Bugs, Mollusks & Other Invertebrates Portal

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col-sm-offset-15"> Yet, in addition to being critically important—because they naturally recycle decaying matter—in maintaining balance within the food chain, bugs can also be fascinating creatures, whether in regard to the water strider's ability to run across the surface of water or the assassin bugs' varied and creative means of catching and killing their prey. Mollusks, another group of invertebrates, get less of a bad rap. Their ranks include nearly 100,000 described species of soft-bodied animals that are usually wholly or partly enclosed in a calcium carbonate shell; examples include snails, clams, oysters, squids, and octopuses.</div> </div> <div class="text-hr text-hr-right border-navy font-12 text-uppercase font-weight-bold mt-30 ls-lg">Browse Subcategories</div> <div class="slider js-slider position-relative d-inline-flex align-items-center mw-100 mt-20 category-snap-slider"> <div class="slider-container js-slider-container overflow-hidden d-flex font-14 overflow-hidden text-nowrap mx-5"> <a href="/browse/Arachnids" class="link-white mr-20 mr-sm-30">Arachnids</a> <a href="/browse/Arthropods" class="link-white mr-20 mr-sm-30">Arthropods</a> <a href="/browse/Aschelminthes" class="link-white mr-20 mr-sm-30">Aschelminthes</a> <a href="/browse/Cnidarians" class="link-white mr-20 mr-sm-30">Cnidarians</a> <a href="/browse/Comb-Jellies" class="link-white mr-20 mr-sm-30">Comb Jellies</a> <a href="/browse/Crustaceans" class="link-white mr-20 mr-sm-30">Crustaceans</a> <a href="/browse/Insects" class="link-white mr-20 mr-sm-30">Insects</a> <a href="/browse/Mollusks" class="link-white mr-20 mr-sm-30">Mollusks</a> <a href="/browse/Moss-Animals" class="link-white mr-20 mr-sm-30">Moss Animals</a> <a href="/browse/Spiny-Skinned-Invertebrates" class="link-white mr-20 mr-sm-30">Spiny-skinned Invertebrates</a> <a href="/browse/Sponges" class="link-white mr-20 mr-sm-30">Sponges</a> <a href="/browse/Worms-Annelids" class="link-white ">Worms & Annelids</a> </div> <button disabled class="prev-button js-prev-button position-absolute btn btn-circle shadow btn-blue " aria-label="Previous"> <span class="material-icons md-24" data-icon="keyboard_arrow_left"></span> </button> <button disabled class="next-button js-next-button position-absolute btn btn-circle shadow btn-blue " aria-label="Next"> <span class="material-icons md-24" data-icon="keyboard_arrow_right"></span> </button> </div> </div> </div> <div class="container"> <h2 class="label my-30">Bugs, Mollusks & Other Invertebrates Encyclopedia Articles</h2> <div class="grid top g-10 mb-40"> <div class="col-33 col-sm-20 col-md-16 col-lg-10"> <div class="border shadow p-10 text-center "> <a class="font-weight-bold font-14 " href="/browse/Bugs-Mollusks-Invertebrates/1">ABA-CED</a> </div> </div> <div class="col-33 col-sm-20 col-md-16 col-lg-10"> <div class="border shadow p-10 text-center "> <a class="font-weight-bold font-14 " href="/browse/Bugs-Mollusks-Invertebrates/2">CEN-EAS</a> </div> </div> <div class="col-33 col-sm-20 col-md-16 col-lg-10"> <div class="border shadow p-10 text-center "> <a class="font-weight-bold font-14 " href="/browse/Bugs-Mollusks-Invertebrates/3">ECH-HET</a> </div> </div> <div class="col-33 col-sm-20 col-md-16 col-lg-10"> <div class="border shadow p-10 text-center "> <a class="font-weight-bold font-14 " href="/browse/Bugs-Mollusks-Invertebrates/4">HIS-MAY</a> </div> </div> <div class="col-33 col-sm-20 col-md-16 col-lg-10"> <div class="border shadow p-10 text-center "> <a class="font-weight-bold font-14 " href="/browse/Bugs-Mollusks-Invertebrates/5">MEA-PLE</a> </div> </div> <div class="col-33 col-sm-20 col-md-16 col-lg-10"> <div class="border shadow p-10 text-center "> <a class="font-weight-bold font-14 " href="/browse/Bugs-Mollusks-Invertebrates/6">PLE-SKI</a> </div> </div> <div class="col-33 col-sm-20 col-md-16 col-lg-10"> <div class="border shadow p-10 text-center "> <a class="font-weight-bold font-14 " href="/browse/Bugs-Mollusks-Invertebrates/7">SLI-VIN</a> </div> </div> <div class="col-33 col-sm-20 col-md-16 col-lg-10"> <div class="border shadow p-10 text-center "> <a class="font-weight-bold font-14 " href="/browse/Bugs-Mollusks-Invertebrates/8">VOL-ZOR</a> </div> </div> </div> <h2 class="label my-30 text-center">Featured Articles</h2> <div