Chapter 34: The Invertebrates (Part 1, Week 7)

Question 1

What are animals that lacks a backbone (vertebrae)?

Answer 1

Invertebrate

Question 2

How many of all animal species are invertebrate?

Answer 2

95%!

Question 3

What is the phylogenetic tree summarizing our current understanding about the evolutionary relationships among animal groups?

Answer 3

Animal phylogenic tree.

Question 4

[Start 34.1 Ctenophores: The Earliest Animals]

What constitutes the earliest-diverging animal lineage?

Answer 4

Ctenophores (pronounced teen-o-for’-ah), also known as comb jellies.

All marine and all look like jellyfish. They have eight rows of cilia on their surfaces that resemble combs.

Question 5

What does the name of Ctenophores mean in Greek?

Answer 5

Greek ktenos, meaning comb, and phora, meaning bearing.

Question 6

T/F Comb jellies are probably the largest animals to use cilia for locomotion and possess two long tentacles that secrete a sticky substance onto which small prey adhere.

Answer 6

True

Question 7

What is a body cavity with a single opening to the outside; it functions as both a digestive system and circulatory system in cnidarians and comb jellies?

Answer 7

Gastrovasular cavity.

Question 8

Since all ctenophores possess both ovaries and testes, what are they called?

Answer 8

Hermaphrodites (from the Greek, for the god Hermes and the goddess Aphorodite)

Gametes are shed into the water to unite and eventually form a free-swimming larva that is very similar in form to the adult.

Question 9

Ctenophores are bioluminescent, which means?

Answer 9

They give off light instead of heat from chemical reactions.

Question 10

What do ctenophores share with bilaterians in the embryonic stages?

Answer 10

They have the prescense of muscle cells originating from the mesoderm (middle layer of three layers in early embryonic development). This suggests that ctenophores share a three-germ-layer embryonic structure with bilaterians.

However, recent analyse of the genome shows that ctenophores lack true Hox genes and possess a ctenophore-specific cleavage program

Hox genes are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of ‘position’, ensuring that the correct structures form in the correct places of the body.

Question 11

What is another thing that ctenophores lack from their bilaterian descendants?

Answer 11

Neuron-specfic genes are either absent or not expressed.

Question 12

[Start 34.2 Porifera: The Sponges]

What are members of the phylum Porifera (from the Latin, meaning porebearers), are commonly referred to as?

They are second to the Ctenophora in the animal phylogenetic tree.

Answer 12

Sponges

Question 13

What do sponges lack, which are a group of cells that have a similar structure and function?

Answer 13

True tissue

Question 14

Facts about Sponges!

1. Even though sponges carry most of the genes that are needed for a functioning nervous system, they have lost the ability to produce neurons during evolution.
2. Approximately 8,000 species of sponges, the vast majority of which are marine.
3. Range in size from only a few millimeters across to more than 2 m in diameter.
4. Smaller sponges may be radially symmetric, but most have no apparent symmetry.
5. Some sponges have a low, encrusting growth form, whereas others grow tall and erect.
6. Although adult sponges are sessile—that is, anchored in place—the larvae are free-swimming.
7. Many have a vaselike shape pierced with small holes or pores.

Answer 14

N/A

Question 15

If sponges are soft and sessile, why aren’t they eaten by other organisms?

Answer 15

Sponges aren’t eaten by other organisms because they produce toxic chemicals and contain needle-like silica spicules that are hard to digest.

Question 16

How is water drawn into a sponge and where does it flow into and then out of?

Two terms are in this answer!

Answer 16

1. Water is drawn in through pores on the walls of the sponge.
2. The water then enters into a central cavity, called the spongocoel.
3. The water then flows out throught the large opening at the top called the osculum.

Question 17

How does the water initially enter the pores on the walls of the sponge into the spongocoel?

Answer 17

The beating action of flagella of the choanocytes, or collar cells, that line the spongocoel.

In the process, the choanocytes trap and eat small particulate matter and tiny plankton.

Question 18

What do sponges have that are flattened on the outside of their body that also makes up the outer layer of animals in other phyla which protects the body?

Answer 18

Epithelial cells

Question 19

What is the area in between the choanocytes and the epithelial cells that is a gelatinous, protein-rich matrix and contains amoebocytes?

Answer 19

The mesohyl.

Question 20

What absorbs the food from the choanocytes, digests it, and carries the nutrients to other cells within the sponge’s body?

Answer 20

The amoebocytes

Thus, considerable cell-to-cell contact and communicationexist in sponges. Sponges are unique among the major animal phyla inusing intracellular digestion, the uptake of food particles by cells, as a mode of feeding.

Question 21

What, in sponges, are tough skeletal fibers that support the sponge’s body and can consist of sharp objects formed of protein, calcium carbonate, or silica with the help of amoebocytes?

Answer 21

Spicules - Needle-like structures that are made of protein, calcium carbonate, or silica and form lattice-like skeletons in sponges, possibly helping to reduce predation.

They kinda look like jacks (little metal stars)

For example, some deep-ocean species, called glass sponges, are distinguished by having needle-like silica spicules that form elaborate lattice-like skeletons. The presence of such tough spicules may explain why predation of sponges is rare.

Question 22

What is another type of tough protein in sponges that lend in skelatal support?

Answer 22

Spongin

Spongin skeletons are still commercially harvested and sold as bath sponges. Many species produce toxic defensive chemicals, some of which are being tested as possible anticancer and anti-inflammatory agents in humans.

