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Predicted shifts in mean and extreme temperatures associated with climate change can have variable impacts on organisms, and the sign and magnitude of these impacts may depend upon local context. For Hedophyllum sessile, a habitat-forming intertidal kelp, the impacts of warming may vary with local density and position in the intertidal zone. To assess the potential context-dependence of warming, we manipulated H. sessile densities across an intertidal gradient and experimentally imposed periodic thermal stress in the field. The recruitment of H. sessile juveniles was unimodally related to shore level, peaking near the center of the species’ vertical distribution and falling off at the upper and lower distributional limits. Experimental warming tended to have mildly positive effects on recruitment lower on the shore regardless of adult density, and in upper zone, high density plots. However, warming had strongly negative effects on recruitment in upper zone, low density plots. Temperature manipulations also had context-specific effects on adult plant growth; seasonal increases in blade number and canopy cover were slightly enhanced by warming in high-density plots but greatly reduced by warming in low-density plots. Finally, experimental heating had context-dependent effects on an understory herbivore, the chiton Katharina tunicata, which increased in abundance following heating in high density plots but decreased in low density plots. Our results demonstrate that extreme temperature events can affect multiple species and multiple life history stages, and that the impacts of such events can depend upon both environmental (e.g. intertidal height) and biological (e.g. adult density) context.

As a highly diverse phyla, Mollusca is both intriguing to study and difficult to define. No single common feature distinguishes the phyla, but the most common and recognizable is the radula. Throughout Molluscan history, there have been many developments to the radular structure. Evolutionary development of unique radular structures may have been made possible by developmental modularity. This histological study examines the development of polyplacophoran internal gut development. Here, I describe the developmental sequence of chiton feeding structures for the first time. Feeding structures are present by 10 days post hatch. Future research should examine larval stages prior to this in order to determine whether developmental modularity exists in polyplacophorans.

Polyplacophoran molluscs show low morphological diversity compared to other marine invertebrate clades, yet chitons are ecologically important grazers that occupy a range of distinct ecological niches. We investigated a potential functional correlate of niche separation in three species of co-occurring mopallid chitons that have total ranges across differing environments (Mopalia muscosa, Mopalia lignosa, Katharina tunicata). We found that the force needed to fracture the protective valves varied significantly among species. K. tunicata, whose valves have a relatively reduced exposed dorsal surface, was significantly more resistant to fracture than the two Mopalia species (mean force: K. tunicata = 31.9 ± 4.5 N; M. lignosa = 12.5 ± 0.8 N; M. muscosa = 20.2 ± 0.8 N). In Mopalia spp., the terminal valves were significantly stronger than intermediate valves (i.e. higher force to fracture), whereas all valves in K. tunicata appeared to be functionally equivalent. To assess whether future chemical changes predicted under ocean acidification (OA) will affect these species differently, we measured the force to fracture of valves after 10 days of exposure to elevated pCO2 (control = 8.0 pH [407 ± 104, pCO2], elevated = 7.5 pH [1544 ± 249, pCO2]) for both live animals and dissected individual valves. Although previous experimental OA work found significant impacts of elevated pCO2 on adult mollusc shells over similar timescales, we saw no reduction in total strength related to treatment. Our data demonstrate that diversity in chiton valve morphology has functional implications and that physical changes in local topology and wave exposure may have stronger impacts on adult chitons than changes in ocean chemistry under future climate change.

Few studies have documented chiton growth rates, and lifespans for most chiton species remain unknown. This study presents the first size-at-age and longevity estimates for Cryptochiton stelleri and Katharina tunicata, two of the largest known species of chitons. Age estimates were based on growth ring counts obtained by cross-sectioning and polishing valves. This process alone showed clear growth rings in shell plates of K. tunicata. Valves of C. stelleri did not show conspicuous growth rings in cross section, so the acetate peel technique was used to highlight growth bands. Linear growth in terms of body length and shell width approached an asymptote in both species and was described with the von Bertalanffy growth function. Both C. stelleri and K. tunicata displayed indeterminate growth with regard to tissue weight and shell weight, continuing to maintain a steady growth rate throughout their lifespans. The oldest K. tunicata specimen was estimated to be 17 years old. The oldest C. stelleri was estimated to be 40 years old, making it the longest-lived chiton species known.

