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Searching for Amnesic (ASP), Paralytic (PSP) and Lipophilic (LT) toxins in seafood is of great importance for consumer protection. Studies are usually focused on the most aquacultured species, the mussel. But, there are a number of potentially commercially important shellfish species as rough cockle Acanthocardia tuberculata (Linnaeus, 1758) and smooth clam Callista chione (Linnaeus, 1758) which are common in the Croatian Adriatic Sea. Investigation of marine biotoxins accumulation in these two species of shellfish from the Adriatic Sea has not been conducted up to now. In order to detect the potential marine biotoxin profile of A. tuberculata and C. chione wild populations, samples were taken monthly during one-year survey from the estuarine area in the central Adriatic Sea. HPLC-FLD with pre-column oxidation and HPLC-UV-DAD methods were employed for PSP and ASP toxins determination, respectively, while LTs were determined by LC-MS/MS. This research had revealed the differences in the accumulation of ASP, PSP and LT toxins between the two studied species, as Acanthocardia tuberculata showed more diverse profile with higher concentrations of analysed toxins. Both investigated shellfish species had shown levels of these biotoxins under the legal limits set by the European Commission.

The smooth clam Callista chione is distributed in Moroccan Mediterranean coasts in considerable densities. This study examines the population structure, age, growth, mortality, longevity and exploitation level of the smooth clam on Martil coast. Samples were collected monthly from July 2016 to July 2017. Morphometric relationships were studied and showed negative allometric growth for the width/length, height/length and weight/length relationships. Four age groups were determined by Bhattacharya’s method. Growth parameters were estimated from the Ford–Walford method to be L ∞ = 103 . 1 mm, K = 0 . 38 yr − 1 and t 0 = 0 . 43 . Growth performance indices were found as ϕ ′ = 3.60 and P = 5 . 61 . Total mortality, natural mortality and fishing mortality were estimated to be Z = 2 . 64 yr−1, M = 0 . 55 yr−1 and F = 2 . 09 yr−1 respectively. The exploitation rate was calculated to be E = 0.79 proving an overexploitation of the species. The longevity was estimated to be 8 years. Results present necessary biological parameters to ensure the conservation, management and sustainable exploitation of Callista chione in Morocco.

International audience; Excavated in 1949, Grotta dei Moscerini, dated MIS 5 to early MIS 4, is one of two Italian Neandertal sites with a large assemblage of retouched shells (n = 171) from 21 layers. The other occurrence is from the broadly contemporaneous layer L of Grotta del Cavallo in southern Italy (n = 126). Eight other Mousterian sites in Italy and one in Greece also have shell tools but in a very small number. The shell tools are made on valves of the smooth clam Callista chione. The general idea that the valves of Callista chione were collected by Neandertals on the beach after the death of the mollusk is incomplete. At Moscerini 23.9% of the specimens were gathered directly from the sea floor as live animals by skin diving Neandertals. Archaeological data from sites in Italy, France and Spain confirm that shell fishing and fresh water fishing was a common activity of Neandertals, as indicated by anatomical studies recently published by E. Trinkaus. Lithic analysis provides data to show the relation between stone tools and shell tools. Several layers contain pumices derived from volcanic eruptions in the Ischia Island or the Campi Flegrei (prior to the Campanian Ignimbrite mega-eruption). Their rounded edges indicate that they were transported by sea currents to the beach at the base of the Moscerini sequence. Their presence in the occupation layers above the beach is discussed. The most plausible hypothesis is that they were collected by Neandertals. Incontrovertible evidence that Neandertals collected pumices is provided by a cave in Liguria. Use of pumices as abraders is well documented in the Upper Paleolithic. We prove that the exploitation of submerged aquatic resources and the collection of pumices common in the Upper Paleolithic were part of Neandertal behavior well before the arrival of modern humans in Western Europe.