Question 23

T/F Sponges reproduce asexually only.

Answer 23

False, they reproduce sexually and asexually.

Question 24

What do ctenophores and most sponges have in common when it comes to reproduction?

Answer 24

They are hermaphrodites, and thus can produce both sperm and eggs.

The eggs remain in the mesohyl, and the sperm are released into the water and carried by water currents to fertilize the eggs of neighboring sponges. Zygotes develop into flagellated swimming larvae that eventually settle on a suitable substrate to become sessile adults.

In asexual reproduction, a small fragment or bud may detach and form a new sponge.

Question 25

Where are the gametes within sponges derived from?

Answer 25

Amoebocytes or choanocytes.

Question 26

[Start 34.3 Cnidaria: Jellyfish and Other Radially Symmetric Animals]

What phylum have members mostly found in marine environments, although a few are freshwater species, and includes hydra, jellyfish, box jellies, sea anemones, and corals?

Answer 26

Cnidaria (from the Greek knide, meaning nettle, and aria, meaning related to; pronounced nid-air’-e-ah)

Question 27

How many embryonic germ layers do cnidaria have and what are they?

Answer 27

2; the ectoderm and the endoderm.

Question 28

What is a gelatinous substance between the epidermis and the gastrodermis in cnidarians? And also connects the embryonic germ layers known as the endoderm and ectoderm.

Answer 28

The mesoglea.

In jellyfish, the mesoglea is enlarged and forms a transparent jelly, whereas in hydra and corals, the mesoglea is very thin.

Question 29

What do most cnidarians have around their mouths that aid in prey detection and capture?

Answer 29

Tentacles

Question 30

What are the four main classes of the phylum Cnidaria? Answer by size in species.

Hint: AHSC

Answer 30

Anthozoa (sea anemones, sea fans, most corals) 6,000 species.
- All marine; polyp stage dominant; medusa stage absent; many are colonial.

Hydrozoa (portuguese man-of-war, Hydra, some corals) 2,700 species.
- Mostly marine; polyp stage usually dominant and colonal; medusa stage reduced

Scyphozoa (jellyfish) 200 species.
- All marine; medusa stage dominant and large (up to 2 m); reduced polyp stage

Cubozoa (box jellies, sea wasps) 20 species.
- All marine; medusa stage dominant; box-shaped

Question 31

What do most cnidarians exist in one or two different body forms associated with life style?

Name the two lifestyles.

Answer 31

Sessile Polyp - Corals and sea anemones

OR

Motile Medusa - predominately jellyfish

Question 32

What is a type of cnidarian body form that is sessile and occurs mouth up?

Answer 32

Polyp

Question 33

What is a type of of cnidarian body form that is motile and usually floats mouth down?

Answer 33

Medusa

Question 34

What do both polyp and medusa forms have that layers the organism which was previously talked about in embryonic stages?

Answer 34

Outer layer called the ectoderm and inner called the endoderm.

Question 35

What are the body forms of the following typesof cnidarians: jellyfi sh, sea anemone, and Portuguese man-of -war?

Answer 35

The dominant life stages are jellyfish: medusa; sea anemone: polyp; Portuguese man-of-war: polyp (in a large floating colony).

Question 36

What does the opening on a polyp and medusa cnidarian act as?

Answer 36

Mouth and anus.

Question 37

T/F Sea anemones are collonial polyps much like coral.

Answer 37

False, they enjoy being solitary.

Question 38

How do corals make their huge underwater limestone deposits called coral reefs?

Answer 38

They take dissolved calcium and carbonate ions from seawater and precipitate them as limestone underneath their bodies.

With some species, this leads to a buildup of limestone deposits. As each successive generation of polyps dies, the limestone remains in place, and new polyps grow on top.

The largest of these is Australia’s Great Barrier Reef, which stretches over 2,300 km. Many other extensive coral reefs are known, including the reef system along the Florida Keys. All coral reefs occur in warm water, generally between 20°C and 30°C.

Question 39

What do more mobile medusae possess which are simple sense organs near the bell margin… Give exampls of two.

Answer 39

Organ of equilibrium called statocysts.

Organ of photosensitivity called ocelli.

When one side of the bell tips upward, the statocysts on that side are stimulated, and muscle contraction is initiated to right the medusa. The ocelli allow medusae to position themselves in particular light levels.

Question 40

What is one of the unique and characteristic features of the cnidarians is the existence of certain cells that function in defense or the capture of prey?

Answer 40

Stinging cells called cnidocytes.

Question 41

What in a cnidarian, is a powerful capsule with an inverted coiled and barbed thread that functions to immobilize small prey which are contained within cnidocytes?

Answer 41

Nematocysts

Question 42

What is on the surface of a cnidocyte, a hairlike trigger that detects stimuli?

Answer 42

Cnidocil

When the cnidocil is touched or detects a chemical stimulus, the nematocyst is discharged, and its filament penetrates the prey and injects a small amount of toxin.

Small prey are immobilized and passed into the mouth by the tentacles. After discharge, the cnidocyte is absorbed, and a new one grows to replace it.

The nematocysts of most cnidarians are not harmful to humans, but those on the tentacles of the larger jellyfish and the Portuguese man-of-war can cause extreme pain or even death.

Question 43

Are cnidocytes recycled for reuse once they have been fired?

Answer 43

Cnidocytes are not reused. New ones form to replace the discharged ones.