BIOL172 Exam 2: Ecdysozoa

Ecdysozoa

Nematoda (roundworms), Tardigrada (tardigrades), Arthropoda (arthropods) --> Monophyletic group

Cuticle / exoskeleton

Exoskeletal molting

Ecdysis: outer cuticular layer

Cryptobiosis

A state in which an animal's metabolic activities come to a reversible standstill

Nematoda

Roundworms

Cylindrical body form (round bodies)

Triploblastic

Bilaterally symmetrical

Pseudocoelomates

Free-living and parasitic forms

Epidermis with one cell layer or a syncytium

Cuticle: collagen + chitin

External rings do not reflect true internal body segmentation

Rennette cells

- excretory cells

Nervous system

- 4 longitudinal nerve cords (ventral better developed)

- Pharyngeal nerve ring: nerve cells fusion around pharynx

Reproduction

- monoecious, dioecious, parthenogenetic (asexual through unfertilized eggs)

- hermaphrodites: ova and sperm develop at different times in same gonad

- dioecious: internal fertilization)

Tardigrada

Slow-steppers, water bears

Inconspicuous, cylindrical bodies

Marine, freshwater, or damp terrestrial environments

Chitinous cuticle

Cryptobiosis (dormant stage)

- survive the loss of up to 99% of their water content

Mouth, muscular pharynx, and salivary glands

Dioecious, external fertilization

Arthropoda

Jointed feet

85% of all known species

Terrestrial, aquatic, and aerial habitats

Eucoelomates

Protostome organisms

Chitinous exoskeleton

Jointed appendages

Body segmentation

Molting followed by ecdysis

Ecdysis

Shedding of exoskeleton

Arthropoda Subphyla

Trilobita

- all extinct

Chelicerata

- horseshoe crabs, spiders, scorpions, ticks, mites, daddy long legs / harvestmen

Myriapoda

- millipedes, centipedes, relatives

Crustacea

- crabs, lobsters, crayfish, isopods, barnacles, some zooplankton

Hexapoda

- insects and 6-legged relatives

Arthropoda Morphology

Tagmata

- head, thorax, abdomen

- cephalothorax and abdomen

- head and trunk

Appendages

- often in segmental pairs

- antennae (sensing their environment)

- mandibles and maxillae (capturing and manipulating food)

- for walking, jumping, digging, swimming

Hemocoel: blood cavity, hemocoel liquid

N excretion

- green glands in crustaceans

- Malpighian tubules in insects

Arthropoda Nervous System

Nervous cells in all segments, larger ganglia in segments with sensory structures, ganglia connected by ventral nerve cord

Arthropoda Respiratory System

Tracheae: insects and myriapods

Gills: crustaceans

Book lungs: terrestrial chelicerates

Book gills: aquatic chelicerates

Arthropoda: Chelicerata

Chelicerae: segmented clawlike or fanglike mouthparts

Terrestrial, some aquatic (freshwater and marine)

Dioecious: internal and external fertilization

Parental care present or absent

Two tagmata: prosoma and opisthosoma

No antennae (pedipalps sense environment)

Hemolymph contains hemocyanin

Nervous system: brain and 2 ventral nerve cords

Arthropoda: Myriapoda

Numerous legs

Chilopoda: centipedes

Pair of legs per segment

Mandibles as mouthparts

Dorsoventrally flattened

Predators

Legs in the first segment are modified to form poison claws (forcipules)

Arthropoda: Crustacea

Marine and terrestrial

Open circulatory system

Hemolymph contains hemocyanin and hemoglobin

Most dioecious

Arthropoda: Hexapoda

6 legs

Tagmata: head, thorax, abdomen

Metamorphosis