Sypharochiton Pelliserpentis Research Articles

WASTING AWAY IN THE INTERTIDAL: THE FATE OF CHITON VALVES IN AN ACIDIFYING OCEAN

Chitons are locally common in New Zealand, and several studies have suggested that their valves are resistant to dissolution, so it seems contradictory that they are under-represented in the sediment and fossil records of New Zealand. Indeed, special resistance to dissolution seems counterintuitive since the valves are primarily made of aragonite. Here we examine the resistance of chiton skeletal material to dissolution in order to expand our understanding of how taphonomic forces affect chitons and to provide insight into the preservation potential of chiton valves. Live individuals of eight species of chitons were collected from Otago Peninsula, South Island, New Zealand. The valves were subjected to one of two pH treatments: ambient pH of 8.10 and reduced pH of 7.70. Notoplax violacea, Sypharochiton pelliserpentis, and S. sinclairi were the most resistant to dissolution while Acanthochitona zelandica, Chiton glaucus, Onithochiton neglectus, and Ischnochiton maorianus were more vulnerable to dissolution. Leptochiton inquinatus lost the most mass in both treatments, but did not show a significant difference between them. SEM images of the dorsal and ventral surfaces on each valve revealed low-pH damage to crystal structures in the articulamentum, while the tegmentum showed no significant damage. Chiton skeletal material in general does not appear to resist dissolution any better than other examined mollusks, but the resistant tegmentum confers considerable resilience to lowered pH. Chiton valves can last up to an estimated 45 years before becoming unrecognizable, which is much shorter than the normal temperate shallow-water exposure time of hundreds to thousands of years.

A rare example of non-native chitons: broad intertidal habitat range and large densities of Sypharochiton pelliserpentis show no evidence of habitat engineering effect in South Australia

A rare example of non-native chitons: broad intertidal habitat range and large densities of Sypharochiton pelliserpentis show no evidence of habitat engineering effect in South Australia

Abrasion provides clues on a chiton taphonomic conundrum

Chitons are common marine invertebrates found worldwide that use aragonite to form their shell and are rare in the sedimentary and fossil records. Their rarity in the fossil record is interesting due to how abundant live chitons are. Previous work suggests that chitons resist dissolution, which appears inconsistent with their rarity in the sediment and fossil records and aragonite composition. This result warrants examination of other taphonomic processes on chiton skeletal material since other taphonomic processes may play a larger role in removal than previously thought. As many chitons are intertidal, mechanical abrasion of chiton valves is likely to occur; its extent is largely unknown and yet necessary to provide insight to the taphonomy of chiton material. Eight species of chitons were collected from the Otago Peninsula, South Island, New Zealand. A total of 129 valves were isolated, cleaned, weighed, and tumbled in a Lortone 3A rock tumbler for 96 h. The valves from each species lost an average of between 9 and 44% of their weight; damage varied among species. Leptochiton inquinatus (the sole lepidopleuran) lost the most material while the acanthochitonids (Acanthochitona zelandica, and Notoplax violacea) and the chitonids (Chiton glaucus, Onithochiton neglectus, Sypharochiton pelliserpentis, and S. sinclairi) were more resistant to abrasion. The dorsal layer of the valves (the tegmentum), which is penetrated by aesthete tissue and has a granular crystal microstructure, was the most damaged by abrasion in all species. The ventral layer (the articulamentum), which has a highly-organised crystal structure with fewer organic components than the tegmentum, showed the least signs of abrasion. Since abrasion reduces the tegmentum and changes the valve shape, it is likely that abraded chiton material is present but unrecognisable in the fossil record. The valves are estimated to last about seven years when in the intertidal zone when enduring abrasion alone, which is much less than the hundreds to thousands of years material is exposed.

Valve microstructure and phylomineralogy of New Zealand chitons.

