Maximum Shell Size Research Articles

The Indication of Gastropods Extinctions at Intertidal Zone of the Teluk Nipah Waters, the Pesisir Selatan Regency the Province of the West Sumatera

Intensive observation of gastropods, every March from the year 2008 to the year 2012, was carried out to document some indicators of gastropod extinction. The purposive sampling technic was used in this work. The physicochemical parameters of its habitat were also monitored during every sampling done. It was found that the intertidal substrate consist of sand, while the habitat parameters were more than 5,6 mg/L dissolved oxygen, pH around 7,0-7,2, salinity 30,2-32,2 ppt, temperature 28,6-29,60C, the visibility 100%. The number of species, the number of found gastropods, the abundance, and the maximum shell size of found gastropods showed decreasing from year to year, while routine collecting by the visitor and the marine organism shell collector, and the disturbance by the fisherman activities occurred. This indication showed a tendency for gastropods extinction

Phylogenetic placement, morphology and gill-associated bacteria of a new genus and species of deep-sea mussel (Mytilidae: Bathymodiolinae) from the South China Sea

Mussels in the subfamily Bathymodiolinae are common inhabitants of deep-sea chemosynthetic habitats, but in many places their diversity remains unknown. Here we describe Nypamodiolus samadiae n. gen. et n. sp. (Mytilidae: Bathymodiolinae) based on samples collected from the Haima cold seep in the South China Sea. Phylogenetic analyses based on fragments of three mitochondrial (cox1, 16S rRNA and nad4) and three nuclear (18S rRNA, 28S rRNA and histone H3) genes show that this new species belongs to a new genus, Nypamodiolus, which includes three named species (Myrina longissima Thiele and Jaeckel, 1931, Myrina simpsoni Marshall, 1900, Idasola japonica Habe, 1976) and a few undescribed species. Nypamodiolus n. gen. is characterized by small-sized, modioliform to fan-shaped shells with the umbones in a non-terminal position, and by robust anterior and posterior byssal retractor muscles arranged in roughly one plane. Most closely related to Nypamodiolus samadiae n. sp. is an undescribed species from the northern Papua New Guinea, to which it has a Kimura-2-parameter genetic distance of 11.8% for cox1. Sequencing the V3–V4 region of the microbial 16S rRNA gene reveals two dominant gill-associated bacteria in the new species, including one sulfur-oxidizing Gammaproteobacteria (relative abundance: 43.8–58.8%) and one unclassified Spirochaetes (relative abundance: 23.9–28.1%). Morphologically, N. samadiae n. sp. is similar to N. simpsoni, while can be distinguished by a larger maximum shell size (45.0 mm vs. 40.0 mm), larger length/height ratio (2.6–2.9 vs. 2.1–2.4), broader posterior end, slightly curved dorsal margin, and more anterior umbones.

Taphonomy and evolution of Lower Jurassic lithiotid bivalve accumulations in the Apennine Carbonate Platform (southern Italy)

Lower Jurassic Tethyan and Panthalassan marine shallow-water successions are characterized by aberrant lithiotid bivalves belonging to the Lithiotis Fauna. Their widespread occurrence, often in rock-forming abundance, represents a global biofacies, mostly restricted to the Pliensbachian–early Toarcian. Despite their wide occurrence and their prominent role as carbonate producers in shallow-water platforms, the biogeographic and stratigraphic distribution of this group of bivalves and their evolutionary history are obscure, mostly because they commonly have not been identified at the generic or specific level. In particular, their evolution and demise in relation to important global palaeoenvironmental perturbations, such as the Pliensbachian-Toarcian boundary event and the early Toarcian oceanic anoxic event are not yet known in detail.In the Apennine Carbonate Platform of southern Italy, the Lithiotis Member, in the upper part of the Lower Jurassic Palaeodasycladus Limestones Formation, is characterized by the abundant occurrence of lithiotid bivalves. They disappear abruptly in the lowermost beds of the overlying Oolitic-oncolitic Limestones Formation, at the onset of the early Toarcian Oceanic Anoxic Event. More than 60 lithiotid bivalve concentrations occur in a nearly 120m-thick succession spectacularly exposed on freshly cut walls in a quarry west of Mercato San Severino (Salerno). Field observations on the taxonomic composition and fabric of the shell beds (packing, maximum shell size, degree of shell articulation and fragmentation) allowed to distinguish four taphofacies (A–D). Taphofacies A records the appearance and spreading of the lithiotids, with accumulations characterized mainly by small-sized and loosely packed shells. Taphofacies B records the acme of lithiotid bivalves, with densely packed accumulations of large shells. These two taphofacies yield prevailing articulated individuals, commonly in life position. Taphofacies C records a decrease of the shell packing and frequency of articulated shells. However, it is not clear whether this represents the beginning of a prolonged crisis or just the local response to less favourable environmental conditions around a sequence boundary. Taphofacies D consists of three shell beds, one in the uppermost part of the Lithiotis Member and two within the lowermost part of the Oolitic-oncolitic Limestones Formation, in the stratigraphic interval characterized by the negative carbon isotope excursion of the early Toarcian OAE. The bivalve shells of these two beds consist exclusively of disarticulated and fragmented shells, possibly reworked from underlying levels. The demise of the lithiotids carbonate factory in the Apennine Carbonate Platform and the extinction of the largest aberrant bivalves of the Lithiotis Fauna at the onset of the early Toarcian anoxic event were probably due to the physiological stress imposed by ocean acidification and increased nutrient input.

