Classes: Inarticulate and Articulate

BRACHIOPODS

Phylum: Brachiopoda Classes: ‘Inarticulate’ and ‘articulate’

Morphology: Brachiopods are marine organisms which attach themselves to the sea floor by a fleshy stalk (pedicle) which extends from the body cavity.

The shell is made up of two valves of different size (a larger pedicle valve and a smaller brachial valve). Each valve is equilateral.

The exterior of the shell is marked with concentric growth lines and there may be radial ribs for strength. The shell is hinged along the hinge line (which may be straight, curved, long or short) and the valves open slightly along the anterior margin for feeding.

The main part of the body is small and most of the shell is taken up by the lopophore (an organ used to collect food).

Inarticulate brachiopods. The more primitive form. Shells made of chitin and calcium phosphate. Unable to move valves independently of one another. 1. No teeth or sockets 2. Valves open and close by complex muscle system 3. No support for lopophore 4. Pedicle usually extends form a gap between the two halves. Example: Lingula, crania

Articulate brachiopods. Shells made of fibrous calcite. Are able to move valves independently by muscles and hinges. 1. Teeth and sockets along hinge line. 2. Valves opened and closed by on pair of adductor and two pairs of diductor muscles 3. Calcareous framework supports lopophore ] 4. Pedicle extends from hole (foramen). There is a triangular gap between this and the hinge line which may be closed by a plate. (nb . some have no pedicle and attach themselves to the seafloor with cement of spines. Example: terebratula, orthis, spirifer, productus

Mode of Life: All sessile (fixed) marine organisms. Live in shallow marine environment (neritic zone). Found : Cambrian to present day – inarticulate in early times. Max. for all brachiopods was Silurian and Devonian.

Uses and Importance. Environmental indicators. Characteristic of shallow, clear, shelf sea environments (e.g. may be usd to map original coastlines. Rock builders. Limestone (bioclastic) formed from shell banks, e.g. productus in Carb. Limestones. Dating and correlation. Of limited value because of fixed mode of life. Generally used as part of faunal assemblages.