New onychochilid mollusks from the Middle and Upper Ordovician of Baltica and Laurentia

A new sinistrally coiled univalved mollusk Catalanispira n. gen. is described with two species; Catalanispira reinwaldti (Öpik, 1930) from the Middle Ordovician Kõgekallas Formation (Darriwilian) of Estonia and Catalanispira plattevillensis n. gen. n. sp. from the Upper Ordovician Platteville Formation (Sandbian) of northern Illinois, USA. Morphological features include a large, low-trochiform shell, a narrow lenticular aperture, a deep funnel-like umbilicus, a falcate inner lip and a large (1.4 mm wide) protoconch. Ornamentation consists of fine commarginal growth lines or ribs but superimposed on a slightly irregular shell surface. Catalanispira n. gen. is placed within the sinistrally coiled order Mimospirida and the family Onychochilidae, and Catalanispirinae n. subfam. is proposed. The large Lower Ordovician (Tremadocian) Pelecyogyra Ebbestad and Lefebvre, 2015 from Morocco and France is transferred to this new subfamily. The well-preserved initial growth stage of Catalanispira plattevillensis n. gen. n. sp. is cap-shaped, slightly asymmetrical, unusually large, and smooth, and represents either an unusually large embryonic shell (protoconch 1) or a larval shell (protoconch 2). It differs from the smaller protoconch described for the clisospirine Mimospira Koken in Koken and Perner, 1925, which might include a multiwhorled larval shell (protoconch 2). Mimospirids are dominantly Ordovician, and have been classified as untorted mollusks (only distantly related to gastropods), dextral hyperstrophic gastropods, or sinistral orthostrophic gastropods. Sinistral asymmetry already in the embryonic shell and lack of conclusive evidence for coiling direction, e.g., an operculum, could suggest that Catalanispira n. gen. or similar mimosprids were sinistral orthostrophic gastropods. Currently the group is therefore classified as a group of sinistral orthostrophic gastropods, unranked within the Gastropoda.UUID: http://zoobank.org/affc8dcf-4c0f-493d-bee5-75a457996e84

Adaption potential of Crassostrea gigas to ocean acidification and disease caused by Vibrio harveyi

The survival and development of bivalve larvae is adversely impacted by ocean acidification and Vibrio infection, indicating that bivalves need to simultaneously adapt to both stressors associated with anthropogenic climate change. In this study, we use a half-dial breeding design to estimate heritability (h2) for survival to Vibrio harveyi infection and larval shell length to aragonite undersaturated and normal conditions in laboratory-reared Crassostrea gigas. Phenotypic differences were observed between families for these traits with heritability estimated to be moderate for survival to V. harveyi challenge (h2 = 0.25) and low for shell length in corrosive (Ωaragonite = 0.9, h2 = 0.15) and normal conditions (Ωaragonite = 1.6, h2 = 0.15). Predicted breeding values for larval shell length are correlated between aragonite-undersaturated and normal conditions (Spearman r = 0.63, p < 0.05), indicating that larger larvae tend to do better in corrosive seawater. Aquaculture hatcheries routinely cull slow-growing larvae to reduce and synchronize time taken for larvae to metamorphose to spat, thus inadvertently applying size-related selection for larger larvae. This indirect selection in the hatchery populations provides a plausible explanation why domesticated oyster populations are less sensitive to ocean acidification.

Larval and juvenile development of the Iceland cockle Ciliatocardium ciliatum (Fabricius, 1780) (Bivalvia: Cardiidae)

The paper considers the development of Ciliatocardium ciliatum from the stage of straight hinge to juvenile. In the White Sea the spawning of C. ciliatum begins at the end of June, larvae at different stages of development occur in plankton until the end of September. The earliest of the larvae found had shell lengths of 123–130 µm. The paper first examined the anatomy and structure of the larval shell of C. ciliatum. During the development, the main stages of organogenesis were described and special attention was paid to the formation of the digestive and muscular systems. The digestive system begins to function when the larva reaches a size of 170–180 µm. The digestive gland has a two-blade shape and is shifted to the right side. The foot is formed at a size of 230 µm, the gill rudiments appear when the larva reaches 270 µm. The development of the larval shell and larval hinge of the mollusc is considered in detail. The development of the larval shell of C. ciliatum is similar to the development of other family members. Throughout all the larval stages, the shell has a rounded shape with a low umbos, and the prodissoconch II has a clearly visible concentric structure. The C. ciliatum larval hinge is characterized by weak differentiation and the absence of pronounced cardinal teeth typical for other Cardiidae. However, the lateral structures of the castle – ridges and flanges – are well developed. The ligament begins to form at a size of 240–250 µm and occupies a lateral position. The settlement of the cockle takes place in September in the subtidal zone. After the metamorphosis, a large radial sculpture is formed on the dissoconch and a number of small spikes are formed at the rib of the posterior shoulder.

