Set 2: Animal Diversity/Form & Function

General characteristics of animals

Multicellular eukaryotes in a monophyletic clade that lack cell walls, possess an extracellular matrix (ECM), ingest food before digesting (heterotrophic), move under their own power at some life stage, have nerve and muscle cells (except sponges), and exhibit a diploid-dominant life cycle.

Annelida (identifying traits)

Segmented worms characterized by bristles called chaetae and lobe-like appendages called parapodia.

Arthropoda (identifying traits)

Invertebrates with segmented bodies grouped into tagmata, jointed appendages, and an exoskeleton made of chitin.

Tagmata

Prominent body regions formed by the fusion of adjacent segments, such as the head, thorax, and abdomen in arthropods.

Chordata (four diagnostic morphological traits)

Pharyngeal slits or pouches, a dorsal hollow nerve cord, a supportive notochord, and a muscular post-anal tail.

Notochord

A supportive, stiff, yet flexible rod that extends along the length of the body in chordates.

Cnidaria (identifying traits)

Radially symmetrical diploblasts characterized by a gastrovascular cavity with a single opening and specialized cells called cnidocytes.

Cnidocyte

A specialized cell found in cnidarians that ejects a barbed, venomous structure for prey capture and defense.

Echinodermata (identifying traits)

Marine deuterostomes with bilateral symmetry as larvae, five-sided radial symmetry as adults, an oral/aboral body orientation, and an endoskeleton of calcium carbonate.

Mollusca (three primary body components)

The muscular foot (locomotion, digging, or tentacles), the visceral mass (contains internal organs), and the mantle (covers visceral mass and secretes shell).

Mantle (Mollusca)

A specialized fold of epidermal tissue in mollusks that covers the visceral mass and secretes the protective calcium carbonate shell.

Nematoda (identifying traits)

Roundworms characterized by an unsegmented body, absence of appendages, and a pseudocoelom.

Platyhelminthes (identifying traits)

Acoelomate flatworms with broad, flattened bodies lacking specialized organs for gas exchange or nutrient circulation.

Internal fertilization

The union of sperm and egg occurring directly inside the female reproductive tract.

External fertilization

The release and union of sperm and eggs outside the bodies of the parents, typically taking place in an aquatic environment.

Gastrulation

The developmental phase during which cell movements rearrange the early embryo into three distinct primary germ layers.

Ectoderm

The outermost embryonic germ layer that develops into the skin and nervous system.

Endoderm

The innermost embryonic germ layer that develops into the lining of the digestive tract and organs connected to it.

Mesoderm

The middle embryonic germ layer that develops into the circulatory system, muscles, bones, and most internal organs.

Ecdysozoans

A protostome lineage characterized by intermittent growth achieved through the shedding (molting) of an exoskeleton or cuticle.

Ecdysone

The steroid hormone that regulates the molting process in ecdysozoans.

Vertebrata (diagnostic skeletal traits)

Chordates possessing a protective cranium enclosing the brain and a vertebral column of cartilage or bone.

Lophotrochozoans

A protostome lineage characterized by incremental growth, with taxa commonly possessing a lophophore for feeding and/or a trochophore larval stage.

Lophophore

A specialized ring of ciliated tentacles surrounding the mouth that functions in suspension feeding.

Trochophore

A distinct, free-swimming larval type encircled by a central band of cilia used for locomotion and feeding.

Porifera (sponges)

Benthic, sessile animals that lack true tissues, body symmetry, nerve cells, and muscle cells.

Protostome

A major bilaterian lineage in which the mouth develops before the anus during embryonic gastrulation.

Deuterostome

A major bilaterian lineage in which the anus develops before the mouth during embryonic gastrulation.

Traits associated with bilateral symmetry

Triploblastic embryonic development, true muscle layers, a centralized nervous system, and cephalization (evolution of a distinct head).

Cephalization

The evolutionary specialization that concentrates nervous tissue, sensory receptors, and mouthparts at the anterior end of the body.

Diploblast

An animal that develops from only two primary germ layers (ectoderm and endoderm), exemplified by cnidarians and ctenophores.

Mesoglea

A gelatinous non-cellular or sparsely cellular matrix that connects the outer ectoderm and inner endoderm in diploblastic animals.

Coelom

A fluid-filled internal body cavity situated between the inner and outer body tubes that is completely lined by mesoderm-derived tissue.

Coelomate animal taxa

Phyla possessing a true coelom: Annelida, Mollusca, Arthropoda, Echinodermata, and Chordata.

Pseudocoelom

A fluid-filled internal body cavity located between the body wall and digestive tract that is only partially lined by mesoderm.

Pseudocoelomate animal taxa

Animal lineages possessing a pseudocoelom: Nematoda and Rotifera.

Acoelomate

An animal lacking an internal fluid-filled body cavity between the digestive tract and outer body wall, exemplified by Platyhelminthes.

Differences between Lophotrochozoa and Ecdysozoa

Lophotrochozoans grow incrementally and often possess lophophores or trochophore larvae; ecdysozoans exhibit intermittent growth by molting an exoskeleton regulated by ecdysone.

Metamorphosis

A developmental transition from an immature larval stage into a morphologically distinct adult form.

Incomplete metamorphosis

A developmental process where juveniles (nymphs) resemble miniature adults and gradually transition to maturity through successive molts.

Complete metamorphosis

A developmental process characterized by a distinct larval form that transitions through a pupal stage before emerging as a radically different adult.

Complete metamorphosis (evolutionary advantage)

Larvae and adults utilize different habitats and food resources, eliminating intraspecific competition and allowing specialization in feeding (larva) and reproduction/dispersal (adult).

