Opistokonts, Fungi, Animals & Arthropods: Key Concepts and Structures

Opisthokonts

Fungi + animals + choanoflagellates; fungi are sister to animals/choanoflagellates.

Mycelium

Body of multicellular fungus; high surface area to volume ratio.

Hyphae

Tubular branching filaments; have chitin walls and septa.

Rhizoids

Modified hyphae used to anchor fungus.

Mushroom

Fruiting body that produces airborne spores.

Saprobe

Fungi that decompose organic matter; important in C and N cycling.

Parasite (fungal)

Uses haustoria to penetrate host cells.

Mycorrhizae

Symbiotic fungi living in plant roots; increase nutrient & water uptake.

Asexual reproduction (fungi)

Sporation, budding, or fission.

Microsporidia

Unicellular parasites; no mitochondria (have mitosomes).

Chytrids

Aquatic fungi with flagellated spores; chitin cell walls.

Zygomycota

Zygospore is only diploid stage; bubble-like sporangia.

Arbuscular Mycorrhizal Fungi

Symbionts on plant roots; consume glucose, fix nutrients.

Dikarya

Sac & club fungi; karyogamy occurs after plasmogamy.

Basidiomata

Fruiting bodies of club fungi.

Animals

Multicellular, heterotrophic, internal digestion, movement, nervous system.

Choanoflagellates

Closest living relatives to animals; colonial filter feeders.

Triploblastic

Animals with three germ layers.

Protostome

Blastopore becomes mouth.

Deuterostome

Blastopore becomes anus.

Symmetry types

Spherical, radial, bilateral (with cephalization).

Body cavities

Acoelomate, pseudocoelomate, coelomate.

Direct development

Young resemble miniature adults.

Indirect development

Young undergo dramatic changes across stages.

Reproductive trade-off

Many small eggs vs. few large eggs.

Sponges

No true tissues; have spicules + choanocytes for filter feeding.

Ctenophores

Comb jellies; complete gut; radial symmetry; bioluminescent.

Placozoans

Flat plate of cells; no mouth, gut, or nervous system.

Cnidarians

Jellyfish, anemones, corals; polyp + medusa forms; nematocysts.

Anthozoa

Anemones (solitary) & corals (colonial with symbiotic dinoflagellates).

Scyphozoa

True jellyfish; dominant medusa stage.

Hydrozoans

Colonial organisms sharing one stomach cavity.

Bilaterians

Triploblastic; 7 Hox genes; bilateral symmetry.

Lophotrochozoans

United by lophophore feeding structure or trochophore larvae.

Arrow worms

Outgroup to lophotrochozoans.

Annelids

Segmented worms with ganglia in each segment.

Polychaetes

Segmented worms with parapodia ("tube-feet").

Pogonophorans

Tube-dwelling worms near hydrothermal vents.

Clitellates

Earthworms & leeches; no coelom divisions.

Mollusks

Foot, mantle, visceral mass.

Gastropods

Snails, slugs; glide on foot.

Bivalves

Clams, oysters; hinged shells; filter feeders.

Cephalopods

Squid, octopi; jet propulsion; advanced eyes.

Nematodes

Unsegmented; gas exchange via diffusion.

Tardigrades

"Water bears"; endure dormancy for years.

Arthropods

Most diverse animals; jointed limbs; exoskeleton.

Chelicerates

Arachnids, horseshoe crabs; 4 leg pairs; chelicerae (fangs).

Mandibulates

Myriapods, crustaceans, insects; have mandibles.

Myriapods

Millipedes (harmless) & centipedes (predatory).

Crustaceans

Dominant marine arthropods; carapace; 5 appendage pairs.

Hexapods

Insects; 6 legs; 3 body regions; tracheal breathing.

Echinoderms

Sea stars, sand dollars; pentaradial; water vascular system.

Hemichordates

Proboscis, collar, trunk; includes pterobranchs.

Chordates

Dorsal nerve cord, notochord, post-anal tail, pharyngeal slits.

Lancelets

Sand-dwelling filter feeders.

Tunicates

Sea squirts; colonial filter feeders.

Vertebrates

Skull, vertebral column, heart, skeleton.

Chondrichthyes

Cartilaginous fish; sharks & rays; lateral swimming.

Bony Fish

Calcified bones; swim bladder; operculum.

Lobe-finned fish

Coelacanths, lungfish; precursor to tetrapods.

Amphibians

Require water for reproduction; larvae aquatic.

Amniotes

Lay amniotic eggs; include reptiles, birds, mammals.

Reptiles

Lepidosaurs, turtles, crocodilians, birds.

Mammals

Hair, mammary glands, 4-chamber heart, specialized teeth.

Marsupials

Develop in pouches.

Eutherians

Placental mammals.

Precocial vs. Altricial

Precocial = independent young; altricial = need parental care.