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Gastropods ( / ˈɡæstrəpɒdz / ), commonly known as slugs and snails, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ( / ɡæsˈtrɒpədə / ). [ 5] This class comprises snails and slugs from saltwater, freshwater, and from the land. There are many thousands of species of sea snails and slugs ...
Cephalopod appendages surround the mouth, so logically they could be derived from embryonic head tissues. [146] However, the "Arms as Foot" hypothesis, proposed by Adolf Naef in 1928, has increasingly been favoured; [ 145 ] for example, fate mapping of limb buds in the chambered nautilus indicates that limb buds originate from "foot" embryonic ...
Mollusca is the second-largest phylum of invertebrate animals, after Arthropoda; members are known as molluscs or mollusks[ a] ( / ˈmɒləsks / ). Around 76,000 extant species of molluscs are recognized. [ 4] The number of fossil species is estimated between 60,000 and 100,000 additional species. [ 5] The proportion of undescribed species is ...
See text for superfamilies. The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, and includes crabs, lobsters, crayfish, shrimp, and prawns. Most decapods are scavengers. The order is estimated to contain nearly 15,000 extant species in around 2,700 genera, with around 3,300 fossil species ...
Flatworm. The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, platy, meaning "flat" and ἕλμινς (root: ἑλμινθ-), helminth-, meaning "worm") [ 4] are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates. Being acoelomates (having no body cavity ), and having no ...
The evolution of fish began about 530 million years ago during the Cambrian explosion. It was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. The first fish lineages belong to the Agnatha, or jawless fish. Early examples include Haikouichthys.
Thelenota ananas, a giant sea cucumber from the Indo-Pacific tropics. Sea cucumbers are echinoderms from the class Holothuroidea ( / ˌhɒləˌθjʊəˈrɔɪdiə, ˌhoʊ -/ HOL-ə-thure-OY-dee-ə, HOHL- ). They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. They are found on the sea floor ...
Isopoda. Isopoda is an order of crustaceans. Members of this group are called Isopods and include both terrestrial and aquatic species such as woodlice. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, and five pairs of branching appendages on the abdomen that are used in respiration.