International audience; Studies on phytoplankton and in particular Harmful Algal Blooms (HABs) species in southern Mediterranean waters are scarce. We performed from April 2008 to June 2009 weekly investigations on microphytoplankton community structure and abundance in two contrasted marine ecosystems located in the western Moroccan Mediterranean coast, M'diq Bay and Oued Laou Estuary. Simultaneously, we measured the main physico-chemical parameters. Globally, the two studied areas showed comparable values of the assessed abiotic environmental factors. Temperature and salinity followed seasonal variation with values ranging from 13.5°C to 21.4°C and 31 to 36.8, respectively. Average nutrient values in surface water ranged from 0.7 to 45.76 μM for dissolved inorganic nitrogen, 0.02-2.10 μM for PO 4 and 0.23-17.46 μM for SiO 4 in the study areas. A total of 92 taxa belonging to 8 taxonomic classes were found. The highest number of microphytoplankton abundance reached 1.2 × 10 6 cells L −1 with diatoms being the most abundant taxa. Factorial Discriminant Analysis (FDA) and Spearman correlation test showed a significant seasonal discrimination of dominant microphytoplankton species. These microorganisms were associated with different environmental variables, in particular temperature and salinity. Numerous HABs species were encountered regularly along the year. Although Dinophysis species and Prorocentrum lima were present in both sites, no Lipophilic Shellfish Poisoning was detected for the analyzed bivalve mollusks. Domoic acid (DA), produced by toxic species of Pseudo-nitzschia was found with concentrations up to 18 µg DA g −1 in the smooth clam Callista chione. Data showed that the observed persistent and dramatic Paralytic Shellfish Poisoning (PSP) intoxication of mollusks resulted probably of Gymnodinium catenatum pro-liferations in both studied areas. Contrary to C. chione, the cockle Achanthocardia tuberculatum showed a permanent and extremely high toxicity level during the 15 months survey with up to 7545 µg Equivalent Saxitoxin kg −1 flesh (ten times higher than the sanitary threshold of 800 µg eqSTX Kg −1 flesh). The present work highlights for the first time the dynamic of microphytoplankton including HABs species and their associated toxin accumulation in the commercially exploited shellfish in the southern western Mediterranean waters of Morocco. Furthermore, the acquired data will help us to improve the monitoring of HABs species and related toxins in these coastal marine systems.

Summary The soft clam Callista chione is highly appreciated among marine inhabitants for nutritional, commercial and economic reasons. This work aims to determine the lipid classes’ profile of C. chione and the effect of different preservation treatments on them. C. chione meat was found to be a rich source of dietary phospholipids (PhLs), ω-3 fatty acids and carotenoids, encouraging the exploitation of the species as human food. Among treatments, only marinating reduced the PhLs content. Parboiling and freezing resulted in a significant decrease in unsaturated fatty acids, while marinating caused partial replacement of polyunsaturated with monounsaturated fatty acids. Lipid quality indices remained favourable for a healthy diet. With the exception of astaxanthin, the rest of the carotenoids identified were susceptible to processing and frozen storage. Parboiling and freezing of the vacuum-packed meats for up to 4 months would be most appropriate, among the treatments applied, for preserving the lipid quality of C. chione.

Summary: The smooth clam Callista chione is an Atlantic-Mediterranean species that is commercially exploited in several European countries. Several aspects of its reproduction were studied in a coastal location of the northwestern Mediterranean as a tool for sustainable fisheries management. Gonadal development was classified into 6 different stages, ranging from immature to degradation of the remaining sexual structures. Results showed that C. chione was able to reproduce throughout the year but a main spawning period occurred in spring. First records of hermaphrodites were found for this species. The mature spermatozoa measured 4.70±0.66 µm (without the flagellum), including a very short acrosome of 0.75±0.09 µm. The mid-piece of the spermatozoa had a mitochondrial sheath composed of five mitochondria. Ripe oocytes ranged from 60 to 80 µm in length. Size at first maturity (SL50) was estimated for the first time in a Mediterranean population, showing values of 30.26 mm in 2005-2006 but only 21.45 mm in 2014.

The smooth clam, Callista chione (Linnaeus, 1758), is a venerid bivalve widely appreciated in southern Spain where it represents the top commercial bivalve species in terms of landings and economic value. In this area, a total of 223 artisanal boats (68% of the artisanal fleet) are involved in shellfishing targeting bivalve molluscs, including the smooth clam. The artisanal mechanised dredging that targets C. chione in the northern Alboran Sea is described and the current exploitation status of its populations is analysed. A surplus-production model was run using ASPIC and used to assess the temporal variation in the levels of fishing for this bivalve throughout the study period (2002-2015), as well as to suggest conservation reference points that could guarantee the sustainable exploitation of this resource. During the study period, the maximum C. chione catch was registered in 2003 (306 t) and the minimum in 2006 (93 t). The ASPIC model for C. chione stock suggests that a Maximum Sustainable Yield (MSY) of 216 t could be produced from a total stock biomass of 983 t (Bmsy) at a fishing mortality rate of total biomass of 0.22 (Fmsy), with B/Bmsy and F/Fmsy values of 1.34 and 0.82, respectively, indicating that the stock is approaching good status.

