Sponges and Cnidarians

Biology II: Chapter 26

The Animal Kingdom

• Multicellular

• Eukaryotic

• Heterotrophs

• Cells lack cell walls

• 95% are invertebrates

What Animals Do to Survive

• Feeding

• Respiration

• Circulation

• Excretion

• Response

• Movement

• Reproduction

Trends in Animal Evolution

• Cell specialization and levels of organization

• Early development

• Body symmetry

• Cephalization

• Body cavity formation

SPONGES

Sponges• Phylum Porifera

• Have tiny openings, or pores, all over their bodies

• Sessile: they live their entire life attached to a single spot

• They are animals! Why…?

Sponges are Animals!!!

• Multicellular

• Heterotrophic

• No cell walls

• Contain a few specialized cells

Form and Function in Sponges

• Have nothing resembling a mouth or gut

• Have no tissues or organ systems

• Simple functions are carried out by a few specialized cells

Asymmetrical

• Have no front or back ends, no left and right sides

• A large, cylindrical water pump

• The body forms a wall around a large central cavity through which water flows continually

Choanocytes

• Specialized cells that use flagella to move a steady current of water through the sponge

• Filters several thousand liters/day

Osculum

• A large hole at the top of the sponge, through which water exits

• The movement of water provides a simple mechanism for feeding, respiration, circulation and excretion

Simple Skeleton

• Spicule: a spike-shaped structure made of chalk-like calcium carbonate or glasslike silica in hard sponges

• Archaeocytes: specialized cells that make spicules

Feeding

• Filter feeders

• Sift microscopic food from the water

• Particles are engulfed by choanocytes that line the body cavity

Respiration, Circulation, & Excretion

• Rely on the movement of water through their bodies to carry out body functions

• As water moves through the cavity:

• Oxygen dissolved in the water diffuses into the surrounding cells

• Carbon dioxide and other wastes, diffuse into the water and are carried away

Response

• No nervous system

• Many sponges protect themselves by producing toxins that make them unpalatable or poisonous to potential predators

Reproduction

• Sexually or asexually

• A single spore forms both eggs and sperm; usually at different times

Sexual Reproduction

• Internal fertilization: Eggs are fertilized inside the sponge’s body

• Sperm are released from one sponge and carried by currents to the pores of another sponge

Asexual Reproduction

• Budding

• Gemmules: groups of archaeocytes surrounded by spicules

Ecology of Sponges

• Ideal habitats for marine animals such as snails, sea stars, sea cucumbers, and shrimp

• Mutually beneficial relationships with bacteria, algae and plant-like protists

– Many are green due to these organisms living in their tissues

Ecology of Sponges

• Attached to the seafloor and may receive little sunlight

• Some have spicules that look like cross-shaped antennae

• Like a lens or magnifying glass, they focus and direct incoming sunlight

CNIDARIANS

Cnidarians• Phylum Cnidaria

• Hydras, jellies, sea anemones, and corals

• Soft-bodied

• Carnivorous

• Stinging tentacles arranged in circles around their mouths

• Simplest animals to have body symmetry and specialized cells

Cnidocytes

• Stinging cells that are located on their tentacles

• Used for defense and to capture prey

Nematocyst

• A poison-filled, stinging structure that contains a tightly coiled dart

• Found within cnidocytes

Form and Function in Cnidarians

• Only a few cells thick

• Simple body systems

• Most of their responses to the environment are carried out by specialized cells and tissues

Radially Symmetrical

• Central mouth surrounded by numerous tentacles that extend outward from the body

• Life cycles includes a polyp and a medusa stage

Body Plan

• Polyp: cylindrical body with arm-like tentacles; mouth points upward

• Medusa: motile, bell-shaped body; mouth on the bottom

Feeding

• Polyps and medusas have a body wall that surrounds an internal space: the gastrovascular cavity

• Gastrovascular cavity: a digestive chamber with one opening

– Food enters and wastes leave the body

Respiration, Circulation, & Excretion

• Following digestion, nutrients are usually transported throughout the body by diffusion

• Respire and eliminate wastes by diffusion through body walls

Response• Specialized sensory cells are used to gather

information from the environment

• Nerve net: loosely organized network of nerve cells that together allow cnidarians to detect stimuli

– Distributed uniformly throughout the body in most species

– In some species it is concentrated around the mouth or in rings around the body

Response

• Statocysts: groups of sensory cells that help determine the direction of gravity

• Ocelli: eyespots made of cells that detect light

Movement

• Hydrostatic skeleton: a layer of circular muscles and a layer of longitudinal muscles that enable cnidarians to move

Reproduction: Sexually and Asexually

• Polyps can reproduce asexually by budding

• External sexual reproduction

– The sexes are separate-each individual is either male or female

– Both egg and sperm are released into the water

Groups of Cnidarians

• Jellies (formerly jellyfishes)

• Hydras and their relatives

• Sea anemones

• Corals

Ecology of Corals• The worldwide distribution is determined by:

– Temperature

– Water depth

– Light intensity

• Many suffer from human activity• Coral bleaching has become common • Global warming may add to the problem