Brachiopod Morphology

Brachiopod morphology can be quite variable, here we outline basic morphological characters of the phylum.

External Characters

  • WL dorsal valve Dorsal Valve: Also called the brachial valve; smaller valve of the brachiopod; the lophophore attaches to this valve
  • Ventral Valve: Also called the pedicle valve; larger valve of the brachiopod; pedicle attaches to this valve
  • Beak: Pointed portion(s) at the posterior end of the brachiopod
  • Commissure: The edge of the shell along its line of closure between valves
  • Fold: Elevation of a brachiopod valve along the midline, accompanied by a depression (sulcus) on the other valve
  • Sulcus: Depression of a brachiopod valve along the midline, accompanied by an elevation (fold) on the other valve
  • Pedicle Foramen: Subcircular to circular opening in the vental valvue through which the pedicle penetrates
  • Growth Line: Concentric markings that run from the beak to the commissure
  • Plication: Major undulation (waves) on the shell surface; particularly visible along the commissure

fold sulcus

Shell Configuration
brachiopod shell typeshorz

  • Biconvex: Both valves are convex
  • Plano-convex: Dorsal valve is planar
  • Concavo-convex: Dorsal valve is concave; ventral valve is convex; valves fit inside one another

Plane of Symmetry

  • The plane of symmetry bisects the shell down the center as shown by the orange plane in the diagram. This is a distinctive character difference between brachiopods and bivalves. The plane of symmetry in bivalves is between the valves, making them mirror images. This plane would be equivalent to the commissural plane in brachiopods.