class="js-pinboard grid gy-20"> <div class="p-10 d-inline-flex js-pin col-100 col-sm-33 col-md-25 "> <div class="card text-normal col-100 "> <div class="card-media position-relative"> <a href="https://www.britannica.com/animal/nematode" style="--aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/03/143903-050-DD38BCBE/scanning-electron-micrograph-soybean-cyst-nematode-egg.jpg?w=400&h=225&c=crop" alt="microfauna" class="col-100" /> </a> </div> <div class="col"> <div class="card-body text-hyphenate"> <a href="https://www.britannica.com/animal/nematode" class="font-weight-bold font-16 lh-sm">nematode</a> <div class="font-serif mt-10 font-14"> Nematode, any worm of the phylum Nematoda. 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Worms are members... </div> </div> </div> </div> </div> <div class="p-10 d-inline-flex js-pin col-100 col-sm-33 col-md-25 "> <div class="card text-normal col-100 "> <div class="card-media position-relative"> <a href="https://www.britannica.com/animal/tapeworm" style="--aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/mendel-resources/3-130/images/shared/default3.png?v=3.130.14" class="default col-100" /> </a> </div> <div class="col"> <div class="card-body text-hyphenate"> <a href="https://www.britannica.com/animal/tapeworm" class="font-weight-bold font-16 lh-sm">tapeworm</a> <div class="font-serif mt-10 font-14"> Tapeworm, any member of the invertebrate class Cestoda (phylum Platyhelminthes), a group of parasitic flatworms containing about 5,000 species. Tapeworms, which occur worldwide and range in size from about... </div> </div> </div> </div> </div> <div class="p-10 d-inline-flex js-pin col-100 col-sm-33 col-md-25 "> <div class="card text-normal col-100 "> <div class="card-media position-relative"> <a href="https://www.britannica.com/animal/octopus-mollusk" style="--aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/98/157198-050-8B4735F2/Octopus-swimming.jpg?w=400&h=225&c=crop" alt="octopus" class="col-100" /> </a> </div> <div class="col"> <div class="card-body text-hyphenate"> <a href="https://www.britannica.com/animal/octopus-mollusk" class="font-weight-bold font-16 lh-sm">octopus</a> <div class="font-serif mt-10 font-14"> Octopus, in general, any eight-armed cephalopod (octopod) mollusk of the order Octopoda. The true octopuses are members of the genus Octopus, a large group of widely distributed shallow-water cephalopods.... </div> </div> </div> </div> </div> <div class="p-10 d-inline-flex js-pin col-100 col-sm-33 col-md-25 "> <div class="card text-normal col-100 "> <div class="card-media position-relative"> <a href="https://www.britannica.com/animal/mantid" style="--aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/81/176681-050-BB071D7F/mantis-rain-shower.jpg?w=400&h=225&c=crop" alt="Praying mantis" class="col-100" /> </a> </div> <div class="col"> <div class="card-body text-hyphenate"> <a href="https://www.britannica.com/animal/mantid" class="font-weight-bold font-16 lh-sm">mantid</a> <div class="font-serif mt-10 font-14"> Mantid, (family Mantidae), any of approximately 2,000 species of large, slow-moving insects that are characterized by front legs with enlarged femurs (upper portion) that have a groove lined with spines... </div> </div> </div> </div> </div> <div class="p-10 d-inline-flex js-pin col-100 col-sm-33 col-md-25 "> <div class="card text-normal col-100 "> <div class="card-media position-relative"> <a href="https://www.britannica.com/animal/bee" style="--aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/35/240435-050-85E68CCE/blue-banded-bee-Amegilla.jpg?w=400&h=225&c=crop" alt="Solitary bee" class="col-100" /> </a> </div> <div class="col"> <div class="card-body text-hyphenate"> <a href="https://www.britannica.com/animal/bee" class="font-weight-bold font-16 lh-sm">bee</a> <div class="font-serif mt-10 font-14"> Bee, (superfamily Apoidea), any of more than 20,000 species of insects in the suborder Apocrita (order Hymenoptera), including the familiar honeybee (Apis) and bumblebee (Bombus) as well as thousands more... </div> </div> </div> </div> </div> <div class="p-10 d-inline-flex js-pin col-100 col-sm-33 col-md-25 "> <div class="card text-normal col-100 "> <div class="card-media position-relative"> <a href="https://www.britannica.com/animal/coral" style="--aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/08/150608-050-73A3EAE4/Fish-brain-coral.jpg?w=400&h=225&c=crop" alt="Fish (centre) in brain coral." class="col-100" /> </a> </div> <div class="col"> <div class="card-body text-hyphenate"> <a href="https://www.britannica.com/animal/coral" class="font-weight-bold font-16 lh-sm">coral</a> <div class="font-serif mt-10 font-14"> Coral, any of a variety of invertebrate marine organisms of the class Anthozoa (phylum Cnidaria) that are characterized by skeletons—external or internal—of a stonelike, horny, or leathery consistency.... </div> </div> </div> </div> </div> <div class="p-10 d-inline-flex js-pin col-100 col-sm-33 col-md-25 "> <div class="card text-normal col-100 "> <div class="card-media position-relative"> <a href="https://www.britannica.com/animal/centipede" style="--aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/67/7267-004-4FD7E434/Centipede.jpg?w=400&h=225&c=crop" alt="centipede" class="col-100" /> </a> </div> <div class="col"> <div class="card-body text-hyphenate"> <a href="https://www.britannica.com/animal/centipede" class="font-weight-bold font-16 lh-sm">centipede</a> <div class="font-serif mt-10 font-14"> Centipede, (class Chilopoda), any of various long, flattened, many-segmented predaceous arthropods. Each segment except the hindmost bears one pair of legs. Centipedes generally remain under stones, bark,... </div> </div> </div> </div> </div> </div> <div class="adm my-30"></div> <div class="subcategories"> <h2 class="h4 mt-40 mb-30 font-weight-bold">Bugs, Mollusks & Other Invertebrates Subcategories</h2> <div class="grid gy-30 mb-30"> <div class="col-100 col-sm-33 col-md-25"> <a href="/browse/Arachnids"> <img loading="lazy" src="https://cdn.britannica.com/26/6926-004-C38173DF/Brown-recluse-spider-cephalothorax.jpg?w=400&h=225&c=crop" alt="brown recluse spider" class="col-100 mb-20" /> </a> <a href="/browse/Arachnids" class="font-weight-bold font-16">Arachnids</a> <div class="font-serif mt-10 line-clamp clamp-3">When it comes to creepy-crawlies, arachnids are some of the first critters that might come to mind. This arthropod group includes spiders, daddy longlegs, and scorpions, among other creatures that many of us would prefer to avoid.</div> <div class="label mt-20">Articles</div> <ul class="list-unstyled"> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/brown-recluse">brown recluse</a> <div class="font-serif">spider</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/tarantula">tarantula</a> <div class="font-serif">spider</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/black-widow-spider">black widow</a> <div class="font-serif">spider</div> </li> </ul> </div> <div class="col-100 col-sm-33 col-md-25"> <a href="/browse/Arthropods"> <img loading="lazy" src="https://cdn.britannica.com/67/7267-004-4FD7E434/Centipede.jpg?w=400&h=225&c=crop" alt="centipede" class="col-100 mb-20" /> </a> <a href="/browse/Arthropods" class="font-weight-bold font-16">Arthropods</a> <div class="font-serif mt-10 line-clamp clamp-3">Arthropoda is the largest phylum in the animal kingdom; about 84 percent of all known species of animals fall into this category. Lobsters, crabs, spiders, mites, insects, centipedes, and millipedes are all arthropods. </div> <div class="label mt-20">Articles</div> <ul class="list-unstyled"> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/trilobite">trilobite</a> <div class="font-serif">fossil arthropod</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/king-crab">king crab</a> <div class="font-serif">crustacean</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/barnacle">barnacle</a> <div class="font-serif">crustacean</div> </li> </ul> </div> <div class="col-100 col-sm-33 col-md-25"> <a href="/browse/Aschelminthes"> <img loading="lazy" src="https://cdn.britannica.com/01/35701-004-ADF1176E/Horsehair-worm.jpg?w=400&h=225&c=crop" alt="Horsehair worm (Gordius villoti)" class="col-100 mb-20" /> </a> <a href="/browse/Aschelminthes" class="font-weight-bold font-16">Aschelminthes</a> <div class="font-serif mt-10 line-clamp clamp-3">Aschelminth, phylum name Aschelminthes, or Nemathelminthes, a name referring to an obsolete phylum of wormlike invertebrates, mostly of microscopic size. Previously, phylum Aschelminthes included seven diverse classes of animals: Nematoda (or Nemata), Rotifera, Acanthocephala, Gastrotricha, Kinorhyncha (or Echinodera), Nematomorpha, and Gnathostomulida. (According to some authorities, Gnathostomulida was replaced by Priapula in this list.) At present, each of these classes, including Priapula, has been reclassified as a separate phylum.