Invertebrate Biology and Behavior Introduction

The Invertebrate Behavior Project

• Total Point Value: The project is worth a total of $25$ points.

• Objective: Students must select an invertebrate phylum not covered in class, choose a specific species (or a small group of closely related species in the same genus), and discuss their specific behaviors.

• Points Breakdown:

  • Classification ($5$ points): Students must provide the correct taxonomic hierarchy: Phylum, Class, Order, Family, Genus, and Species. Wikipedia is an acceptable starting point for finding taxonomic frameworks, though students should cite the source for classification because scientific disagreement exists.

  • Behavioral Summary ($4$ points each): Summarize the following four classes of behavior that impinge directly on organismal fitness:

    • Reproductive behaviors.

    • Feeding behaviors.

    • Predator avoidance behaviors.

    • Environmental tolerance behaviors.

  • Interesting Behaviors ($2$ points): Document any other unique or interesting behaviors performed by the organism.

  • Reference Formatting ($2$ points): Provide at least one primary reference formatted in a logical, scientific manner (e.g., APA, MLA, or the style of the journal the paper was found in).

• Primary Reference Definition: This must be a first-person account of novel research, typically a peer-reviewed paper in a scientific journal, rather than a secondary source like a textbook.

• Research Resources:

  • Google Scholar: A reliable search engine for primary literature.

  • Galileo: Accessed through the library; provides access to academic journals.

  • Interlibrary Loan: Available if an article is not immediately accessible.

  • Direct Outreach: If a paper is behind a firewall, students can email the corresponding author for a PDF reprint.

  • Digital Object Identifier (DOI): A short, embedded link found at the top of electronic papers used for verification.

• Deadlines and Restrictions:

  • Topic Selection: Must be submitted by Thursday. No two students may choose the same species.

  • Due Date: Wednesday, September 2.

  • Excluded Phylum: Do not choose Placozoans. These are the simplest animals, consisting of sheets of cells that absorb nutrients or grab bacteria; they are too simple to provide enough behavioral data for the project requirements.

Behavioral Studies in Non-Animal Organisms

Paramecium

• Classification: These are ciliates, a type of protist.

• Feeding Structures: They are predatory cells possessing an oral groove (a cellular mouth). This groove ends in a food vacuole.

• Internal Digestion: Cilia draw organic debris or other cells into the food vacuole. Lysosomes (digestive organelles) fuse with these vacuoles to digest molecules, which are then distributed throughout the cell.

• Waste Removal: They possess a cytoproct, which functions as a cellular anus where vacuole waste is dumped outside the cell.

Slime Molds

• Life Cycle: They begin as spores that erupt into amoeba-like cells. When stressed, these cells coalesce into larger masses called slugs.

• Forms of Slime Molds:

  • Syncytial Slime Molds: These form a syncytium (plural: syncytia), defined as a "together cell." Cellular membranes dissolve, creating a large mass with multiple nuclei (similar to skeletal muscle cells in humans).

  • Cellular Slime Molds: In these forms, individual cell membranes remain in place during the slug stage.

• Stress Response and Reproduction:

  • Slugs form a hard molecular mass and grow a stalk leading to a fruiting body (sporing body).

  • Stressors include lack of food, lack of resources, and specifically a lack of liquid water.

  • This process is an example of altruism, as cells forming the stalk or base do not pass on their DNA, while those in the fruiting body do.

  • Scientific studies suggest that cells in the sporing body are often closely related, indicating a genetic advantage for certain lines over others in determining who reproduces.

• Navigation: Time-lapse photography shows slime molds navigating complex laboratory mazes to avoid adverse areas and seek resources.

Introduction to the Major Invertebrate Phyla

• The Big Nine: Historically, nine phyla are considered the most successful based on species richness. Eight of these are invertebrates, while the ninth is Chordata.

• Phylum Chordata: Named for the notochord, a cartilaginous support rod along the back during development. While vertebrates replace this with a vertebral column, there are invertebrate chordates that retain it.

• Developmental Pathways:

  • Protostomes: Literally "mouth first." The original opening in development becomes the mouth, and the anus develops second.

  • Deuterostomes: Literally "mouth second." The original opening becomes the anus, and the mouth is the new opening. Humans are deuterostomes.

  • Evolutionary Advantage: Having two openings (a through-gut) allows organisms to process one meal while eating another, increasing efficiency.

