IB-202-2

3-10-06

Chapter 33

Invertebrates

Sponges

• Overview: Life Without a Backbone

• Invertebrates– Are animals that lack a backbone– Account for 95% of known animal species

Figure 33.1

• A review of animal phylogeny

Ancestral colonialchoanoflagellate

Eumetazoa

Bilateria

Deuterostomia

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Figure 33.2

• Sponges are sessile and have a porous body and choanocytes

• Sponges, phylum Porifera– Live in both fresh and marine waters– Lack true tissues and organs

• Sponges are suspension feeders– Capturing food particles suspended in the

water that passes through their body

Azure vase sponge (Callyspongia plicifera)

Osculum

Spicules

Waterflow

Flagellum

CollarFood particlesin mucus

Choanocyte

Phagocytosis offood particles Amoebocyte

Choanocytes. The spongocoel is lined with feeding cells called choanocytes. By beating flagella, the choanocytes create a current that draws water in through the porocytes.

Spongocoel. Water passing through porocytes

enters a cavity called the spongocoel.

Porocytes. Water enters the epidermis through

channels formed by porocytes, doughnut-shaped cells that span the body wall.

Epidermis. The outer layer consists of tightly

packed epidermal cells.

Mesohyl. The wall of this simple sponge consists of

two layers of cells separatedby a gelatinous matrix, themesohyl (“middle matter”).

The movement of the choanocyte flagella also draws water through its collar of fingerlike projections. Food particles are trapped in the mucus coating the projections, engulfed by phagocytosis, and either digested or transferred to amoebocytes.

Amoebocyte. Amoebocytes transport nutrients to other cells ofthe sponge body and also produce materials for skeletal fibers (spicules).

5

6

7

4

3

2

1

Figure 33.4

• Choanocytes, flagellated collar cells– Generate a water current through the sponge

and ingest suspended food

• Most sponges are hermaphrodites

• Meaning that each individual functions as both male and female

Experiment: If a sponge is forced througha fine mesh screen and the cells put in aBeaker, within a few days they will reassembleand form an intact sponge. What does thismean? Do sponge cells communicate with each other?

Variations in Form or Shapes of Sponges

Sponges come in a variety of shapes, sizes and Colors!

Since sponges are an aggregation of cells and not organized into tissues, how do they achieve this variability in structure and color??? Something to think about!

The Shape of Life

Episode 1- Origins (Sponges)The Story of Science.

Video

• One hypothesis of animal phylogeny based mainly on molecular data

Figure 32.11

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“Radiata”

“Porifera” Deuterostomia Lophotrochozoa Ecdysozoa

Bilateria

Eumetazoa

Metazoa

Ancestral colonialflagellate

• One hypothesis of animal phylogeny based mainly on morphological and developmental comparisons

Figure 32.10

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“Radiata” Deuterostomia Protostomia

Bilateria

Eumetazoa

Metazoa

Ancestral colonialflagellate

Phylum Cnidaria• Cnidarians have radial symmetry, a

gastrovascular cavity, and cnidocytes

• All animals except sponges– Belong to the clade Eumetazoa, the animals

with true tissues

• Phylum Cnidaria– Is one of the oldest groups in this clade

• Cnidarians– Have diversified into a wide range of both

sessile and floating forms including jellies, corals, and hydras

– But still exhibit a relatively simple diploblastic, radial body plan

• The basic body plan of a cnidarian– Is a sac with a central digestive

compartment, the gastrovascular cavity

• A single opening– Functions as both mouth and anus

• There are two variations on this body plan– The sessile polyp and the floating medusa

Mouth/anus

TentacleGastrovascularcavity

Gastrodermis

Mesoglea

Epidermis

Tentacle

Bodystalk

Mouth/anus

MedusaPolyp

Figure 33.5

Tentacle

“Trigger”

Nematocyst

Coiled thread

DischargeOf thread

Cnidocyte

Prey

Figure 33.6

• Cnidarians are carnivores– That use tentacles to capture prey

• The tentacles are armed with cnidocytes– Unique cells that function in defense and the

capture of prey

• The phylum Cnidaria is divided into four major classes

Table 33.1

– Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa

(a) These colonial polyps are members of class Hydrozoa.

(b) Many species of jellies (classScyphozoa), including thespecies pictured here, are bioluminescent. The largest scyphozoans have tentaclesmore than 100 m long dangling from a bell-shaped body up to 2 m in diameter.

(c) The sea wasp (Chironex fleckeri) is a member of class Cubozoa. Its poison,which can subdue fish andother large prey, is more potent than cobra venom.

(d) Sea anemones and othermembers of class Anthozoaexist only as polyps.

Figure 33.7a–d

Hydrozoans• Most hydrozoans

– Alternate between polyp and medusa forms

Feeding polyp

Reproductivepolyp

Medusabud

ASEXUALREPRODUCTION(BUDDING)

GonadMedusa

MEIOSIS

FERTILIZATION

SEXUALREPRODUCTION Egg Sperm

Developingpolyp

Portion ofa colonyof polyps

Maturepolyp

Planula(larva) Key

Haploid (n)Diploid (2n)1 mm

Zygote

Figure 33.8

A colony ofinterconnected

polyps (inset,LM) results

from asexualreproductionby budding.

1

Some of the colony’s polyps, equipped with tentacles, are specialized for feeding.

2 Other polyps, specialized for reproduction, lack tentacles and produce tiny medusae by asexual budding.

3

The medusae swim off, grow, and reproduce sexually.

4

The zygote develops into a solid ciliated larva called a planula.5 The planula eventually settles

and develops into a new polyp.6

Scyphozoans

• In the class Scyphozoa– Jellies (medusae) are the prevalent form of

the life cycle

Cubozoans

• In the class Cubozoa, which includes box jellies and sea wasps. Nematocysts full of

• toxic venom– The medusa is box-shaped and has complex

eyes unlike scyphozoa

Anthozoans

• Class Anthozoa includes the corals and sea anemones– Which occur only as polyps