</div> <div class="label mt-20">Articles</div> <ul class="list-unstyled"> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/horsehair-worm">horsehair worm</a> <div class="font-serif">invertebrate</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/rotifer">rotifer</a> <div class="font-serif">invertebrate</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/kinorhynch">kinorhynch</a> <div class="font-serif">marine invertebrate</div> </li> </ul> </div> <div class="col-100 col-sm-33 col-md-25"> <a href="/browse/Cnidarians"> <img loading="lazy" src="https://cdn.britannica.com/58/4058-004-FE007D6E/Sea-whip.jpg?w=400&h=225&c=crop" alt="Sea whip (Ellisella)" class="col-100 mb-20" /> </a> <a href="/browse/Cnidarians" class="font-weight-bold font-16">Cnidarians</a> <div class="font-serif mt-10 line-clamp clamp-3">The phylum Cnidaria is made up of more than 9,000 living species, mostly marine animals. Corals, jellyfish, sea anemones, and sea fans are all cnidarians.</div> <div class="label mt-20">Articles</div> <ul class="list-unstyled"> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/organ-pipe-coral">organ-pipe coral</a> <div class="font-serif">coral</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/sea-pansy">sea pansy</a> <div class="font-serif">invertebrate</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/tube-anemone">tube anemone</a> <div class="font-serif">invertebrate</div> </li> </ul> </div> <div class="col-100 col-sm-33 col-md-25"> <a href="/browse/Comb-Jellies"> <img loading="lazy" src="https://cdn.britannica.com/mendel/resources/encyclopedia-placeholder.jpg?w=400&h=225&c=crop" alt="subcategory placeholder" class="col-100 mb-15" /> </a> <a href="/browse/Comb-Jellies" class="font-weight-bold font-16">Comb Jellies</a> <div class="font-serif mt-10 line-clamp clamp-3">Comb jellies are any of the numerous marine invertebrates that constitute the phylum Ctenophora.</div> <div class="label mt-20">Articles</div> <ul class="list-unstyled"> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/moon-jelly">moon jelly</a> <div class="font-serif">jellyfish</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/sea-anemone">sea anemone</a> <div class="font-serif">invertebrate</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/Hydra-hydrozoan-genus">Hydra</a> <div class="font-serif">hydrozoan genus</div> </li> </ul> </div> <div class="col-100 col-sm-33 col-md-25"> <a href="/browse/Crustaceans"> <img loading="lazy" src="https://cdn.britannica.com/89/9689-004-C00DAC2D/Pea-crab-shell.jpg?w=400&h=225&c=crop" alt="Pea crab (Pinnotheres pisum) in opened shell" class="col-100 mb-20" /> </a> <a href="/browse/Crustaceans" class="font-weight-bold font-16">Crustaceans</a> <div class="font-serif mt-10 line-clamp clamp-3">Crustaceans are a group of invertebrate animals consisting of some 45,000 species worldwide. Crabs, lobsters, and shrimps are all counted among the subphylum Crustacea. Crustaceans are found primarily in water, as noted by Sebastian the crab in Disney’s “The Little Mermaid” (1989).</div> <div class="label mt-20">Articles</div> <ul class="list-unstyled"> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/pea-crab">pea crab</a> <div class="font-serif">crustacean</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/pill-bug">pill bug</a> <div class="font-serif">crustacean</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/branchiopod">branchiopod</a> <div class="font-serif">crustacean</div> </li> </ul> </div> <div class="col-100 col-sm-33 col-md-25"> <a href="/browse/Insects"> <img loading="lazy" src="https://cdn.britannica.com/90/173990-050-D2E9FD72/walkingstick-stick-insect.jpg?w=400&h=225&c=crop" alt="Masterful mimic" class="col-100 mb-20" /> </a> <a href="/browse/Insects" class="font-weight-bold font-16">Insects</a> <div class="font-serif mt-10 line-clamp clamp-3">When people talk about “insects,” they often mean pests or disease carriers such as bedbugs, houseflies, beetles, mosquitoes, fleas, and hornets. To be fair, though, many insects are beneficial to humans, albeit sometimes indirectly: they pollinate plants, produce useful substances, control pest insects, act as scavengers, and serve as food for other animals. Some insects, such as butterflies, are beautiful to behold, and insects such as ladybugs flaunt eye-catching colors and patterns.