Lesson 12 of 12 · 13 min
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Must-know facts
20 facts
- 01Cellular level: Porifera. Tissue level: Coelenterata and Ctenophora. Organ level: Platyhelminthes. Organ-system level: Aschelminthes onwards.
- 02Incomplete gut (one opening): Platyhelminthes. Open circulation: arthropods and hemichordates; closed: annelids and chordates.
- 03Radial symmetry: coelenterates, ctenophores, adult echinoderms. Echinoderm larvae are bilateral. Sponges are mostly asymmetrical.
- 04Diploblastic with mesoglea: Coelenterata (and Ctenophora). Triploblastic: Platyhelminthes to Chordata.
- 05Acoelomate: Platyhelminthes. Pseudocoelomate: Aschelminthes. Coelomate: annelids onwards, including hemichordates and chordates.
- 06Metamerism is first seen in Annelida (earthworm).
- 07Water path in sponges: ostia → spongocoel → osculum; choanocytes line the canals; digestion intracellular.
- 08Cnidoblasts with nematocysts: Coelenterata. Metagenesis: Obelia. Coral skeleton: calcium carbonate.
- 09Ctenophores: eight rows of comb plates, bioluminescence, only sexual reproduction.
- 10Flame cells: Platyhelminthes. Nephridia: Annelida. Malpighian tubules: Arthropoda. Proboscis gland: Hemichordata. No excretory system: Echinodermata.
- 11Parapodia: Nereis (dioecious). Earthworm and leech: monoecious.
- 12Arthropoda: largest phylum, over two-thirds of named species; Limulus is a living fossil.
- 13Mollusca: second largest phylum; radula for feeding; gills in the mantle cavity.
- 14Water vascular system: Echinodermata. Stomochord: Hemichordata (now a non-chordate phylum).
- 15Notochord only in the larval tail: Urochordata. Head to tail and lifelong: Cephalochordata.
- 16Cyclostomes: 6-15 pairs of gill slits, jawless sucking mouth, ectoparasites on fishes.
- 17Chondrichthyes: placoid scales, no air bladder, no operculum, claspers in males. Osteichthyes: four pairs of gills under an operculum, air bladder.
- 18Heart: fishes 2 chambers; amphibians and most reptiles 3; crocodiles, birds and mammals 4.
- 19Poikilotherms: fishes, amphibians, reptiles. Homoiotherms: birds and mammals.
- 20Birds: pneumatic bones, crop and gizzard, air sacs, only an oil gland at the tail base. Platypus: an egg-laying mammal.
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Where marks are lost
Key terms
20 terms
- Choanocyte
- A collar cell lining the spongocoel and canals of a sponge.
- Spongocoel
- The central cavity of a sponge; water leaves it through the osculum.
- Cnidoblast
- A cnidarian cell carrying a stinging capsule, the nematocyst.
- Metagenesis
- Alternation of polyp and medusa forms in a cnidarian such as Obelia.
- Mesoglea
- The undifferentiated layer between ectoderm and endoderm in diploblastic animals.
- Coelom
- A body cavity lined by mesoderm, between body wall and gut wall.
- Pseudocoelom
- A body cavity not lined by mesoderm; the mesoderm lies as scattered pouches.
- Metamerism
- Division of the body into serially repeated segments, outside and inside.
- Notochord
- A dorsal, mesoderm-derived rod formed in the embryo of chordates.
- Flame cells
- Excretory and osmoregulatory cells of flatworms.
- Nephridia
- Excretory and osmoregulatory organs of annelids.
- Parapodia
- Lateral swimming appendages of aquatic annelids such as Nereis.
- Malpighian tubules
- Excretory organs of arthropods.
- Radula
- The file-like rasping feeding organ in a mollusc's mouth.
- Water vascular system
- The echinoderm system used for locomotion, food capture and transport, and respiration.
- Stomochord
- A rudimentary notochord-like structure in the collar of hemichordates.
- Placoid scales
- Minute scales in the skin of cartilaginous fishes; their teeth are modified placoid scales.
- Cloaca
- A common chamber into which the gut, urinary and reproductive tracts open.
- Pneumatic bones
- Hollow long bones of birds with air cavities.
- Homoiothermous
- Able to keep a constant body temperature; birds and mammals.