In this study, the influence of food availability on the gonadal development of the smooth clam Callista chione was analyzed for the first time. Callista chione adults were maintained for 60 days under controlled conditions with two different diet rations: a scarce diet (3% of dry weight of algae by meat dry weight per day) and a high diet (6%). The condition index, gonadal stage, and oocyte size were measured throughout the experiment. Maturation of gonad was achieved in both groups. Nevertheless, the condition index and oocyte diameter were significantly less in the scarce-diet group. These low values seem to be related to a loss in reserve tissue, not to the release of gametes. Thus, in food-limited conditions, the animals use the energy to mature instead of grow. Comparisons with animals from the field were made during all the study periods, and differences were found. In fact, these individuals were primarily in the postspawning stage, and the oocyte size was considerably smaller, coinciding...

We studied 127 samples of bivalve mollusks (Mediterranean mussel, Mytilus galloprovincialis; smooth clam, Callista chione; grooved carpet-shell clam, Tapes decussatus; and striped venus clam, Chamelea gallina) obtained in the winter and spring of 2009 from retail fish and shellfish vendors in Granada, Spain. Samples were analyzed (raw and after steaming) to determine the prevalence of Escherichia coli, mesophilic aerobes, Staphylococcus aureus and the disease-causing microorganisms Salmonella spp., Listeria monocytogenes and Vibrio parahaemolyticus. E. coli was found in 25% of raw samples and 4% of cooked samples. Aerobes were found in 89% of raw samples (more than 1,000 cfu/g), and S. aureus was found in 37.0%. Only one raw sample was positive for V. parahaemolyticus. The percentage of positive findings was fourfold as high in the spring sample as in the winter sample. Contamination was most frequent in the smooth clam, and samples obtained on Mondays were more frequently contaminated than those obtained on other days of the week. PRACTICAL APPLICATIONS Current Spanish legislation establishes that all bivalve mollusks intended for commercial sale and human consumption must be treated at a detoxification center. The application of detoxification is of fundamental importance because it constitutes a barrier against the transmission of bacterial and viral diseases of aquatic origin. We analyzed possible differences in contamination parameters in this type of shellfish, indicated characteristics that may be affected by alterations in quality, and discussed the potential effects of these alterations on human health.

The age and growth of the smooth clam Callista chione from the southwestern coast of Portugal were estimated during a 1 yr study period by using both the surface growth rings and internal shell microgrowth lines (by acetate peel method). The von Bertalanffy growth curves obtained by these 2 methods were, respectively: Lt = 91.9(1 - e - 0.18 (t + 0.22) ) and Lt = 98.1(1 - e - 0.15 (t + 0.43) ). Based on these, the counting of surface growth rings is appropriate for a quick age estimation of individuals up to 10 yr old (~75 mm shell length, SL). For older specimens, analysis of the growth lines in the cross section of shells is recommended, because close to the shell border it becomes difficult to distinguish growth rings on the shell surface. Rapid shell growth occurred in spring and summer, whereas slow growth occurred during autumn and winter, with the deposition of an annual growth ring. The over- all growth performance and the phi-prime index were used to compare growth parameters with data from literature about venerid bivalves. These parameters indicated that Callista spp. have a higher growth performance than other venerid bivalves and this is correlated with geographical latitude. The smooth clam achieves sexual maturation at 4 yr of age and reaches the minimum landing size (60 mm SL) after 5 yr.

The gametogenic cycle of the smooth clam Callista chione off the Arrábida region was studied throughout a 17-month period (from January 2004 to May 2005) using standard histological techniques, mean oocyte diameters and a condition index. This species showed a synchronism between sexes both in terms of gametogenic development and spawning. The results indicated that sex-ratio was not significantly different from parity. In January 2004, the gametogenic cycle had already begun and ended in late October 2004. Three spawning peaks were detected: January–March, April–May and August–October. No resting period was observed and a new gametogenic cycle began in early November, immediately after the spawning period. The analysis of the oocyte diameter enabled predicting the main spawning periods, which appear to be largely governed by seawater temperature. The condition index evolved according to the reproductive cycle of the species, with the highest values being observed prior to the main spawning periods. The size at first maturity estimated for C. chione was 50.81 mm.

