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. As the name suggests, marine invertebrates lack any mineralized axial endoskeleton, i.e. the vertebral column, and some have evolved a rigid shell, test or exoskeleton for protection and/or locomotion, while others rely on internal fluid pressure to support their bodies. Marine invertebrates have a large variety of body plans, and have been categorized into over 30 phyla.
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In this Dossier
Marine invertebrate in the context of Miocene
The Miocene (/ˈmaɪ.əsiːn, -oʊ-/ MY-ə-seen, -oh-) is the first geological epoch of the Neogene Period and extends from about 23.04 to 5.333 million years ago (Ma). The Miocene was named by Scottish geologist Charles Lyell and comes from Ancient Greek μείων (meíōn), meaning "less", and καινός (kainós), meaning "new, recent", and thus, means "less recent", because it has 18% fewer modern marine invertebrates than the Pliocene has. The Miocene followed the Oligocene and preceded the Pliocene.
As Earth went from the Oligocene through the Miocene and into the Pliocene, the climate slowly cooled towards a series of ice ages. The Miocene boundaries are not marked by distinct global events but by regionally defined transitions from the warmer Oligocene to the cooler Pliocene Epoch.
Marine invertebrate in the context of Placozoa
Placozoa (/ˌplækəˈzoʊə/ PLAK-ə-ZOH-ə; lit. 'flat animals') is a phylum of free-living (non-parasitic) marine invertebrates. They are blob-like animals composed of aggregations of cells. Moving in water by ciliary motion, eating food by engulfment, reproducing by fission or budding, placozoans are described as "the simplest animals on Earth". Structural and molecular analyses have supported them as among the most basal animals, thus constituting a primitive metazoan phylum.
The first known placozoan, Trichoplax adhaerens, was discovered in 1883 by the German zoologist Franz Eilhard Schulze (1840–1921). Describing the uniqueness, another German, Karl Gottlieb Grell (1912–1994), erected a new phylum, Placozoa, for it in 1971. Remaining a monotypic phylum for over a century, new species began to be added since 2018. So far, three other extant species have been described, in two distinct classes: Uniplacotomia (Hoilungia hongkongensis in 2018 and Cladtertia collaboinventa in 2022) and Polyplacotomia (Polyplacotoma mediterranea, the most basal, in 2019). A single putative fossil species is known, the Middle Triassic Maculicorpus microbialis.