Crustaceans grow by periodically replacing their external cuticle, the body covering that forms much of the exoskeleton. The shedding event itself is called ecdysis, but molting is a longer cycle. Before ecdysis, the animal separates from parts of the old cuticle and prepares a new one underneath. During ecdysis it withdraws from the old covering. … Read more
Crustacean anatomy is built on a segmented arthropod framework, but there is no single body diagram that fits every crustacean. A crab, shrimp, copepod, barnacle, isopod, and ostracod can all share deep structural themes while looking radically different on the outside. Their segments may be grouped into different body regions, their appendages may be modified … Read more
Crabs, shrimp, and lobsters are the crustaceans most people recognize first, but they represent only a fraction of the group. The major types of crustaceans also include copepods, barnacles, isopods, amphipods, krill, branchiopods, ostracods, remipedes, mantis shrimps, and many other lineages. Some are large and heavily armored. Others are nearly transparent, microscopic or near-microscopic, permanently … Read more
A crustacean is an arthropod that belongs to the broad evolutionary radiation that includes familiar animals such as crabs, lobsters, shrimp, crayfish, barnacles, copepods, krill, and isopods. The useful part of that definition is not a single visible feature. Crustaceans are recognized by a combination of body-plan traits, including a segmented arthropod body, jointed appendages, … Read more
Crustaceans are arthropods best known through animals such as crabs, shrimp, lobsters, and crayfish, but those familiar forms show only part of the group. The animals conventionally called crustaceans also include copepods drifting through lakes and oceans, barnacles fixed to hard surfaces as adults, krill moving through open water, terrestrial pill bugs beneath logs, tiny … Read more
Arachnid conservation is difficult to summarize with one number because the group is vast, unevenly studied, and incompletely assessed. Spiders receive far more attention than many mites, harvestmen, pseudoscorpions, whip spiders, and other smaller lineages, yet even spider monitoring is patchy across regions and habitats. Many species are known from few records, tiny ranges, isolated … Read more
Arachnids are important because they occupy many different positions in food webs. Spiders and scorpions are predators, ticks and some mites are parasites, plant-feeding mites consume living vegetation, other mites graze fungi or feed in decomposer systems, harvestmen can act as predators, scavengers, or omnivores, and pseudoscorpions hunt tiny arthropods in soil, litter, and bark. … Read more
Arachnids live in an extraordinary range of habitats. Spiders, scorpions, mites, ticks, harvestmen, pseudoscorpions, whip spiders, and other arachnids occur in forests, grasslands, deserts, mountains, caves, soil, leaf litter, tree bark, freshwater, intertidal zones, animal hosts, plants, gardens, buildings, and many other microhabitats. Most arachnids are associated with land, but “arachnids are terrestrial” is only … Read more
Arachnids defend themselves in many ways, and venom is only one part of the story. Spiders may hide, run, drop away, use silk retreats, display threat postures, or bite when pressed. Scorpions combine pincers, a stinger, armor, posture, and shelter use. Harvestmen may freeze, release defensive chemicals, shed a leg, vibrate, group together, or feign … Read more
Arachnid reproduction is far more varied than the familiar image of a spider guarding an egg sac. Most spiders lay eggs, scorpions give birth to live young, ticks pass through egg, larval, nymphal, and adult stages, mites show several developmental patterns, and harvestmen include species with maternal or paternal egg care. Mating can involve direct … Read more