Phylum Porifera: The Sponges

• Body Structure: These are porous-bodied animals without a centralized nervous system. They possess a large opening at the top called an osculum.

• Feeding Mechanism: Cells called choanocytes have tiny flagella that whip around to move water through the body walls and out the osculum.

• Foraging Behavior: Dye tests show that water moves through a sponge Body in less than $2$ seconds, demonstrating a high-speed, continuous flow for filtering organic material.

• Reproductive Behavior: Sponges were the first animals to reproduce sexually. They utilize external fertilization, scattering millions of sperm into the water. This "broadcast spawning" requires high volume because most gametes will be lost.

Phylum Cnidaria: The Stinging Animals

• General Characteristics: Jelly-like animals characterized by a "silent c" in their name. They have an internal digestive chamber with one opening.

• Body Forms:

  • Medusa: Free-swimming forms (e.g., jellyfish).

  • Polyp: Attached forms (e.g., anemones, corals, hydra).

• Composition: They are approximately $95\%$ water, compared to humans who are typically between $50\%$ and $60\%$ water. The "goo" between cell layers is called mesoglea.

• Cnidocytes: Specialized cells containing spring-loaded harpoons used for defense and prey capture. These often contain neurotoxic venoms.

• Key Species and Behaviors:

  • Stomphia: A unique anemone that can free itself from a rock and swim away to escape predators (e.g., sea stars). This complex behavior is controlled by a simple nerve net by increasing the frequency/tempo of neural pulses.

  • Turritopsis dornii (Immortal Jellyfish): This species can reverse its life cycle through transdifferentiation, reverting from a mature medusa back to a polyp stage when stressed.

  • Chironex fleckery (Australian Box Jellyfish): The most venomous marine animal. Tentacles can grow to $10$ feet long. Stings can cause cardiac arrest or death in humans within minutes.

  • Comb Jellies (Ctenophores): A separate phylum often grouped with jellies. They use bioluminescence for attracting prey (e.g., copepods) or as a warning to predators (aposematism).

Phylum Platyhelminthes: The Flatworms

• Cephalization: The first animals to develop a head, a centralized nervous system, and a brain. They possess eye spots that detect light intensity and direction, though they do not form images.

• Locomotion: They use muscles and millions of tiny cilia to glide over a self-made cushion of mucus.

• Feeding: The mouth is located on the underside of the body. They use a device called a pharynx to suck down prey.

• Anatomy: They lack a circulatory system. To compensate, the digestive system branches extensively to reach every square millimeter of the body to distribute nutrients.

• Types: Includes free-living planarians and parasitic forms like tapeworms, which lack their own digestive systems because they absorb nutrients directly from the host.

Phylum Nematoda: The Roundworms

• Ecology: Free-living nematodes are vital for soil health, with concentrations of up to $9,000,000$ per cubic meter ($m^3$) of topsoil. They aerate soil and cycle nutrients.

• Parasitism: Includes species that parasitize insects.

  • Examples: Nematodes that kill mosquito larvae or large roundworms found inside grasshoppers.

  • Horsehair Worms: Often seen emerging from the bodies of preying mantises.

Phylum Annelida: The Segmented Worms

• Defining Feature: Segmented bodies.

• Polychaete Worms: Marine cousins of Earthworms (which are also annelids). Features include:

  • Parapodia: Paddle-like feet on each segment.

  • Chaetae: Bristles used for swimming, crawling, or defense.

• Diversity of Polychaetes:

  • Deep Sea Modalities: Some live in hydrothermal vents or eat whale skeletons.

  • Flota and Swima: Mid-water worms that use glowing organs to startle predators.

  • Chaetopterus pugaporcinus: A species named the "rump of a pig" due to its appearance.

  • Tomopteris (Dancing Bristle Worm): Transparent predator that emits a brilliant yellow glow to distract predators.

Questions & Discussion

• Question: Do you want us to use APA seventh edition for citation?

• Response: Any logical, standard scientific publication format is acceptable. If unsure, format the reference exactly as it appears at the end of the primary paper being cited. Chicago style is generally avoided in these science classes.

• Question: Are there any freshwater sponges?

• Response: Yes, there are small, less impressive freshwater sponges in North Georgia streams.

• Question: Are there freshwater cnidarians?

• Response: Yes, Hydra are freshwater polyps, essentially tiny freshwater anemones.

• Question: Is bioluminescence for attracting mates?

• Response: No, because jellies and comb jellies have no eyes. It is likely for attracting food or warning predators (aposematism).