BIO104 Chapter 7 Laboratory Study Guide: Animal Diversity I

Introduction to Animal Diversity and Characteristics

• Animals are defined as multicellular organisms composed of many different cell types, typically organized into distinct tissues.
• These tissues consist of highly differentiated cells that perform specialized functions.
• Animals are characterized as extremely efficient consumers with several key derived evolutionary traits that contribute to their adaptive success:     - Heterotrophy: Animals are heterotrophic, meaning they obtain nutrients by consuming other organisms or non-living organic material.     - Embryonic Tissue Layers: Animals possess tissues (ectoderm, endoderm, and mesoderm) that form during embryonic development.     - Internal Processing: Food is often processed internally through highly evolved and complex digestive systems.     - Motility: Animals are motile, possessing the ability to move, detect, and catch prey for consumption and digestion.

Embryonic Development and Tissue Differentiation

• Despite morphological diversity, animals share significant similarities in development.
• Cleavage: After fertilization, the zygote undergoes cleavage, a series of mitotic divisions, to form a blastula.
• Blastula: A hollow, ball-like structure containing an internal cavity called the blastocoel.
• Gastrulation: The process where an invagination forms at one end of the blastula, creating a blastopore.
• Archenteron: The new internal cavity formed during gastrulation; the original blastocoel becomes reduced and moved toward the outer region of the gastrula.
• Germ Layer Differentiation:     - Ectoderm: The outermost layer; differentiates into the outer covering of the animal (epidermis) and the nervous system.     - Endoderm: The innermost layer; differentiates into the lining of the digestive system and specific organs such as the lungs and liver.     - Mesoderm: The middle layer (when present); differentiates into muscle, blood vessels, cartilage, connective tissue, reproductive structures, kidneys, the heart, and endocrine glands.
• Tissue Complexity:     - Diploblastic: Animals containing only two tissue types (endoderm and ectoderm), such as cnidarians.     - Triploblastic: Animals containing all three embryonic tissues (ectoderm, endoderm, and mesoderm), such as flatworms, arthropods, and vertebrates.

Body Cavities and Classifications

• Coelom: A fluid-filled body cavity lined with mesoderm.
• True Coelom: A cavity fully enclosed by mesoderm cells. These cells eventually differentiate into muscles surrounding the digestive system, allowing for the contraction and propulsion of material, which increases the efficiency of nutrient extraction.
• Metazoans: All animals are metazoans, characterized by specialized, multicellular eukaryotic cells.
• Parazoans: Animals that do not possess true tissues but contain groups of differentiated cells (e.g., sponges/Phylum Porifera).
• Eumetazoans: Animals comprised of true tissues with specialized cells; this group includes both diploblastic and triploblastic organisms.
• Body Symmetry:     - Radial Symmetry: Common in sessile or planktonic animals (e.g., corals, jellyfish).     - Bilateral Symmetry: Characterized by distinct anterior, posterior, dorsal, and ventral sides; common in mobile animals (e.g., arthropods, mammals).     - Asymmetry: No distinct body plan (e.g., sponges).

Developmental Patterns: Protostomes vs. Deuterostomes

• Protostomes:     - The blastopore develops into the mouth.     - The mesoderm splits into two masses on either side of the blastopore to form the coelom.     - The digestive tube eventually forms the anal opening at the opposite end of the gastrula.     - Represented by Lophotrochozoans (annelids, molluscs, flatworms) and Ecdysozoans (nematodes, arthropods).
• Deuterostomes:     - The blastopore develops into the anal opening.     - Mesoderm cells aggregate in two masses near the top of the archenteron and form outpockets to create the coelom.     - The digestive tube pushes through to form the mouth at the opposite end.     - Represented by hemichordates, echinoderms, and chordates.

Phylum Porifera (Sponges)

• General Characteristics: Known as "pore bearers," sponges are asymmetric and lack true organized tissues or organs.
• Structure:     - Osculum: A large opening at the top of the sponge where water exits.     - Spongocoel: The central hollow cavity (not a true coelom).     - Mesohyal: A gelatinous, non-cellular layer between two cell layers that acts as an endoskeleton. It is hardened by mineral spicules, spongin fibers, or both, providing support and protection.
• Specialized Cells:     - Choanocytes (Collar Cells): Line the inner surface; possess a single flagellum surrounded by a cylindrical collar. The whip-like motion of the flagellum drives water through the body.     - Amoebocytes: Motile cells in the inner layer responsible for digestion, nutrient absorption, and reproduction.
• Water Flow: Water and food particles enter through pores in the body wall, move into the spongocoel (or canals in complex sponges), and exit through the osculum.

