Arthropods Flashcards
Largest living phylum
Arthropods
Arhropods
Largest living phylum. About 75% of all described species.
+external skeleton
+Exoskeleton periodically shed to allow growth
+segmented
+metameric
+jointed apendages
Major groups of arthropods.
Crustacea (crabs, shrimp barnacles)
chelicerate (spiders, scorpions, horsehow crabs.)
Hexapodas (insects)
Trilobita (trilobites)
Fossil Record of Trilobites
Early Cambrian-Permian. About 75% of all cambrian species are trilobites. Carbiniferous-Permean they are pretty much all gone. Completely exctinct during the end of the Permean.
Class Trilobita
Mostly benthic mobile deposit feeders or predators. Some are filter feeders, and there are a few pelagic. Calcitic exoskeleton. 3 lobe division laterally.
Pydigium
Tail section (segments that fuse together)
Thorax
Body section
Cephalon
Head sections (segments that fuse together)
Librigena
“free cheeks”
Glabella
Internal organs of trilobites are found here.
Biramous apendages
2 branches (ex-trilobites)
Trilobite eyes
The lenses are part of the skeleton-pure calcite. Most have compound (many lensed) eyes, some are blind
Holochroal
Fewer, larger separated lenses in eyes.
Protapsid
Larval stage of trilobite. Composed of unarticulated exoskeleton yields
Meraspid
Body with 2 or more articulated segments usually one or two articulated thoractic segments added to the body of the growing trilobite during each molt.
Holapsid
Stage in trilobite growth. Number of thoracic segments reaches no further. They just grow bigger.
Trilobite lifestyles
mostly epifaunal, some infaunal ,some pelagic
Pelagic trilobites
Much smaller with much bigger eyes
chelicerata
Includes modern arachnids (spiders, scorpions) and horseshoe crabs, extince eurypterids (sea scorpions). Nearly all are predators. Aquatic and terrestrial. Have small grasping apendages instead of antennae. Cuticle is not mineralized.
Ziphosura
Horseshoe crab and extinct relatives. Benthic. Can burrow and swim. Eurytopic. Relatively rare as a fossil. “a living fossil”
Eurytopic
Wide environmental tolerance (ex-horseshoe crab)
Eurypterida
sea scorpion. Ordovician-permean. Diviersity peak in Silurian. Presumed to be predatory
Arachnicds
Spiders, scorpions, mites, ticks. Usually refers to terrestrial chelicerates. May be polyphyletic.
Crustacea
Crabs, lobsters, shrimps, pill bugs. Most common and diverse marine arthropod group. Mostly marine, some may be freshwater (Crayfish) or terrestrial (pillbugs). Tremendous diversity among body forms and life habits.
General morphology of Arthropods
Chitinous cuticle (may be reinforced with calcite or other material). Body broken into regions comprised of multiple segments. Two pairs of antannae. Three pairs of limbs function as mouth parts. Wide variety of limb morphology.
Cirripedia
Barnacles. Sedentary epifauna. Filter feeders and some parasites. Body protected by calcareous plates (not molted) Chitinous part of body is molted. Highly modified body plan.
Malacostraca
Shrimp, lobsters, crabs. Earliest probably crustacean is a cambrain malacostracan.
Hexapoda
Single branched (uniramous limb) 3/4 of all animal species on the planet. terrestrial and freshwater. 6 legged arthropods.
Insect
Hexapoda with body divided into head, thorax and abdomen with 11 segments on the abdomen, 3 pairs of appendages on the thorax. Many described species. Major extinction of orders at the end of the permian and then diversity increased steadily.
Myriapoda
Single unbranched limb. Centipedes. Terrestrial predator, poisonous jaw.
Millipides
calcified skeleton. 2 legs/body segment.
