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56-684: Hermit crabs are anomuran decapod crustaceans of the superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. There are over 800 species of hermit crab, most of which possess an asymmetric abdomen concealed by a snug-fitting shell. Hermit crabs' soft (non- calcified ) abdominal exoskeleton means they must occupy shelter produced by other organisms or risk being defenseless. The strong association between hermit crabs and their shelters has significantly influenced their biology. Almost 800 species carry mobile shelters (most often calcified snail shells ); this protective mobility contributes to

112-536: A convenient and nutritionally balanced foundation for a hermit crab's diet. These foods are specially formulated to meet the species' specific needs and should form the majority of their daily intake. It is important to select a product that is designed for hermit crabs, as general pet foods may lack the necessary nutrients. In the wild, hermit crabs are omnivorous scavengers, feeding on a varied diet of plant matter, decaying organic material, small invertebrates, and marine detritus. They look for algae, seaweed, fruits, and

168-756: A family within Paguroidea. The molecular data has disproven an alternate view based on morphological arguments that the Lithodidae (king crabs) nest with the Hapalogastridae in a separate superfamily, Lithodoidea. As such, in 2023, the family Lithodidae was placed back into Paguroidea after having been moved out of it in 2007. Nine families are formally recognized in the superfamily Paguroidea, containing around 1200 species in total in 135 genera. The placement of Paguroidea within Anomura can be shown in

224-595: A healthy hermit crab. A key component of a hermit crab's diet is calcium, which supports the health and hardness of their exoskeleton. Crushed cuttlebone, calcium-rich commercial supplements, or even ground eggshells can be provided to meet this need. Additionally, carotene-rich foods such as carrots or squash are essential for promoting the development of their reddish-orange exoskeleton. Occasional treats can be offered to hermit crabs to enrich their diet. These may include nuts (such as almonds or sunflower seeds), seeds, and dried seaweed. While these treats should not make up

280-721: A large portion of the diet, they can provide additional nutrients and variety. Hermit crabs are nocturnal feeders, so they should be provided with food in the evening, and any uneaten food should be removed the next morning to prevent spoilage. It is important to monitor the amount of food provided, as hermit crabs tend to eat small portions over extended periods and may consume food slowly. In addition to solid food, hermit crabs require constant access to both freshwater and saltwater for hydration and health. These should be provided in separate dishes to meet their needs for drinking and bathing. As hermit crabs grow, they require larger shells. Since suitable intact gastropod shells are sometimes

336-402: A limited resource, competition often occurs between hermit crabs for shells. The availability of empty shells at any given place depends on the relative abundance of gastropods and hermit crabs, matched for size. An equally important issue is the population of organisms that prey upon gastropods and leave the shells intact. Hermit crabs kept together may fight or kill a competitor to gain access to

392-399: A number of "raps", the defender may come out of its shell completely, usually positioning itself of one of the shells. The attacker then checks the now free shell, and then changes shell rapidly. As the crab tries its new shell, it usually holds its old shell, as it may decide to come back to the old one. The defeated crab then runs to the empty shell. If the defeated crab does not stay close to

448-409: A very social and peaceful crab. The Purple Pincher ( Coenobita clypeatus ) is a purple and orange crab that is typically found near the shore and especially in the tropical islands. While they are also nocturnal these crabs have aggressive behaviors as well as cannibal tendencies. They forage in a big groups, and are able to eat anything from fish to wood. Though they are terrestrial they travel back to

504-689: Is Platykotta , from the Norian – Rhaetian (Late Triassic) Period in the United Arab Emirates . [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Late Cretaceous During the Late Cretaceous, the climate was warmer than present, although throughout the period a cooling trend is evident. The tropics became restricted to equatorial regions and northern latitudes experienced markedly more seasonal climatic conditions. Due to plate tectonics ,

560-410: Is a behavior observed in all hermit crabs. It is a process in which the attacker hermit crab attempts to steal the shell of the victim, using a fairly intricate process. It usually only occurs if there is no empty shell suitable for the growing hermit crab. These fights are usually between the same species, though they can also occur between two separate species. If the defending crab does not retreat to

616-506: Is brought down. This movement is sometimes called an "ambulatory poke". They also use their chelipeds as a warning display, usually used in two distinct variations. The first one consists of the crab lifting its whole body (shell included), and spreading its legs, then moving its cheliped forward until the dactylus (top part of the claw) is perpendicular with the ground. This movement is usually called an "cheliped presentation" This position may be more distinct in some species, such as those in