The smooth clam, Callista chione (Linnaeus, 1758), is a shallowburrowing filter feeder, inhabiting sandy sediments, from just offshore to a depth of about 130m. It is widely distributed in Mediterranean and Atlantic waters, from the British Isles to the Moroccan coast. In the Mediterranean Sea, C. chione is among the most abundant bivalve species inhabiting shallow softbottomed shores and, in some areas, the most prominent suspension-feeding bivalve species in terms of biomass. The smooth clam is economically important in France, Portugal, Spain (Catalan Sea) and Italy (Adriatic Sea), and part of an extensive clam fishery carried out by artisanal dredging. Although it is not a very marketable species, C. chione is currently widely exploited as a consequence of the overexploitation of other clams, such as Ensis siliqua, Spisula solida, Chamelea gallina and Venus striatula. However, a decline of populations due to overfishing has been observed over a number of years, thus a reduction of fishing effort is now suggested. Despite the fact that C. chione is a common inhabitant of the sandy shores of the Thracian Sea, no systematic fishery exists similar to that present along the coasts of the western Mediterranean. Smooth clams are collected almost circumstantially by divers and are usually landed in small quantities together with other bivalves (Galinou-Mitsoudi, personal communication). Thus, no reliable fishery statistics are available. As C. chione is the object of an intensive uncontrolled fishery, mainly in the western Mediterranean, the study of its population dynamics is important for developing appropriate fishery management strategies. However, research on the biology and ecology of C. chione is limited. In the eastern Mediterranean, records refer only to its geographical distribution. The purpose of the current study is to contribute to the knowledge of the biology of the species in the Thracian Sea by providing information on shell banding, morphometric relationships, age and growth rates. Smooth clams were collected during December 2001 and June 2002 from two sites (St S and St K) along the western coast of Thassos Island, Greece, which are free of any source of major pollution. The two sites differ in wave exposure, anthropogenic activity and clam population density. At both sites the sediment mainly consisted of fine and medium sand, which together accounted for 78–92% of the particles. The redox-potential discontinuity (RPD) layer lay significantly closer to the surface at St K and within the depth range inhabited by C. chione. This resulted in a black biofilm on the shell periostracum, probably of anaerobic bacteria, which disappeared within 2–3 days when the clams were kept in aerobic conditions (immersed in continuously renewed seawater). Sampling of clams was carried out at depths between 1 and 3m at 0.5 m intervals, using a metal box quadrat (100 £ 100 £ 10 cm), which was pushed into the sediment and sifted by hand in situ. A random sample was also collected by hand from shallower depths at both sites in order to increase the number of captured animals. Fifteen clams from each site at each sampling season, chosen to cover the full size range of each sample, were pooled (shell length: 16–72mm) and size parameters, such as shell length (maximum distance of the anterior–posterior axis), shell height (distance of the ventral–dorsal axis, across the shell middle axis), shell width (maximum distance on the lateral axis, between both valves of the closed shell; to the nearest 0.1mm), shell weight, wet flesh weight and dry flesh weight (to the nearest 0.0001 g) were measured. Linear regressions were fitted to the log10-transformed data and the constants a (intercept 1⁄4 the initial growth coefficient) and b (slope 1⁄4 relative growth rate of size parameters) were estimated. t-Tests (H0 1⁄4 1, H0 1⁄4 3) with a confidence level of 95% (a 1⁄4 0.05) were also applied in order to determine whether the relative growth of size parameters is allometric. In order to identify spatial or seasonal fluctuations in the morphometric relationships of the clam, an analysis of variance with a covariate (ANCOVA) was carried out. Morphometric relationships between the shell-size parameters were compared only between the two sampling sites. The relationships between the wet and dry flesh weight against the shell length, and that of the wet flesh weight versus the dry flesh weight (which examines the flesh water content) were compared spatially and seasonally, as these parameters in bivalves are known to vary throughout the year. Characteristic ring-like patterns were noticed on the external surface, consisting of a wide opaque area of shell accretion followed by a transparent narrow area. It was assumed that they form annual increments. Acetate peel replicas of polished and etched shell sections were additionally prepared in order to examine the general shell structure and microgrowth patterns. The patterns of growth lines (see later) were used to identify the position of each growth ring. Distance measurements (to the nearest 0.1mm) were taken from the umbo to the end of each ring along the axis of maximum growth. Both external rings and microgrowth patterns were used for age determination as it soon became apparent that all growth lines identified on the shell surface were also clearly visible in the peel replicas of shell sections, and that measurements taken in the shell surface were in full correspondence with those taken on the peels. The von Bertalanffy growth model was applied to the size-at-age data and growth parameters (L1, K, t0) were estimated using a nonlinear regression under the FiSAT II software package. Morphometric relationships between several size parameters in C. chione are presented in Table 1. The allometric coefficient (b, slope) of these relationships is related allometrically in all cases and reflects ontogenetic changes in the shell and flesh. The shell of C. chione tends to become proportionally higher, wider and heavier, possibly providing better anchorage in the mobile sediment for larger animals. The flesh grows relatively faster than shell length, while the water content is reduced as the clams grow. The spatial comparison of the relationships between shell variables did not show any significant differences (ANCOVA, Correspondence: P. K. Leontarakis; e-mail: fri@otenet.gr