Phylum Cnidaria (Hydra)

• General Characteristics: Small, freshwater animals with radial symmetry, stinging tentacles, and an incomplete digestive system. They lack a coelom.
• Tissue Structure: Diploblastic (epidermis derived from ectoderm; gastrodermis derived from endoderm) separated by a jelly-like matrix called the mesoglea.
• Feeding and Response:     - Nematocysts (Cnidocytes): Stinging structures used to capture prey.     - Gastrovascular Cavity: A central cavity where food is digested and waste is eliminated through the same opening.     - Nerve Net: A non-centralized system that detects and responds to stimuli from all directions.
• Life Stage: Hydra only exists in the polyp stage; it lacks a medusa stage.

Phylum Platyhelminthes (Planaria)

• General Characteristics: Triploblastic, acoelomate (lacks a body cavity), and bilaterally symmetrical flatworms found in marine, freshwater, and terrestrial habitats.
• Anatomy:     - Eyespots: Located at the anterior end; detect light intensity variations to help the organism move toward dark habitats.     - Gastrovascular Cavity: Highly branched to support all cells nutritionally; possesses only one opening.     - Pharynx: A tube used to take in food particles and eliminate waste.
• Movement: Driven by two main structures (cilia and muscular contractions, as indicated in context).

Phylum Arthropoda (Crayfish)

• General Characteristics: Part of the clade Ecdysozoans; triploblastic, bilaterally symmetrical, and segmented.
• Exoskeleton: Made of chitin and called a carapace. It provides protection and muscle attachment but must be shed via molting to allow growth.
• Body Regions:     - Cephalothorax: The fused head and thorax.     - Abdomen: The posterior segmented region.
• Appendages:     - Head: $2$ antennae, $4$ antennules (sensory), mandibles, $2$ pairs of maxillae, and $3$ pairs of maxillipeds (feeding).     - Thorax: $5$ pairs of walking legs. The first pair, the cheliped, is modified for defense and food capture.     - Abdomen: $5$ pairs of swimmerets, a central telson (tail), and $2$ uropods.
• Respiration: Gills located in gill chambers under the carapace; swimmerets circulate water over them.
• Sexual Dimorphism: Males have modified copulatory swimmerets; females have an oviduct opening and a seminal receptacle.

Anatomical Terminology and Body Planes

• Frontal Plane: Separates the body into Dorsal (back/top) and Ventral (belly/bottom) regions.
• Transverse Plane: Runs perpendicular to the long axis, separating the body into Cranial (anterior/head) and Caudal (posterior/tail) regions.     - Rostral: Toward the nose or beak.
• Sagittal Plane (Median Plane): Separates the body into left and right sides along the midline.     - Medial: Toward the midline.     - Lateral: Away from the midline.     - Proximal: Nearer to the midline/point of attachment.     - Distal: Farther from the midline/point of attachment.

Dissection Procedures and Safety

• Safety Protocols:     - Specimens are preserved in formaldehyde. Gloves and goggles must be worn at all times.     - Do not touch personal belongings or skin with contaminated gloves.     - Dispose of scalpels and T-pins in the Red Sharps Waste container.     - Dispose of tissue waste in the Specimen Waste Drum and liquid waste in the designated waste bottle.
• Tools: Fine-end and blunt-end scissors, fine forceps (straight/curved), straight and curved needles, Huber Mall probe, dropping pipet, and scalpel.
• Fetal Pig Dissection Preparation:     - Secure the specimen to the tray using twine tied around limbs.     - Initial Incision (Cut 1): From the base of the umbilical cord cranially along the ventral midline to the chin.     - Identify the diaphragm (muscular obstruction near the ribs).     - Provide lateral cuts around the umbilical cord (based on sex), abdomen, ribs, and neck to expose internal structures.     - Fetal pigs are double-injected: red latex for the arterial system and blue latex for the systemic (venous) system.
• Cleaning: All tools and trays must be cleaned with Alconox and dried thoroughly to prevent rust or mold.