Animals resembling crabs have arisen at least five separate times in history. Scientists refer to this occurrence as carcinization since it is so fascinating. We go into great length on why animals continue to evolve into crabs here.
What Is Convergent Evolution?
The emergence of comparable traits in creatures that do not share a common ancestor with those traits is known as convergent evolution. Animals that have experienced convergent evolution seem linked to one another from a purely visual standpoint. They did, however, come into being in quite different ways.
Convergent evolution can be seen in the wings of birds and bats. Another example are the streamlined bodies of dolphins and sharks, which are made for swimming.
What Is Carcinization?
A particular type of convergent evolution known as “carcinization” occurs when certain decapod crustaceans transform into creatures that resemble crabs. Approximately 250 million years have passed since the common ancestor of some of the various crab-like species that inhabit the globe did not resemble crabs.
The ancestors of today’s crabby crustaceans had enormous tails and cylindrical bodies. Eventually, they transformed into smaller-tailed, rounder-bodied animals.
4 Examples of Animal Types Representing Carcinizaton
Numerous distinct species are examples of carcinization. Some of these species are false crabs, while just a small number of them are real crabs. The Brachyura infraorder contains true crabs, while the Anomura infraorder contains fake crabs.
The intriguing thing about the Anomura species of fake crabs is that, three times within its infraorder, they independently developed into organisms resembling crabs. This is not the same as the singular evolutionary event that gave rise to genuine crabs.
A few of the planet’s crabby-bodied creatures that participate in carcinization are listed below. There is talk of both real and fake crabs.
1. True Crabs
The infrastructure True crabs are found in the genus Brachyura, which also includes about 7000 species of brachyurans. The genuine crab species all have comparable traits, even if each has distinct qualities that set it apart from other species. Among these features include bodies that are longer than they are wide, as well as one complete upper shell.
The gaper pea crab (Pinnixa littoralis or faba), red rock crab (Cancer productus), blue swimmer crab (Portunas pelagicus), and green shore crab (Hemigrapsus oregonensis) are a few examples of real crab species. Among the more well-known species that are frequently caught for human food are Maryland blue crabs (Callinectes sapidus) and Dungeness crabs (Cancer magister).
2. King Crabs
False crabs are any crabs that aren’t actually crabs.False crabs are all those after king crabs on this list and are regarded as such. Unless otherwise noted, they belong to the infraorder Anomura.
The creatures referred to as king crabs, or Lamouelle and Lithodidae families, are an illustration of a branch of false crabs that underwent autonomous evolution to become their crabby forms. The ancestors of king crabs are hermit crabs (Paguroidea), which, despite their name, are not very similar to crabs. Hermit crabs differ from other fake crabs in that they lack the hard exoskeleton and have spiraling abdomens.
3. Porcelain Crabs
The Porcellanidae family of fake crabs includes porcelain crabs. Hairy stone crabs (Lomis hirta) and porcelain crabs most likely descended from a common ancestor that looked like a squat lobster. Due to their lack of true crab resemblance, squat lobsters (Munidopsis serricornis) are classified as partially carcinized creatures. They resemble a cross between a lobster and a crab due to their squat yet somewhat cylindrical architecture.
There are significant differences between deriving from a hermit crab and a squat lobster. This is due to the fact that a distinct evolutionary selection was required during their carcinization process because the anatomy of these two ancestors varies greatly.
4. Hairy Stone Crabs
A false crab species known as hairy stone crabs most likely descended from the same squat lobster progenitor as porcelain crabs. Its transformation into its crabby form, nevertheless, might have resulted from a different evolutionary process that spun off from the king crab’s development. This indicates that while the details of their specific evolutionary history remain mostly unknown, it is generally acknowledged that they underwent a unique process of carcinization.
Carcinization: What Is a Crab-Like Body?
The body of a crab is broad and flat. Because their abdomens are on the underside of their low-lying bodies, they are vulnerable and difficult to reach. This indicates that their pleon is near to the ground and sheltered, and that their carapace is rounded and flattened, according to biology.
Crabs possess pincers and strong exoskeletons as well. They also have walking legs, albeit false crabs have three pairs of walking legs while true crabs have four. Although they still have four pairs of legs, false crabs can’t walk on one of them due to its diminutive size.
True crabs can also be distinguished from counterfeit ones by looking at where their antennae are located. Antennae are only present between the eyes of true crabs. On the other hand, antennae on the outside of the eyes are also possible in fake crabs.
Why Do Animals Keep Evolving Into Crabs?
The reason behind animals’ repeated evolution into crabs is unknown, although it is most likely due to the success of the body plan. Crustaceans might have preferred flat crab bodies because they made it easier for them to move sideways and squeeze into confined areas. Because it is more difficult to reach and chew off, smaller tails may help protect more of their meat.
What Is Decarcinization?
Certain creatures have started to evolve away from their crabbiness after first acquiring crab-like traits. Scientists believe that this has happened over seven times in total. What gave rise to the cranky countenance is now giving way to adaptations that require a distinct body type.
Frog crabs (Ranina ranina) and coconut crabs (Birgus latro) exhibit decarcinization. The body of these two crabs are evolving from the traditional crab shape into something different.
Compared to several other false crab species, these two are not as low to the ground or as squat. They no longer like these traits, albeit they have some grumpy aspects now. Rather than sticking to their grumpy nature, they are taking new and distinct evolutionary routes.