Biological Conservation of Giant Limpets: The Implications of Large Size.

Patellogastropods, also known as true limpets, are distributed throughout the world and constitute key species in coastal ecosystems. Some limpet species achieve remarkable sizes, which in the most extreme cases can surpass 35cm in shell length. In this review, we focus on giant limpets, which are defined as those with a maximum shell size surpassing 10cm. According to the scientific literature, there are a total of 14 species across five genera that reach these larger sizes. Four of these species are threatened or in danger of extinction. Inhabiting the intertidal zones, limpets are frequently affected by anthropogenic impacts, namely collection by humans, pollution and habitat fragmentation. In the case of larger species, their conspicuous size has made them especially prone to human collection since prehistoric times. Size is not phylogeny-dependent among giant limpets, but is instead related to behavioural traits instead. Larger-sized species tend to be nonmigratory and territorial compared to those that are smaller. Collection by humans has been cited as the main cause behind the decline and/or extinction of giant limpet populations. Their conspicuously large size makes them the preferred target of human collection. Because they are protandric species, selectively eliminating larger specimens of a given population seriously compromises their viability and has led to local extinction events in some cases. Additionally, sustained collection over time may lead to microevolutionary responses that result in genetic changes. The growing presence of artificial structures in coastal ecosystems may cause population fragmentation and isolation, limiting the genetic flow and dispersion capacity of many limpet species. However, when they are necessitated, artificial structures could be managed to establish marine artificial microreserves and contribute to the conservation of giant limpet species that naturally settle on them.

Growth of Mya arenaria L. at the northern edge of the range: heterogeneity of soft-shell clam growth characteristics in the White Sea

Linear growth of soft-shell clams, Mya arenaria L., was studied at six locations in the White Sea situated in the middle and low tidal zones. The main aim was to analyse the growth heterogeneity both within beds (with respect to individual growth) and between beds (with respect to group growth). Mya population was characterized by a slow growth and a long lifespan. Maximum shell size was 70–80 mm, and longevity was at least 25 years. In addition, growth rates were highly variable, statistically significant differences being present both within and between the beds. No differences were found in group growth between different tidal horizons of the same site. The slowest growth of soft-shell clams was observed at sites with the greatest content of fine particles (silt and clay) in sediments. Differences between beds in Mya group growth could reflect variability of feeding conditions, which were probably determined by some local features (e.g. hydrodynamic regime). However, the variation of the individual growth rate within beds was comparable to that of the group growth rate between studied locations. To a great extent it seemed to be determined by the characteristics of the initial period of soft-shell clam growth.

The effects of flow and stream characteristics on the variation in freshwater mussel growth in a Southeast US river basin

Summary The evaluation of the age and growth of animal populations is essential for understanding and predicting how populations will respond to changes in environmental conditions and anthropogenic stressors. We used a novel, von Bertalanffy hierarchical modelling approach to quantify relationships between the growth of three freshwater mussel species and various site‐ and watershed‐level factors including seasonal discharge, land cover and stream size in the lower Flint River Basin, Georgia, U.S.A. Our modelling approach quantified the mussel‐to‐mussel variation in the von Bertalanffy parameters and accounted for biases associated with multiple measurements made on each mussel specimen, which are generally not accounted for as sources of bias in age and growth studies. Modelling results suggested that maximum shell size parameter and the Brody growth coefficient varied across species, on average, 19 and 33%, respectively, among individual mussels within sample sites. The variation was related to short‐term high streamflows during the spring season, stream size, channel geomorphology and land cover in the watershed. This study provides insight to the factors affecting the growth of stream‐dwelling freshwater mussels. Although hierarchical von Bertalanffy growth models are rarely used for freshwater mussel age and growth studies, this approach can provide important information regarding the ecology of freshwater mussels.