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672-479: Is it particularly evident that a true systematic decline was ever in place, especially with the discovery of smaller pterosaur species. Several old mammal groups began to disappear, with the last eutriconodonts occurring in the Campanian of North America . In the northern hemisphere, cimolodont , multituberculates , metatherians and eutherians were the dominant mammals, with the former two groups being

728-431: Is reduced in size, and often hidden inside the gill chamber (under the carapace ) to be used for cleaning the gills. Since this arrangement is very rare in true crabs (for example, the small family Hexapodidae ), a "crab" with only eight visible pereiopods is generally an anomuran. The infraorder Anomura belongs to the group Reptantia , which consists of the walking/crawling decapods ( lobsters and crabs). There

784-513: Is wide acceptance from morphological and molecular data that Anomura and Brachyura ("true" crabs) are sister taxa , together making up the clade Meiura. Anomura likely diverged from Brachyura in the Late Triassic period, with the earliest discovered Anomuran fossil Platykotta akaina dating from the Norian – Rhaetian aged Ghalilah Formation of the United Arab Emirates . The cladogram below shows Anomura's placement within

840-669: The Late Cretaceous . Before that time, at least some hermit crabs used ammonite shells instead, as shown by a specimen of Palaeopagurus vandenengeli from the Speeton Clay Formation , Yorkshire , UK , from the Lower Cretaceous , as well as a specimen of a diogenid hermit crab from the Upper Jurassic of Russia. The earliest record of the superfamily extends back to the earliest part of

896-764: The cladogram below, which also shows the king crabs of Lithodidae as sister taxon to the hermit crabs of Paguridae : Brachyura ("true" crabs) [REDACTED] Porcellanidae (porcelain crabs) [REDACTED] Munididae (squat lobsters) [REDACTED] Parapaguridae (deep water sea anemone hermit crabs) [REDACTED] Eumunididae (squat lobster-like) [REDACTED] Hippidae (mole crabs or sand crabs) [REDACTED] Lithodidae (king crabs) [REDACTED] Paguridae (hermit crabs) [REDACTED] Diogenidae (left-handed hermit crabs) [REDACTED] Coenobitidae (terrestrial hermit crabs) [REDACTED] The fossil record of in situ hermit crabs using gastropod shells stretches back to

952-590: The Americas were gradually moving westward, causing the Atlantic Ocean to expand. The Western Interior Seaway divided North America into eastern and western halves; Appalachia and Laramidia . India maintained a northward course towards Asia. In the Southern Hemisphere, Australia and Antarctica seem to have remained connected and began to drift away from Africa and South America. Europe

1008-859: The Cretaceous Period derived from the German name Kreidezeit , and T is the abbreviation for the Tertiary Period (a historical term for the period of time now covered by the Paleogene and Neogene periods). The event marks the end of the Mesozoic Era and the beginning of the Cenozoic Era. "Tertiary" being no longer recognized as a formal time or rock unit by the International Commission on Stratigraphy ,

1064-542: The Jurassic, with the oldest known species being Schobertella hoelderi from the late Hettangian of Germany. Hermit crabs can be informally divided into two groups: aquatic hermit crabs and terrestrial hermit crabs. The first group, the land hermit crabs, spend most of their life on land as terrestrial species in tropical areas, though even they require access to both freshwater and saltwater to keep their gills damp or wet to survive and to reproduce. They belong to

1120-850: The K-T event is now called the Cretaceous—Paleogene (or K-Pg) extinction event by many researchers. Non- avian dinosaur fossils are found only below the Cretaceous–Paleogene boundary and became extinct immediately before or during the event. A very small number of dinosaur fossils have been found above the Cretaceous–Paleogene boundary, but they have been explained as reworked fossils , that is, fossils that have been eroded from their original locations then preserved in later sedimentary layers. Mosasaurs , plesiosaurs , pterosaurs and many species of plants and invertebrates also became extinct. Mammalian and bird clades passed through

1176-618: The North American varieties. Pachycephalosaurs were also present in both North America and Asia. Dromaeosaurids shared the same geographical distribution, and are well documented in both Mongolia and Western North America. Additionally therizinosaurs (known previously as segnosaurs) appear to have been in North America and Asia. Gondwana held a very different dinosaurian fauna, with most predators being abelisaurids and carcharodontosaurids ; and titanosaurs being among

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1232-524: The boundary with few extinctions, and evolutionary radiation from those Maastrichtian clades occurred well past the boundary. Rates of extinction and radiation varied across different clades of organisms. Many scientists hypothesize that the Cretaceous–Paleogene extinctions were caused by catastrophic events such as the massive asteroid impact that caused the Chicxulub crater , in combination with increased volcanic activity , such as that recorded in

