BIOL120 Animal Diversity & Development – Lectures 3-9 Vocabulary

Lecture 3 - Animalia in Context: the Unikonta

Understanding of the diversity of the Unikonta.

Unikonta Super-group

• Definition: Large group of eukaryotes containing Amoebozoans and Opisthokonts.

• Evolutionary Significance: Shows wide diversity; multicellularity arose many times independently.

Amoebozoans

• Shared Traits: Use lobe- or tube-shaped pseudopods for movement and feeding. Mostly unicellular, but some form large multicellular or syncytial (multi-nucleated) stages.

• Mycetozoans (“Slime Moulds”): About 500 species. Alternate between feeding and fruiting-body phases. Two types: Plasmodial (single giant multinucleate cell) and Cellular (amoebae aggregate when starved). Used to study cooperation and multicellularity.

• Tubulinids: ~2400 free-living species. Feed by phagocytosis. Difflugia forms a protective silica shell.

• Archamoebae: Strictly anaerobic, lack classical mitochondria. Includes Entamoeba histolytica (causes amoebic dysentery) and Neoparamoeba perurans (causes Amoebic Gill Disease).

Opisthokonts & Immediate Relatives

• Nucleariids: Unicellular bacterivores, sister group to Fungi. Some produce silica scales.

• Fungi (high-level recap): Heterotrophs with extracellular digestion. Have sexual & asexual cycles. Exhibit radiotropism (growth stimulated by radiation).

• Major Fungal Groups: Distinguishing features of Chytrids, Zygomycetes, Glomeromycetes, Ascomycetes, and Basidiomycetes (e.g., flagellated spores, food molds, mycorrhizae, yeasts/truffles, mushrooms).

Understanding the place of Animalia in relation to other groups within Unikonta.

Kingdom Animalia in Context

• Nests within Opisthokonts alongside Fungi & Choanoflagellates.

Understanding why Choanoflagellates are the closest living relative of Animalia.

Choanoflagellates

• Morphology mirrors sponge choanocytes.

• Molecular and morphological data identify them as the closest living relatives of Animalia, important for understanding early animal evolution.

Lecture 4 - What are Animals and Animal Development

Understanding the basic characteristics of Animalia.

Kingdom Animalia in Context

• Multicellular, heterotrophic, aerobic, motile. Possess specialised tissues and organs.

• Size spectrum: From 8.5 \mu\text{m} to 30 \text{ m}.

• Approximately 1.5 million described species (≈1 million insects).

Understanding the basics of animal sexual cycle and reproduction.

Sexual Reproduction & Early Development

• \text{egg}+\text{sperm}\rightarrow\text{zygote} (fertilization).

Understanding cell division and development of the zygote.

Sexual Reproduction & Early Development

• Cleavage: Rapid cell divisions (2\rightarrow4\rightarrow8\rightarrow16…) with shrinking cell size.

• Blastula: Hollow sphere of cells; internal cavity is the blastocoel.

• Gastrulation: Inward folding forms the gastrula, establishing the primitive gut (archenteron) and blastopore, and producing germ layers.

Germ Layers & Derivatives

• Diploblastic: Two germ layers (ectoderm + endoderm).

• Triploblastic: Three germ layers (ectoderm, mesoderm, endoderm).

• Ectoderm: Develops into epidermis and nervous system.

• Mesoderm: Develops into muscles, blood, bones, reproductive, and connective tissues.

• Endoderm: Develops into gut lining and its derivatives.

Understanding the difference and significance of radial and bilateral symmetry.

Body Symmetry

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

• Radial Symmetry: Many planes of symmetry (e.g., cnidarians).

• Bilateral Symmetry: A single sagittal plane divides the body; promotes cephalisation (head development) and is often a “tube-within-tube” plan.

• Pentaradial (adult echinoderms): Five-part radial symmetry, adapted from bilateral larval ancestry.

Understanding the difference between protostome and deuterostome animals.

Protostome vs Deuterostome Development

Understanding the different types of animal skeletons.

Animal Skeletons

• Porifera: Internal skeleton of spicules (Calcium Carbonate (\text{CaCO}3) or Silica (\text{SiO}2)).

• Arthropoda: Exoskeleton of chitin + proteins.