The venerid bivalve Callista chione is the most prominent suspension-feeding bivalve inhabiting the soft bottom of coastal areas in the northern Euboikos Gulf (Aegean Sea), where it is exploited by small-scale fishery. The parameters of the von Bertalanffy growth function were estimated and the somatic production-to-biomass ratio was found to be 0.45 y −1 . The maximum age of adult individuals was 17 years. The species is gonochoristic, its oocyte diameter ranged from 54.5 to 120 μm with a conspicuous jelly-coat. Microscopical examination of the gonads showed that gonadal production did not start until the second year of life. The observations on the gonadal cycle indicate that this bivalve is capable of year-round reproduction.

The branchiopods found in inland aquatic habitats are a heterogeneous group of crustaceans. There are more than 2,000 described species, and new taxa are still being discovered. Included in this group are fairy shrimps (Anostraca), tadpole shrimps (Notostraca), smooth clam shrimps (Laevicaudata), spiny clam shrimps (Spinicaudata), tropical clam shrimps (Cyclestherida), (the so called “large branchiopods”) and the various species of “water-fleas” (Cladocera). In this chapter, we review the similarities and differences among the groups in their morphology, physiology, reproduction, behavior and ecology. We also provide methods for field collections, sample preparation and culturing.

11 pages, 10 figures, 4 tables, Bivalves are considered key species in many marine communities and the decline of their populations usually causes changes in the structure of the ecosystems. The aim of the present study was to investigate changes in the spatial distribution and population structure of an exploited shellfish bed of Callista chione at a location of the northwestern Mediterranean Sea and analyse its potential causes. To this end field surveys for the years 2004 and 2010 covering the whole distribution area of the species were performed and all historical data on commercial landings, clam biomass and density, and locations and volume of dredged sand for beach nourishment were compiled. Results showed that the distribution had been hugely reduced, showing a sharp decline in density and biomass and a decrease in the mean population size in 2010. Our results confirm that the species is a slow-growing bivalve that is highly vulnerable to disturbances prolonged in time. Persistent sand dredging operations since 1987 have gradually reduced the distribution area of the smooth clam to the northeastern part of the clam bed. Consequently, fishing activity has concentrated on a smaller area, thus increasing the fishing effort in the northern part. Therefore, the results clearly suggest that the decline of C. chione bed was mainly caused by the interaction of two coastal uses: sand dredging and clam fisheries. Based on this study, some management guidelines are proposed, This paper is a result of the research project “Avaluació de l’estat del banc natural de petxina lluenta del Maresme” (Evaluation of the condition of the smooth clam bed in the Maresme) funded by the Department d’Agricultura, Ramaderia i Pesca (Generalitat de Catalunya) and the Dirección General de Costas (Ministerio de Agricultura, Alimentación y Medio Ambiente)

