The class Thecostraca is a group of marine crustaceans known mainly for including sessile organisms, such as barnacles and parasitic copepods. Species of this class have in common the characteristic of living attached to hard substrates (such as rocks, shells or even marine animals) or being ectoparasites. The scientific name ‘Thecostraca‘ derives from the Greek ‘theke‘ meaning box or receptacle, and ‘ostrakon,’ meaning shell, which refers to the protective calcareous covering that surrounds many members of this group, such as barnacles. Tecostráceos species are predominantly marine, distributed throughout the world’s oceans and seas, from coastal waters to the abyssal depths. Some species can also be found in freshwater habitats.
In terms of morphology, the members of Tecostráceos present a wide variety of shapes and sizes. The best known, barnacles, have bodies enclosed in a calcareous shell formed by articulated plates. These plates can vary in number and shape depending on the species. Barnacles can measure from a few millimeters to several centimeters in length, depending on the species. They have a segmented body that includes a reduced thorax and abdomen. One of their most distinctive features are cirri, long, feathery projections that they use for feeding, extending into the water when submerged. Other members of Tecostráceos, such as the parasitic copepods, have much more simplified forms, adapted to their life as parasites of fish and other marine animals.
The feeding habits of Tecostráceos species vary according to the subgroup to which they belong. Barnacles are filter feeders that feed on plankton and organic particles suspended in the water. They use their cirri to trap these small particles as the water flows around them. On the other hand, parasitic copepods feed on the body fluids of their hosts, which are usually fish or marine invertebrates. These copepods have evolved specialized adaptations to efficiently attach to and feed on the host. In general, Tecostráceos species are very efficient in their feeding methods and play an important role in marine food webs.
An interesting curiosity about Tecostráceos is that the group includes about 2,500 described species, divided into three main subclasses:
- Cirripedia: which includes barnacles and balans.
- Ascothoracida: parasitic crustaceans living on echinoderms and cnidarians.
- Facetotecta: an enigmatic group whose larvae are known, but the adult form is still unknown
Barnacles are of particular economic interest, as some species, such as barnacle Pollicipes pollicipes, are consumed as a delicacy in various cultures. In addition, many Cirripedia species are known to biofoul ships and underwater structures, which has led to research into methods to prevent this type of colonization due to the economic impact it has on the maritime industry.