Why is an Octopus Considered a Mollusk Instead of a Fish?
Octopuses, despite their aquatic nature and fish-like appearance, are classified as mollusks rather than fish due to several key anatomical and physiological differences.
1. Body Composition: Mollusks, like octopuses, have soft bodies composed of a mantle and foot, while fish have bony or cartilaginous skeletons.
2. Nervous System: Octopuses belong to the phylum Mollusca, characterized by a ventral nervous system with several connected ganglia, unlike the dorsal nervous system found in fish.
3. Respiration: Octopuses use gills for respiration, which are housed in a specialized mantle cavity, whereas fish typically have external gills.
4. Reproduction: Octopuses lay eggs that are fertilized externally, while most fish reproduce through internal fertilization. Additionally, octopuses have a unique life cycle involving a planktonic larval stage that differs from fish larvae.
5. Body Plan: Mollusks, including octopuses, typically have a three-part body plan (head, foot, visceral mass), while fish exhibit a two-part body plan (head and trunk).
Related Questions:
- What is the primary difference between mollusks and fish? (Soft vs. bony skeletons)
- How do octopuses breathe? (Through gills in a mantle cavity)
- Are octopuses viviparous? (No)
- What is the common name for a mollusk with a hard shell? (Clam)
- Which phylum do octopuses belong to? (Mollusca)
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