Lecture 16 Flashcards
Meaning of arthopods
Joint foot
Name 5 phyla of arthropoda
Trilobitomorpha
Crustacea
Chelicerata
Myriapoda
Insecta
Arthropods external characteristics
Body with bilateral symmetry, divided in a few or many segments (metameres) that make up specialized groups of body parts (tagmata)
Jointed appendages/limbs
Chitinous external carapace (exoskeleton)
Successive moults during growth
Abandoned exoskeletons
Exuviae
Exoskeleton advantages
Led to arthropods’ success
Physical and chemical barrier
Protection of body and appendages
Anchors muscles
Term for successive moults
Ecdysis
Arthropods internal features
Triploblastic metaozoans (3 embryonic cell layers) –> Segmentation of internal organs
Internal fertilisation
High level of evolution
Compound eye
Several small lenses
Arthropods shared features
3 distinct body parts
Anterior = head
Median = thorax
Posterior = abdomen (pygidium/telson)
Trilobites environment
Exclusively marine
Trilobites stratigraphic range
Early Cambrian-Permian
Trilobite morphology
Body divided in 3 lobes: left pleural lobe, axial lobe, right pleural lobe
Cephalon
Thorax
Pygidium
Trilobite ecology
Strictly marine - benthic (epifaunal or infaunal), nektonic, or planktonic
Hunters, scavengers, and grazers
Trilobite stratigraphy
Cambrian-Permian
Important feature in cephalon of trilobites
Sutures –> weaker zones; moulting
What are the oldest known visual organs in the fossil record?
Trilobite eyes
Radially placed calcite lenses
What are most trilobites in terms of their thorax?
Polymerids (several thoracic segments)
Evolutionary features of trilobites
Enrollment
Development of spines
Gigantism
Where was the largest specimen of trilobite discovered? Name? Year?
Manitoba
Isotelus rex
1998