• Echinodermata: Internal calcite endoskeleton of ossicles (test).

• Vertebrata: Mineralised endoskeleton that grows with the body; notochord replaced by a vertebral column.

Lecture 5 – Introduction to Animals

Understanding the level of organisation in animal bodies.

Levels of Organisation

• Cellular only: Porifera (Sponges).

• Tissue (diploblastic & triploblastic): Cnidaria and others.

• Organ systems: Most Bilateria (e.g., Platyhelminthes onward).

Understanding the difference between Parazoa and Eumetazoa.

Early-Branching Animal Phyla

• Parazoa: Animals without true tissues, like Porifera (sponges).

• Eumetazoa: Animals with true tissues (tissue-level organization or higher), including Cnidaria and all more complex animal phyla.

Understanding the key characteristics and diversity of Cnidaria.

Eumetazoa – Cnidaria

• Characteristics: Radial symmetry, diploblastic (two germ layers), tissue-level organization.

• Gastrovascular cavity: Single opening serves as both mouth and anus.

• Cnidocytes: Specialized stinging cells housing nematocysts (explosive harpoons).

• Dimorphic life cycle: Alternates between sessile Polyp (mouth upward) and free-swimming Medusa (mouth downward) forms.

• Major lineages: Medusozoa (jellyfish, hydrozoans), Anthozoa (anemones, corals – no medusa stage), Myxozoa (parasitic cnidarians).

Understanding key characteristics of free-living Platyhelminthes

Platyhelminthes (Flatworms) - Free-living

• Body Plan: Bilateral symmetry, triploblastic (three germ layers), acoelomate (no body cavity). Dorsoventral flattening aids diffusion.

• Organization: Organ-level integration with clear cephalisation (head development), cerebral ganglia, and sensory auricles.

• Digestion: Digestive sac with a single opening; branched gut increases surface area.

• Movement: Complex musculature (outer circular, inner longitudinal, dorsoventral fibers) allows diverse movements.

• Excretion: Protonephridia regulate water and ions.

• Reproduction: Asexual through fission/fragmentation (astonishing regeneration). Simultaneous hermaphrodites with complex mating behaviors (e.g., “penis fencing”).

• Class: Turbellaria (mostly free-living flatworms).

Lecture 6 – Worms and Body Cavities

Understanding the difference types of body cavities found in animals.

Body Cavities

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

• Pseudocoelomate: Body cavity partially lined by mesoderm (e.g., nematodes).

• Eucoelomate: True coelom fully lined by mesoderm (e.g., annelids, chordates).

Understanding the diversity, adaptations and life cycles of parasitic worms

Parasitic Worms

• Platyhelminthes (Flatworms): Many parasitic classes, often with complex life cycles involving multiple hosts and adaptations like loss of gut (tapeworms) or suckers/hooks.

• Tapeworms (Cestoidea): Endoparasitic, absorb nutrients directly through body surface.

• Flukes (Trematoda, Monogenea): Endoparasitic (Trematoda) or ectoparasitic (Monogenea), often with complex life cycles involving intermediate hosts.

• Nematoda (Roundworms): Many are parasitic, infecting plants, animals, and humans (e.g., pinworms, hookworms). Have a tough cuticle for protection within hosts.

Understanding the key characteristics and diversity of parasitic Platyhelminthes.

Platyhelminthes (Flatworms) - Parasitic Classes

• Cestoidea (Tapeworms): Endoparasitic, characterized by absorption of nutrients and loss of gut.

• Trematoda (Flukes): Endoparasitic with complex life cycles, often affecting multiple hosts.

• Monogenea (Flukes): Ectoparasitic, typically on fish skin/gills.

Understanding the key characteristics and diversity of Nematoda.

Phylum Nematoda (Roundworms)

• Body Plan: Bilateral, triploblastic, pseudocoelomate; unsegmented body covered by a tough cuticle that is molted.

• Digestive System: Complete digestive tract (mouth and anus).

• Ecology: Many are parasitic (e.g., pinworms, hookworms), others are free-living in soil or water.

• Abundance: Soil nematodes are extremely abundant (e.g., 4.4\times10^{20} individuals globally).

Understanding the key characteristics and diversity of Annelida.