Ocean pH fluctuations affect mussel larvae at key developmental transitions

Coastal marine ecosystems experience dynamic fluctuations in seawater carbonate chemistry. The importance of this variation in the context of ocean acidification requires knowing what aspect of variability biological processes respond to. We conducted four experiments (ranging from 3 to 22 days) with different variability regimes (pH T 7.4–8.1) assessing the impact of diel fluctuations in carbonate chemistry on the early development of the mussel Mytilus galloprovincialis . Larval shell growth was consistently correlated to mean exposures, regardless of variability regimes, indicating that calcification responds instantaneously to seawater chemistry. Larval development was impacted by timing of exposure, revealing sensitivity of two developmental processes: development of the shell field, and transition from the first to the second larval shell. Fluorescent staining revealed developmental delay of the shell field at low pH, and abnormal development thereof was correlated with hinge defects in D-veligers. This study shows, for the first time, that ocean acidification affects larval soft-tissue development, independent from calcification. Multiple developmental processes additively underpin the teratogenic effect of ocean acidification on bivalve larvae. These results explain why trochophores are the most sensitive life-history stage in marine bivalves and suggest that short-term variability in carbonate chemistry can impact early larval development.

Growth series of one: case studies in time-transgressive morphology

The study of ontogeny in the fossil record is complicated by two main factors: growth series are not available for many taxa, and correctly assigning juveniles and adults to the same taxon is often difficult, especially where several related taxa coexisted. Ontogenetic change can also be revealed in single individuals whose morphology records characters from multiple ontogenetic stages. A snail shell is an intuitive example: the shell grows by accretion at its margin, starting from the larval shell (protoconch), and moving outward. Larval shell shape varies predictably between planktotrophic and non-planktotrophic lineages; and since the protoconch is embedded in the adult shell, larval ecology can be inferred in adults from the size and morphology of the retained protoconch. In many extinct lagomorphs, the occlusal surface of the molars changed markedly over the lifespan of an individual, as features such as enamel ridges were revealed and then obliterated by wear. In this case, the complete ‘stack’ of potential occlusal morphologies was present in the adult tooth as soon as it was done mineralizing, and further change progressively erased the ontogenetically early character states. In sauropodomorph dinosaurs, morphological complexity of the vertebrae increases along the cervical series. The simple morphology of anterior cervicals reflects both earlier ontogenetic stages and more primitive character states. More posterior vertebrae reveal the sequential formation of complex structures. Individuals that record multiple ontogenetic stages can help solve palaeobiological problems, such as inferring life histories, assessing ranges of variation, and determining the origin of complex morphological characters.

Growth series of one: case studies in time-transgressive morphology

The study of ontogeny in the fossil record is complicated by two main factors: growth series are not available for many taxa, and correctly assigning juveniles and adults to the same taxon is often difficult, especially where several related taxa coexisted. Ontogenetic change can also be revealed in single individuals whose morphology records characters from multiple ontogenetic stages. A snail shell is an intuitive example: the shell grows by accretion at its margin, starting from the larval shell (protoconch), and moving outward. Larval shell shape varies predictably between planktotrophic and non-planktotrophic lineages; and since the protoconch is embedded in the adult shell, larval ecology can be inferred in adults from the size and morphology of the retained protoconch. In many extinct lagomorphs, the occlusal surface of the molars changed markedly over the lifespan of an individual, as features such as enamel ridges were revealed and then obliterated by wear. In this case, the complete ‘stack’ of potential occlusal morphologies was present in the adult tooth as soon as it was done mineralizing, and further change progressively erased the ontogenetically early character states. In sauropodomorph dinosaurs, morphological complexity of the vertebrae increases along the cervical series. The simple morphology of anterior cervicals reflects both earlier ontogenetic stages and more primitive character states. More posterior vertebrae reveal the sequential formation of complex structures. Individuals that record multiple ontogenetic stages can help solve palaeobiological problems, such as inferring life histories, assessing ranges of variation, and determining the origin of complex morphological characters.

Mobergellans from the early Cambrian of Greenland and Labrador: new morphological details and implications for the functional morphology of mobergellans

New morphological features of the mobergellan Discinella micans (Billings, 1871) from the lower Cambrian (Stage 4) of Northeast Greenland and southern Labrador are described. The new features include: (1) the morphology of the larval shell, which is shown to be cap-shaped, subcircular, and with impressions of the internal muscle attachment scars; (2) a range of unusual shell deformations (changes in growth direction resulting in thickened shells, partial detachment of shell laminae and subsequent regrowth, internal projections of shell material increasing the depth of the shell by up to 150%, disturbances and irregular fusion of muscle scars). In addition, we provide new details about the variability in number and shape of the anteriormost internal muscle scars, which often fuse and may vary in number from one to three (resulting in nine to 11 scars in total). Together the new observations provide additional strength for the hypothesis that mobergellan shells represent opercula of an as yet unknown tubular organism.