Vasconcelos, P., Morgado-André, A., Morgado-André, C., and Gaspar, M. B. 2011. Shell strength and fishing damage to the smooth clam (Callista chione): simulating impacts caused by bivalve dredging. – ICES Journal of Marine Science, 68: 32–42. The smooth clam Callista chione is exploited by a fleet of dredgers along the southwestern coast of Portugal and suffers from a high incidence of shell damage. The force required to break C. chione shells in relation to fishing impacts and dredge damage is quantified. Fishing trials and shell-strength measurements (compression and compaction experiments) were performed to determine whether shell damage was attributable to the direct impact of the dredge teeth or to sediment compaction. A three-dimensional model of C. chione was subjected to simulated force by the finite element method. Analyses of damage areas and breakage patterns revealed two groups of samples, one containing the samples from compression experiments and another with the samples from dredging and compaction experiments, suggesting that most shell damage was attributable to compaction within the sediment. Information is provided to help improve the design of bivalve dredges, by increasing both length and angle of the dredge teeth, which would reduce the compaction force and distribute it differentially within the sediment, forcing upward movement of the bivalves.

This study describes the first data on larval development and growth of the smooth clam Callista chione under two different temperature regimes (19 and 23 ºC). The mean diameter of the oocytes was 89.5 ± 0.7 µm. After seven days, the mean length of D-shaped larvae was 132.9 ± 7.8 µm at 19 ºC and 148.38 ± 12.74 µm at 23 ºC. Metamorphosis took place between days 32 and 39. Differences in length associated with different culture temperatures were statistically significant on days 11, 13, and 20. At 23 ºC, larvae reached a length of 175.15 µm within 11 days, whilst during the same period they reached 137.88 µm at 19 ºC (a difference in growth of 39%); however, survival rate was higher at 19 ºC (8%) than at 23 ºC (2%)., Este trabajo describe los primeros datos sobre el desarrollo y el crecimiento larvario del almejón de sangre Callista chione bajo dos regímenes diferentes de temperatura (19 y 23 ºC). El diámetro medio de los ovocitos observado fue de 89.5 ± 0.7 µm. Después de siete días, el tamaño medio de las larvas D fue de 132.9 ± 7.8 µm a 19 ºC y 148.38 ± 12.74 µm a 23 ºC. La metamorfosis se llevó a cabo entre los días 32 y 39. Las diferencias de longitud asociadas a las diferentes temperaturas de cultivo fueron estadísticamente significativas en los días 11, 13 y 20. A 23 ºC las larvas alcanzaron una longitud de 175.15 µm a los 11 días, mientras que durante el mismo periodo alcanzaron 137.88 µm a 19 ºC (una diferencia en el crecimiento de 39%); sin embargo, la tasa de supervivencia fue mayor a 19 ºC (8%) que a 23 ºC (2%).

The age, growth, and population structure of the smooth clam Callista chione were determined from samples collected by hydraulic dredge and SCUBA at four locations in the eastern Adriatic during 2007 and 2008. The age of 436 clam shells was determined from internal growth lines present in shell sections, and the timing of growth line formation was ascertained from monthly collections of clams to occur between August and September when sea water temperatures were maximal. In addition, age of 30 older individuals was verified with acetate peels of polished and etched shell sections. Differences were apparent in the age structure and growth rates of clams collected from the four locations studied. Von Bertalanffy growth (VBG) curves obtained for clams from these locations were L t = 72.4 (1−e−0.25(t − 2.68)) (Rab Island), L t = 74.5 (1−e−0.15(t + 0.57)) (Pag Bay), L t = 79.3 (1−e−0.34(t − 0.97)) (Cetina estuary), and L t = 82.5 (1−e−0.11(t + 2.88)) (Kastela Bay). The age of the clams ranged between 3 and 44 years; median clam ages were similar at three of the four locations (14, 12, and 12 years, respectively), but was significantly lower in the Cetina estuary (4 years). The VBG growth constants recorded from clams were within the range of values obtained for this species by previous authors. The observed local differences in population structure indicate different levels of exploitation and illustrate the need to establish long-term strategies for a sustainable exploitation of smooth clams in the Croatian Adriatic.

The Vickers micro-hardness of three different sea mollusc shell structures has been determined as a function of the indentation load. The following shells from the Adriatic Sea have been investigated: abalone (Haliotis tuberculata), smooth clam (Callista chione), and warty venus (Venus verrucosa). The results show that the measured micro-hardness depends on the load for all of the investigated seashell structures, which indicates the influence of the indentation size effect (ISE). The load dependence of micro-hardness has been analyzed by using the known Meyer's Law, the proportional specimen resistance model (PSR), and the modified proportional specimen resistance model. The best correlation between measured values and used models has been achieved by using the modified PSR model.