The microstructure and mineralogy of chiton valves has been largely ignored in the literature and only described in 29 species to date. Eight species: Acanthochitona zelandica, Notoplax violacea (Family Acanthochitonidae, Suborder Acanthochitonina, Order Chitonida), Chiton glaucus, Onithochiton neglectus, Sypharochiton spelliserpentis, Sypharochiton sinclairi (Family Chitonidae, Suborder, Chitonina, Order Chitonida), Ischnochiton maorianus (Family Ischnochitonidae, Suborder Chitonina, Order Chitonida), and Leptochiton inquinatus (Family Leptochitonidae, Suborder Lepidopleurina, Order Lepidopleurida) were collected from the Otago Peninsula, South Island, New Zealand. The valves of these chitons were analysed with X-ray diffractometry, Raman spectrometry, and Scanning Electron Micrography (SEM) to determine their mineralogy and microstructure. Both the XRD and Raman data show that the valves consisted solely of aragonite. The observed microstructures of the valves were complex, typically composed of four to seven sublayers, and varied among species. The dorsal layer, the tegmentum, of each species was granular and the ventral layer, the articulamentum, was predominately composed of a spherulitic sublayer, a crossed lamellar sublayer, and an acicular sublayer. The chitonids Sypharochiton pelliserpentis and S. sinclairi had the most complex microstructure layering with three crossed lamellar, two spherulitic sublayers, and a ventral acicular sublayer while the acanthochitonids Acanthochitona zelandica and Notoplax violacea as well as the ischnochitonid Ischnochiton maorianus had the simplest structure with one spherulitic, one crossed lamellar sublayer, and a ventral acicular sublayer. Terminal valves were less complex than intermediate valves and tended to be dominated by the crossed lamellar structure. The leptochitonid Leptochiton inquinatus generated a unique crossed lamellar sublayer different from the other analysed chitonids. Acanthochitona zelandica is the only analysed chitonid that utilizes two different crossed lamellar structures. Clearly, many of these properties do not reflect the currently recognized polyplacophoran phylogeny.

The complete mitochondrial genomes of two chiton species (Sypharochiton pelliserpentis and Sypharochiton sinclairi) obtained using Illumina next generation sequencing

Using an Illumina platform, we shot-gun sequenced the complete mitochondrial genomes of two sister chiton species (Sypharochiton pelliserpentis and Sypharochiton sinclairi) to an average coverage of 172× and 60×, respectively. We performed a de novo assembly using SOAPdenovo2 and determined the total mitogenome lengths to be 15,048 and 15,028 bps, respectively. The gene organization was similar to that of other chitons, with 13 protein-coding genes, 24 transfer RNAs and 2 ribosomal RNAs. These data will contribute for resolving the taxonomy and population genetic structures of these species.

Phylogeography of the snakeskin chiton Sypharochiton pelliserpentis (Mollusca: Polyplacophora) around New Zealand: are seasonal near-shore upwelling events a dynamic barrier to gene flow?

We present a phylogeographic study of the New Zealand andAustralian intertidal chiton Sypharochiton pelliserpentis that was conducted to ascertain levels of population connectivity and to investigate the effect of previously hypothesized general phylogeographic boundaries. The analysis incorporated both cytochrome oxidase subunit 1 sequence data (approximately 700 bp) and RFLP data from 29 populations around New Zealand, and from one Australian population, for a total of N = 472. The major population structure observed was a strong disjunction between northern and southern populations (FST = 0.47), with the genetic breaks located at Cloudy/Clifford Bay and Farewell Spit, at the northern tip of the South Island. This finding corresponds with a common phylogeographic barrier observed in a number of other marine invertebrates, highlighting its significance and ubiquity.Athird barrier to gene flow was identified between Spirits Bay and Ahipara, around the northern tip of the North Island. All three of these areas that exhibit significant population disjunctions have strong near-shore upwelling along with water current movement offshore, and these features are prevalent during the time of year when S. pelliserpentis spawns. That these seasonal hydrographic patterns contribute to the population structuring of S. pelliserpentis is supported by comparison with other phylogeographic studies of marine invertebrates, where the strength of this barrier seems to correlate with spawning season. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104, 552‐563.

Abundance, diversity and fidelity of macroinvertebrates sheltering beneath rocks during tidal emersion in an intertidal cobble field: Does the intermediate disturbance hypothesis hold for less exposed shores with smaller rocks?

