Invertebrates

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Most sponges are hermaphrodites: Each individual functions as both male and female.

Slide 10

Concept 33.2: Cnidarians are an ancient phylum of eumetazoans

All animals except sponges and a few other groups belong to the clade Eumetazoa, animals with true tissues.

Phylum Cnidaria is one of the oldest groups in this clade.

Slide 11

Fig. 33-UN2

Calcarea and Silicea

Cnidaria

Lophotrochozoa

Ecdysozoa

Deuterostomia

Slide 12

Cnidarians have diversified into a wide range of both sessile and motile forms including jellies, corals, and hydras.

The basic body plan of a cnidarian is a sac with a central digestive compartment, the gastrovascular cavity.

A single opening functions as mouth and anus.

There are two variations on the body plan: the sessile polyp and motile medusa.

Cnidarians - radial symmetry

Slide 13

Polyp and medusa forms of cnidarians

Polyp

Mouth/anus

Body

stalk

Tentacle

Gastrovascular

cavity

Gastrodermis

Mesoglea

Epidermis

Tentacle

Mouth/anus

Medusa

Slide 14

Cnidarians are carnivores that use tentacles to capture prey.

The tentacles are armed with cnidocytes, unique cells that function in defense and capture of prey.

Nematocysts are specialized organelles within cnidocytes that eject a stinging thread.

Slide 15

A cnidocyte of a hydra

Tentacle

Nematocyst

“Trigger”

Cuticle

of prey

Thread

discharges

Thread

(coiled)

Cnidocyte

Thread

Slide 16

Phylum Cnidaria is divided into four major classes:

Hydrozoa

Scyphozoa

Cubozoa

Anthozoa

Slide 17

Table 33-1

Slide 18

Fig. 33-7 Cnidarians

(a) Colonial polyps (class

Hydrozoa)

(b) Jellies (class

Scyphozoa)

Sea wasp (class

Cubozoa)

(d) Sea anemone (class

Anthozoa)

(c)

Slide 19

Most hydrozoans alternate between polyp and medusa forms

Feeding

polyp

Reproductive

polyp

Medusa

bud

Medusa

ASEXUAL

REPRODUCTION

(BUDDING)