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Distribution |
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Geographical distributionIn spite of the fact that brachiopods have few representatives in the total marine fauna, they are found in seas all around the world. |
A gllmpse of mediterranean, tethysian or paratethysian species : Argyrotheca cistellula (Searles-Wood,1841),Argyrotheca cuneata (Risso,1826),Grypheus vitreus (Born, 1778),Gwynia capsula (Jeffreys, 1859),Lacazella mediterranea (Risso, 1826),Megathyris detruncata (Gmelin, 1790),Megerlea truncata (L.,1767),Novocrania animalia (Müller, 1776),Novocrania turbinata (Poli, 1776),Platidia anomioides (Scacchi & Philippi, 1844),Platitia davidsoni (Desl.1855),Terebratulina retusa (L., 1758),Tethyrhynchia mediterranea (Logan, 1994). |
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Mediterranean...
Some of themhave been there since the Oligocene age, when Tethys still covered the "Mare Mediterraneum", mostly colonizing infralittoral or circalittoral zones. Others prefer deeper water. Two ways of anchoring are distinguished : cementing or pedicular fixing. Most species are attached by their pedicle; cementing is not common (Neocrania, Lacazella). The nature of the substrat is also very important. A good number of brachiopods occupy walls and roofs of submarine caves, the others live on stones, broken shells... in the seabed. (Logan, A. & al., 2004) |
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High population densityBrachiopods are often found in great abundance : indeed, 700 individuals of Grypheus vitreus per square meter near the Mediterranean coasts and 100 shells of Hemithiris psittacea on a single rock in the cold arctic waters. |
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This is a shell of Lacazella mediterranea (Risso) anchored to a broken wormburrow. Both organisms are from Pliocène strata of Spain | ||||||||||||||||||
Ubiquitous or endemic ?
Living creatures like brachiopods may spread out or just colonize a restricted space. In the first case they are ubiquitous, but in the second case endemic. Endemism often follows a more or less ancient form of isolation. After discovering an ecological niche, providing them with basic needs, the populations may conquer new environments (adaptive radiation & evolution). So, some groups even become nearly cosmopolitan, while others were confined to very limited geographical areas. The Devonian Spinatrypa is a good example for ubiquitous genera. Plicarostrum is an endemic genus of the Cretaceous of Switzerland. |
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It's hard to be ... a brachThe competition between lamellibranchia (bivalvia) and brachiopoda was fierce. These creatures often cohabited in the same environments. At the first glance, they could be confused : both have two valves, prefer to colonize neritic zones and are filterers. During the Palaeozoic times these two groups peacefully lived side by side, although the brachiopoda were much more branched out. Nevertheless, things changed from the Permian on. Why ? A significant biological crisis than affected the animal kingdom. Undoubtedly, the brachiopods didn't recover completely from this crisis, but lamellibranchia went up and even had a spectacular development. Bit by bit, they filled out all the ecological niches, henceforth occupied by their competitors. Their expansion did not stop there, because they also invaded fresh waters. Infortunately, the brachiopoda never refound their supremacy of the past.
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More good pictures ? Please click here
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Glossary
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