Sea hare <i>Aplysia punctata</i> (Mollusca: Gastropoda) can maintain shell calcification under extreme ocean acidification

Ocean acidification is expected to cause energetic constraints upon marine calcifying organisms such as molluscs and echinoderms, because of the increased costs of building or maintaining shell material in lower pH. We examined metabolic rate, shell morphometry, and calcification in the sea hare Aplysia punctata under short-term exposure (19 days) to an extreme ocean acidification scenario (pH 7.3, ∼2800 μatm pCO2), along with a group held in control conditions (pH 8.1, ∼344 μatm pCO2). This gastropod and its congeners are broadly distributed and locally abundant grazers, and have an internal shell that protects the internal organs. Specimens were examined for metabolic rate via closed-chamber respirometry, followed by removal and examination of the shell under confocal microscopy. Staining using calcein determined the amount of new calcification that occurred over 6 days at the end of the acclimation period. The width of new, pre-calcified shell on the distal shell margin was also quantified as a proxy for overall shell growth. Aplysia punctata showed a 30% reduction in metabolic rate under low pH, but calcification was not affected. This species is apparently able to maintain calcification rate even under extreme low pH, and even when under the energetic constraints of lower metabolism. This finding adds to the evidence that calcification is a largely autonomous process of crystallization that occurs as long as suitable haeomocoel conditions are preserved. There was, however, evidence that the accretion of new, noncalcified shell material may have been reduced, which would lead to overall reduced shell growth under longer-term exposures to low pH independent of calcification. Our findings highlight that the chief impact of ocean acidification upon the ability of marine invertebrates to maintain their shell under low pH may be energetic constraints that hinder growth of supporting structure, rather than maintenance of calcification

Belatedly hatching ornithology collections at the National Museum of Ireland

For the first time, summary details are presented for the ornithological collections of the National Museum of Ireland (Natural History) (NMINH). To date, new cataloguing efforts in collaboration with University College Dublin have documented close to 10,000 non-passerine bird skins and taxidermy mounts

Deep molluscan phylogeny: synthesis of palaeontological and neontological data

The position of the earliest-derived living molluscs, the Polyplacophora (chitons) and shell-less vermiform Aplacophora, remains highly contentious despite many morphological, developmental and molecular studies of extant organisms. These two groups are thought to represent either a basal molluscan grade or a clade (Aculifera) sister to the ‘higher’ molluscs (Conchifera). These incompatible hypotheses result in very different predictions about the earliest molluscs. A new cladistic analysis incorporating both Palaeozoic and extant molluscs is presented here. Our results support the monophyly of Aculifera and suggest that extant aplacophorans and polyplacophorans both derive from a disparate group of multivalved molluscs in two major clades. Reanalysis of the critical Ordovician taxon ‘Helminthochiton’ thraivensis shows that this animal lacks a true foot despite bearing polyplacophoran-like valves. Its position within our phylogenetic reconstruction indicates that many fossil ‘polyplacophorans’ in the order Palaeoloricata are likely to represent footless stem-group aplacophorans. ‘H.’ thraivensis and similar forms such as Acaenoplax may be morphological stepping stones between chitons and the shell-less aplacophorans. Our results imply that crown-group molluscan synapomorphies include serial repetition, the presence of a foot, a mineralized scleritome and a creeping rather than worm-like mode of life