1288-600: The diversity and multitude of these crustaceans which are found in almost all marine environments. In most species, development involves metamorphosis from symmetric, free-swimming larvae to morphologically asymmetric, benthic -dwelling, shell-seeking crabs. Such physiological and behavioral extremes facilitate a transition to a sheltered lifestyle, revealing the extensive evolutionary lengths that led to their superfamily success. The hermit crabs of Paguroidea are more closely related to squat lobsters and porcelain crabs than they are to true crabs ( Brachyura ). Together with

1344-401: The dominant herbivores. Spinosaurids were also present during this time. Birds became increasingly common, diversifying in a variety of enantiornithe and ornithurine forms. Early Neornithes such as Vegavis co-existed with forms as bizarre as Yungavolucris and Avisaurus . Though mostly small, marine Hesperornithes became relatively large and flightless, adapted to life in

1400-608: The family Coenobitidae . Two of the most common crabs are the Ecuadorian Hermit crab and the Purple Pincher. The Ecuadorian Hermit Crab (Coenobita compressus) is a grayish black crab that are commonly found in tropical areas as well as beaches and rainforests. They are nocturnal, and are very social. They eat washed up plants, and are recommended they eat mostly plants. They must have seawater close to them, as they need to keep their gills moistened. Overall they are

1456-419: The family Paguridae , have another distinct type of movement. Individuals may crawl upon another's crab shell. If the size is just right the crab climbed upon may move rapidly up and down or sideways, usually causing the other crab to fall off. Anomura Anomura (sometimes Anomala ) is a group of decapod crustaceans , including hermit crabs and others. Although the names of many anomurans include

1512-469: The female moulting, and usually continuing after she has moulted, the male performs precopulatory behaviors. These vary widely but the most common are rotating/shaking the female, and jerking the female towards the male. After some time, the female moves the chelipeds in her mouth region, signaling the male. Then they both move their bodies mostly out of their shells, and mate. Both crabs then go back inside their shells, and they may mate again. In some species

1568-437: The final larval stage, the megalopa . The sexual behavior exhibited by hermit crabs varies from species to species, but a general description is as follows. If the female possesses any larvae from a previous mating, she moults and lets them go. Female hermit crabs are ready to mate shortly before moulting, and she may come in contact with a male. In certain species the male grabs the pre-moult female for sometimes hours. Prior to

1624-403: The first two walking legs, or both the first and second pair. This is referred to as "double ambulatory raise", and "quadruple ambulatory raise", respectively. The exact form of this movement is variable between species. In some other species there is another distinct movement, where they move their leg away and upwards from the body, while it moves forwards, this same movement continues as the limb

1680-402: The genus Pagurus . The second variation called the "cheliped extension", is usually a purely visual movement, though it may sometimes be used to strike a crab. The chelipeds move forward and upwards, until the limb is parallel with the ground, usually used to push another crab out of the way. If a larger crab pushes a smaller one, the smaller one may be moved multiple centimeters. The crabs of

1736-420: The hermit crabs (as they can climb into, but not out of, slippery plastic debris). This can even create a chain reaction of fatality, because a dead hermit crab will release a signal to tell others that a shell is available, luring more hermit crabs to their deaths. More specifically, they are attracted to the scent of dead hermit crab flesh. For some larger marine species, supporting one or more sea anemones on

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1792-419: The inside of its shell, an aggressive interaction will usually take place, until the defending crab retreats, or the attacker flees. After the defender has retreated, the attacker will usually turn the shell over multiple times, holding it with its legs. It then places its chelipeds into the shell's opening. Then the crabs start the "positioning" behavior, this consists of the attacker moving side to side, over

1848-887: The internal relationships within Anomura are shown in the cladogram below, which shows Hippidae as sister to Paguroidea, and resolves Parapaguridae outside of Paguroidea: Brachyura ("true" crabs) [REDACTED] Porcellanidae (porcelain crabs) [REDACTED] Munididae (squat lobsters) [REDACTED] Parapaguridae (deep water sea anemone hermit crabs) [REDACTED] Eumunididae (squat lobster-like) [REDACTED] Hippidae (mole crabs or sand crabs) [REDACTED] Lithodidae (king crabs) [REDACTED] Paguridae (hermit crabs) [REDACTED] Diogenidae (left-handed hermit crabs) [REDACTED] Coenobitidae (terrestrial hermit crabs) [REDACTED] The infraorder Anomura contained seven extant superfamilies: The oldest fossil attributed to Anomura