The dispersal capabilities of intertidal organisms may represent a key factor to their survival in the face of global warming, as species that cannot adapt to the various effects of climate change will have to migrate to track suitable habitat. Although species with pelagic larval phases might be expected to have a greater capacity for dispersal than those with benthic larvae, interspecies comparisons have shown that this is not always the case. Consequently, population genetic approaches are being increasingly used to gain insights into dispersal through studying patterns of gene flow. In the present study, we used nuclear single-nucleotide polymorphisms (SNPs) and mitochondrial DNA (mtDNA) sequencing to elucidate fine-scale patterns of genetic variation between populations of the Black Katy Chiton, Katharina tunicata, separated by 15–150 km in south-west Vancouver Island. Both the nuclear and mitochondrial data sets revealed no genetic differentiation between the populations studied, and an isolation-with-migration analysis indicated extensive local-scale gene flow, suggesting an absence of barriers to dispersal. Population demographic analysis also revealed long-term population stability through previous periods of climate change associated with the Pleistocene glaciations. Together, the findings of the present study suggest that this high potential for dispersal may allow K. tunicata to respond to current global warming by tracking suitable habitat, consistent with its long-term demographic stability through previous changes in the Earth's climate. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 589–597.

Taphonomic analyses of modern Katharina tunicata and Mopalia muscosa valves (Mollusca, Polyplacophora) collected from San Juan Island, Washington, USA, demonstrate that preservation potential of chitons varies by species and locality. Damage levels observed in the valves reflect differences in extrinsic environmental conditions, but intrinsic characters affect response of the skeletal material to local processes. Although both are more likely to become fossils at the lower energy site, K. tunicata valves in poor condition are more likely to occur than poor-condition M. muscosa valves at either site. Mopalia muscosa valves are least likely to be preserved at the higher energy site. Katharina tunicata valves appear more resistant to destruction than M. muscosa valves, suggesting that the former are more likely to become fossilized. The preservation potential of the three types of valves (normally one head, six medials, and one tail per individual) differs for both species. Medials are more likely to be preserved than either terminal valve of K. tunicata or M. muscosa. Head valves are least likely to be preserved, but K. tunicata heads are less likely to be preserved than M. muscosa heads. The biases are not due to greater frequency of medials, because valves do not occur in the 3:1 ratio seen in living animals. Divergence from expected ratios and variation in taphonomic condition for all three valve types in modern environments agrees with observations in the fossil record. The rarity of fossil chitons may be due to biases against preservation rather than absence in ancient environments.

Canopy-forming plants and algae, in addition to their role as food, can positively affect higher trophic levels by providing protection from predation or stressful abiotic conditions. In the low rocky intertidal zone of the Pacific Northwest, the chiton Katharina tunicata is closely associated with the canopy-forming alga Hedophyllum sessile. In a 27-month field experiment, I used experimental devices to mimic characteristics of the Hedophyllum canopy and monitored the abundance and physiology of Katharina to determine the mechanism behind this association. The data show that this association is due to selection of shaded microhabitats by Katharina, and that neither predation nor Hedophyllum per se influenced the distribution of the chiton. Exclusion of visual predators had no effect on chiton abundance, and tests of the effects of shade independent of Hedophyllum presence indicated that the shade produced by the alga was critical to the chiton. Seasonal fluctuations in levels of 70 kDa (1.16 × 10−19 g) heat shock proteins (Hsp70) indicate that Katharina experience sublethal physiological stress during the spring and summer. The corresponding use of shaded areas during spring and summer low tides suggests that the chiton's distribution is limited during these seasons by the availability of refugia from sublethal abiotic stresses. Subtle variations in environmental conditions are also important to this association; the strength of the positive interaction varied annually, becoming more positive in warm summers (1998 and 2000) and neutral in a cooler summer (1999). On a finer scale, physiological measurements indicate that the response of chitons to summertime temperatures depends on both absolute temperature change and the animal's recent thermal history. In particular, the seasonal onset of daytime low tides in the spring is associated with increased Hsp70 levels, indicating that this is a significant physiological event for Katharina. The importance of facultative positive interactions that allow consumers to escape from sublethal abiotic stresses will likely be variable in time but can have large impacts on communities both by affecting the small-scale distribution of consumers over the short term and potentially by affecting the persistence of organisms over the long term.

