and attached to the left chondrophore only at its margin, its interior being occupied by an epithelium, which is an extension of the mantle isthmus. The lamellar layer is a pyramidal body which merges into and constitutes the posterior extension of the fibrous layer. The whole structure is internal and may rotate around the dorsoventral axis, thus being suited to allow rocking of the valves. This kind of movement is used when Mya contracts the anterior adductor muscle to eject water from the mantle cavity during burrowing. In this respect the ligament is unique among those known in bivalves.

During low tide, up to 50% of Mya arenaria values were observed in the unstable concave-up position on a tidal flat of the Dutch Wadden Sea. These shells were overturned by foraging birds (turnstones, Arenaria interpret L.). During high tide most of these shells are overturned again by the flood current. Turnstones overturned more left than right Mya arenaria values. This cannot be explained by selectivity of the bird, but left Mya values have a projecting chondrophore that acts as an anchor in the concave-down position. Therefore, more left than right values remain on the tidal flat. This, together with turnstone activity, can also explain high left/right ratios in floating and eolian transported Mya shells

Hatchery-reared juvenile Mya arenaria L. were grown for 11 wk in replicated gravel, sand, mud, and pearl net treatments under flow-through sea-water conditions in Maine. Analyses of variance showed significant differences between sediment treatments for final shell length, dry meat weight, chondrophore growth increment, and percent shell weight. Growth of juvenile M. arenaria was more rapid in fine sediments than in coarse sediments or nets. Regression slopes of shell length-shell height and shell length-shell depth varied significantly between sediment treatments. Slower-growing clams from nets and gravel were more globose than clams from sand or mud treatments. Clams grown in sand were longer and narrower than those from mud. Differences in growth rates and shell form were attributed primarily to the physical properties of the substrata, and their effects on the scope for growth of M. arenaria.

The genus Chondroplon, known from only 2 specimens worldwide, is re-interpreted as a deformed Dickinsonia.

Yochelson, Ellis L. & Stanley, George D., Jr. 1981 12 15: An early Ordovician patelliform gastropod, Palaelophacmaea, reinterpreted as a coelenterate. Lethaia, Vol. 15, pp. 323–330. Oslo. ISSN W24–1164. The fossil Palaelophacmaea criola Donaldson, from the early Ordovician Stonehenge Formation of central Pennsylvania, was described as a patelliform gastropod. A reinterpretation of the type lot and study of a few additional specimens provide the basis for an alternative placement. Palaelophacmaea is here assigned to the Hydrozoa, as a possible chondrophore. It has an exceptionally thin shell or test and concentric but irregular corrugations. Cambrian univalve genera having a more or less circular outline that are currently assigned to the Gastropoda or Monoplacophora should be reexamined to see whether they have the features of fossil chondrophore coelenterates rather than those of molluscs. The late Cambrian Palaeoacmaea Hall & Whitfield is removed from the monoplacophoran Mollusca and left unassigned as to phylum. We judge that at least some early Cambrian species of Scenella are probably coelenterate remains. *Early Ordovician, Palaelophacmaea, Gastropoda, Monoplacophora, Hydrozoa.

The medusoid fossils that were conventionally referred to Cyclomedusa Sprigg 1947 are among the commonest elements of the late Precambrian Ediacara metazoan assemblage in South Australia. Specimens showing varying degrees of similarity have been reported worldwide from Precambrian occurrences. This study indicates that the fossils traditionally named Cyclomedusa are a morphological plexus consisting of heterogeneous medusae. The type species C. davidi Sprigg and C. radiata Sprigg are considered as a single species because of differences due to preservation. C. davidi can be compared with a living hydrozoan medusa Aequorea in general configuration and an affinity with the family Aequoreidae is suggested for the typical Cyclomedusa. Spriggia Southcott 1949, which was once regarded as a synonym of Cyclomedusa , is now re-interpreted as a float-bearing chondrophore (hydrozoan colonial medusa). The newly described S. wadeae sp. nov. provides remarkable evidence for the amazingly conservative evolutionary history of the family Porpitidae. ‘C’. plana Glaessner and Wade, 1966 may be also chondrophoran in affinity but its configuration remains uncertain. A critical review on the previously supposed Cyclomedusa and other medusoids from the upper Precambrian in southern Liaoning, China demonstrates that they are Cyclomedusa -like pseudofossils made by upwards escaping gas bubbles and water currents. Therefore they can not be used for stratigraphic correlation. This example suggests the need for extreme caution in studies of various Cyclomedusa -like circular structures.

Both species were collected from pinewood panels immersed at 10 m depth. Xylophaga nidarosiensis sp.n. resembles X. dorsalis though differing in the nature of the mesoplax and in the presence of a well-developed protuberance anterior to the chondrophore, like that found in X. foliata, from which the new species differs in other details. X. noradi is closely related to X. dorsalis, from which it differs only in the nature of the siphon, which is massive and short in X. noradi and long and slender in X. dorsalis. Furthermore, in X. noradi the incurrent and excurrent siphons are of equal length with their openings situated close together, whereas in X. dorsalis the excurrent siphon is much shorter than the incurrent one.

only qualitative data, but is easy to carry out and requires only a few common chemicals, whereas the procedure invented by Jeuniaux must be very laborious as it requires the isolation and purification of the enzymes chitinase and chitobiase. I believe the following results obtained by the chitosan method are valid qualitatively. Hydroids. It is generally accepted that the periderm of hydroids is chitinous. Tests made on the athecate hydroid Tubularia and the thecate hydroids Obelia and Aglaop/zenia are confirmatory ; their periderm gave a good positive test. Medusae. Hydrozoan medusa Polyorchis and scyphozoan medusa Linuche dissolved in the hot alkali and hence are devoid of chitin. Velelia. The sail of this well-known chondrophore is supported by an internal plate of cartilaginous consistency which gave a good color test. Nematocysts. Pieces of the tentacles of Physalia loaded with nematocysts dissolved completely in the hot alkali, an indication that the capsular wall of the nematocysts is not chitinous as sometimes thought. Entoprocts. Barentsia zorbunai and Barentsia disoreta dissolved completely in the hot alkali, hence are devoid of chitin, in sharp contrast with the ectoprocts which are mostly highly chitinous, except cyclostomes. Cyclostomatous ectoprocts. I previously reported a negative result with the one cyclostome available, Crisia eburnea. I have now made tests on the following species : Crisia eburnea, Crisia maxima, Crisina radians, Bicrisia edwardsiens, Crisulipora occiden talis, Filicrisia francanciscana, Diaperoecia californica, and Tubulipora tuba. All were negative. Jeuniaux reported a feeble content of chitin in Crisia denticulata and attributed my negative result to the less sensitive chitosan method. In any case the chitin content of cyclotomatous estoprocts must be very small in comparison with that of other ectoprocts. Brachiopods. Pieces of the shell of Lingula including the bristles gave a strong color test as previously known. An effort was made to recover the bristles, lost in the previous test ; they are strongly chitinous. In previous tests on Discinisca the bristles also were not recovered, hence a special effort was made this time to recover them; they also gave a strong color test.