Exam II – Ch. 32 – Sheet 2

Chapter 32 – An Introduction to Animal Diversity

1 . Can you name and describe the four stages of embryonic development?

·  1) Zygote – fertilized egg

·  2) Cleavage – 8 cell stage

·  3) Cleavage (2nd) – normal cytoplasmic/nuclei ratio

- Blastula: round mass of cells

- Blastocoel: hollow pocket inside Blastula

·  4) Gastrulation – embryo folds inward at the blastopore

2. What historical phenomenon is responsible for half of all creatures alive today? What are some explanations as to why this occurred?

·  Cambrian Explosion

- predator/prey relationships

- increase in oxygen (cellular respiration)

- Hox genes (regulatory genes involved in development and spacing)

3. What are the “5 Breaks” in the evolutionary advancement of animals?

·  1st Break: Tissue Development

- Parazoa: Phylum Porifera

- Sponges

- no tissues

- do NOT follow gastrulation development

- Eumetazoa: all other Phyla

- have true tissues

·  2nd Break: Types of Symmetry

- Radial Symmetry

- Dipoplastic: 2 germ layers (ectoderm and endoderm)

- Bilateral Symmetry

- Triploplastic: 3 germ layers (ecto, endo, and mesoderm)

- most have a distinct head

- sense organs

·  3rd Break: Body Cavity Development

- Coleom: body cavity separating the digestive tract from the outer body

- place for organs (provides cushion)

- Coelomate: mesoderm lines body cavity

- Pseudocoelomate: mesoderm does not completely line body cavity

- Acoelomate: lack of a body cavity

·  4th Break: Fate of the Blastopore

- Protostome: “first mouth”

- Blastopore becomes mouth

- Determinant cleavage: determined developmental fate of each embryonic cell

- Spiral Cleavage: cells don’t line up

- Coelom forms from splits in mesoderm

- Deuterostome: “mouth last”

- Blastopore becomes anus

- Indeterminate growth: each cell retains capacity to develop into an embryo

- Radial cleavage

- Coelom forms from mesodermal folds on the archenteron

·  5th Break: Segmentation

- Segmentation: duplication and separation of segments

4.  Can you complete this table?

Phylum / Type of Body Symmetry / Type of Tissue Organization
Porifera (sponges) / Asymmetrical / Multicellular, no tissues
Cnidaria (jellies, anemones, etc) / Radial / 2 tissue layers
Ctenophora (comb jellies) / Radial / 2 tissue layers
Platyhelminthes (flatworms) / Bilateral / Acoelomates
Rotifera (rotifers) / Bilateral / Pseudocoelomates
Nematoda (roundworms) / Bilateral / Pseudocoelomates

5.  Phylum Cnidaria: (a.) Can you describe the importance of the gastrovascular cavity? (b.) What are the two forms of cnidarians that can be found? (c.) How do cnidarians get their nutrition? (d.) Can you list and describe the four classes of cnidarians?

(a.)  Cnidarians have a simple anatomy that consists of a sac-type body with a gastrovascular cavity, the place where food is brought in for digestion

(b.)  Polyp (sessile) & medusa (free-swimming)

(c.)  Have both extra- and intra-cellular digestion; actual digestion takes place in the gastrovascular cavity and then the nutrients are taken into the cells by phagocytosis

(d.)  Four classes of cnidarians:

1.  Hydrozoans

·  Alternate b/w an asexually reproducing polyp (main stage of life cycle) and a sexually reproducing medusa form; larvae are called planula

·  Adult hydras exist only in polyp form

2.  Scyphozoans (true jellies)

·  Medusa stage is dominant, and the sessile polyp stage often does not occur in the jellies of the open ocean

3.  Cubozoans (box jellies & sea wasps)

·  Have a box-shaped medusa stage and complex eyes in the fringe of their medusae

·  Many species (including the sea wasps) have highly toxic cnidocytes and are deadly

·  Sea turtles are immune to their stings, allowing them to eat cubozoans in large quantities

4.  Anthozoans (sea anemones & corals)

·  Occur only as polyps

·  Corals secrete calcified external skeletons, and the accumulation of such skeletons produces coral

·  Some have symbiotic relationships with algae (zooxanthellae)

6.  Phylum Ctenophora: Why are these animals called comb jellies, and how do they move around?

·  Called comb jellies due to their eight comb rows

·  Largest animal to use cilia for locomotion

7.  Phylum Platyhelminthes: (a.) Can you describe the structure/function of the flatworm’s gastrovascular cavity? (b.) How do gas exchange and the excretion of wastes occur in the flatworm? (c.) Can you list and describe the three classes of flatworms?

(a.)  Have a branching gastrovascular cavity that functions in both digestion and distribution of food; digestion is both extracellular & intracellular

(b.)  Gas exchange and diffusion of nitrogenous wastes occur across the body wall; Excretion is via flame cells in the protonephridia; Protonephridia – networks of tubules with ciliated flame bulbs that pull fluid out of the body and function in osmoregulation

(c.)  Three classes of flatworms:

1.  Turbellarians (planarians)

·  Eyespots on the head detect light, and lateral head flaps detect chemicals

·  Nervous system consists of pairs of anterior ganglia and ventral nerve cords

·  Reproduce asexually by regeneration or sexually by copulation b/w hermaphroditic worms

·  Capable of primitive learning

2.  Trematodes (flukes)

·  All flukes are parasites (either internal or external) – usually they are vertebrate parasites

·  Have a tough outer covering, suckers, and extensive reproductive organs

·  Complex life cycles with several hosts, usually including asexual & sexual stages

3.  Cestodes (tapeworms)

·  Tapeworms are vertebrate parasites and absorb predigested food from their host’s intestinal lining

·  Scolex – head region that has suckers & hooks for attaching to a host’s intestinal lining

·  Proglottids – body region consisting of repeating packets of reproductive organs

·  Life cycles often include multiple hosts

8.  Phylum Rotifera: (a.) Why are rotifers called cell-constant animals? (b.) How do rotifers reproduce?

(a.)  Cell constant animals – all members of the same species have the same number of cells; Once a cell is lost, it is not replaced by mitosis

(b.)  Can reproduce using parthenogenesis (eggs develop w/out being fertilized by sperm); there are significantly more females present in rotifer populations

9.  Phylum Nematoda: (a.) What type of muscles do roundworms have, and how does that affect their movement? (b.) Can you describe how the Trichinella and Ascaris parasites affect their respective hosts?

(a.)  Roundworms have longitudinal muscles and a hydrostatic skeleton; this makeup allows for simple movements only

(b.)  Parasite mechanisms:

·  Ascaris worms – get into intestines and burrow into lymphatic & circulatory system; get into the heart and lung alveoli; cough them up and then re-swallow the worms (returning them to the intestine)

·  Trichinella – parasite obtained from undercooked pork; larvae encyst in muscle