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This chapter discusses the composition of seagrass communities. Seagrass communities comprise epiphytes and sessile epifauna growing on seagrass leaves and rhizomes, as well as more mobile animals, many of which move between seagrass and other habitats at different times or life-cycle stages. These include herbivores (ranging from tiny feeders on microscopic epiphytic algae to massive turtles and seacows), detritus feeders, and predators.

This chapter presents summaries of each taxonomic group inhabiting temporary waters, providing examples of habitat-specific requirements and adaptations throughout. Insects and crustaceans are the dominant community members and, consequently, the best studied groups. However, information is also provided on lesser known groups, such as the prokaryotes, fungi, nematodes, tardigrades, and rotifers. Higher plants, fishes, amphibians, reptiles, birds, and mammals are discussed. Detailed case histories are given of the biotas from common habitat types. Global and regional comparisons of temporary water communities are made and commonality is demonstrated.

This chapter begins with a brief discussion of the factors that make crustaceans an excellent model for the study of aggressive behavior. It then discusses the natural contexts of aggression, aggression in development, aggressive behavior, dominance hierarchy formation, hormonal control of aggressive behavior, and neural mechanisms of aggressive behavior.

Walking with legs is the main form of locomotion in most species of decapod Crustacea. This chapter focuses on the walking movements in molluscs such as crayfish and lobster. In addition, some species, such as crayfish and lobsters, can swim both forward with the swimmerets and backward with flips of the abdomen. Crustaceans have been extensively examined at the behavioural, network, and cellular levels, and the corresponding neuronal mechanisms have been understood to a considerable extent. The lobster exhibits a walking pattern characteristic of many decapods, and can walk in any direction, using all or only a subset of ten walking legs. The coordination of the numerous legs in the walking crayfish or lobster is achieved due to the interactions between their controllers. Mutual influences between the leg controllers were revealed in experiments where the movement of one leg was perturbed. The locomotor system can be activated by stimulation of command neurons in both crayfish and lobsters.

This chapter focuses on locomotion in stick insects and locusts. To walk with their six legs is the main form of land locomotion in most insects. Most of the information available on the nervous control of walking in insects has been obtained from three animal models: the stick insect, the locust, and the cockroach. The goal of the chapter is not to present a detailed review of the field but rather to highlight how the studies of walking in two animal models have increased our understanding of basic principles of locomotor control. The insect leg consists of five segments: the coxa, the trochanter, the femor, the tibia, and the tarsus. Femor and trochanter are sometimes fused into one segment. Insects can walk both forward and backward. The main design of the walking control system in insects is similar to that in Crustacea. Each of the six legs is controlled by the leg controller.

This chapter focuses on the idea that during locomotion, each of the four limbs is driven by its individual control mechanism, which is relatively independent of the controllers for the other limbs. This idea emerged from the observation that, under certain conditions, the rhythms of stepping in different limbs may differ from each other. Divergence of rhythms of individual limbs was later observed by other investigators when the animal walked on a treadmill with split belts. Thus, the basic principle of the control of locomotion in walking animals, that is a considerable autonomy of the individual limb controllers, is common for different species – from crustaceans and insects to mammals. A detailed analysis of the motor pattern of the hind limb of the cat was carried out by a number of investigators. The step cycle in the cat consists of two principal parts, the stance (or support) phase and the swing (or transfer) phase. The three main joints (hip, knee, and ankle) of the hind limb perform considerable flexion–extension movements during the step cycle. To increase the speed of locomotion, there are two principal ways: to increase the frequency of stepping and to increase the amplitude of the stepping movements.