Several animals and microbes have been shown to be sensitive to magnetic fields, though the exact mechanisms of this ability remain unclear in many animals. Chitons are marine molluscs which have high levels of biomineralised magnetite coating their radulae. This discovery led to persistent anecdotal suggestions that they too may be able to navigationally respond to magnetic fields. Several researchers have attempted to test this, but to date there have been no large-scale controlled empirical trials. In the current study, four chiton species (Katharina tunicata, Mopalia kennerleyi, Mopalia muscosa and Leptochiton rugatus, n = 24 in each) were subjected to natural and artificially rotated magnetic fields while their movement through an arena was recorded over four hours. Field orientation did not influence the position of the chitons at the end of trials, possibly as a result of the primacy of other sensory cues (i.e. thigmotaxis). Under non-rotated magnetic field conditions, the orientation of subjects w...

The nucleotide sequence of a 9240-base pair DNA fragment of the mitochondrial (mt) genome of a squid, Loligo bleekeri, was determined, in which 8 protein and 14 tRNA genes were identified. The gene organization of the mt-genome exhibits a greater resemblance to the gene organization of arthropods and a chiton, Katharina tunicata, than to those of a mussel, Mytilus edulis, and land snails. A cloverleaf-like structure was observed between the genes for subunits 4 and 5 of NADH dehydrogenase (ND4 and -5), which is considered to have originated from histidine tRNA. It is presumed that this structure functions as a transcriptional punctuation signal for the maturation of the ND4 and ND5 mRNAs.

Sequences of partial mitochondrial cytochrome oxidase III gene (533 bp) were obtained for 17 species of cephalopods, 14 decapods, 2 octopods, and 1 vampyromorph. This study aimed to: (1) compare partial COII and COIII amino acid sequences of three species of cephalopods with other invertebrates in terms of base composition and phylogenetic relationships. Cephalopod sequences are closer to Katharina tunicata sequences than to Mytilus edulis (marine bivalve) and Albinaria turrita (terrestrial gastropod); (2) investigate the phylogenetic relationships among cephalopods. Nucleotides as well as amino acid sequence variations of a COIII fragment were examined with parsimony and distance methods. Our data confirm the monophyly of the Decapoda and of each family. A high hierarchical rank for sepiolids, already suggested by other authors, appears justified. The order Sepioidea comprising five families should be abandoned, with Spirula being excluded. The surprising position of Idiosepius as the sister group of some oegopsids and not of sepioids or sepiolids is confirmed. Vampyroteuthis is the sister group of octopods. However, the data do not allow resolution of the phylogenetic relationships between the orders of Decapoda; consequently we suspect a rapid radiation.

We investigated the relative roles of natural factors and shoreline harvest leading to recent declines of the black leather chiton (Katharina tunicata) on the outer Kenai Peninsula, Alaska (U.S.A.). This intertidal mollusk is a strongly interacting grazer and a culturally important subsistence fishery for Sugpiaq (Chugach Alutiiq) natives. We took multiple approaches to determine causes of decline. Field surveys examined the significant predictors of Katharina density and biomass across 11 sites varying in harvest pressure, and an integrated analysis of archaeological faunal remains, historical records, traditional ecological knowledge, and contemporary subsistence invertebrate landings examined changes in subsistence practices through time. Strong evidence suggests that current spatial variation in Katharina density and biomass is driven by both human exploitation and sea otter (Enhydra lutris) predation. Traditional knowledge, calibrated by subsistence harvest data, further revealed that several benthic marine invertebrates (sea urchin, crab, clams, and cockles) have declined serially beginning in the 1960s, with reduced densities and sizes of Katharina being the most recent. The timing of these declines was coincident with changes in human behavior (from semi-nomadic to increasingly permanent settlement patterns, improved extractive technologies, regional commercial crustacean exploitation, the erosion of culturally based season and size restrictions) and with the reestablishment of sea otters. We propose that a spatial concentration in shoreline collection pressure through time, increased harvest efficiency, and the serial depletion of alternative marine invertebrate prey have led to intensified per capita predator impacts on Katharina and thus its recent localized decline.

The proper reconstruction of the relationships among the animal phyla is central to interpreting patterns of animal evolution from the genomic level to the morphological level. This is true not only of the more speciose phyla, but also of smaller groups. We report here the nearly complete DNA sequence of the mitochondrial genome of the phoronid Phoronis architecta, which has a gene arrangement remarkably similar to that of a protostome animal, the chiton Katharina tunicata. Evolutionary analysis of both gene arrangements and inferred amino acid sequences of these taxa, along with those of three brachiopods and other diverse animals, strongly supports the hypothesis that lophophorates are part of the large group that includes mollusks and annelids, i.e., the Lophotrochozoa, and solidly refutes the alternative of their being deuterostomes.