Egg retention in the clausiliid <i>Balea</i> (<i>Pseudalinda</i>) <i>fallax</i> (Rossmässler, 1836) from Roztocze (S. E. Poland)

1. Baur A. 1990. Intra- and interspecific influences on age at first reproduction and fecundity in the land snail Balea perversa. Oikos 57: 333–337. https://doi.org/10.2307/356596.... CrossRef Google Scholar

Maximum Shell Size, Growth Rate, and Maturation Age Correlate With Longevity in Bivalve Molluscs

Bivalve molluscs are newly discovered models of successful aging, and this invertebrate group includes Arctica islandica, with the longest metazoan life span. Despite an increasing biogerontological focus on bivalves, their life history traits in relation to maximum age are not as comprehensively understood as those in vertebrate model aging organisms. We explore the allometric scaling of longevity and the relationship between development schedules (time to maturity and growth rate) and longevity in the Bivalvia. Using a traditional nonphylogenetic approach and the phylogenetically independent contrasts method, the relationship among these life history parameters is analyzed. It is demonstrated that in bivalves, maximum shell size, development, and growth rates all associate with longevity. Our findings support the observations of life history patterns in mammals and fish. This is the first investigation into the relationship among longevity, size, and development schedules throughout this group, and the results strengthened by the control for phylogenetic independence.

Middle‐Late Jurassic bivalves of the superfamily Veneroidea from New Zealand and New Caledonia

Bivalves of the families Arcticidae, Isocyprinidae n. fam., and Veneridae are described from the Middle‐Late Jurassic of New Zealand and New Caledonia. Morphology of shells from several genera in Arcticidae, Isocyprinidae, Veniellidae n. fam., and Veneridae is analysed in detail. These families are shown to be closely related in terms of morphological shell characters, especially ontogenetic and evolutionary hinge development. This is highlighted by identical ranges in commissural outline and shell form together with similar strength and form of ornamentation, and the fact that hinge plate development is an uninterrupted evolutionary process between Arcticidae and Isocyprinidae to Veneridae. These converging lineages show that Veneridae is at least diphyletic. This same evolutionary process is also shown to be an ontogenetic function of shells, with the final state of hinge development limited by maximum shell size. The family Corbiculidae is considered to be a major offshoot from one of the two lineages defined by Arcticidae‐Veneridae or Isocyprinidae‐Veneridae. These factors justify the superfamilies Arcticoidea and Corbiculoidea being synonymised with Veneroidea. In New Zealand, Isocyprinidae is represented by Austrocyprina n. gen. (one species). Veneridae is present in the form of Eocallista (one new species), and Austrocardilanx n. gen. (two new species). Arcticidae has been recorded from New Zealand and New Caledonia, and is represented by Antarctica n. gen. (one species).

Environmentally Controlled Variation in Shell Size of Ambonychia Hall (Mollusca: Bivalvia) in the Type Cincinnatian (Upper Ordovician)

The common Ordovician bivalve genus Ambonychia Hall of the type Cincinnatian Series displays great variation in shell size that is strongly correlated with paleoenvironment. In older Cincinnatian sequences the largest mean and maximum shell size are found in the highest energy paleo-environments with decreasing size found in lower energy paleoenvironments. Further, the smallest size class of Ambonychia frequently is excluded from the higher energy paleoenvironments, possibly associated with differential taphonomic destruction of smaller shells. The deep-to-shallow water trend in mean and maximum shell size is not present in younger Cincinnatian sequences, perhaps because of a change in the morphology of the younger Ambonychia species, such as the development of a keeled umbo.

Dynamic of population-dynamics in a medically important snail species Lymnaea (Radix) Luteola (Lamarck)

The life-cycle parameters of the snail Lymnaea (Radix) luteola and the factors influencing the same have been studied under laboratory conditions. Ins each month, from July 1990 to June 1991, a batch of 100 zero-day old individual were considered for studies. The snails of April batch survived for 19.42 days while those in December batch survived for 87.45 days. The May batch individual though survived for 65.67 days gained maximum shell size (15.84 mm in length) and body weight (419.87 mg). All individuals of April batch died prior to attainment of sexual maturity. In the remaining 11 batches the snails became sexually mature between 32 and 53 days. At this stage, they were with varying shell lengths, 9.3 mm to 13,11 mm in respect to batches. The reproduction period varied from 1-67 days. An individual laid, on an average, 0,25 (March batch) to 443.67 (May batch) eggs in its life-span. A batch of such snails would leave 24312, 22520, 720268, 80408, 76067, 418165, 214, 9202, 0, 0, 2459386 and 127894 individuals at the end of 352nd day. Since the environmental conditions were almost similar the 'dynamic' of population dynamics seems to be involved with the 'strain' of the snail individuals of the batches concerned.