Phylum Annelida (Segmented Worms)

• Body Plan: Bilateral, triploblastic, eucoelomate; characterized by a segmented body (metamerism).

• Examples: Includes earthworms, leeches, and marine polychaetes.

• Systems: Possess a complete digestive tract and a closed circulatory system.

• Locomotion: Achieved through muscle contraction within individual segments.

Understanding the role and function of metameric segmentation in Annelida.

Phylum Annelida (Segmented Worms) - Metameric Segmentation

• Definition: Body is composed of repeated segments or metameres.

• Function: Allows for specialization of different body regions and provides more efficient, localized muscle contraction for movement. Each segment can operate somewhat independently, giving flexibility and control.

Lecture 7 – Arthropoda

Understanding the key characteristics and differences between different Arthropoda subphyla

Phylum Arthropoda - Core Blueprint

• Bilateral, triploblastic, segmented, eucoelomate. Characterized by an exoskeleton, jointed appendages, and tagmosis (fusion of segments into body regions).

• Success Factors: Exoskeleton, jointed appendages, and segmentation contribute to their ecological success.

Living Subphyla and Key Differences

• Chelicerata: Has 6 pairs of appendages (chelicerae, pedipalps, 4 walking legs). Breathe using book lungs/gills. Includes spiders, scorpions, mites, horseshoe crabs.

• Crustacea: Has 2\text{–}3 tagmata (body sections) and \ge3 leg pairs, often biramous (branched) limbs. Mostly aquatic.

• Myriapoda: Has many trunk segments. Divided into millipedes (2 leg pairs/segment, detritivores) and centipedes (1 pair/segment, predators).

• Hexapoda (Insecta): Body has head–thorax–abdomen, 3 leg pairs, usually 2 wing pairs. Overwhelmingly terrestrial. Extremely diverse (>$9.25\times10^5 described species). Exhibit various feeding modes and metamorphosis types (incomplete vs. complete).

• Trilobita: Entirely extinct (Cambrian–Permian).

Understanding the significance and function of the exoskeleton in Arthropod.

Phylum Arthropoda - Exoskeleton

• Significance: Provides rigid armor, leverage for muscles, a barrier against desiccation, sensory spines, and coloration.

• Architecture: Composed of an Epicuticle (thin, waxy, hydrophobic) and a Procuticle (subdivided into hardened exocuticle and flexible endocuticle).

• Limitations: Non-living, so it must be periodically shed (moulting/ecdysis), making the animal vulnerable during this time.

Lecture 8 – Mollusca and Echinodermata

Understanding the key characteristics and diversity of Mollusca.

Phylum Mollusca

• Overview: >85,000 extant species; soft-bodied, unsegmented, coelomate.

• Universal Features:

  • Muscular foot (can be modified into arms/tentacles).

  • Mantle secretes the protein–\text{CaCO}_3 shell.

  • Mantle cavity facilitates gas exchange, feeding, and locomotion.

  • Radula (rasping tongue, absent in bivalves).

Understanding the key characteristics and differences between different Mollusca classes

Phylum Mollusca - Classes & Adaptations

• Polyplacophora (Chitons): Has 8 dorsal shell plates for flexibility. Marine grazers.

• Gastropoda (Snails, Slugs, Nudibranchs): Found in all habitats; exhibit torsion (visceral mass rotated 180^{\circ}).

• Bivalvia (Clams, Oysters, Scallops): Have two lateral valves, large mantle cavity, and ciliated gills for suspension feeding.

• Cephalopoda (Octopus, Squid, Cuttlefish, Nautilus): Highly active predators; foot transformed into tentacles. Use jet propulsion, ink, and chromatophores. Have internal/reduced shells (or absent). Exhibit complex learning and problem-solving (largest brain-to-body ratios).

Understanding the key characteristics and diversity of Echinodermata.

Phylum Echinodermata

• Overview: Marine deuterostomes with an internal calcite endoskeleton made of ossicles (test).

• Water Vascular System: A unique hydraulic system (madreporite \rightarrow radial canals \rightarrow tube feet) for locomotion, adhesion, feeding, and gas exchange.

• Symmetry: Bilateral larvae metamorphose into adults with pentaradial (five-part radial) symmetry.