</div> <div class="label mt-20">Articles</div> <ul class="list-unstyled"> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/walkingstick">walking stick</a> <div class="font-serif">insect</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/mantid">mantid</a> <div class="font-serif">insect</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/beetle">coleopteran</a> <div class="font-serif">insect</div> </li> </ul> </div> <div class="col-100 col-sm-33 col-md-25"> <a href="/browse/Mollusks"> <img loading="lazy" src="https://cdn.britannica.com/63/12863-050-D12BEABD/Quahog.jpg?w=400&h=225&c=crop" alt="(Left) Quahog (Mercenaria); (right) soft-shell clam (Mya)" class="col-100 mb-20" /> </a> <a href="/browse/Mollusks" class="font-weight-bold font-16">Mollusks</a> <div class="font-serif mt-10 line-clamp clamp-3">Mollusk, also spelled mollusc, any soft-bodied invertebrate of the phylum Mollusca, usually wholly or partly enclosed in a calcium carbonate shell secreted by a soft mantle covering the body. Along with the insects and vertebrates, it is one of the most diverse groups in the animal kingdom, with nearly 100,000 (possibly as many as 150,000) described species. Each group includes an ecologically and structurally immense variety of forms: the shell-less Caudofoveata; the narrow-footed gliders (Solenogastres); the serially valved chitons (Placophora or Polyplacophora); the cap-shaped neopilinids (Monoplacophora); the limpets, snails, and slugs (Gastropoda); the clams, mussels, scallops, oysters, shipworms, and cockles (Bivalvia); the tubiform to barrel-shaped tusk shells (Scaphopoda); and the nautiluses, cuttlefishes, squids, and octopuses (Cephalopoda).</div> <div class="label mt-20">Articles</div> <ul class="list-unstyled"> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/clam">clam</a> <div class="font-serif">mollusk</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/octopus-mollusk">octopus</a> <div class="font-serif">mollusk order</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/murex-mollusk-family">murex</a> <div class="font-serif">mollusk family</div> </li> </ul> </div> <div class="col-100 col-sm-33 col-md-25"> <a href="/browse/Moss-Animals"> <img loading="lazy" src="https://cdn.britannica.com/96/146896-050-2429E745/Eurystomella-bilabiata-Order-Cheilostomata.jpg?w=400&h=225&c=crop" alt="Cheilostomata" class="col-100 mb-20" /> </a> <a href="/browse/Moss-Animals" class="font-weight-bold font-16">Moss Animals</a> <div class="font-serif mt-10 line-clamp clamp-3">Moss animal, also called bryozoan, any member of the phylum Bryozoa (also called Polyzoa or Ectoprocta), in which there are about 5,000 extant species. Another 15,000 species are known only from fossils. As with brachiopods and phoronids, bryozoans possess a peculiar ring of ciliated tentacles, called a lophophore, for collecting food particles suspended in the water. The bryozoans are a widely distributed, aquatic, invertebrate group of animals whose members form colonies composed of numerous connected units called zooids (hence the term Polyzoa, which means “many animals”).</div> <div class="label mt-20">Articles</div> <ul class="list-unstyled"> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/stenolaemate">stenolaemate</a> <div class="font-serif">bryozoan</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/Trepostomata">Trepostomata</a> <div class="font-serif">fossil bryozoan order</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/Constellaria">Constellaria</a> <div class="font-serif">fossil bryozoan genus</div> </li> </ul> </div> <div class="col-100 col-sm-33 col-md-25"> <a href="/browse/Spiny-Skinned-Invertebrates"> <img loading="lazy" src="https://cdn.britannica.com/80/6880-004-AACBC768/Brittle-star.jpg?w=400&h=225&c=crop" alt="Brittle star (Ophiocoma imbricatus)" class="col-100 mb-20" /> </a> <a href="/browse/Spiny-Skinned-Invertebrates" class="font-weight-bold font-16">Spiny-skinned Invertebrates</a> <div class="font-serif mt-10 line-clamp clamp-3">Echinoderm, any of a variety of invertebrate marine animals belonging to the phylum Echinodermata, characterized by a hard, spiny covering or skin. Beginning with the dawn of the Cambrian Period (542 million to 488 million years ago), echinoderms have a rich fossil history and are well represented...