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Questions and Answers
What characteristic distinguishes phylum Platyhelminthes from other invertebrate phyla?
Which of the following phyla contains organisms that can survive extreme conditions, including the vacuum of space?
What do comb jellies, belonging to phylum Ctenophora, mainly use for locomotion?
What is a primary feature of phylum Acanthocephala that distinguishes it from other phyla?
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Which group of mollusks is known for having two hinged shells?
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What characteristic is common to all arthropods?
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Which group within arthropods has hard pincers or fangs called chelicerae?
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What is a unique feature of echinoderms?
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What distinguishes hemichordates from other invertebrates?
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What defines the organisms in phylum Sipunculoidea?
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What characteristic distinguishes vertebrates from invertebrates?
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Which phylum contains organisms known as sponges?
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What percentage of all animal species on Earth are invertebrates?
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What type of cells are found in organisms of Phylum Coelenterata?
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Which of the following statements about invertebrates is true?
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Study Notes
Animal Kingdom
- All animals are multicellular, heterotrophic organisms whose cells lack cell walls.
- Animals are classified into two main categories: vertebrates and invertebrates.
- Vertebrates have a backbone or spinal column (vertebral column).
- There are five major categories of vertebrates: fish, amphibians, reptiles, birds, and mammals.
- Invertebrates lack a backbone or vertebral column.
- Over 90% of all animals on Earth are invertebrates, comprising more than 1.3 million species.
Invertebrate Phyla
- Invertebrates are classified into nearly 30 different phyla, with diverse levels of complexity.
- Vertebrates belong to a single phylum: Chordata.
Phylum Porifera (Sponges)
- Contains 5,500 species, known as sponges.
- Predominantly sessile organisms, with motile larval stages.
- Filter feeders, drawing water into their pores, absorbing nutrients, and expelling water through an opening called an osculum.
Phylum Cnidaria (Coelenterates)
- Includes 10,000 species, characterized by stinging cells called cnidocytes.
- Contains jellyfish, corals, sea anemones, and hydra.
- Possesses a simple gastrovascular system serving as both digestive and circulatory system with a single opening acting as both mouth and anus.
- Exhibits radial symmetry, lacking left and right sides.
Phylum Ctenophora (Comb Jellies)
- Encompasses 100 species, characterized by comb-like cilia used for swimming.
- Resemble jellyfish but lack cnidocytes and have more complex body plans and organ systems.
Phylum Platyhelminthes (Flatworms)
- Contains 20,000 species, small, simple organisms with bilateral symmetry.
- First organisms to exhibit a central nervous system and a simple brain.
- Most are marine.
- Planaria, a notable flatworm, can regenerate from fragmented bodies.
Phylum Nemertea (Ribbon Worms)
- Includes 900 species, often round and thin, ranging in size from 1 cm to 30 meters.
- Also known as proboscis worms due to their sticky, branched proboscis used for prey capture and defense.
Phylum Rotifera
- Contains 1,800 species of microscopic aquatic organisms, typically 50 µm to 2 mm in length.
- Named for the circle of cilia surrounding their mouths, constantly pushing food and liquid into their bodies.
Phylum Gastrotricha
- Consists of 800 species of worm-like, microscopic animals, nicknamed "hairy bellies" due to cilia covering their ventral surface.
- All are aquatic, inhabiting either freshwater or marine environments.
Phylum Nematomorpha
- Contains 325 species, resembling nematodes but also called horsehair worms or hairsnakes.
- Usually around 10 cm long and 2 cm in diameter, with the longest recorded specimen reaching 2 m.
- Often parasitic on insects.
Phylum Nematoda (Roundworms)
- Contains 25,000 species, found in soils and waters worldwide.
- Some are parasitic, infecting humans (hookworms, pinworms, Trichinella) or plants.
- Others decompose and recycle dead organic material.
Phylum Acanthocephala
- Contains 1,100 species of parasitic spiny-headed worms, using hooks on their heads to attach to host digestive systems.
- Genetic analysis suggests they are highly modified descendants of rotifers, leading some scientists to propose their combination into a single phylum.
