Invertebrates grow more complex
Looking across the animals without a notochord.
From sponge to starfish
Sponges have no tissues. Starfish have a hard internal skeleton.
What pattern do you think appears if you go from sponges to echinoderms?
What this lesson covers
The idea
From sponges to echinoderms, animal body organisation becomes increasingly complex; new structural features improve feeding, movement and protection but often bring new challenges.
From sponge to starfish
Sponges have no tissues. Starfish have a hard internal skeleton.
What pattern do you think appears if you go from sponges to echinoderms?
- Body organisation becomes more complex
- Body organisation becomes simpler
- Body organisation stays exactly the same
Climbing the staircase
Press Next step until the end. The numbered bars show the order used in the book.
A pattern of increasing complexity
Going from sponges to echinoderms, each group adds new structural features. The features improve feeding, movement and protection. But the book also notes that new features often bring new challenges.
From sponges to echinoderms, animal body organisation becomes increasingly complex; new structural features improve feeding, movement and protection but often bring new challenges.
- Group | A feature given in the book
- Porifera | pores let water bring food and oxygen to cells
- Cnidaria | tissues, and tentacles that capture prey
- Platyhelminthes | bilateral symmetry and directional movement
- Nematoda | a body with two openings, mouth and anus
- Annelida | segments for flexible, precise movement
- Arthropoda | a hard external skeleton for protection
- Mollusca | a shell protects the soft body in many
- Echinodermata | a hard internal skeleton for protection
Notes
From sponges to echinoderms, body organisation becomes increasingly complex; new features improve feeding, movement and protection but often bring new challenges.
Check yourself
From sponges to echinoderms, how does body organisation change?
Which group first shows tissue-level organisation among those you have studied?
Which feature helps annelids control their movements precisely?
What do new structural features often bring along with their benefits?
- It becomes simpler. The book describes a pattern of increasing complexity.
- It becomes increasingly complex — correct. Yes!
- It does not change. The book says body structure shows a pattern of increasing complexity.
- Porifera. Sponges lack organisation of tissues and organs.
- Echinodermata. Echinoderms come later in the sequence, and tissue-level organisation first appears in cnidarians.
- Cnidaria — correct. Yes!
- Segmentation — correct. Yes!
- A hard external skeleton. A hard external skeleton is a feature of arthropods.
- Pores in the body. Pores are a feature of sponges.
- An end to all challenges. The book says new features often introduce new challenges.
- New challenges — correct. Yes!
- Loss of the ability to move. The book says new features improve movement as well as feeding and protection.