1904-634: The larger order Decapoda , from analysis by Wolfe et al. (2019). Dendrobranchiata (prawns) [REDACTED] Stenopodidea (boxer shrimp) [REDACTED] Procarididea Caridea ("true" shrimp) [REDACTED] Achelata (spiny lobsters and slipper lobsters) [REDACTED] Polychelida (benthic crustaceans) Astacidea (lobsters and crayfish) [REDACTED] Axiidea (mud shrimp, ghost shrimp, and burrowing shrimp) Gebiidea (mud lobsters and mud shrimp) [REDACTED] Anomura (hermit crabs and allies) [REDACTED] Brachyura ("true" crabs) [REDACTED] Some of

1960-457: The legs and the chelipeds , also known as the claw or pincer. Usually these displays are enough to avoid confrontation. Sometimes two opposing crabs will do multiple actions, with no apparent pattern. These confrontations usually last a few seconds, though some may last a few minutes, for those especially stubborn crabs. They can also raise a leg which is sometimes referred to as an "ambulatory raise". This can happen with multiple legs such as with

2016-513: The male performs post-copulatory behavior until the female has the eggs on her pleopods . Hermit crabs are omnivorous scavengers that require a varied and balanced diet to thrive. Their dietary needs can be met with a combination of commercial hermit crab food, fresh fruits, vegetables, and occasional treats. A well-rounded diet is essential not only for their general health but also for the proper development of their exoskeleton and overall vitality. High-quality commercial hermit crab food provides

2072-636: The most common mammals in North America. In the southern hemisphere there was instead a more complex fauna of dryolestoids , gondwanatheres and other multituberculates and basal eutherians ; monotremes were presumably present, as was the last of the haramiyidans , Avashishta . Mammals, though generally small, ranged into a variety of ecological niches, from carnivores ( Deltatheroida ), to mollusc-eater ( Stagodontidae ), to herbivores (multituberculates, Schowalteria , Zhelestidae and Mesungulatidae ) to highly atypical cursorial forms ( Zalambdalestidae , Brandoniidae ). True placentals evolved only at

2128-476: The next size. If the original shell was taken from another hermit crab, the victim is usually left without a shell, and gets eaten. Hermit crabs often "gang up" on one of their species with what they perceive to be a better shell, and pry its shell away from it before competing for it until one takes it over. Aggressive behaviors for hermit crabs are quite similar to one another, with some variations present between species. It usually consists of moving or positioning

2184-540: The numerous teleost fishes, which in turn evolved into new advanced and modern forms ( Neoteleostei ). Ichthyosaurs and pliosaurs , on the other hand, became extinct during the Cenomanian-Turonian anoxic event . Near the end of the Cretaceous Period, flowering plants diversified. In temperate regions, familiar plants like magnolias , sassafras , roses , redwoods , and willows could be found in abundance. The Cretaceous–Paleogene extinction event

2240-436: The ocean to release their larvae, however they cannot submerge themselves in the water as their gills prevent them. Most species have long, spirally curved abdomens , which are soft, unlike the hard, calcified abdomens seen in related crustaceans. The vulnerable abdomen is protected from predators by a salvaged empty seashell carried by the hermit crab, into which its whole body can retract. Most frequently, hermit crabs use

2296-407: The open sea. Though primarily represented by azhdarchids , other forms like pteranodontids , tapejarids ( Caiuajara and Bakonydraco ), nyctosaurids and uncertain forms ( Piksi , Navajodactylus ) are also present. Historically, it has been assumed that pterosaurs were in decline due to competition with birds, but it appears that neither group overlapped significantly ecologically, nor

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2352-415: The opening of the defender's shell. This movement usually forms a figure 8. The attacker then goes into the aptly named "rapping" behavior. The attacker holds its legs and chepelothorax stationary, while it moves its shell down on the defender's shell. It is done quite rapidly, and is usually enough to produce an audible sound. It seems like little to no contact happens directly between the two crabs. After

2408-561: The remains of dead animals, providing them with essential nutrients like calcium for their exoskeleton. This diverse diet helps support their health, energy, and successful molting. In addition to commercial food, hermit crabs benefit from a variety of fresh fruits and vegetables. Recommended options include leafy greens such as spinach, as well as carrots, sweet potatoes, and broccoli. Non-citrus fruits like mango, coconut, and papaya can also be offered. These foods provide essential vitamins, minerals, and hydration, which are vital for maintaining

2464-518: The shell can scare away predators. The sea anemone also benefits, because it is in a prime position to consume fragments of the hermit crab's meals. Other very close symbiotic relationships are known from encrusting bryozoans and hermit crabs forming bryoliths . In February 2024, Polish researchers reported that 10 of 16 terrestrial hermit crab species were observed using artificial shells, including discarded plastic waste, broken glass bottles and light bulbs, in lieu of natural shells. Shell fighting

