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kingdom Amelia unit 3

Important Anatomical Terminology

  • Dorsal vs. Ventral

  • Anterior vs. Posterior

  • Distal vs. Proximal

  • Anatomy Orientation:

    • Right (lateral) side

    • Left (lateral) side

    • Dorsal side

    • Ventral side

    • Dorsoventral axis

    • Anteroposterior axis

    • Proximal end

    • Distal end

Invertebrate Phyla Overview

  • Phylum Platyhelminthes: Flatworms

  • Phylum Rotifera: Rotifers

  • Phylum Nematoda: Roundworms

  • Phylum Mollusca: Molluscs

    • Class Bivalvia: Clams

    • Class Cephalopoda: Octopuses and Squid

    • Class Gastropoda: Snails and Slugs

    • Class Polyplacophora: Chitons

Flatworms: Overview

  • Classification:

    • Free-living vs. Parasitic

  • Example Species:

    • Dugesia (nonparasitic planarian)

    • Tapeworms (parasitic flatworm)

  • Tapeworms Details:

    • Live attached to the inner wall of the small intestine

    • Absorb nutrients through the body wall

  • Characteristics of Flatworms:

    • Distinguished by:

    1. Saclike body plan

    2. Elongated body

    3. Bilateral symmetry

    4. Dorsoventrally flattened

    • Presence of all three embryonic tissues

    • Organ level of organization

    • Absence of a coelom (body cavity)

  • Reproductive System: All flatworms are hermaphroditic (they exchange sperm during mating)

Rotifers: Overview

  • Phylum: Rotifera

  • Characteristics:

    • Pseudocoelomate

    • Body divided into 4 regions: head, neck, trunk, foot

    • Corona (ciliated structure) on the head that draws water into the mouth for feeding

    • Trophi: Jaw-like structures in pharynx used to grind food

    • Cryptobiosis: State allowing survival in unfavorable conditions

  • Observations for the class:

    • Live rotifers show movements of the corona

Roundworms: Overview

  • Phylum: Nematoda

  • Characteristics:

    • Cylindrical, bilateral body tapered at each end

    • Tube-within-a-tube body plan

    • Organ system level of organization

    • Presence of a false coelom (body cavity)

    • Majority are free-living, some are parasites

Roundworm Ascaris

  • Characteristics:

    • Large roundworm parasite in the small intestine of humans and swine

    • Feeding: on partially digested food

    • Morphology: Females are longer, straight posterior end

  • Body Structure:

    • Body wall consists of longitudinal muscles, dermis, and a cuticle

    • Cuticle protects worm from the host’s small intestine

    • Pseudocoelom: Space between intestine and body wall, incompletely lined with mesoderm

    • Contains female reproductive system and ribbon-like intestine

Phylum Mollusca

  • Habitat: Primarily marine, some in freshwater or terrestrial ecosystems (e.g., Apple and Nerite Snails)

  • Body Features:

    • Ventral muscular foot for movement or burrowing

    • Dorsal visceral mass housing important organs

    • Mantle that surrounds the visceral mass and secretes a shell (not all species possess a shell)

    • Radula: File-like mouth part for scraping food

Class Bivalvia (Clams)

  • Body Structure:

    • Flattened laterally, enclosed by two valves (shell halves)

    • Hinge on the dorsal surface connecting the two shells

    • Adductor muscles (anterior and posterior) close the valves

    • Foot: Used for burying into mud or sand

    • Incurrent Siphon: Brings water into the Mantle Cavity; Excurrent Siphon for exiting water

    • Gas exchange occurs in gills (between water and clam’s blood)

    • Food filtration through mucus trapping particles, moved by cilia to mouth

    • Circulatory System: Open circulatory system (absence of veins)

Class Cephalopoda (Octopuses and Squids)

  • Evolutionary Peak: Represent peak of molluscan evolution

  • Body Structure:

    • Foot modified into arms or tentacles, bearing suction cups for prey capture

    • Arms: Suckers all along their length

    • Tentacles: Suckers only at the tips

    • Beaks for piercing and feeding on food

    • Water intake through a siphon for gas exchange; expelled for propulsion

    • Allows rapid swimming

    • Ink expulsion for escape mechanism

    • Some possess shells, e.g., Nautilus; squid have a thin, transparent plate (pen)

    • Octopuses lack a shell

Class Gastropoda (Slugs and Snails)

  • Body Features:

    • Generally, an external spiral-shaped shell (not all have it)

    • Foot modified for creeping locomotion

    • Many snails can retract into their shell and use an operculum to cover the opening

Cone Snails (Gastropoda)

  • Venom: Capable of producing enough venom to kill 700 people

  • Hunting Mechanism: Use a harpoon-like structure to shoot a venomous mucus at prey