Animal Diversity: Invertebrates and Vertebrates – Study Guide

Animal Diversity: Overview

Introduction to Animal Diversity

Animal diversity encompasses the vast range of body plans, developmental patterns, and evolutionary adaptations found within the Kingdom Animalia. Understanding these differences is essential for classifying animals and tracing their evolutionary history.

• Diplontic life cycle: A life cycle in which the diploid stage is dominant; animals are primarily diploid, with gametes as the only haploid cells.

• Grades: Groups of organisms sharing a similar level of organizational complexity, not necessarily a clade.

• Body plan: The structural and developmental characteristics of an organism, including symmetry, tissue organization, and body cavities.

• Intertwining aspects of a body plan: Symmetry, number of tissue layers, presence/type of body cavity, and patterns of development.

Symmetry in Animals

• Radial symmetry: Body parts arranged around a central axis (e.g., jellyfish).

• Bilateral symmetry: Single plane divides body into left and right halves (e.g., humans, insects).

• Asymmetry: No plane of symmetry (e.g., sponges).

Reproduction and Early https://canva.link/muqdvy0v5b7vk8y

• Parthenogenesis: Development of an organism from an unfertilized egg.

• Zygote: Fertilized egg cell.

• Blastomeres: Cells resulting from early cleavage divisions of the zygote.

• Cleavage: Series of rapid mitotic divisions following fertilization.

• Blastula: Hollow ball of cells formed after cleavage.

• Blastocoel: Fluid-filled cavity within the blastula.

• Gastrulation: Process forming embryonic germ layers; establishes the basic body plan.

• Gastrula: Embryo with distinct germ layers after gastrulation.

• Archenteron: Primitive gut formed during gastrulation.

Embryonic Germ Layers and Body Cavities

• Embryonic germ layers: Primary tissue layers formed during development.

• Endoderm: Forms lining of digestive tract and associated organs.

• Ectoderm: Forms outer covering and nervous system.

• Mesoderm: Forms muscles, skeleton, and other internal organs (in triploblastic animals).

• Diploblastic: Animals with two germ layers (ectoderm and endoderm; e.g., cnidarians).

• Triploblastic: Animals with three germ layers (most animals).

• Body cavity (coelom): Fluid-filled space between digestive tract and body wall.

• Acoelomate: No body cavity (e.g., flatworms).

• Pseudocoelomate: Body cavity not fully lined by mesoderm (e.g., roundworms).

• Coelomate: True body cavity completely lined by mesoderm (e.g., annelids, vertebrates).

Developmental Patterns

• Blastopore: First opening formed during gastrulation; becomes mouth in protostomes, anus in deuterostomes.

• Protostomes vs. Deuterostomes:

  • Protostomes: Mouth develops from blastopore (e.g., mollusks, annelids, arthropods).

  • Deuterostomes: Anus develops from blastopore (e.g., echinoderms, chordates).

• Hox genes: Regulatory genes controlling body plan development along the anterior-posterior axis.

• Homeobox genes: DNA sequences found in genes that regulate development; includes Hox genes.

Evolutionary Events

• Cambrian explosion: Rapid diversification of animal body plans ~541 million years ago.

• Mass extinctions: Events causing widespread loss of species, reshaping animal diversity.

Key Concepts Table: Germ Layers and Derivatives

Germ Layer	Major Derivatives
Ectoderm	Skin, nervous system
Mesoderm	Muscles, skeleton, circulatory system
Endoderm	Lining of gut, liver, lungs

Additional info: Animal evolution began over 600 million years ago. Collagen is a key protein supporting animal cell membranes. Animal diversity increased during the Cambrian due to ecological, genetic, and environmental factors (e.g., increased oxygen, Hox gene evolution, predator-prey dynamics).

Invertebrates

Introduction to Invertebrates

Invertebrates are animals lacking a vertebral column and comprise over 95% of animal species. They display a wide range of body plans and occupy diverse ecological niches.

• Invertebrate: Animal without a backbone.

