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Squat lobster

life science Maturity 7-9 Next article →

Squat lobsters are unique crustaceans that live in oceans across the entire world. They belong to the infraorder Anomura, which is a group that includes hermit crabs and mole crabs. These animals are characterized by being dorsoventrally flattened, meaning they are pressed thin from top to bottom. This shape makes them look like a morphological intermediate between a true lobster and a crab. They are found in many different environments, from the ocean surface to deep-sea hydrothermal vents. One remarkable species even lives in caves located above sea level.

Expl1573 - Flickr - NOAA Photo Library
Expl1573 - Flickr - NOAA Photo Library

The body of a squat lobster is divided into two primary regions. The first is the cephalothorax, which combines the head and the thorax. This section is covered by a thick carapace, a hard shell that protects the body. The carapace can vary greatly in shape and ornamentation. In some species, it forms a rostrum, which is a forward-pointing structure in front of the eyes. Other species have a wide, serrated carapace, while some have long, narrow versions with supraorbital spines. The cephalothorax contains 19 body segments, or somites, though these are difficult to see.

Kiwa puravida
Kiwa puravida

Squat lobsters have a variety of specialized appendages attached to their cephalothorax. They possess two pairs of antennae and six pairs of mouthparts. These mouthparts, including the mandibles and maxillipeds, do more than just move food. They allow the animal to gather prey, move sediment, and sort through particles. The most visible appendages are the pereiopods, or walking legs. The first pair are the chelipeds, which end in large claws called chelae. These claws can sometimes be more than six times the length of the animal's body.

Porcelain crab Nick Hobgood
Porcelain crab Nick Hobgood

The second main body part is the pleon, also known as the abdomen. The pleon consists of six somites and ends in a structure called a telson. Most squat lobsters keep their pleon curled tightly beneath the cephalothorax. Attached to the pleon are several pairs of appendages called pleopods. These appendages differ between males and females. In females, some pleopods have long bristles called setae to which they attach their eggs. In males, the first two pairs are modified into gonopods, which are used to transfer a spermatophore to the female during mating.

Kiwa puravida
Kiwa puravida

Scientists have identified a massive diversity of these creatures. There are more than 900 described species across about 60 genera. If the family Aeglidae is included, the number rises to over 1,000 species in 61 genera. These animals can be found at altitudes up to 3,600 meters above sea level. A 2020 study discovered that squat lobsters are even more diverse than previously believed. This research described 16 new species within the Leiogalathea genus. The study also noted that the Atlantic Ocean has fewer species than the Pacific Ocean.

Expl1573 - Flickr - NOAA Photo Library
Expl1573 - Flickr - NOAA Photo Library

Many squat lobster species engage in interesting social behaviors like aggregation. Benthic squat lobsters often gather in high densities around productive areas like hydrothermal vents or shipwrecks. They may use these structures as shelter from predators or as places where food accumulates. Some species, such as Munida gregaria, perform vertical migrations in the water column. They can form massive swarms that are 200 meters tall and 10 kilometers wide. In these swarms, they rely on tidal streams to help them feed. These aggregations can reach densities of 2,700 individuals per cubic meter.

Expl1573 - Flickr - NOAA Photo Library
Expl1573 - Flickr - NOAA Photo Library

Squat lobsters also use specific body movements to interact with their environment. They may extend their claws into the water column as an active fishing strategy to catch prey. This behavior can also act as an illusory display to make them look larger to predators. While they can be aggressive during competition for food or mates, they are generally unaggressive toward one another. Most aggressive displays are ignored 70% of the time. In some cases, the behavior is met with submission or reciprocal aggression. This helps maintain stability in dense populations where food is a shared resource.

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🖼️ Images & Media (3)
Kiwa puravida.tif
File:Expl1573 - Flickr - NOAA Photo Library.jpg
Expl1573 - Flickr - NOAA Photo Library.jpg
File:Porcelain crab Nick Hobgood.jpg
Porcelain crab Nick Hobgood.jpg
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