The DNA sequence of the 15,532-base pair (bp) mitochondrial DNA (mtDNA) of the chiton Katharina tunicata has been determined. The 37 genes typical of metazoan mtDNA are present: 13 for protein subunits involved in oxidative phosphorylation, 2 for rRNAs and 22 for tRNAs. The gene arrangement resembles those of arthropods much more than that of another mollusc, the bivalve Mytilus edulis. Most genes abut directly or overlap, and abbreviated stop codons are inferred for four genes. Four junctions between adjacent pairs of protein genes lack intervening tRNA genes; however, at each of these junctions there is a sequence immediately adjacent to the start codon of the downstream gene that is capable of forming a stem-and-loop structure. Analysis of the tRNA gene sequences suggests that the D arm is unpaired in tRNA(ser)(AGN), which is typical of metazoan mtDNAs, and also in tRNA(ser)(UCN), a condition found previously only in nematode mtDNAs. There are two additional sequences in Katharina mtDNA that can be folded into structures resembling tRNAs; whether these are functional genes is unknown. All possible codons except the stop codons TAA and TAG are used in the protein-encoding genes, and Katharina mtDNA appears to use the same variation of the mitochondrial genetic code that is used in Drosophila and Mytilus. Translation initiates at the codons ATG, ATA and GTG. A + T richness appears to have affected codon usage patterns and, perhaps, the amino acid composition of the encoded proteins. A 142-bp non-coding region between tRNA(glu) and CO3 contains a 72-bp tract of alternating A and T.

Scanning electron microscopy was employed to study the ultrastructure of the magnetite-bearing cap in mature tricuspid teeth of four chiton species: Lepidochitona cinerea, Mopalia muscosa, Katharina tunicata, and Cryptochiton stelleri. The cap is composed of parallel rod-shaped units. In the part that leads in the cutting direction there are two sets of intersecting structural units. In the trailing part a single set of units occurs. The construction of the cap in relation to its function is discussed.

1. 1. Hemocyanin from the chiton, Katharina tunicata , has a sedimentation coefficient (S o 20.w ) of 61.2S, M r = 4.2 × 10 6 , at pH 7.0 in the presence of 10 mM MgCl 2 . 2. 2. In electron micrographs, the 61S hemocyanin appears as a three-tiered cylinder, 31 nm in dia. and 19 nm in length, with a polar profile. 3. 3. An increase in alkalinity results in gradual dissociation to 20S and 11S components, which correspond to one-fifth and one-tenth molecules, respectively. The 61S molecule is stabilized in buffers containing MgCl 2 . 4. 4. SDS and regular gel electrophoresis of K. tunicata hemocyanin show a single subunit with an apparent M r of about 350,000 or greater. 5. 5. Although the 11S subunits are homogeneous, digestion studies indicate that the functional domains are heterogeneous. 6. 6. The hemocyanins from each molluscan class, chiton, cephalopod and gastropod, appear to be distinctive.

Recent theory has suggested that in systems in which resource taxa compete, the abundance of a consumer specialized on one prey should be positively affected by the presence of a specialized consumer of the other prey. We have shown that the type of competition between prey (i.e., hierarchical vs. symmetrical) strongly affects the nature of the interaction between consumers. In the low intertidal zone on San Juan Island, Washington, two species of acmaeid limpets overlap substantially in habitat and food use with the large chiton Katharina tunicata. The limpets in this region consume microalgae, especially diatoms, while the chiton is a generalist, eating both microalgae and macroalgae. The experimental removal of Katharina from two large areas resulted (over 3 yr) in a dramatic rise in macroalgal cover and the disappearance of limpets. Artificially increased densities of Katharina at another site led to greater limpet abundances and increased reproductive output of both limpets and chitons. The probable ...

