Shrimps belong to the infraorder Caridea, a large and diverse group of decapod crustaceans that includes thousands of species distributed across all aquatic ecosystems on the planet. To date, more than 3,000 species of shrimps have been described, although the actual number is estimated to be considerably higher due to the existence of still unidentified species, especially in deep waters and poorly explored habitats.
One of the main distinctive characteristics of shrimps in the infraorder Caridea is the presence of a curved fold on the second abdominal segment, giving them a ‘flexible’ and more arched body shape compared to other crustaceans. They also have a well-developed rostrum (an extension of the carapace on the head) and slender legs, although in some species the first pair is modified into small pincers.
Their size varies greatly depending on the species, from a few millimeters to over 20 centimeters in some cases. Most display muted colors to camouflage with the seabed, although some reef species, such as those in the genus Lysmata, have bright colors and striking patterns.
Shrimps are found in all the world’s oceans, from tropical coastal zones to abyssal depths, and also in freshwater environments. In fact, many species of the infraorder Caridea have colonized rivers and lakes, especially in tropical regions. Some species are migratory, spending part of their life cycle in freshwater and another part in the sea, a phenomenon known as ‘amphidromous life’.
Regarding their classification, the infraorder Caridea is divided into several important families:
- The family Palaemonidae, one of the largest, which includes freshwater and saltwater species such as Macrobrachium rosenbergii (giant freshwater prawn) and Palaemon elegans (common striped shrimp in the Mediterranean).
- The family Hippolytidae, which groups decorative reef species such as Lysmata amboinensis (cleaner shrimp), famous for removing parasites from fish.
- The family Alpheidae, which includes the well-known pistol shrimps, such as Alpheus heterochaelis, capable of producing a powerful snap with one of their claws used for hunting or communication.
Shrimps have a very varied diet. They are omnivores and feed on small invertebrates, organic debris, algae, and plankton. Many species play an essential ecological role as recyclers of the seabed. Others, like Lysmata, establish symbiotic relationships by cleaning the skin of fish.
Regarding reproduction, they have separate sexes, although some species can change sex throughout their life (sequential hermaphroditism). Females carry the eggs under their abdomen until hatching. Larval development is usually indirect: the offspring hatch as planktonic larvae that go through several stages before becoming juveniles with the adult form.
