Vertebrate Zoology Lecture Notes

• Architectural Pattern of an Animal, Reproduction
• Phylum Chordata
• Introduction to the subphylum Vertebrata
• The Amphibians
• The Reptile
• The Birds
• The Mammals

Architectural Pattern of an Animal, Chapter 6, 7, and 10

• Levels of organization in animal complexity
1. Protoplasmic grade of organization
   unicellular organisms such as protozoa, unicellular algae, bacteria, and unicellular fungi.
2. Cellular grade
   aggregation of cells that are functionally differentiated. Division of labor is evident (e.g. reproduction vs. vegetative growth); protozoan colonies, colonial unicellular algae such as Volvox spp., and some lower invertebrates such as metazoans (sponges).
3. Cell-tissue grade
   aggregation of similar cells into definite patterns or layers, thus becoming a tissue (e.g. jellyfish).
4. Tissue-organ grade
   aggregation of tissues into organs (e.g. flatworms).
5. Organ-system grade
   when organs work together to perform a related function; highest level of organization (e.g. organisms ranging from ribbon worms to vertebrates).
• Patterns of Animal Development
  Developmental terminology.

Phylum Chordata

General Chordate Characteristics

1. deuterostomate embryo development
2. eucoelomic body cavity
3. nervous system most highly-developed of all animal phyla (central nervous system of brain and dorsal, tubular nerve cord)
4. all other systems, usually very well developed (organ / system level of complexity)

Four key chordate characteristics

All animals of the phylum Chordata must have during all or part of their developmental life cycle the following:

1. Notochord - a slender rod of cartilage-like connective tissue lying near the dorsal side of the body and extending most of the length of the animal. It is regarded as an early endoskeleton and has the function of such in the protochordates. In more complex vertebrates, the notochord is present only during embryo development, not during adulthood. In some of the less complex vertebrates, the notochord persists throughout the life cycle and is found during embryo development and in adult stages.
2. Pharyngeal gill slits - a series of paired, slender openings which serve as passageways for water into the gills of many aquatic chordates and facilitates filter feeding in the protochordates. In complex vertebrates, they appear only in the embryonic stages. In many chordates, the gill slits never break through from the pharynx, but merely form pouches that have no function.
3. Dorsal tubular nerve cord - along with the brain, forms the CNS. It lies dorsal to the digestive tract and has a fluid-filled cavity in contrast to the ventral, solid nerve cord of most invertebrates.
4. Postanal tail - serves as a means of propulsion in water; may or may not persist in the adult.

Classification

• group protochordata (acrania) - the protochordates (invertebrate chordates) - lack cranium and vertebral column; sometimes referred to as the acrania group.
• Subphylum Urochordata (Tunicata), the tunicates; sea squirts, Molgula sp. - only larval forms have all chordate characteristics; adults are sessile, without the notochord and dorsal nerve chord; body enclosed in a tunic. Approx. 2,000 spp., all marine and are widely distributed in all seas from near the shoreline to deep waters; tunic contains cellulose; terminal incurrent or oral siphon at the mouth and excurrent siphon on the dorsal side; ciliated pharynx which facilitates filter feeding and movement of water through the gill slits and into an atrial cavity for gas exchange.
• Subphylum Cephalochordata, the lancelets; sea lancelet or amphioxus (sometimes Amphioxus sp., "pointed or sharp at both ends"), Branchiostoma lanceolatus, "gills and mouth"; Asymmetron sp. - notochord and nerve cord persist throughout life; lance-shaped; approx. 25 spp. in two genera of entire subphylum; 4 spp. are found in North American coastal waters; all four key chordate characteristics are present in the adult form; notochord and nerve cord are found along entire length of body and persist throughout the life cycle; wormlike to mostly fishlike (compressed laterally) in form; cilia facilitate water movement into the body and aid in filter feeding; lack a true heart; blood and water movement through the body are by peristaltic-like contractions of the body wall; the brain is a single enlarged region at the anterior end of the nerve cord; sexes are separate, fertilization is external; sometimes regarded as a degenerative member of the Chordata phylum.
• group craniata - possess a cranium and vertebral column (the vertebrates).

Subphylum Vertebrata - bony or cartilaginous vertebrae surrounding spinal cord; notochord in all embryonic stages, persisting in some of the fish; also may be divided into two groups (superclasses) according to presence of jaws.

• Superclass Agnatha (without jaw) - hagfishes and lampreys; lack true jaws and appendages.
• Class Myxini - hagfishes; mouth with four pairs of tentacles; 5 to 15 pairs of gill slits and gill pouches; partially hermaphroditic.
• Class Cephalaspidomorphi - lampreys; sucker-like mouth with teeth; seven pairs of gill slits and pouches.
• Superclass Gnathostomata (jaw mouth) - jawed fishes and all tetrapods (all other vertebrates); having jaws and, usually, paired appendages.
• Class Chondrichthyes - cartilaginous fishes such as sharks, and rays; streamlined body with heterocercal (asymmetrical dorsoventrally) tail; cartilaginous skeleton; Five to seven gills with separate openings, no operculum (covering); no swim bladder.
• Class Osteichthyes (Teleostomi) - bony fishes; primarily fusiform body but variously modified; mostly ossified skeleton; single gill opening on each side covered with an operculum; usually a swim bladder or lung.
• Class Amphibia (double life) - amphibians; Ectothermic tetrapods; respiration by lungs, gills, or through the skin; development through larval stage via metamorphosis; skin moist, containing mucous glands, and lacking scales.
• Class Reptilia (to creep) - reptiles; Ectothermic (mostly; some are endothermic) tetrapods; respiration by lungs; embryo develops within a shelled egg; no larval stage; skin dry, lacking mucous glands, and covered by epidermal scales.
• Class Aves (bird) - birds; Endothermic vertebrates with front limbs modified for flight; body covered with feathers; scales on feet.
• Class Mammalia - mammals; Endothermic vertebrates possessing mammary glands; body more or less covered with hair; well-developed brain.

Distinguishing characteristics of chordates:

1. Integument - body covering of epidermis [outer, stratified (layered) epithelium derived from the ectoderm (outermost germ layer of the gastrula from which primarily the epidermis and other associated cells and tissues are derived)] and dermis [connective tissue derived from the mesoderm (middle germ layer of the gastrula from which other connective, muscle, urinogenital, vascular, and body cavity lining (peritoneum) tissues are derived].
2. Notochord mostly replaced by the spinal column of vertebrae composed of cartilage, bone or both; distinctive endoskeleton consisting of vertebral column, cranium, rib cage, and two pairs of jointed appendages (usually).
3. Highly-developed muscle system attached to the skeleton to provide support and movement.
4. Complete digestive system ventral to the spinal column and provided with large digestive glands, liver, and pancreas.
5. Circulatory system consisting of a ventral heart of two to four chambers; a closed blood vessel system of arteries, veins, and capillaries; blood fluid containing red blood cells with hemoglobin and white blood cells.
6. Well-developed coelom (body cavity) mostly filled with the internal organs and lined by the peritoneum.
7. Excretory system consisting of paired kidneys.
8. Brain typically divided into five regions.
9. Ten or 12 pairs of cranial nerves with, usually, both motor and sensory functions; an autonomic nervous system in control of involuntary functions of internal organs.
10. Endocrine system of ductless glands scattered throughout the body.
11. Usually separate sexes; each sex containing paired gonads.
12. Body plan somewhat segmented, consisting typically of head, trunk, and postanal tail; neck present in some, especially terrestrial forms; coelom divided into a pericardial space and a general body cavity; mammals having a thoracic cavity as well.
13. Segmented muscles in an unsegmented trunk.

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