Ancestral Colonial Protist

figure 32-4

The palm spider, Nephila sp., is an arthropod, with a segmented body and body parts specialized for trapping, killing, and eating its prey.

figure 32-4

The palm spider, Nephila sp., is an arthropod, with a segmented body and body parts specialized for trapping, killing, and eating its prey.

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www.scilinks.org Topic: Vertebrates Keyword: HM61602

www.scilinks.org Topic: Vertebrates Keyword: HM61602

Invertebrates

Invertebrate body plans range from the absence of body symmetry and true tissues, as is found in sponges, to bilateral symmetry and specialized body parts found in arthropods, such as the spider shown in Figure 32-4. Invertebrates do not have a backbone. Invertebrates make up the greatest number of animal species.

Chordates

The name chordate (KAWR-DAYT) refers to animals with a notochord, a firm, flexible rod of tissue located in the dorsal part of the body. At some stage in development, all chordates have a notochord, a dorsal nerve cord, pharyngeal pouches, and a postanal tail. The dorsal nerve cord is a hollow tube above the notochord. Pharyngeal (fuh-RlN-jee-uhl) pouches are small outpockets of the anterior digestive tract. The postanal tail consists of muscle tissue and lies behind the posterior opening of the digestive tract. A few chordates retain their early chordate characteristics all their lives. In most vertebrates, a subphylum of the chordates, the dorsal nerve cord develops into the brain and the spinal cord, and the notochord is replaced by the backbone. In aquatic vertebrates, the pharyngeal pouches have evolved into gills for breathing.

Although vertebrates are only one small subphylum of animals, they merit discussion from a human perspective. Humans are vertebrates, and the ecology of humans includes extensive interaction with other vertebrate species.

Careers in BIOLOGY

Veterinarian

Job Description Veterinarians are doctors who are trained to protect the health of animals, such as pets and livestock. Some veterinarians also protect animals and people from the diseases that they each carry.

Focus on a Veterinarian

Dr. Jack Walther grew up on a ranch, so animals were always part of his life. Today, Dr. Walther practices two days each week in a veterinary practice with another veterinarian. When he arrives each day, animal patients who have experienced overnight injuries or illnesses are already waiting. Dr. Walther handles these emergencies. He also sees patients with appointments for vaccinations, surgical follow-ups, exams, and other routine needs. Dr. Walther emphasizes that a veterinarian's role extends beyond just treating the family pet. "Vets also work to conserve animal resources; for example, they help study and preserve endangered species in Africa." Veterinarians are also at the forefront in protecting animals and people against diseases, such as Lyme disease and West Nile virus. "As a vet, you help not only the animal world, but also humanity."

Education and Skills

• High school—three years of science courses and four years of math courses

• College—bachelor of science including course work in biology, mathematics,

chemistry, and physics; four years of additional schooling to earn doctor of veterinary medicine (D.V.M.) degree Skills—self-motivation, curiosity, patience, ability to work independently, ability to work with animals

For more about careers, visit go.hrw.com and type in the keyword HM6 Careers.

For more about careers, visit go.hrw.com and type in the keyword HM6 Careers.

(a) NO SYMMETRY

(b) RADIAL SYMMETRY

(c) BILATERAL SYMMETRY

figure 32-5

(a) NO SYMMETRY

(b) RADIAL SYMMETRY

(c) BILATERAL SYMMETRY

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