The community structure of macroinvertebrates occurring beneath cobbles during tidal emersion was investigated in an intertidal cobble field on the east coast of the south island of New Zealand. In order to test whether the intermediate disturbance hypothesis (IDH) holds in less exposed shores comprised exclusively of smaller rocks (cobbles) we measured 1) the size frequency distribution of cobbles (mass and basal surface area), 2) the incidence of barnacle encrustation as an indirect measure of cobble disturbance, 3) the abundances of the dominant macroinvertebrates occurring beneath cobbles (the crab Hemigrapsus crenulatus, the chiton Sypharochiton pelliserpentis and the snail Diloma zealandica), and 4) macroinvertebrate fidelity beneath a range of cobble sizes. Only large cobbles were found to be encrusted with barnacles, indicative of their greater resistance to physical disturbance by waves and currents. Mark and relocate experiments indicated fidelity to a given cobble over two tidal cycles was 11–14% for crabs and did not vary with cobble size. In contrast, fidelity to medium and large cobbles was higher for chitons (26–45%) and snails (17–31%) and generally increased with increasing cobble size. In contrast to the predictions of the IDH, there was a positive correlation between increasing cobble size and increasing species diversity of organisms found under the cobbles. This pattern is not simply attributable to greater space available beneath large cobbles as there was a significantly greater density of macroinvertebrates beneath medium and large, compared to the small cobbles. Increasing species diversity with increasing cobble size appears to be independent of patterns of species recolonization associated with small cobbles being subject to high disturbance or interspecific competitive hierarchies associated with low disturbance beneath large cobbles. Instead, factors such as aggregative behaviors, and reducing vulnerability to predators and desiccation stress are likely to explain the relationship between cobbles and their associated macroinvertebrate communities.

Maintenance of chitons on seawalls using crevices on sandstone blocks as habitat in Sydney Harbour, Australia

Intertidal seawalls support different assemblages and fewer species than do natural habitats. One explanation for these patterns may be the lack of some microhabitats on seawalls. Preliminary observations suggested that some features of sandstone seawalls, such as the presence of crevices among blocks, may provide chitons with an important habitat. To test the hypothesis that numbers of the chiton, Sypharochiton pelliserpentis, would be greater in crevices than on exposed surfaces of seawalls, sampling was done on sandstone seawalls in Sydney Harbour. S. pelliserpentis were more abundant in crevices among blocks than on exposed surfaces. Experimental manipulations transplanting chitons to exposed surfaces showed that they were found in greater numbers in crevices where those were available than on exposed surfaces. Chitons transplanted to blocks where crevices had been filled tended to move to non-filled crevices on other blocks. The design of seawalls could easily be improved to offer a better habitat for survival and maintenance of species such as chitons by incorporating crevices and similar features. In an increasingly urbanized world, understanding how to improve the value as habitat of man-made structures will be essential for conserving biodiversity.

Enzyme variation in marine and estuarine populations of the chitonSypharochiton pelliserpentis

Abstract Enzyme variation in sheltered‐ and exposed‐marine populations and an estuarine mudflat population of the chiton Sypharochiton pelliserpentis was examined by polyacrylamide gel electrophoresis. Six loci were analysed, of which Idh‐1, Idh‐2, and Me‐1 were monomorphic and Est‐2, Mdh‐1, and Me‐2 were polymorphic. All populations shared the same alleles at all loci. A heterozygote deficiency was detected at the Est‐2 locus for the exposed‐marine population and a hetero‐zygote excess was found at the Mdh‐1 locus for the sheltered‐marine population where allele frequencies were associated with chiton age. Differences were found in allele frequencies between the sheltered‐ and exposed‐marine populations at the Est‐2 locus and between females of the marine and estuarine populations at Mdh‐1 locus. The Idh‐2 locus showed variation in enzyme activity which was neither age nor sex specific, but appeared to be associated with different habitats. Marine population subsamples from high‐shore and low‐shore level...

MICROGROWTH BANDS IN CHITONS: EVIDENCE OF TIDAL PERIODICITY

Microgrowth bands of typical molluscan appearance were clearly revealed by the acetate film technique in the sutural laminae of the large chitons, Amaurochiton glaucus, Sypharochiton pelliserpentis, Cryptoconchus porosus and Acanthopleura granulata. In all species there was a cyclical pattern, averaging close to 28 bands per cycle suggesting that one growth increment was laid down per tide. Band widths were unusually small compared with those of bivalves or gastropods, probably because the shell is divided into eight growing plates. Overall rates of growth calculated from band widths were 1–2 mm per month, comparable with field estimates.

