Lamp shells

Habitats

The following habitats are found across the Lamp shells distribution range. Find out more about these environments, what it takes to live there and what else inhabits them.

• Sea bed
• Estuaries
• Intertidal zone
• Shallow seas
• Rockpools

About

Brachiopods, phylum Brachiopoda, are marine animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection. Two major groups are recognized, articulate and inarticulate. Articulate brachiopods have toothed hinges and simple opening and closing muscles, while inarticulate brachiopods have untoothed hinges and a more complex system of muscles used to keep the two halves aligned. In a typical brachiopod a stalk-like pedicle projects from an opening in one of the valves, known as the pedicle valve, attaching the animal to the seabed but clear of silt that would obstruct the opening.

The word "brachiopod" is formed from the Ancient Greek words βραχίων ("arm") and πούς ("foot"). They are often known as "lamp shells", since the curved shells of the class Terebratulida look rather like pottery oil-lamps.

Lifespans range from 3 to over 30 years. Ripe gametes (ova or sperm) float from the gonads into the main coelom and then exit into the mantle cavity. The larvae of inarticulate brachiopods are miniature adults, with lophophores that enable the larvae to feed and swim for months, until the animals become heavy enough to settle to the seabed. Larvae of articulate species are different from the adult forms, live only on yolk, remain only among the plankton for only a few days, and then start metamorphosing.

In addition to the traditional classification into inarticulate and articulate brachiopods, two approaches appeared in the 1990s: one groups the inarticulate Craniida with articulate brachiopods, as both used the same material in the mineral layers of the shell; the other makes the Craniida a third group, as their outer organic layer is different from that of either the others. However, some taxonomists believe it is premature to suggest higher levels of classification such as order, and recommend a bottom-up approach that identifies genera and then groups these into intermediate groups. Traditionally brachiopods have been regarded as members of or as a sister group to the deuterostomes, a super-phylum that includes chordates and echinoderms. One type of analysis of brachiopods' evolutionary relationships has always placed brachiopods as protostomes, while another type has split between placing brachiopods among the protostomes or the deuterostomes.

In 2003 it was suggested that brachiopods evolved from an ancestor similar to Halkieria, a slug-like Cambrian animal with "chain mail" on its back and a shell at the front and rear end, and that the ancestral brachiopod converted its shells into a pair of valves by folding the rear part of its body under its front. However, new fossils found in 2007 to 2008 showed that tommotiids' "chain mail" formed the tube of a sessile animal, and that one tommotiid resembled phoronids, which are close relatives or a sub-group of brachiopod, while the other tommotiid bore two symmetrical plates that might be an early form of brachiopod valves. Lineages of brachiopods that have both fossil and extant taxa appeared in the early Cambrian, Ordovician and Carboniferous periods respectively. Other lineages have arisen and then become extinct, sometimes during severe mass extinctions. At their peak in the Paleozoic era the brachiopods were among the most abundant filter-feeders and reef-builders, and occupied other ecological niches, including swimming in the jet-propulsion style of scallops. Brachiopod fossils have been useful indicators of climate changes during the Paleozoic. However, after the Permian–Triassic extinction event, brachiopods recovered only a third of their former diversity. A study in 2007 concluded that brachiopods were especially vulnerable to the Permian–Triassic extinction, as they built calcareous hard parts (made of calcium carbonate) and had low metabolic rates and weak respiratory systems. It was often thought that brachiopods were in decline after the Permian–Triassic extinction, and were out-competed by bivalves. However, a study in 1980 concluded that both brachiopod and bivalve species increased all the way from the Paleozoic to modern times, but that bivalves increased faster; after the Permian–Triassic extinction, brachiopods for the first time became less diverse than bivalves.

Brachiopods live only in the sea, and most species avoid locations with strong currents or waves. Articulate species have larvae that settle in quickly and form dense populations in well-defined areas, while inarticulate larvae swim for up to a month and have wide ranges. Brachiopods now live mainly in cold water and low light. Fish and crustaceans seem to find brachiopod flesh distasteful and seldom attack them. Among brachiopods only the lingulids have been fished commercially, on a very small scale. One brachiopod species may be a measure of environmental conditions around an oil terminal being built in Russia on the shore of the Sea of Japan.

Read more at Wikipedia