Lewis/Life - Review of Key Concepts

Review of Key Concepts - Chapter 26

Animals are eukaryotic, multicellular heterotrophs whose cells do not have cell walls. More than 1 million animal species are known, most of them invertebrates. The oldest animal fossils date from about 700 million years ago. Animals may have descended from colonial and/or multinucleate protista.
Animals differ in development and body form. Distinguishing characteristics include number of primary germ layers (diploblastic or triploblastic), presence and type of body cavity (coelomate, acoelomate, and pseudocoelomate), and body symmetry (radial symmetry, with oral and aboral ends, or bilateral symmetry, with cephalization).
Animals undergo direct development or metamorphosis. Several major lineages of coelomates differ in development patterns. Protostomes exhibit spiral cleavage, a blastopore developing into a mouth, and determinate cleavage. Deuterostomes have radial cleavage, a blastopore developing into an anus, and indeterminate cleavage.
Sponges (phylum Porifera) are sessile and draw in food through pores and water canals. Their amoebocytes have a variety of functions. Sponge skeletons may consist of spongin or spicules. They may bud asexually using gemmules, or reproduce sexually.
Cnidaria (phylum Cnidaria) capture prey with stinging nematocysts. Cnidaria include jellyfish, corals, and Portuguese men-of-war. They have radial symmetry, are diploblastic, digest extracellularly, and occur in polyp or medusa forms.
Most flatworms (phylum Platyhelminthes) are parasitic and have great reproductive capacity. They are triploblastic, lack coeloms, and have bilateral symmetry. Protonephridia maintain internal water balance. Flatworms reproduce asexually and sexually, and some are hermaphrodites.
Roundworms (phylum Nematoda) include parasites and free-living species in soil or aquatic sediments. They are cylindrical and segmentless and have complete digestive systems and separate sexes.
Phylum Mollusca, the second largest phylum, includes diverse animals that have a shell, foot, and visceral mass and complex organ systems. They are protostomes with bilateral symmetry and have trochophore larvae. Gastropods and cephalopods are mollusks. Sexes are separate.
Phylum Annelida, the segmented worms, includes oligochaetes, characterized by setae bristles and covered with a clitellum; polychaetes, with parapodia as appendages; and the hirudinea, which are leeches with annuli between their segments. Annelids feed in diverse ways and have organ systems. Leeches and oligochaetes are hermaphroditic; polychaetes have separate sexes.
Phylum Arthropoda is the largest phylum. Arthropods are protostomes with bilateral symmetry, and they are segmented with jointed appendages and a chitinous exoskeleton. They have open circulatory systems, spiracles to respire, and a nervous system. Four subphyla include trilobites, horseshoe crabs and arachnids, crustaceans, and insects and myriapods.
Phylum Echinodermata includes spiny-skinned marine animals with pentaradial symmetry that move using water vascular systems with tube feet. Early development is similar to that of chordates.
All chordates (phylum Chordata) share four characteristics at some stage of their life cycle: a dorsal tubular nerve cord, a notochord, pharyngeal gill slits, and a postanal tail. Subphylum Cephalochordata includes the lancelets and subphylum Urochordata the tunicates, both primitive invertebrates. Subphylum Vertebrata includes superclass Agnatha (jawless fishes) and superclass Gnathostomata (jawed fishes and tetrapods).
Class Mammalia includes monotremes, marsupials, and placental mammals, distinguished by how young are carried. Humans belong to order Primates.