Foraging strategies of Glaucous-winged Gulls (Larus glaucescens) were studied in rocky intertidal habitats of the western Aleutian Islands, Alaska. Daily foraging activity was most intense at maximum low tide, and was concentrated in the lowest intertidal zones available to the birds. Barnacles (Balanus glandula) and mussels (Mytilus edulis) comprised most of the gull's diet during neap low tides, but these species were almost entirely abandoned during spring low tides in favor of sea urchins (Strongylocentrotus polyacanthus), chitons (Katharina tunicata), and limpets (Collisella pelta and Notoacmaea scutum). Sea urchins, chitons, and limpets, which had positive prey selection indices, were most abundant in the lower intertidal zones; barnacles and mussels, which had negative prey selection indices, were most abundant in the upper zones. Gulls also generally selected the larger individuals from each prey species, although sea urchins larger than the commissural bill width were avoided and limpets were selected in proportion to availability. Variation in prey availability also occurred among study areas with varying densities of sea otters (Enhydra lutris). With increasing depression of invertebrate prey by sea otter predation, gulls fed on a more diverse prey resource, and they switched to neritic fishes under intense sea otter predation. Preference experiments were conducted in the field, in which the common species and sizes of prey were made equally available to foraging gulls, thus eliminating search and capture times. In comparison with natural food choice, where sea urchins were most preferred, chitons became most preferred. We suggest that chitons are infrequent in natural diets because they adhere more strongly to the substratum than do sea urchins. Benefits of selective foraging were determined by comparing the net rate of energy gain of simulated random foragers with energy gained by selection of intertidal zones, prey species, and prey sizes. Observed selection patterns provided increased energy as gulls became more selective, and averaged 155% more than that obtained by the simulated random foragers. Results of the study support the two main predictions of optimal foraging theory in that (1) foraging patches (intertidal zones) and diets were selected such that net rates of energy gain were maximized, and (2) gulls became more selective foragers when energetically more profitable prey were more available.

The gonadal index cycle of the chiton Katharina tunicata Wood, in a population on the outer coast of Vancouver Island. British Columbia, Canada, has been observed over a five-year period. There is an annual cycle. Gonadal growth starts in the autumn and continues through the winter and early spring. The main spawning period is June, and following this the gonads remain small until autumn. In some years, there is spawning activity in April, followed by additional gonadal growth until the time of the June spawning. The factors controlling the reproductive cycle are considered, using observations from both the present study and from previous studies in California. There is no evidence that gonadal growth is stimulated by a change in food availability in the field, and in the laboratory, gametogenesis follows the normal time sequence, even in starved animals. The onset of gonadal growth is most closely correlated with the decline in sea temperatures in the autumn. In the Monterey area, where temperatures decline during a later period than in British Columbia, gonadal growth starts later. The final stages of gamete production may require increased or increasing temperatures. Spawning nearly always occurs while sea temperatures are increasing, but there is no consistent temperature when spawning occurs. In the present investigation, spawning periods during 1973 coincided with phytoplankton blooms and in other years when phytoplankton observations were not available. Katharina spawned in synchrony with other species which are known to spawn in response to phytoplankton. Phytoplankton was always present when spawning occurred in the Monterey area, but spawning did not always occur when phytoplankton first became abundant. An increase in temperature to about 12 C may be necessary for spawning to occur in the Monterey area.

1. 1. The oxygen affinity of purified Katharina tunicata hemocyanin was measured under a variety of conditions of salinity, temperature and pH. 2. 2. Purified hemocyanin shows a cooperative oxygen binding curve ( n H ranges from 1.6 to 3.0) and a normal Bohr effect ((O ranges from −0.080 to −0.199) at the various ion concentrations and temperatures examined. 3. 3. Oxygen affinities of hemocyanin in a buffer with inorganic ions identical to those measured in animals exposed to 30%. and 10%. sea water (pH 7.4) were slightly lower at the higher salt concentration. When the salinity of the buffer was increased to 35%. or 45%. the oxygen affinity of the hemocyanin was further lowered, most strikingly at 25°C. 4. 4. The cooperativities and Bohr coefficients at high salinities were similar to those at lower salinities. 5. 5. The heat of oxygenation, Δ H , of Katharina hemocyanin was about −9.4kcal/mole (pH 7.4). 6. 6. Several organic molecules, succinate, d -lactate, alanine, propionate and acetate, show little or no effect on hemocyanin oxygen binding at either 30%. or 10%. 7. 7. The oxygen affinity of Katharina hemocyanin could change two fold over salinity and temperature conditions which the animal experiences in the field.

