ArthropodArthropods (ˈɑːrθrəpɒd, (gen. ποδός)) are invertebrate animals in the phylum Arthropoda. They possess an exoskeleton with a cuticle made of chitin, often mineralised with calcium carbonate, a segmented body, and paired jointed appendages. In order to keep growing, they must go through stages of moulting, a process by which they shed their exoskeleton to reveal a new one. They are an extremely diverse group, with up to 10 million species. Haemolymph is the analogue of blood for arthropods.
OpabiniaOpabinia regalis is an extinct, stem group arthropod found in the Middle Cambrian Burgess Shale Lagerstätte (505 million years ago) of British Columbia. Opabinia was a soft-bodied animal, measuring up to 7 cm in body length, and its segmented trunk had flaps along the sides and a fan-shaped tail. The head shows unusual features: five eyes, a mouth under the head and facing backwards, and a clawed proboscis that probably passed food to the mouth. Opabinia probably lived on the seafloor, using the proboscis to seek out small, soft food.
LobopodiaLobopodians are members of the informal group Lobopodia (from the Greek, meaning "blunt feet"), or the formally erected phylum Lobopoda Cavalier-Smith (1998). They are panarthropods with stubby legs called lobopods, a term which may also be used as a common name of this group as well. While the definition of lobopodians may differ between literatures, it usually refers to a group of soft-bodied, marine worm-like fossil panarthropods such as Aysheaia and Hallucigenia.
TardigradeTardigrades (ˈtɑrdᵻˌgreɪdz), known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbär ("little water bear"). In 1777, the Italian biologist Lazzaro Spallanzani named them Tardigrada (tɑrˈdɪgrədə), which means "slow steppers". Popular culture has recently elevated awareness of tardigrades in fictional settings and with fictional attributes, likely extending on the fact of their (actual) extreme hardiness.
ProtostomeProtostomia (ˌproʊtə'stoʊmi.ə) is the clade of animals once thought to be characterized by the formation of the organism's mouth before its anus during embryonic development. This nature has since been discovered to be extremely variable among Protostomia's members, although the reverse is typically true of its sister clade, Deuterostomia. Well known examples of protostomes are arthropods, molluscs, annelids, flatworms and nematodes. They are also called schizocoelomates since schizocoely typically occurs in them.
Articulata hypothesisThe Articulata hypothesis is the grouping in a higher taxon of animals with segmented bodies, consisting of Annelida and Panarthropoda. This theory states that these groups are descended from a common segmented ancestor. The Articulata hypothesis is an alternative to the hypothesis that ecdysis (the shedding of outer cuticle) is a primitive characteristic – this would place Panarthropoda in the group Ecdysozoa. The Articulata hypothesis originates from the phylogenetic analyses of Georges Cuvier in his 1817 published work Le Règne animal, distribué après son organization.
AnimalAnimals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, have myocytes and are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. As of 2022, 2.16 million living animal species have been described—of which around 1.05 million are insects, over 85,000 are molluscs, and around 65,000 are vertebrates—but it has been estimated there are around 7.
AnnelidThe annelids ˈænəlɪdz (Annelida əˈnɛlᵻdə, from Latin anellus, "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, and yet others in moist terrestrial environments. The Annelids are bilaterally symmetrical, triploblastic, coelomate, invertebrate organisms.
InsectInsects (from Latin insectum) are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed legs, compound eyes and one pair of antennae. Their blood is not totally contained in vessels; some circulates in an open cavity known as the haemocoel. Insects are the most diverse group of animals; they include more than a million described species and represent more than half of all known living organisms.
OnychophoraOnychophora Qnᵻ'kQf@r@ (from ονυχής, onyches, "claws"; and φέρειν, pherein, "to carry"), commonly known as velvet worms (due to their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus pəˈrɪpətəs (after the first described genus, Peripatus), is a phylum of elongate, soft-bodied, many-legged panarthropods. In appearance they have variously been compared to worms with legs, caterpillars, and slugs. They prey upon other invertebrates, which they catch by ejecting an adhesive slime.