Phylum Bryozoa
- Also known as Phylum Ectoprocts, includes 4,500 species resembling moss clumps.
- Most are colonial, with hundreds or thousands of individuals forming a united mass.
- Form a hard exoskeleton with feeding openings, found in marine reefs.
Phylum Tardigrada
- Contains 800 species of microscopic (0.5 mm) water bears.
- Found in diverse ecosystems and can survive extreme environments, including vacuum of space.
Phylum Brachiopoda
- Contains 335 species, often mistaken for clams or other mollusks.
- Distinctive feature is a lophophore, a row of cilia-like tentacles surrounding their mouth.
- Also possess a unique stalk-like appendage for anchoring.
Phylum Mollusca
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One of the largest and most diverse invertebrate phyla, second only to Phylum Arthropoda.
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Characterized by a soft body called a visceral mass, often protected by a hard outer shell.
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Shells are produced by a specialized tissue called the mantle.
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Includes squid, snails, and other commercially important species.
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Divided into three main groups:
- Gastropods: The largest class, including snails (shelled) and slugs (shell-less). Their name means "stomach-foot."
- Bivalves: Possessing two hinged shell halves, this class includes clams, oysters, and scallops.
- Cephalopods: This class includes octopuses, squids, and chambered nautiluses. Their name means "head-foot," reflecting their tentacled structure. They are voracious marine predators, with octopuses considered the most intelligent invertebrates.
Phylum Annelida
- Contains 16,500 species, the only worm category with segmented bodies.
- Includes earthworms and leeches.
Phylum Sipunculoidea
- Contains 162 species of animals called peanut worms due to their peculiar shape.
- Lack segments but are genetically related to annelids, leading some to advocate for their merger.
Phylum Arthropoda
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Largest phylum in the Animal Kingdom, both in species and individual numbers, with an estimated 10^18 arthropods on Earth.
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Name means "jointed foot," reflecting their jointed legs or appendages.
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Possess hard exoskeletons and segmented bodies (typically head, thorax, and abdomen).
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Major arthropod categories include:
- Arachnids: Spiders, scorpions, ticks, possessing chelicerae (hard pincers or fangs). All arachnids have 6 pairs of appendages: 4 walking pairs, 1 pair of chelicerae, and 1 pair for feeding (pedipalps).
- Myriapods: Centipedes and millipedes, the name meaning "many feet." Centipedes are carnivorous with one pair of legs per segment, while millipedes are herbivorous with two pairs of legs per segment.
- Crustaceans: A diverse group of mostly aquatic arthropods, including crabs, lobsters, crawfish, shrimp, and the terrestrial pill bug. They have variable numbers of appendages with specialized functions.
- Insects: The largest group of arthropods, with more species than all other animal groups combined. Also known as hexapoda for their six legs. Many insects possess wings. Examples include beetles, butterflies, ants, bees, crickets, flies. Insects are crucial to life on Earth, serving as food sources, pollinators, and decomposers.
Phylum Chaetognatha
- Contains 200 species of arrow worms, marine worms with lateral and tail fins, giving them a torpedo shape.
- All are predators, some inhabiting the deep ocean floor.
Phylum Echinodermata
- Contains 7,000 species, characterized by spiny skin.
- Includes sea stars (starfish), sea urchins, sea cucumbers, and sand dollars.
- Unique for their complexity, with complex organ systems and embryonic development resembling vertebrates.
- However, they exhibit radial symmetry and regeneration, traits found in simpler invertebrates.
- Move via a water-vascular system, using water pressure to power tube feet for adhesion.
Phylum Hemichordata
- Contains 85 species, the most vertebrate-like invertebrate group.
- Share similar embryonic development, gill slits, and a nerve cord (evolutionary predecessor of a backbone).
- The most common hemichordate is the acorn worm, a marine burrowing worm with an "acorn-shaped" head, reaching over 2 meters in length.
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Description
Explore the fascinating world of the Animal Kingdom, including the distinction between vertebrates and invertebrates. This quiz covers various phyla, such as Porifera and Cnidaria, and highlights the complexity and diversity of animal life on Earth.
