Lecture 10 - Multicellular Animals

Multicellular Animals

Overview

• Contains diverse groups of invertebrate and vertebrate animals primarily found in aquatic environments.

Invertebrates

Phylum Porifera (Sponges)

• Predominantly marine and about 300 species found in freshwaters.

• Feed by filtering particles from water, utilizing selective feeding.

• Often host algal endosymbionts.

• Serve as an important food source for predators.

• Spongillaflies are specialized insects adapted to pierce and suck fluids from sponges.

Phylum Cnidaria

• Includes jellyfish, anemones, corals, and hydroids.

• Mostly marine, with members of class Hydrozoa appearing in freshwater.

• Cnidocytes: specialized cells that fire filaments to capture prey.

• Hydra: common cnidarian found in various freshwater environments, typically attached to substrates while feeding on small invertebrates.

Phylum Platyhelminthes (Flatworms)

• Includes three classes:

  • Turbellia: free-living flatworms, mostly predators or scavengers.

  • Trematoda: flukes, some are human parasites (e.g., Schistosoma).

  • Cestoda: tapeworms.

• Phylum Nemertea: non-segmented worms, generally marine with a few freshwater species; primarily predators.

Phylum Gastrotricha

• Found in benthic habitats of lakes, ponds, and wetlands.

• Feed on bacteria, protozoa, algae, and detritus; can be very abundant (up to 100,000 per m²).

• Eggs exhibit resistance to drying, heating, and freezing.

Phylum Rotifera

• Found in all freshwater habitats.

• Exhibit multiple feeding strategies.

• Serve as a major food source for zooplankton.

Phylum Nematoda (Roundworms)

• Non-segmented, cylindrical organisms primarily found in benthic zones.

• Adaptable to extreme habitats with varied feeding strategies (detritivores, predators, algivores).

• Several freshwater species are known to be parasitic.

Phylum Nematomorpha (Horsehair Worms)

• Known for being parasites; macro in size, ranging centimeters.

Phylum Mollusca

Two Classes in Freshwaters:

1. Gastropoda:

   • Includes snails; more diverse class.

   • Characterized by a single-piece shell and primarily herbivorous habits.

   • Important for local primary production control and serve as prey and parasite hosts.

2. Bivalvia:

   • Have two halves of a shell and burrow in lake and stream sediments.

   • Possess parasitic larvae and species are often host-specific; many are endangered.

Phylum Annelidia (Segmented Worms)

• Comprises:

  • Oligochaetes: Similar to terrestrial earthworms; detritivores and burrow in sediments.

  • Leeches (Hirudinae): Predominantly predators, feeding on mollusks, insects, and worms; can also be parasitic.

Phyla Entoprocta and Ectoprocta (Bryozoans)

• Sessile organisms that are primarily marine but also found in freshwater environments.

• Feed on suspended food particles and can form extensive colonies.

Phylum Tardigrada (Water Bears)

• Microscopic animals found globally with 350 species known.

• Renowned for their ability to endure extreme environmental conditions; can survive up to 7 years without water.

• Typically found in benthic zones of semi-aquatic environments.

Phylum Arthropoda

• Exhibits three key subphyla:

  • Chelicerata (Arachnida)

  • Uniramia (Insecta and Collembola)

  • Crustacea

Insecta

• Significant diversity; several orders adapted to aquatic environments.

• Notable orders include:

  • Ephemeroptera (Mayflies): Lentic and lotic; with various feeding strategies.

  • Odonata (Dragonflies): Predators in freshwater habitats.

  • Plecoptera (Stoneflies): Mainly shredders and collectors in lentic waters.

  • Trichoptera (Caddisflies): Various feeding strategies within lentic environments.

Crustacea

Key Groups:

• Ostracoda: Seed shrimp, benthic; can thrive in diverse aquatic habitats and crucial in the food chain.

• Copepoda: Microcrustaceans with varied feeding approaches, showcasing complex behaviors.

• Branchiopoda: Water fleas and shrimps, crucial zooplankton in lakes; significant for filtering and as prey.

• Decapoda: Crayfish, crabs, and shrimps; noteworthy for their size, longevity, and diets.

vertebrates

Fishes

• Most diverse group of aquatic vertebrates, containing jawless (lampreys) to jawed fishes (sharks, rays, bony fishes).

• Bony fish are the most diverse within freshwater habitats and showcase a variety of adaptations.

Tetrapods

• Inclusive of amphibians (larval stage fully aquatic as tadpoles), reptiles, birds, and mammals.

• Amphibians are especially sensitive to environmental pollution, making them one of the most threatened groups.

Mini Quiz

• Complete on the provided platform regarding aquatic invertebrate habitats.

Summary of Key Points

1. Numerous micro-invertebrates with diverse feeding strategies exist, many are parasitic or predaceous.

2. Macroinvertebrates are also diverse, with key groups being Mollusca, Insecta, and Crustacea, encompassed by various feeding strategies.

3. Vertebrates primarily consist of fishes, particularly bony fishes; other vertebrates predominantly spend time on land, with some amphibians as exceptions.