(Supplementing
Lucy-S's writeup above.)
Brachiopods are also known as lamp shells.
Differences between the brachiopods and the bivalves
Phylum Brachiopoda and class
Bivalvia of phylum
Mollusca both have two shells.
One difference between the two groups of marine animals is their
bilateral symmetry.
The Brachiopods' plane of symmetry is
perpendicular to the plane of commission (the plane where the two shells meet), while the bivalves have
coincident planes of symmetry and commission.
Pictoral explanation:
Phylum Brachiopoda - shows symmetry perpendicular to the plane of commission.
,'|'|'|',
/\ | | | /\ ,----, ← ventral valve (larger)
', \ ||| / ,' / ',
',\|||/,' |--------, ← plane of commission
'-----' '------' ← dorsal valve (smaller)
TOP VIEW SIDE VIEW
(symmetric) (asymmetric)
Class
Bivalvia of phylum
Mollusca - plane of symmetry
coincident to the plane of commission.
_____ /|\
__,.'' '', / | \
,' \ | | | ← ventral & dorsal valves symmetric.
| | | | |
'..,___,.,,__,.' ' | '
\_|_/
TOP VIEW SIDE VIEW
(asymmetric) (symmetric)
Brachiopods use hairy
lophophores to eat, while bivalves use a pair of siphons to filter food from the body of water. Lophophores are only found in
brachiopods,
bryozoans, and
phoronids, but not in bivalves. What looks like the brachiopod's siphon are actually legs called pedicles, although not all brachiopods have legs, or pedicles. While a
Lingula anatina uses its pedicle for locomotion, others may use it for anchoring against a rock.
Articulate and inarticulate brachiopods
Inarticulate brachiopods do not have a hinge for their valves, while articulate
brachiopods have a
tooth and socket articulation for a hinge. The inarticulate brachiopods are considered more primitive than the articulate brachiopods, although fossil records both appear around the same time.
Paleontology of brachiopods and bivalves
The inarticulate brachiopods flourished as a member of the
Cambrian marine fauna, later to be slowly outcompeted by the
Paleozoic marine fauna, which includes the
articulate brachiopods. Then, after a massive extinction around the end of the
Paleozoic era, the
Paleozoic marine fauna decreases in population and the
Modern Marine Fauna (which includes the
bivalves) explodes. Each emergence of new faunas causes
brachiopods to withdraw into
refugia, which are habitats difficult to adapt to, such as the antarctic ocean (where
Liothyrella uva antarctica lives), and river
estuaries (where
Lingula anatina lives).
Taxonomy
- Phylum Brachiopoda (Cambrian-Recent)
- Class Inarticulata (Cambrian-Recent)
- Class Articulata (Cambrian-Recent)
Sources:
- Liothyrella uva antarctica -- http://scilib.ucsd.edu/sio/nsf/fguide/brachiopoda1.html
- Phylum Brachiopoda -- http://www.rtis.com/nat/user/elsberry/taxa/brach.html
- Brachiopoda taxonomy -- http://paleo.cortland.edu/tutorial/Brachiopods/brachiopoda.htm
- pages 131 & 137 from "Life of the Past," 4th Ed. by William I. Ausich and N. Gary Lane.