</div> <div class="label mt-20">Articles</div> <ul class="list-unstyled"> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/sea-star">sea star</a> <div class="font-serif">echinoderm</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/carpoid">carpoid</a> <div class="font-serif">fossil echinoderm</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/cystoid">cystoid</a> <div class="font-serif">fossil echinoderm</div> </li> </ul> </div> <div class="col-100 col-sm-33 col-md-25"> <a href="/browse/Sponges"> <img loading="lazy" src="https://cdn.britannica.com/97/11697-004-9041962B/Freshwater-sponge.jpg?w=400&h=225&c=crop" alt="freshwater sponge (Spongilla)" class="col-100 mb-20" /> </a> <a href="/browse/Sponges" class="font-weight-bold font-16">Sponges</a> <div class="font-serif mt-10 line-clamp clamp-3">Sponge, any of the primitive multicellular aquatic animals that constitute the phylum Porifera. They number approximately 5,000 described species and inhabit all seas, where they occur attached to surfaces from the intertidal zone to depths of 8,500 metres (29,000 feet) or more. The members of one family, the Spongillidae, are found in fresh water; however, 98 percent of all sponge species are marine. Adult sponges lack a definite nervous system and musculature and do not show conspicuous movements of body parts.</div> <div class="label mt-20">Articles</div> <ul class="list-unstyled"> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/freshwater-sponge">freshwater sponge</a> <div class="font-serif">invertebrate</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/glass-sponge">glass sponge</a> <div class="font-serif">invertebrate</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/siliceous-sponge">siliceous sponge</a> <div class="font-serif">invertebrate</div> </li> </ul> </div> <div class="col-100 col-sm-33 col-md-25"> <a href="/browse/Worms-Annelids"> <img loading="lazy" src="https://cdn.britannica.com/87/9687-004-1D13A8CC/Peanutworm.jpg?w=400&h=225&c=crop" alt="Peanutworm" class="col-100 mb-20" /> </a> <a href="/browse/Worms-Annelids" class="font-weight-bold font-16">Worms & Annelids</a> <div class="font-serif mt-10 line-clamp clamp-3">Annelid, phylum name Annelida, also called segmented worm, any member of a phylum of invertebrate animals that are characterized by the possession of a body cavity (or coelom), movable bristles (or setae), and a body divided into segments by transverse rings, or annulations, from which they take their name. The coelom is reduced in leeches, and setae are lacking a few specialized forms, including leeches.</div> <div class="label mt-20">Articles</div> <ul class="list-unstyled"> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/peanut-worm">peanut worm</a> <div class="font-serif">marine worm</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/sea-mouse">sea mouse</a> <div class="font-serif">annelid</div> </li> <li class="mt-20"> <a class="font-weight-bold" href="https://www.britannica.com/animal/palolo-worm">palolo worm</a> <div class="font-serif">polychaete</div> </li> </ul> </div> </div> </div> <DIV class="marketing-CATEGORY_PAGE_SUBSCRIPTION marketing-content" data-marketing-id="CATEGORY_PAGE_SUBSCRIPTION"><style> .student-promo-banner-wrapper { container-type: inline-size; margin-bottom: 15px; } @container (min-width: 475px) { .student-promo-banner { flex-direction: row; } .student-promo-banner-img-wrapper { margin-bottom: 0; margin-right: 10px; justify-content: flex-start; } .student-promo-banner-text-wrapper { text-align: left; margin-bottom: 0px; margin-left: 10px; } .student-promo-banner-button-wrapper { margin-right: 0; } }</style> <div class="student-promo-banner-wrapper"> <div class="student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20"> <div class="student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center"> <img class="rounded" style="max-width: 100px; min-width: 80px" src="https://cdn.britannica.com/marketing/BlueThistle.webp" /> </div> <div class="student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white"> <div class="h2 mb-10">Britannica Premium</div> <div class="h4 font-weight-semi-bold">Did you know you're not getting the full Britannica experience? 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