Connective tissue

A fundamental tissue type made of cells loosely scattered within an abundant extracellular matrix of fibers and ground substance.

Loose connective tissue

A subtype of connective tissue with fibrous proteins embedded in a soft matrix that serves as packing material and padding around organs.

Fibroblast

A specialized connective tissue cell responsible for synthesizing and secreting collagen fibers and other extracellular matrix components.

Dense connective tissue

A tough connective tissue dominated by densely packed collagen fibers; forms tendons (connecting muscle to bone) and ligaments (connecting bone to bone).

Supporting connective tissue

A connective tissue type with a firm, rigid extracellular matrix that provides skeletal structure and protection, represented by bone and cartilage.

Fluid connective tissue

A specialized connective tissue consisting of cells suspended in a liquid extracellular matrix, represented by blood and its plasma matrix.

Nervous tissue

An animal-specific tissue specialized for transmitting electrical signals, consisting of neurons and supportive glial cells.

Dendrite

A short, highly branched neuronal projection that receives electrical signals from adjacent cells and carries them toward the cell body.

Axon

A long, single neuronal projection that transmits electrical impulses away from the cell body toward target cells.

Glial cells (glia)

Supportive cells in nervous tissue that protect, nourish, and insulate neurons, including oligodendrocytes in the CNS and Schwann cells in the PNS.

Muscle tissue

An animal-specific contractile tissue responsible for locomotion, mechanical pumping of blood, and moving substances through internal tracts.

Skeletal muscle tissue

Striated, voluntary muscle tissue attached to skeletal elements that generates body movements.

Cardiac muscle tissue

Striated, involuntary muscle tissue that forms the walls of the heart and rhythmically pumps blood.

Smooth muscle tissue

Non-striated, involuntary muscle tissue lining the walls of digestive organs and blood vessels that moves food and regulates vascular pressure.

Epithelial tissue

Sheets of tightly joined, short-lived cells that cover external body surfaces, line internal organs, and form secretory glands.

Epithelial tissue polarity (apical vs. basolateral)

The apical side faces the exterior environment or internal lumen; the basolateral side faces the interior of the animal and binds to connective tissue.

Cell size effect on surface area, volume, and diffusion

As cell size increases, volume increases faster than surface area, lowering the $\text{SA}/\text{V}$ ratio and reducing the relative rate of diffusion across the membrane.

Basal metabolic rate (BMR)

The rate at which an animal consumes oxygen while at rest, in a post-absorptive (empty stomach) state, and under normal temperature and moisture conditions.

Relationship between animal body size and mass-specific BMR

Small animals have much higher mass-specific basal metabolic rates than large animals because higher $\text{SA}/\text{V}$ ratios cause more rapid relative heat and resource dissipation.

Homeostasis

The maintenance of relatively stable internal physical and chemical conditions within an organism's cells, tissues, and organs.

Homeostatic conformity

An approach where an organism allows its internal physiological state to match that of the external environment, conserving energy but limiting activity range.

Physiological regulation

An approach where an organism expends metabolic energy to maintain internal conditions at a constant set point regardless of external fluctuations.

Behavioral regulation

The adjustment of internal state through voluntary actions and posture changes, such as moving into the sun or shade.

Principle of homeostatic regulation (influx vs. efflux)

A physiological state remains regulated when influx equals efflux; regulation fails if the rate of material or energy entering does not balance the rate leaving.

Negative feedback loop

A homeostatic control mechanism in which effectors oppose the direction of a detected deviation, returning the internal state to the set point.

Set point (homeostasis)

The target value or normal physiological range established for a regulated internal variable.

Sensor (homeostasis)

A biological structure that monitors and detects internal or external environmental conditions.

Integrator (homeostasis)

A control component that compares incoming sensory information to the set point to determine whether a corrective response is necessary.

Effector (homeostasis)

A structure, organ, or gland that carries out the physiological action directed by the integrator to restore normal internal conditions.

Thermoregulation

The physiological and behavioral maintenance of internal body temperature achieved by balancing thermal influx and thermal efflux.

Physiological responses to body temperature above set point

Dilation of peripheral blood vessels to increase skin blood flow, activation of sweat glands for evaporative cooling, and panting to expel heat.

Conduction (heat exchange)

The direct transfer of thermal energy between two physical objects that are in direct physical contact.

Convection (heat exchange)

The transfer of thermal energy between a solid surface and a moving fluid medium, such as water or air currents.

Radiation (heat exchange)

The transfer of heat between two bodies that are not in direct physical contact via electromagnetic waves.

Evaporation (heat exchange)

The phase change of liquid water into water vapor, absorbing latent heat and cooling the body surface.

Metabolic heat production

Heat generated within internal tissues as an obligate byproduct of cellular respiration and biochemical reactions.

Endotherm

An organism that generates sufficient internal metabolic heat to warm its own body tissues.

Endothermy (trade-offs)

Advantage: High, sustained aerobic activity and independence from ambient temperatures. Disadvantage: Massive energetic and food consumption requirements.

Ectotherm

An organism that relies primarily on thermal energy absorbed from the external environment to govern its body temperature.

Ectothermy (trade-offs)

Advantage: Low energy demand allows greater allocation of energy to reproduction and survival on little food. Disadvantage: Activity depends on ambient temperature, reducing performance in cold.

Homeotherm

An animal that maintains a relatively constant body temperature regardless of ambient environmental fluctuations.

Poikilotherm

An animal whose core body temperature rises and falls in direct concordance with environmental temperatures.

Countercurrent heat exchange

An arrangement of adjacent blood vessels flowing in opposite directions that maintains a constant thermal gradient, allowing warm arterial blood to transfer heat to cool venous blood to minimize heat loss.