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The majority of animal species are invertebrates; one estimate puts the figure at 97%. [1] Many invertebrate taxa have a greater number and diversity of species than the entire subphylum of Vertebrata. [2] Invertebrates vary widely in size, from 10 μm (0.0004 in) [3] myxozoans to the 9–10 m (30–33 ft) colossal squid. [4]
Invertebrate paleontology - the study of fossil invertebrates These divisions are sometimes further divided into more specific specialties. For example, within arachnology, acarology is the study of mites and ticks ; within entomology, lepidoptery is the study of butterflies and moths , myrmecology is the study of ants and so on.
Marine invertebrates are invertebrate animals that live in marine habitats, and make up most of the macroscopic life in the oceans. It is a polyphyletic blanket term that contains all marine animals except the marine vertebrates , including the non- vertebrate members of the phylum Chordata such as lancelets , sea squirts and salps .
Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are a part of the subphylum Crustacea (/ k r ə ˈ s t eɪ ʃ ə /), a large, diverse group of mainly aquatic arthropods including decapods (shrimps, prawns, crabs, lobsters and crayfish), seed shrimp, branchiopods, fish lice, krill, remipedes, isopods ...
Most animals called "worms" are invertebrates, but the term is also used for the amphibian caecilians and the slowworm Anguis, a legless burrowing lizard. Invertebrate animals commonly called "worms" include annelids , nematodes , flatworms , nemerteans , chaetognaths , priapulids , and insect larvae such as grubs and maggots .
Arthropods are invertebrate animals having an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, often mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages.
These invertebrates are ubiquitous to freshwater ecosystems around the world and are present in both lotic and lentic ecosystems, often living among the rocks and sediment. Aquatic macroinvertebrates include insects, bivalves, gastropods, annelids, and crustaceans.
Balanoglossus, an example of a Hemichordata, represents an "evolutionary link" between invertebrates and vertebrates. In addition to the simple observation that the dorsoventral axes of protostomes and chordates appear to be inverted with respect to each other, molecular biology provides some support for the inversion hypothesis.