Intraspecific variation in the population dynamics and growth of the limpet, Cellana tramoserica.

Populations of the limpet Cellana tramoserica (Sowerby) from high, mid, and low intertidal regions, and from a subtidal zone, were studied at Cape Banks (N.S.W.), Australia. Individuals from the subtidal population had the largest mean and maximum shell size, the low and high shore populations were intermediate, while the midshore population had both the smallest mean and maximum size. The density of adults showed the reverse trend: the midshore region had the greatest adult population density while the subtidal population had the smallest density. The density of juveniles and recruits was negatively correlated with tidal height in the intertidal areas, but the density of both age-classes was smallest in the subtidal region. The rate of growth of individuals was negatively correlated to the adult density of a site; individuals from the subtidal population grew the fastest, while those from the midshore region grew the slowest. The level of adult mortality of the four populations was similar, with an annual rate of between 50-60%. Juvenile mortality did, however, differ among populations; reduced percentages of juveniles reached adult size in the mid and low shore populations than in the highshore and subtidal populations.The expected lifetime fecundity of individual females differed among the four populations. Subtidal individuals were expected to spawn 40 times the amount of gonad material during their life than were individuals from the midshore population. Individuals from the high and low populations probably spawn 10 times more than those from the midshore region. Differences in the fecundities of individuals were not likely to be the result of genetic differences because experimental transplants and manipulations of density showed that individuals from all the intertidal populations could increase their growth rate to match that of subtidal individuals. The implications of the difference in lifetime fecundity among populations are discussed.

Stages in the post-hatching development of Aplysia californica.

In order to study the development of the nervous system of the marine mollusc, Aplysia californica, it is necessary objectively to assess the maturity of individual specimens. This can be done by defining stages in the life cycle. The post-hatching development can be divided into four phases: planktonic, metamorphic, juvenile, and adult. These phases can be further subdivided into 13 stages on the basis of behavioral and morphological characteristics visible in living specimens: Stage 1, newly hatched; Stage 2, eyes develop; Stage 3, the larval heart beats; Stage 4, maximum shell size is reached; Stage 5, the propodium develops; Stage 6, red spots appear; Stage 7, the velum is shed; Stage 8, eyebrows appear; Stage 9, pink color develops; Stage 10, white spots appear; Stage 11, rhinophores grow; Stage 12, the genital groove forms; Stage 13, egg laying begins. Reconstructions from serial sections taken from specimens fixed at each of these stages reveal the sequence of formation of the major organ systems. The nervous system develops gradually. The cerebral and pedal ganglia are present at Stage 1, the optic ganglia develop at Stage 2, the abdominal, pleural, and osphradial ganglia at Stage 3, the buccal ganglia at Stage 5, and the genital ganglion at Stage 13. Because Aplysia develops gradually, it is possible to analyze the contribution which gastropod torsion makes to the different phases of the life cycle. The Aplysia embryo undergoes 120 degrees torsion prior to Stage 1. The major visceral organs, the digestive system, heart, gill, and visceral nervous system, develop sybsequently in their post-torsional positions. After metamorphosis, there is a partial de-torsion which involves only the digestive system. Torsion of the digestive system may therefore be beneficial only to the pre-metamorphic larva, and not to the postmetamorphic juvenile.

Growth studies of the tropical intertidal limpet Acmaea antillarum

The tropical intertidal limpet Acmaea antillarum (Sowerby) was used in a series of field and aquarium growth studies, carried out in Venezuela. Both field and aquarium experiments demonstrated the formation of diurnal growth ridges and subdiurnal periodic growth striations on the shell surface. It was shown in aquarium experiments that the normal growth pattern was inhibited in constant darkness and that continous illumination stimulated the formation of extra growth ridges. Alterations of the experimental sequence of illumination influenced the formation of subdiurnal growth markings. This secondary growth pattern appears to be distinct from the basic system of diurnal ridge formation. Limpet shell lengths were related to estimated age based on diurnal growth ridge counts. It is probable that maximum shell size is attained in less than 1 year. Equations for allometric shell growth characteristics were calculated relative to shell length. Calculations for instantaneous relative growth rate were made from natural populations, experimental field populations and aquarium specimens. These were compared to show that the field and aquarium experiments demonstrated similar growth rates. The results of these observations and calculations are compared with other molluscan growth studies.