Trilobite Anatomy and Morphology Quiz

Phylum Brachiopoda

• Brachiopods were dominant shelly marine invertebrates during the Palaeozoic Era.
• Originated in the early Cambrian and diversified in the Ordovician.
• Declined through the Mesozoic.
• Classified into three subphyla: Linguliformea, Craniformea, and Rhynchonelliformea.
• Exclusively marine filter feeders.
• Shell shape sometimes indicates the substrate type.
• Communities can help study paleoenvironments.
• Some groups, like lingulids, have stayed the same shape for over 500 million years.
• Also known as "lamp shells" because of the resemblance to oil lamps from Biblical times.
• Most modern ones live in marginal marine environments attached to substrates, morphologically similar.
• Palaeozoic ones show more morphological diversity, ranging from coral-like to flattened saucer shapes.

Morphology

• Typical brachiopod shell has one larger (ventral/pedicle) valve and one smaller (dorsal/brachial) valve.
• Pedicle valve has an opening for a stalk (pedicle) that attaches to the substrate.
• Dorsal valve has the lophophore (brachium) attached to it.
• Lophophore filters particles from the water within the mantle cavity.
• Mantle cavity contains most internal organs and a kidney-like nephridium for waste removal.
• Setae (bristles) around the margin help sense the environment.
• Adductors run perpendicularly, closing the shell.
• Diductors pull the dorsal valve open.

Morphology (continued)

• Pedicle opening (foramen) can be a simple opening or a delthyrium, which is a notch.
• The delthyrium can be a shallow notch, or it can be enclosed by plates (deltidial/chilidial plates).
• Spoon-shaped platform (spondylium) in some (e.g. pentameride) ventral valves for the hinge muscles.
• A cruralium, a corresponding spoon-shaped feature in the dorsal valve, is also present in pentameride brachiopods.
• These internal structures subdivide the shell into chambers.

Morphology (continued)

• The brachial valve is usually the smaller one.

Classification

• Traditionally classified as inarticulates (lacking hinges) and articulates (with hinges).
• Inarticulates are phosphatic, lack teeth and sockets, rely on muscles to attach to substrate (e.g., Order Lingulida).
• Articlulates are calcareous, have teeth and sockets, for more complex hinge movements (all others).

Classification (continued)

• Modern classification groups Brachiopods into subphyla:
  • Linguliformea
  • Rhynchonelliformea
  • Craniiformea

Subphylum Linguliformea

• Order Lingulida (Cambrian to Recent):
• Common genus Lingula.
• Live buried in mudflats using their pedicle to burrow.
• Extraordinary longevity.

Subphylum Craniiformea

• Order Craniida (Ordovician to Recent)
• Circular to subcircular.
• Their dorsal valves are calcified and they tend to encrust onto hard surfaces, including other brachiopod shells.

Subphylum Rhynchonelliformea

• Orders Athyriada (Ordovician to Jurassic), Atrypida (Ordovician to Devonian), and Orthida (Cambrian-Permian).
• Juvenile atrypids have a pedicle which is lost during maturation.
• They were amongst the first brachiopods to evolve a spiral-shaped lophophore brachidium.
• Common in the Paleozoic.

Subphylum Rhynchonelliformea (continued)

• Order Orthida
• Long, straight hinge line with a wide delthyrium and notothyrium.
• The interarea (a flat or curved surface) between the beak and margin of the valve is wide.
• Majority has very fine radial ribs.

Subphylum Rhynchonelliformea (continued)

• Order Pentamerida
• Deeply biconvex shells and highly curved hinge lines.
• The spondylium is a large scoop shaped feature on the ventral side, the shell is divided into five chambers.

Subphylum Rhynchonelliformea (continued)

• Order Rhynchonellida (Ordovician-Recent)
• Strongly biconvex shells with a large pedicle foramen.
• The shell is smooth.
• Ancestor of some still living species.

Subphylum Rhynchonelliformea (continued)

• Order Terebratulida

• The most well-known living brachiopods.

• Strongly biconvex, large pedicle foramen.

• Smooth, no ornamentation.

• Have loop-shaped brachidium.

Ecology and Paleoecology

• Exclusively benthic marine animals.
• Primarily filter feeders; don't actively hunt.
• Live on or partially within the substrate.
• Depend on currents for food and oxygen.
• Fossil forms show a wide variety of habitats.

Classification: Inarticulates vs. Articlulates

• Inarticulates lack defined hinges.
• Articlulates have defined hinges; use teeth and sockets; are primarily calcerous.

Phylum Mollusca

• Diverse and abundant phylum.
• Marine, freshwater, and terrestrial habitats.
• The phylum includes snails, slugs, oysters, and squids.

Phylum Mollusca (continued)

• Molluscs are first known from the early Cambrian.
• Utilize two/three part chitin, calcite and aragonite shell.

Phylum Mollusca (continued)

• 3 main groups:
  • Gastropoda
  • Bivalvia
  • Cephalopoda

Basic Morphology

• Elongate, unsegmented bodies.
• Internal organs are between a muscular foot and a calcareous shell secreted by the mantle.
• Mantle overhangs the body to form a chamber.
• The chamber contains sensory organs, such as eyes, and gills.

Test your knowledge on the anatomy and morphology of trilobites with this quiz. Explore various parts such as the cephalon, thorax, and pygidium, while also examining morphological variations and their significance. Perfect for palaeontology enthusiasts!