This chapter summarizes global patterns and mechanisms of both ecological and historical crustacean biogeography resulting in the contemporary species distributions described over the past decades. In the pelagic realm, hydrographic features such as ocean currents, physical depth profiles, and latitudinal temperature gradients are major structuring elements, as well as selection pressure exerted by the environment and species interactions, which have resulted in speciation over evolutionary time. Benthic crustacean distributions are additionally constrained longitudinally by continental barriers and submarine features such as ridges and seamounts. The main biogeographic patterns of both benthic and pelagic crustaceans are described for all ocean basins and the polar regions, of which the Indian Ocean is the least well studied. The Copepoda and Decapoda are generally represented with the highest number of described species, followed by Amphipoda and Isopoda. Life cycles with pelagic larvae (e.g., decapods and stomatopods) increase dispersal and enable wide distributions, while a lack of dispersive larvae promotes endemism in benthic forms (e.g., amphipods). Restricted regions with high species richness and endemism, such as the “coral triangle” (the Indo-Australian Archipelago), the Red Sea, and the Mediterranean, represent important biodiversity hotspots. Endemics are also suitable markers for past earth history events. Only a few studies cover the biogeography of crustacean taxa in all of the world’s oceans, but a few exceptions exist for decapods, amphipods, and isopods. Although the world’s oceans have been reasonably well studied for crustacean distribution and diversity, species complexes and cryptic species lacking morphological diagnostic features leave us with a large number of unconsolidated taxa. Emerging molecular tools may be able to assist with refinement of nomenclature and hence increase the resolution of crustacean biogeography in the future.

Crustacean reproductive traits are highly diverse, and this chapter illustrates some of the most extreme cases, placing them in the context of the more typical crustaceans. It highlights, for example, the male and female records of size and age, the “hottest” and “coolest” reproducers, the longest penises, the largest sperm and eggs, the smallest and largest brood sizes, the longest mate guarding, the most massive sexually selected weapons, the flashiest courtship, the most fathers per brood, the longest incubation of broods, the smallest and largest larvae, the longest larval duration, the longest dormancy of eggs, and the oldest fossil evidence of penis, sperm, brood care, and larvae. Using these illustrious case studies, this chapter briefly examines the adaptive advantages of these extremes and discusses why few species have evolved unusual reproductive traits. Crustaceans indeed appear to hold animal records with respect to relative penis length, aflagellate sperm length, dormant egg viability and fossil ages of penis, giant sperm, and brood care. These captivating examples may be of applied importance in terms of restoring human-altered ecosystems (resurrection ecology using egg banks) and in management strategies of important fisheries.

This chapter provides an introduction to the Crustacea, one of the most abundant and diverse components of the plankton. Within a single net-haul, the vast diversity within this group, coupled with the large number of species and the morphological similarity both between species and between developmental stages, can often pose a significant identification challenge even to experienced taxonomists. Although all Crustacea originally share a common body plan, their morphology can differ quite markedly due to different degrees of expression of body segmentation patterns and as a result of the loss or morphological modifications of paired appendages. There is also considerable variation between groups in the structure and function of the appendages on different body regions.

This introductory chapter looks into the physiology and diversity of crabs, including certain species which defy conventional definitions of what a crab is. It largely concerns itself with the question of what makes a crab recognizable as a crab, by delving into the world of crustaceans, arthropods, decapods, and so on, in order to differentiate crabs from other similar marine life—such as lobsters. The chapter then provides classifications on the major families of Brachyuran (true) crabs, which are the largest group of crabs, as well as those of the anomuran crabs. Finally, the chapter highlights some notable species of crabs, rounding out the discussion by providing information on the largest, smallest, and oddest crabs to date.

This chapter examines the relationship between the fish faunas of the Amazon and Orinoco river basins and the distributions of species across the Vaupes Arch region and the Casiquiare Canal. It analyzes the differences and similarities in the two faunas and the historical and contemporary geographic and environmental factors that influence fish distributions, speciation, and adaptation. It explains that the Amazon and Orinoco river basins contain extraordinarily diverse assemblages of fishes, crustaceans, and other aquatic organisms, and have long been considered separate biogeographic provinces.