The effects of consumers on prey populations are traditionally expressed as a function of the intensity or frequency of consumption. Interactions among the intertidal alga Iridaea cordata and five common herbivores of the Oregon coast emphasize that the variety of consumers can be as important as the magnitude of feeding. The five herbivores in this system divide into two functional groups with respect to feeding on Iridaea. (1) Katharina tunicata (chiton), Strongylocentrotus purpuratus (sea urchin), and Collisella pelta (limpet) readily feed on Iridaea in all reproductive conditions. In contrast, (2) Lacuna marmorata (coiled snail) and Idotea wosnesenskii (isopod) feed on reproductively mature plants, but avoid nonfertile individuals. Idotea is deterred from eating immature plants by the alga's cuticle. Lacuna, while impartial to the presence of the cuticle, avoids nonfertile plants for an unidentified reason. At several locations along the Oregon coast these herbivores are abundant and spatially segregated. In these areas Iridaea has a restricted distribution (isolated on vertical walls) that correlates with the qualitative feeding differences among the five herbivores. Iridaea persists with Idotea and Lacuna (although reproductively mature blades are heavily damaged), but is rare or absent when either Katharina or Strongylocentrotus is common. When Katharina is removed from isolated rocky benches, Iridaea establishes in areas where it was previously absent. Qualitative variation in herbivory as a result of feeding by different species enhances between—habitat algal diversity by restricting the distribution of Iridaea. When the effects of herbivores are experimentally reduced, Iridacea shows a more uniform distribution.

Laboratory-cultured larvae of the black chiton Katharina tunicata (Wood), collected from central California in May and June of 1979 and 1980, settled preferentially on the encrusting coralline alga Lithothamnium sp. Metamorphosis, which involves the loss of the prototrochal ciliary band, occurred within a period of 2.5 h after larvae began crawling upon the alga. In response to gamma-aminobutyric acid (GABA) at a concentration of 10^(-6) M, the lecithotrophic trochophore larvae ceased swimming and settled rapidly. Developmental metamorphosis did not follow settlement in the absence of encrusting coralline alga. However, when both GABA and Lithothamnium sp. were present, larval metamorphosis occurred within 2 h of settlement. Significantly different rates of settlement exist for sibling larvae of different ages; 12 d-old larvae responded more rapidly and in greater numbers to treatment with GABA than 10 d-old larvae. Differences in settling rates are attributed to the onset of metamorphic competence.

Ecological factors regulating the species composition and abundance of the plant assemblage in the low intertidal zone were studied in the semiprotected San Juan Islands in Washington state. In particular, the roles of an abundant herbivore (the chiton Katharina tunicata) and competition among plants were evaluated experimentally. Densities of Katharina were manipulated in large areas to establish 3 treatments: Katharina removals (N=2), controls (N=2), and Katharina addition (N=1). These sites were monitored for 4 years. Over this time, algal abundance and diversity increased in the Katharina-removal areas; algae in most functional groups proliferated, and a multi-storied intertidal kelp bed eventually developed. In the Katharina-addition, the abundance of all plants except crusts, diatoms, and surfgrass decreased, and overall diversity declined. Control sites underwent year-to-year fluctuation in the abundance of the most conspicuous alga, Hedophyllum sessile, but remained otherwise unchanged.At the end of the third year, the dominant space occupiers (the large brown algae) were removed from half of each of the Katharina removal and control areas. These kelps positively affect abundances of Katharina but are negatively correlated with limpet numbers. In the absence of competition from the kelps, the abundance and diversity of most other algal groups increased. This change was especially dramatic in the areas lacking both chitons and kelps, indicating that herbivory and competition have negative, additive effects on smaller algae. However, even in the absence of Katharina, abiotic disturbance (desiccation and storms) apparently mediates the competitive dominance of the kelps.

Seasonal changes in gonald size and stages of gametogenesis in the black abalone Haliotis cracheroidii were related to changes in environmental parameters. H. cracheroidii showed an annual reproductive cycle terminating in a synchronized spawning in late summer. Gametogenesis was initiated immediately after spawning. Gametes were present in the gonad through the winter months. Gametogenesis was initiated a second time in the spring months. Maximal gonad growth (to a gonad index of 20%) occurred during summer months prior to spawning. Changes in gonad size andperiods of initiation of gametogenesis revealed no apparent correlation with changes in seasonal water temperature. Changes in gonad size showed no apparent relation to change in day length. Total polysaccharide levels in foot tissue changed seasonally, indicating that food availability is probably not a factor in directly regulating gonad growth. Gonad index data for the chiton Katharina tunicata (collected over a 10 year period) showed no apparent correlation to seasonal change in water temperature.