2520-413: The shell they favour. However, if the crabs vary significantly in size, fights over empty shells are rare. Hermit crabs with undersized shells cannot grow as fast as those with well-fitting shells, and are more likely to be eaten if they cannot retract completely into the shell. Shells used by hermit crabs have usually been remodeled by previous hermit crab owners. This involves a hermit crab hollowing out

2576-722: The shell, making it lighter. Only small hermit crabs are able to live without remodelled shells. Most big hermit crabs that have been transferred to a normal shell die. Even if they were able to survive, hollowing out a shell takes precious energy, making it undesirable to any hermit crab. They achieve this remodeling by both chemically and physically carving out the interiors of their shell. These shells can last for generations, explaining why some hermit crabs are able to live in areas where snails have become locally extinct. There are cases when seashells are not available and hermit crabs will use alternatives such as tin cans, custom-made shells, or any other types of debris, which often proves fatal to

2632-472: The shells of sea snails (although the shells of bivalves and scaphopods and even hollow pieces of wood and stone are used by some species). The tip of the hermit crab's abdomen is adapted to clasp strongly onto the columella of the snail shell. Most hermit crabs are nocturnal . Hermit crab species range in size and shape, from species with a carapace only a few millimetres long to Coenobita brevimanus , which can live 12–70 years and can approach

2688-399: The shells, it is usually eaten. Several hermit crab species, both terrestrial and marine , have been observed forming a vacancy chain to exchange shells. When an individual crab finds a new empty shell, or steals one from another, it will leave its own shell and inspect the vacant shell for size. If the shell is found to be too large, the crab goes back to its own shell and then waits by

2744-446: The size of a coconut. The shell-less hermit crab Birgus latro (coconut crab) is the world's largest terrestrial invertebrate . The young develop in stages, with the first two (the nauplius and protozoea) occurring inside the egg. Most hermit crab larvae hatch at the third stage, the zoea . In this larval stage, the crab has several long spines, a long, narrow abdomen, and large fringed antennae. Several zoeal moults are followed by

2800-486: The squat lobsters and porcelain crabs, they all belong to the infraorder Anomura , the sister taxon to Brachyura. However, the relationship of king crabs to the rest of Paguroidea has been a highly contentious topic. Many studies based on their physical characteristics, genetic information, and combined data demonstrate the longstanding hypothesis that the king crabs in the family Lithodidae are derived hermit crabs descended from pagurids and should be classified as

2856-441: The vacant shell for up to 8 hours. As new crabs arrive they also inspect the shell and, if it is too big, wait with the others, forming a group of up to 20 individuals, holding onto each other in a line from the largest to the smallest crab. As soon as a crab that is the right size for the vacant shell arrives and claims it—leaving its old shell vacant—all the crabs in the queue swiftly exchange shells in sequence, each one moving up to

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2912-418: The various groups of anomurans are quite dissimilar. The group has been moulded by several instances of carcinisation – the development of a crab-like body form. Thus, the king crabs (Lithodidae), porcelain crabs (Porcellanidae) and hairy stone crab (Lomisidae) are all separate instances of carcinisation. As decapods (meaning ten-legged ), anomurans have ten pereiopods , but the last pair of these

2968-433: The very end of the epoch; the same can be said for true marsupials . Instead, nearly all known eutherian and metatherian fossils belong to other groups. In the seas, mosasaurs suddenly appeared and underwent a spectacular evolutionary radiation. Modern sharks also appeared and penguin-like polycotylid plesiosaurs (3 meters long) and huge long-necked elasmosaurs (13 meters long) also diversified. These predators fed on

3024-516: The word crab , all true crabs are in the sister group to the Anomura, the Brachyura (the two groups together form the clade Meiura ). The name Anomura derives from an old classification in which reptant decapods were divided into Macrura (long-tailed), Brachyura (short-tailed) and Anomura (differently-tailed). The alternative name Anomala reflects the unusual variety of forms in this group; whereas all crabs share some obvious similarities,

3080-537: Was a large-scale mass extinction of animal and plant species in a geologically short period of time, approximately 66  million years ago (Ma). It is widely known as the K–T extinction event and is associated with a geological signature, usually a thin band dated to that time and found in various parts of the world, known as the Cretaceous–Paleogene boundary (K–T boundary). K is the traditional abbreviation for

3136-514: Was an island chain. Populating some of these islands were endemic dwarf dinosaur species. In the Late Cretaceous, the hadrosaurs , ankylosaurs , and ceratopsians experienced success in Asiamerica (Western North America and eastern Asia). Tyrannosaurs dominated the large predator niche in North America. They were also present in Asia, although were usually smaller and more primitive than

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