Questions and Answers
What is the classification of trilobites?
Trilobites are called trilobites as their exoskeleton is divided into _____ lobes.
3
What is an arthropod skeleton made of?
Chitin
The exoskeleton of arthropods is flexible and allows for growth.
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What does the cephalon of a trilobite consist of?
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What is the purpose of the facial sutures in trilobites?
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What does ecdysis refer to?
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What does the pygidium of a trilobite do?
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The thorax is made up of thoracic segments, each possessing a pair of ______ and ______.
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Match the following parts of the cephalon with their functions:
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The thorax of trilobites is characterized by which feature?
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Study Notes
Classification of Trilobites
- Earliest known organisms in the phylum Arthropoda, which includes lobsters, crabs, and spiders.
- Class Trilobita characterized by exoskeleton divided into three lobes along a longitudinal axis.
- Three main body sections: cephalon (head), thorax, and pygidium (tail).
- Originated in the Cambrian period and went extinct by the end of the Permian period.
Arthropod Skeleton
- Features a hard exoskeleton made of chitin, providing muscle attachment and armor-like protection.
- Composed of jointed appendages such as legs and antennae, essential for movement and feeding.
- Each pleuron is equipped with jointed legs for locomotion or swimming and may have gills for respiration.
- Preservation of appendages is rare, exemplified by findings in the Burgess Shale.
Exoskeleton Structure
- Comprises three layers: a waxy outer layer, with two inner layers of chitin and protein.
- Middle layer may include calcium carbonate to enhance strength.
- Sensory hairs possibly emerged from the exoskeleton for environmental detection.
Cephalon Composition
- Includes structures like eyes, facial sutures, free cheeks, fixed cheeks, and glabella.
- Compound eyes are similar to modern arthropods with multiple calcite lenses, allowing for wide-angle vision.
- Spines at the glabella may serve as defense or help distribute body weight.
Cephalon - Free Cheeks (Librigenae)
- These parts detach from the skeleton during ecdysis (molting).
Cephalon - Glabella
- Forms as a result of the stomach's position within the head structure.
Cephalon - Facial Sutures
- Weakness lines in the exoskeleton that break first during ecdysis, important for the organism's molting process.
Cephalon - Facial Sutures Types
- Proparian: located forward of the genal angle (common in Phacopina).
- Gonatoparian: situated at the genal angle (common in Calymenina).
- Opisthoparian: runs along the hind cephalic margin adjacent to the genal angle.
Cephalon - Fixed Cheek (Fixigena)
- Stays attached to the exoskeleton during the start of ecdysis.
Cephalon - Genal Angle
- Possible location for spines; angle measurements available in some species.
Cephalon - Appendages (Headlegs)
- Utilize for environmental sensing and feeding.
Thorax Structure
- Composed of thoracic segments, each with a pair of appendages and gills.
- Individual plates articulate for flexibility, enabling defensive curling (enrolment).
- Each thoracic segment consists of two pleurae and a segment from the axis.
Thorax - Thoracic Segment
- Each segment is made up of three articulated plates.
Thorax - Pleuron
- Segment adjacent to the main axis of the thorax.
Thorax - Appendages for Movement
- Appendages facilitate locomotion or are linked to gill structures for respiration.
Dorsal Morphology
- Refers to the upper side of the organism.
Ventral Morphology
- Pertains to the underside anatomy of the organism.
Pygidium Structure
- Comprised of several fused segments, potentially with spines to stabilize the animal.
Ecdysis Process
- Similar to modern arthropods like crabs, trilobites underwent molting, where the exoskeleton couldn’t grow.
- Ecdysis results in fractures along facial sutures, facilitating the shedding process.
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Description
Test your knowledge of trilobites with these flashcards. Learn about their classification, body structure, and evolutionary history. Perfect for students studying arthropods and paleozoic life.