The biochemical composition of Katharina tunicata has been studied. Of the body components only the gonads and the digestive gland showed seasonal changes in size. The protein level of gonads was maximal in gravid and minimal in immature condition; the reverse was true of the carbohydrate level. Lipid level was highest in the gravid ovary. Water levels were highest in the tissues of head and radula, mantle, and gut and lowest in the digestive gland, foot, and gonad. The body component indices were found to vary little with size of specimens over a tenfold range.

1. Iso-agglutination occurs in the black chiton, Katharina tunicata. This is the first report of unmistakable iso-agglutination of spermatozoa of a mollusc; also of iso-agglutination of spermatozoa which are inactive in sea-water.2. The iso-agglutinated masses of spermatozoa of K. tunicata differ from those of sea-urchins and of Nereis. In the former the agglutinating masses resemble three-dimensional pinwheels.In these the spermatozoa are so oriented that the center consists of a nucleus of sperm heads with tails radiating outward, and the periphery is composed of a dense zone of sperm heads with tails radiating inward.In sea-urchins and in Nereis the iso-agglutinating masses resemble whirling swarms in which the spermatozoa either are not oriented or are oriented with their heads forming the central nucleus of the swarm. However, a pinwheel type of iso-agglutination can be obtained with stale Arbacia spermatozoa. The motility of the latter is decidedly subnormal. It is possible that the variation in sha...

1. 1. The radular muscle myoglobins of the amphineuran molluscs Katharina tunicata, Cryptochiton stelleri, and Mopalia muscosa have been purified. 2. 2. In each species the myoglobin can be separated into two components: Mb-1, a putative dimer with a molecular weight of about 34,000, and Mb-2, a monomer with a molecular weight of approximately 17,000. 3. 3. In K. tunicata the amino-acid composition to the nearest half residue of the half molecule of Mb-1 is: Lys13, His2, Arg8, Cys1.5, Asp13.5, Thr2, Ser13, Glu13.5, Pro3.5 Gly15.5, Ala11, Val11, Met7, Ileu8.5, Leu10.5, Tyr2, Phe10, Trp2. 4. 4. The amino-acid composition of K. tunicata Mb-2 is: Lys17, His3, Arg1, Cys1, Asp16, Thr5, Ser7, Glu12, Pro6, Gly21, Ala16, Val12, Met8, Ileu8, Leu8, Tyr3, Phe4, Trp3. 5. 5. In C. stelleri the amino-acid composition to the nearest half residue of the half molecule of Mb-1 is: Lys14, His2, Arg5.5, Cys1, Asp16.5, Thr5, Ser10, Glu10, Pro4, Gly14.5, Ala10, Val10.5, Met6, Ileu9.5, Leu9.5, Tyr2, Phe9, Trp2. 6. 6. The amino-acid composition of C. stellen Mb-2 is: Lys17, His2, Arg1, Cys1, Asp15, Thr5, Ser6, Glu13, Pro6, Gly20, Ala19, Val12, Met6, Ileu10, Leu10, Tyr4, Phe4, Trp4. 7. 7. In M. muscosa the amino-acid composition to the nearest half residue of the half molecule of Mb-1 is: Lys16, His2, Arg5, Cys1, Asp13, Thr4.5, Ser13, Glu12, Pro4, Gly15.5, Ala10.5, Val11, Met7.5, Ileu9, Leu9.5, Tyr2, Phe9.5, Trp2. 8. 8. The amino-acid composition of M. muscosa Mb-2 is: Lys17, His2, Arg1, Cys1, Asp16, Thr7, Ser6, Glu13, Pro6, Gly22, Ala17, Val11, Met6, Ileu10, Leu9, Tyr4, Phe4, Trp4. 9. 9. The quaternary structure of Mb-1 from K. tunicata is discussed. 10. 10. The radular muscle myoglobins of the amphineurans are compared.

In Cryptochiton stelleri (Polyplacophora), variation in the size of the glandular oviduct parallels the cyclic variation in the size of the gonad. In Katharina tunicata the digestive gland reaches its maximum size in the fall then decreases to a minimum size in the spring when the gonad is at its maximum size. These variations are not due to changes in the water content of the glandular oviduct and digestive gland.