What happened in the Cambrian period?
First appearance of shells, hard skeletons, emergence of predators.
are precisely placed in both endoskeletons and exoskeletons for movement of seaments relative to one another.
Predatory mollusks dominated during the --------- era, and included ancient Ammonites.
Major groups of animals with hard body parts:
Mollusks - one or two external shells. Arthropods - jointed exoskeleton. Echinoderms - endoskeleton of plates. Vertebrates - endoskeleton of bones.
The Mollusks evolved from
worm-like creatures that developed a hard shell made primarily of calcium carbonate.
the shell is segmented.
Clams feed by
filter-feeding via a siphon system, and have a strong foot for digging and ''hopping''.
a single, spiral shell, and rasping radulas for feeding.
are primitive Cephalopods with shells similar to Gastropods.
have segmented bodies, jointed appendages, and an exoskeleton made of chitin. The rigid exoskeleton must be shed and replaced periodically as the animal grows.
Each segment of a Crustacean has a pair of
sessile, filter-feeding Crustaceans.
How do animals with hard coverings grow?
In an open circulatory system,
blood flows out into the sinuses then bathe the internal organs. (Grasshopper)
A closed circulatory system
has blood entirely contained in arteries and veins. (worms)
The excretory of many Crustaceans consist of a
kidney-like antennal gland connected to a bladder-like sac.
spines emerge from the plate-like endoskeleton, along with gills and scissor-like pedicellaria.
A feather star
(crinoid) is sessile and its mouth and anus face upward.
Echinoderms show a
nearly radial symmetry; most have a tough, spine-covered skin; sea stars are predatory.
Sea cucumbers are
soft-bodied, and have tube feet around the mouth modified as feeding tentacles.
Transitions in animal life:
prokaryote to eukaryote. Colonial to Multicellular. Multicellular to Diploblastic. Diploblastic to Triploblastic. Radial to bilateral symmetry. Gastrovascular cavity to Tube-within-a-tube. Worm to animal with skeleton, legs or fins. Aquatic to terrestrial environment.