Adaptations of the chitonSypharochiton pelliserpentisto rocky and estuarine habitats

Abstract Various morphological and physiological features of Sypharochiton pelliserpentis (Quoy & Gaimard, 1835) were examined in relation to the different physico‐chemical characteristics experienced at 4 sites on Kaikoura Peninsula and 2 sites in the Avon‐Heathcote Estuary. Body water content of chitons from high‐shore exposed and estuarine rocky sites was significantly greater (P<0.005) and desiccation rates were significantly less (P<0.05) than those of chitons from low‐shore marine sites and an estuarine mudflat. The percentage of body water loss causing death was greatest for high‐shore marine chitons and least for estuarine chitons. Estuarine chitons had relatively more gill tissue than marine individuals. Body shape appeared to be correlated with intensity of wave action, and narrow animals were found in more wave‐exposed areas. Variations in radula length showed no clear‐cut trends among localities.

The aesthetes of chitons. III. Shell surface observations.

The shells of the chitons Lepidochitona cinereus, Sypharochiton pelliserpentis, Amaurochiton glaucus and Onithochiton neglectus were examined by scanning electron microscopy. In all species the surface terminations of the megalaesthete and micraesthete organs could be identified lying flush with the shell surface, as well as, lenses of the shell eyes in O. neglectus. Periostracal debris and encrusting diatoms were a usual feature of the shell surfaces. The micraesthete subsidiary caps normally appear featureless, but the megalaesthete apical caps sometimes appear to be perforated. The reasons for this perforate appearance are discussed and it is concluded that it provides no evidence for the normal passage of substances out of or into the megalaesthete.

Aspects of the ecology of a littoral chiton,Sypharochiton pellisekpentis(Mollusca: Polyplacophora)

Summary On several Auckland shores, a littoral chiton, Sypharochiton pelliserpentis (Quoy and Gaimard, 1835), was widely distributed and common. At Castor Bay it was the commonest chiton, and its density equalled or exceeded that of the commonest limpet (Cellana spp.) over most of the inter‐tidal range. Spot measurements of population density were made at other sites including exposed and sheltered shores. The smallest animals were restricted to the lower shore in pools or on areas of rock which were slow to drain. Exclusive of these small animals, the population structure was similar in pools and water‐filled crevices situated either high or low on the shore. This was also true for populations of animals from drained surfaces, but, at both shore levels, the population structure in the two micro‐habitats (pools and drained surfaces) was distinct. Single measurements of salinity in the very small volumes of water in which chitons were living gave a range of 13.3–45.8‰. In laboratory experiments at normal temperatures this species could survive these fluctuations for the maximum time possible between tides. Desiccation experiments, in which weight loss was expressed as a percentage of total water content, showed weight loss to depend on size. No significant differences in weight loss were found between populations from the two shore levels and the two micro‐habitats considered, though there were slight survival differences. Desiccation is probably an important factor influencing population structure, but loss of up to 75% of water content could be tolerated before 50% mortality occurred. Osmotic and desiccation stress evoked a characteristic behaviour pattern.

THE SURVIVAL OF OSMOTIC STRESS BYSYPHAROCHITON PELLISERPENTIS(MOLLUSCA: POLYPLACOPHORA)

1. The survival, weight changes and pericardial fluid osmotic pressure changes of the chiton Sypharochiton pelliserpentis, when subjected to hypo- and hypertonic media (0% to 150% seawater), have been measured. Three experimental temperatures were used, 10, 20 and 30° C, and the size of the animals was taken into account. 2. The chiton was found to be an osmoconformer, its pericardial fluid O.P. adjusting to that of the medium within the range 50% to 150% seawater. It was able to survive these changes for periods of at least 24 hours. In freshwater (0% seawater) dilution of the internal fluid was more rapid, but mortality occurred before equilibrium was reached. 3. Attachment to the substrate is significant in restricting the rate of water entry. The animal detects hypotonic salines and reacts accordingly by clamping down tightly. A limited weight regulation was observed in dilutions down to 50% seawater. 4. Temperature affects the osmotic response, higher temperatures increasing the rate of osmotic adjustment, and the mortality rate. 5. Field measurements suggest that microhabitat osmotic fluctuations are unlikely to limit the distribution of S. pelliserpentis on the shore.