Phylum Placozoa

• Simple, flat, marine animals with few cell types.

Phylum Porifera (Sponges)

• Spicules: Structural elements providing support.

• Spongocoel: Central cavity.

• Ostia: Small pores for water entry.

• Osculum: Large opening for water exit.

• Choanocytes: Flagellated cells that generate water flow and capture food.

• Amoebocytes: Mobile cells involved in digestion and structure.

• Porocytes: Cells forming pores.

• Mesohyl: Gelatinous matrix within sponge body.

Phylum Cnidaria

• First eumetazoans (true tissues).

• Dimorphic: Two body forms: polyp (sessile) and medusa (motile).

• Incomplete digestive system: Single opening serves as mouth and anus.

• Cnidocytes: Specialized stinging cells.

• Nematocysts: Organelles within cnidocytes that discharge toxins.

• Classes: Hydrozoa, Scyphozoa, Cubozoa, Anthozoa.

• Siphonophores: Colonial cnidarians (e.g., Physalia).

• Gastrodermis: Inner tissue layer lining the gut.

• Pedalia: Muscular pads at the base of tentacles (in Cubozoa).

• Coral reefs: Structures formed by colonial anthozoans; threatened by bleaching due to climate change.

Superphylum Lophotrochozoa

• Cephalization: Concentration of sensory organs at the anterior end.

• Lophophore: Ciliated feeding structure.

• Trochophore: Larval stage with bands of cilia.

Phylum Mollusca

• Foot: Muscular structure for movement.

• Visceral mass: Contains internal organs.

• Mantle: Secretes shell.

• Gills: Respiratory organs.

• Radula: Feeding organ (absent in bivalves).

• Classes: Gastropoda (snails), Cephalopoda (octopus, squid), Bivalvia (clams).

• Planospiral vs. Conispiral: Types of shell coiling.

• Torsion: Twisting of body during development in gastropods.

• Fouling: Waste contamination due to torsion.

• Closed vs. Open circulatory system: Closed: blood in vessels (cephalopods); Open: blood bathes organs directly (most mollusks).

• Chromatophores, Iridophores, Leucophores: Pigment cells for color change in cephalopods.

• Umbo: Oldest part of bivalve shell.

Phylum Annelida

• Metamerism: Segmentation; allows specialization and efficient movement.

• Clitellum: Reproductive structure.

• Setae: Bristles for movement.

• Parapodia: Paired appendages in polychaetes.

• Classes: Polychaeta (marine worms), Oligochaeta (earthworms).

Superphylum Ecdysozoa

• Cuticle: Protective outer layer.

• Chitin: Main component of cuticle.

• Ecdysis: Molting of cuticle for growth.

• Cryptobiosis: State of extreme dormancy.

Phylum Arthropoda

• Jointed appendages: Specialized for various functions.

• Tagmata: Fused body segments (e.g., head, thorax, abdomen).

• Three body plans: Head-thorax-abdomen (insects), cephalothorax-abdomen (spiders), head-trunk (centipedes).

• Hemocoel: Primary body cavity containing hemolymph.

• Uniramous vs. Biramous appendages: Single-branched (insects) vs. double-branched (crustaceans).

• Subphylum Chelicerata: Chelicerae (feeding appendages), pedipalps, hemocyanin (oxygen transport).

• Subphylum Crustacea: Biramous appendages, carapace (protective shell).

• Subphylum Hexapoda: Insects; wings evolved from outgrowths of thoracic segments.

Superphylum Deuterostomia

• Phylum Echinodermata: Marine animals with radial symmetry as adults.

• Ossicles: Calcareous plates forming endoskeleton.

• Water vascular (ambulacral) system: Network of fluid-filled canals for movement and feeding.

• Tube feet: Extensions for locomotion and feeding.

• Madreporite: Entry point for water into vascular system.

