Zoo U2

Chapter 9: Multicellular Life in Animals

Colonial Theory of Haeckel (1874): Proposes that multicellular organisms evolved from colonies of single-celled organisms. This theory emphasizes the importance of cooperation among cells for survival and adaptation.
Synctial Hypothesis: Suggests that multicellular structures develop from a single cell with multiple nuclei. In this model, the nervous system consists of neurons that share cytoplasm, allowing for coordinated functioning of the cells.

Multicellular with loose cell layers, not differentiated into specialized tissues, allowing for adaptability.
Body features spicules, which can have different shapes and structures aiding in defense (like sharp spikes) and support (providing structural integrity).
Sponges filter large volumes of water, up to 900,000 gallons a day, using a unique water-filtering system that contributes significantly to aquatic ecosystems.

Choanocytes (flagellated cells) play multiple roles: aiding in feeding by capturing food particles, participating in reproduction, and facilitating water circulation through the sponge structure.
Water is absorbed through the sponge, bringing in nutrients which are captured and digested by the choanocytes.

Most sponges are hermaphrodites, meaning they can produce both sperm and eggs, enhancing reproductive success.
Sperm is released into the water, typically during a full moon, which helps synchronize breeding events. Sperm can settle on substrates to develop into sessile adults.

Body Plan: Exhibits radial symmetry, which means the body can be divided into similar halves about a central axis.
Key anatomical features include:
- Osculum: The exit point for water after it has flowed through the sponge, crucial for filtering and respiration.

One of the earliest animal groups to swim in the ocean, utilizing the Gastrovascular Cavity for both digestion and excretion. This cavity acts as a hydrostatic skeleton as well.
Two dominant forms:
- Polyp: Sessile form, typically mouth-up, using tentacles to capture prey.
- Medusa: Free-swimming form, mouth-down with tentacles hanging, adapted for mobility and dispersal.

Cnidarians are carnivorous, using cnidocytes (specialized cells) and their nematocysts (stinging structures) to capture and immobilize prey, making them effective predators.
They possess a simple nerve net, allowing for coordinated movement and reflexes without a centralized brain, demonstrating an early form of a nervous system.

They exhibit both sexual reproduction (in the medusa stage) and asexual reproduction (in the polyp stage) with budding, showcasing versatility in their life cycles.

Major Classes include:
- Hydrozoa
- Scyphozoa
- Anthozoa
- Cubozoa (notable for long, non-stinging tentacles, often found in coastal water)

Acoelomates: Organisms that lack a body cavity, characterized by tightly packed tissues.
Eucolomates: Organisms possessing a true coelom (fluid-filled body cavity), allowing for the development of complex organs.
Pseudocoelomates: Organisms with a partially formed cavity, which provides some degree of organization.
Bilateral Symmetry: Body plan in which left and right parts are mirror images, often observed in more complex organisms, promoting directional movement.

Cilia: Small hair-like structures that facilitate locomotion in some species, allowing for movement through water and against currents.
Ganglion: A cluster of nerve cells that coordinate muscular actions, functioning as a primitive brain, particularly in more complex forms.

Many species exhibit the ability to regenerate lost body parts, including heads in specific types of flatworms, allowing them to adapt after injury.
Hermaphroditic features enable diverse reproductive strategies, increasing the likelihood of successful reproduction across environments.

Nudibranchia: Vibrant sea slugs known for remarkable colorations and adaptations, which can be used for camouflage.
Flatworms: Including
- Turbellarians: Free-living, hunters, generally non-harmful to humans, found in various aquatic environments.
- Trematodes: Parasitic forms that penetrate skin, impacting animal and human health.
- Cestodes: Tapeworms that inhabit hosts, known for their extensive growth and developmental cycles within their hosts, impacting host nutrition and health.