Understanding the key characteristics and differences between different Echinodermata classes

Phylum Echinodermata - Main Classes

• Asteroidea (Sea Stars): Arms radiate from a central disc; tube feet with suckers. Carnivores or scavengers, known for regeneration.

• Ophiuroidea (Brittle/Basket Stars): Distinct central disc; long flexible arms. Diverse feeders (>$2000 spp.).

• Echinoidea (Sea Urchins & Sand Dollars): Urchins have a globose test and spines; sand dollars are flattened and burrowing. Larvae can clone themselves.

• Crinoidea (Sea Lilies & Feather Stars): Up to 700 arms, tube feet lack suckers. Sea lilies are stalked, feather stars are free-living.

• Holothuroidea (Sea Cucumbers): Elongated body, reduced skeleton. Defend via evisceration or sticky Cuvierian tubules.

Understanding the significance of pentaradial symmetry and the water vascular system in Echinodermata.

Phylum Echinodermata - Significance of Key Features

• Pentaradial Symmetry: The five-part radial symmetry in adult echinoderms is an adaptation for their sessile or slow-moving lifestyle, despite their larvae being bilaterally symmetrical.

• Water Vascular System: This unique system (madreporite, radial canals, tube feet) is crucial for their locomotion, adhesion to surfaces, feeding, and gas exchange. It is a defining characteristic of the phylum.

Lecture 9 – Chordata

Understanding the key characteristics and diversity of Chordata.

Phylum Chordata

• Basic Traits: Deuterostome, bilateral, coelomate, triploblastic.

• Four Diagnostic Characters (present at some stage of development):

  • Notochord: Flexible axial rod, becomes vertebral column in vertebrates.

  • Dorsal hollow nerve cord: Forms brain anteriorly, protected by cranium in craniates.

  • Pharyngeal slits: Used for filter feeding, develop into gills or ear/Eustachian tube derivatives.

  • Post-anal tail: Used for propulsion; can be modified or reduced.

Understanding the key characteristics and differences between different invertebrate chordates and vertebrate chordates.

Invertebrate Chordates (Basal Lineages)

• Urochordata (Tunicates): Larval stage has chordate traits; sessile adult filter-feeds, encased in a tunic.

• Cephalochordata (Lancelets): Retain all four chordate traits throughout life; a model for ancestral chordate morphology.

Vertebrate Chordates (Craniata / Vertebrata)

• Defining Features: Notochord mostly replaced by articulated vertebrae. Dorsal nerve cord protected by vertebral column. Endoskeleton grows with body. Paired appendages. Epidermis + dermis with specialized glands and sensors.

Understanding the key characteristics and differences between different Vertebrate classes

Craniata / Vertebrata - Evolutionary Milestones & Examples

• Head (cranium): Concentrated sense organs.

• Vertebral column: Enhanced body support and flexibility.

• Jaws (from gill arches): Efficient predation, diverse feeding niches.

• Mineralised skeleton: Stronger support, teeth.

• Lungs / swim bladder: Air breathing & buoyancy control (e.g., Devonian hypoxia led to lung out-pockets).

• Lobed fins: Muscular limb precursors.

• Tetrapody: Terrestrial locomotion (e.g., Tiktaalik intermediary showed fish fin rays + weight-bearing limb bones).

• Amniotic egg: Embryonic independence from water.

• Lactation & hair (mammals): Nourishment & endothermic insulation.

• Notable ancient forms: Dunkleosteus (early jawed placoderm) had bite forces >8000 psi.

Major Living Vertebrate Groups (abridged)

• Actinopterygii (ray-finned fishes): >32,000 species, most diverse vertebrate class.

• Amphibia: Moist skin respiration, aquatic larvae, metamorphosis.

• Reptilia (incl. birds): Amniotic eggs, keratin scales/feathers. Birds have pneumatized skeleton, air-sacs, endothermy.

• Mammalia: Hair, mammary glands, heterodont dentition, three middle-ear ossicles from jaw bones.

Metabolic Strategies

• Ectothermy: Low metabolic cost, relies on external heat.

• Endothermy: High metabolism, internal heat generation; requires efficient four-chambered heart and specialized lungs/air sacs.