The dominant mode of reproduction in eucaryotes is sexual. This has been described as a paradox given that sex is much more costly than reproducing asexually, such as by parthenogenesis. In the Crustacea, parthenogenesis is commonly found in the Ostracoda and Branchiopoda (Artemia and Cladocera), and studies of these species have made important contributions to understanding the ecological and evolutionary relationship between sexual and asexual reproduction. With respect to parthenogenesis, researchers have explored its taxonomic distribution and phylogeny, origin and mode, ecological genetics, and genomic signatures. Parthenogenetic Crustacea include both diploid and polyploid clones that have originated multiple times from related sexual species but appear to have a relatively limited evolutionary lifespan. Darwinulid ostracods may be one exception, with no known sexual forms and possibly an example of ancient asexuality, although this is controversial. Most parthenogenetic crustacean groups appear to have a wider geographic distribution than related sexual species and are often found in marginal habitats associated with higher latitudes and altitudes. Such patterns of geographic parthenogenesis have yet to be fully explained, but could possibly be due to colonization and adaptation advantages of asexuality; further studies are required to eliminate polyploidy alone as an explanation. There are many examples of parthenogenetic ostracods, cladocerans, and Artemia showing high levels of genetic diversity likely due to recent multiple origins from related sexual species. Phylogenetic analyses support this explanation and for Artemia and Daphnia, cases have been documented for rare functional males produced by parthenogenetic females that can mate with sexual females as a mechanism for generating new clonal lineages. The diversity of asexual species, combined with prior ecological and genetic information, suggests that crustaceans will continue as important models for understanding parthenogenesis, particularly with the application of new genomic tools.

The evolution of the Crustacea following their origins in the Cambrian is outlined, with an overview of their paleontological history and global distributions into modern times. Major recent developments in arthropod evolution include recognition that Hexapoda is nested within Crustacea. Perspectives also changed during the last decades of the 20th century on the form of the crustacean ancestor, from being a long-bodied, serially homonomous form (like a remipede or cephalocarid) to a short-bodied, possibly ostracod-like form similar to Cambrian stem and crown group fossil forms. These changes have come through a shift to formal methods of phylogenetic analysis combined with the much larger volume of both morphological and molecular data now available. The most extensive current phylogenies typically recover the short-bodied Oligostraca (containing ostracods and a few minor groups) as basal crustaceans; Malacostraca and Maxillopoda are high in the tree; and Cephalocarida and Remipedia are derived forms as sister to Branchiopoda and Hexapoda, respectively. Each of these major groups can be understood through variations in tagmatization (differentiation of body segments into regions). The early crustacean fossil record (especially the Ordovician) is dominated by ostracods. Malacostracans, although having Cambrian origins, did not significantly radiate until the Mesozoic. Eumalacostraca continued to actively radiate in the Cenozoic and are now the most ubiquitous and morphologically disparate crustaceans. The processes driving crustacean evolution remain to be fully evaluated. Contingency and external factors are undoubtedly important, but most deep lineages of the Crustacea show pervasive macroevolutionary trends toward increasing tagmatization. These trends are apparently driven, meaning the formation of new body plans is not merely a contingent outcome—intrinsic factors may contribute to increasing tagmatization. Further data are required from ontogeny and developmental genetics, paleontology, and phylogenetics in order to better understand how crustaceans have evolved.

The deep sea is the largest habitat on Earth, but it is the least accessible and comprehensible. This apparently harsh environment is inhabited by Crustacea of diverse evolutionary lineages that have, to various degrees, evolved uniquely specialized morphologies and lifestyles. Following a century of debate about the antiquity of the deep-sea fauna, studies of Crustacea reveal that the faunas of the deep and shallow oceans have been continuously and repeatedly exchanged, probably since the Mid-Paleozoic. Deep-sea colonization and subsequent diversification has occurred across many crustacean lineages, during several periods, and may still be underway. Despite a commonly held view that shallow–deep phylogenetic relationships are unidirectional, there is also evidence for evolutionary emergence from the abyss into shallower zones. As a result, the present-day fauna represents an amalgamation of clades of various ages. Environmental factors such as pressure, temperature, and energy supply differ substantially between shallow- and deep-water layers, creating gradients that pose important ramifications for crustacean physiology. Consequently, depth-range expansions require adaptations, which may lead to peculiar phenomena such as gigantism and dwarfism, as well as diverse crustacean radiations.