Key Concepts Table: Circulatory Systems

Type	Description	Examples
Open	Hemolymph bathes organs directly	Arthropods, most mollusks
Closed	Blood confined to vessels	Annelids, cephalopods, vertebrates

Additional info: Coral reefs are vital marine ecosystems threatened by bleaching (loss of symbiotic algae due to warming). Flight in insects enabled access to new habitats and resources; wings likely evolved from thoracic outgrowths.

Vertebrates

Phylum Chordata

Chordates are defined by five key characteristics present at some stage of development.

• Notochord: Flexible rod providing support; becomes vertebral column in vertebrates.

• Dorsal hollow nerve cord: Develops into central nervous system.

• Pharyngeal gill slits/arches: Functions in feeding or respiration; forms parts of ear, head, and neck in terrestrial vertebrates.

• Post-anal tail: Tail extending beyond anus; may be reduced in adults.

• Endostyle: Mucus-secreting structure; becomes thyroid gland in vertebrates.

Subphyla of Chordata

• Cephalochordata (lancelets): Retain all five chordate features as adults; possess atrium and atriopore.

• Urochordata (tunicates): Adults have only pharyngeal slits and endostyle; surrounded by a tunic.

• Craniata (vertebrates): Possess a skull; includes infraphylum Vertebrata.

Major Vertebrate Innovations

• Haikouella: Early vertebrate-like fossil.

• Derived characters: Vertebral column, jaws, legs, amniotic egg.

• Agnatha (jawless fish): Lampreys; ectoparasites.

• Gnathostomes: Jawed vertebrates.

Fish

• Heterocercal, homocercal, diphycercal fins: Types of tail fin shapes.

• Class Chondrichthyes: Cartilaginous fish (sharks, rays); placoid scales; ovoviviparous reproduction.

• Osteichthyes (bony fish): Includes Actinopterygii (ray-finned) and Sarcopterygii (lobe-finned); swim bladder for buoyancy.

Tetrapods

• Amphibians (Class Amphibia): Permeable skin, vomerine teeth, metamorphic life cycle; Order Anura (frogs) with saltatorial locomotion and aposematic coloration.

• Amniotic egg membranes: Chorion (gas exchange), amnion (protects embryo), yolk sac (nutrients), allantois (waste storage).

Reptiles (Class Reptilia)

• Orders: Crocodilia, Squamata (lizards, snakes), Testudines (turtles).

• Poikilothermic/Ectothermic: Body temperature varies with environment.

Birds (Class Aves)

• Theropods: Dinosaur ancestors of birds.

• Homeothermic/Endothermic: Maintain constant body temperature.

• Pneumatic bones: Hollow bones for flight.

• Arboreal Hypothesis: Flight evolved from tree-dwelling ancestors.

• Terrestrial Hypothesis: Flight evolved from ground-running ancestors.

Mammals (Class Mammalia)

• Hair/fur, vibrissae (whiskers), mammary glands, sebaceous, eccrine, apocrine glands.

• Subclass Prototheria: Monotremes (egg-laying mammals).

• Subclass Theria: Includes Metatheria (marsupials) and Eutheria (placental mammals).

• Placenta: Organ for nutrient and waste exchange in eutherians.

Key Concepts Table: Chordate Characteristics and Fate

Characteristic	Fate in Adult Vertebrates
Notochord	Vertebral column
Dorsal hollow nerve cord	Brain and spinal cord
Pharyngeal slits	Gills, jaws, ear structures
Post-anal tail	Tail (may be reduced)
Endostyle	Thyroid gland

Thermoregulation in Vertebrates

• Poikilothermy: Variable body temperature (reptiles, amphibians).

• Homeothermy: Stable body temperature (birds, mammals); allows activity in varied environments.

Evolution of Flight in Birds

• Arboreal hypothesis: Ancestors glided from trees; evidence: climbing adaptations.

• Terrestrial hypothesis: Ancestors ran and leapt; evidence: running adaptations.

Additional info: The evolution of jaws, limbs, and the amniotic egg enabled vertebrates to exploit new habitats. Homeothermy provides metabolic advantages in cold climates.