Information

15.2: Sponges and Cnidarians - Biology

15.2: Sponges and Cnidarians - Biology



We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

The kingdom of animals is informally divided into invertebrate animals, those without a backbone, and vertebrate animals, those with a backbone. Although in general we are most familiar with vertebrate animals, the vast majority of animal species, about 95 percent, are invertebrates. Invertebrates include a huge diversity of animals, millions of species in about 32 phyla, which we can just begin to touch on here.

The sponges and the cnidarians represent the simplest of animals. Sponges appear to represent an early stage of multicellularity in the animal clade. Although they have specialized cells for particular functions, they lack true tissues in which specialized cells are organized into functional groups. Sponges are similar to what might have been the ancestor of animals: colonial, flagellated protists. The cnidarians, or the jellyfish and their kin, are the simplest animal group that displays true tissues, although they possess only two tissue layers.

Sponges

Animals in subkingdom Parazoa represent the simplest animals and include the sponges, or phylum Porifera (Figure 15.2.1). All sponges are aquatic and the majority of species are marine. Sponges live in intimate contact with water, which plays a role in their feeding, gas exchange, and excretion. Much of the body structure of the sponge is dedicated to moving water through the body so it can filter out food, absorb dissolved oxygen, and eliminate wastes.

The body of the simplest sponges takes the shape of a cylinder with a large central cavity, the spongocoel. Water enters the spongocoel from numerous pores in the body wall. Water flows out through a large opening called the osculum (Figure 15.2.2). However, sponges exhibit a diversity of body forms, which vary in the size and branching of the spongocoel, the number of osculi, and where the cells that filter food from the water are located.

Sponges consist of an outer layer of flattened cells and an inner layer of cells called choanocytes separated by a jelly-like substance called mesohyl. The mesohyl contains embedded amoeboid cells that secrete tiny needles called spicules or protein fibers that help give the sponge its structural strength. The cell body of the choanocyte is embedded in mesohyl but protruding into the spongocoel is a mesh-like collar surrounding a single flagellum. The beating of flagella from all choanocytes moves water through the sponge. Food particles are trapped in mucus produced by the sieve-like collar of the choanocytes and are ingested by phagocytosis. This process is called intracellular digestion. Amoebocytes take up nutrients repackaged in food vacuoles of the choanocytes and deliver them to other cells within the sponge.

Physiological Processes in Sponges

Despite their lack of complexity, sponges are clearly successful organisms, having persisted on Earth for more than half a billion years. Lacking a true digestive system, sponges depend on the intracellular digestive processes of their choanocytes for their energy intake. The limit of this type of digestion is that food particles must be smaller than individual cells. Gas exchange, circulation, and excretion occur by diffusion between cells and the water.

Sponges reproduce both sexually and asexually. Asexual reproduction is either by fragmentation (in which a piece of the sponge breaks off and develops into a new individual), or budding (an outgrowth from the parent that eventually detaches). A type of asexual reproduction found only in freshwater sponges occurs through the formation of gemmules, clusters of cells surrounded by a tough outer layer. Gemmules survive hostile environments and can attach to a substrate and grow into a new sponge.

Sponges are monoecious (or hermaphroditic), meaning one individual can produce both eggs and sperm. Sponges may be sequentially hermaphroditic, producing eggs first and sperm later. Eggs arise from amoebocytes and are retained within the spongocoel, whereas sperm arise from choanocytes and are ejected through the osculum. Sperm carried by water currents fertilize the eggs of other sponges. Early larval development occurs within the sponge, and free-swimming larvae are then released through the osculum. This is the only time that sponges exhibit mobility. Sponges are sessile as adults and spend their lives attached to a fixed substrate.

CONCEPT IN ACTION

Watch this video that demonstrates the feeding of sponges.

Cnidarians

The phylum Cnidaria includes animals that show radial or biradial symmetry and are diploblastic. Nearly all (about 99 percent) cnidarians are marine species. Cnidarians have specialized cells known as cnidocytes (“stinging cells”) containing organelles called nematocysts. These cells are concentrated around the mouth and tentacles of the animal and can immobilize prey with toxins. Nematocysts contain coiled threads that may bear barbs. The outer wall of the cell has a hairlike projection that is sensitive to touch. When touched, the cells fire the toxin-containing coiled threads that can penetrate and stun the predator or prey (see Figure 15.2.3).

Cnidarians display two distinct body plans: polyp or “stalk” and medusa or “bell” (Figure 15.2.4). Examples of the polyp form are freshwater species of the genus Hydra; perhaps the best-known medusoid animals are the jellies (jellyfish). Polyps are sessile as adults, with a single opening to the digestive system (the mouth) facing up with tentacles surrounding it. Medusae are motile, with the mouth and tentacles hanging from the bell-shaped body. In other cnidarians, both a polyp and medusa form exist, and the life cycle alternates between these forms.

Physiological Processes of Cnidarians

All cnidarians have two tissue layers. The outer layer is called the epidermis, whereas the inner layer is called the gastrodermis and lines the digestive cavity. Between these two layers is a non-living, jelly-like mesoglea. There are differentiated cell types in each tissue layer, such as nerve cells, enzyme-secreting cells, and nutrient-absorbing cells, as well as intercellular connections between the cells. However, organs and organ systems are not present in this phylum.

The nervous system is primitive, with nerve cells scattered across the body in a network. The function of the nerve cells is to carry signals from sensory cells and to contractile cells. Groups of cells in the nerve net form nerve cords that may be essential for more rapid transmission. Cnidarians perform extracellular digestion, with digestion completed by intracellular digestive processes. Food is taken into the gastrovascular cavity, enzymes are secreted into the cavity, and the cells lining the cavity absorb the nutrient products of the extracellular digestive process. The gastrovascular cavity has only one opening that serves as both a mouth and an anus (an incomplete digestive system). Like the sponges, Cnidarian cells exchange oxygen, carbon dioxide, and nitrogenous wastes by diffusion between cells in the epidermis and gastrodermis with water.

Cnidarian Diversity

The phylum Cnidaria contains about 10,000 described species divided into four classes: Anthozoa, Scyphozoa, Cubozoa, and Hydrozoa.

The class Anthozoa includes all cnidarians that exhibit a sessile polyp body plan only; in other words, there is no medusa stage within their life cycle. Examples include sea anemones, sea pens, and corals, with an estimated number of 6,100 described species. Sea anemones are usually brightly colored and can attain a size of 1.8 to 10 cm in diameter. These animals are usually cylindrical in shape and are attached to a substrate. A mouth opening is surrounded by tentacles bearing cnidocytes (Figure 15.2.5).

Scyphozoans include all the jellies and are motile and exclusively marine with about 200 described species. The medusa is the dominant stage in the life cycle, although there is also a polyp stage. Species range from 2 cm in length to the largest scyphozoan species, Cyanea capillata, at 2 m across. Jellies display a characteristic bell-like body shape (Figure 15.2.6).

CONCEPT IN ACTION

Identify the life cycle stages of jellies using this video animation game from the New England Aquarium.

The class Cubozoa includes jellies that are square in cross-section and so are known as “box jellyfish.” These species may achieve sizes of 15–25 cm. Cubozoans are anatomically similar to the jellyfish. A prominent difference between the two classes is the arrangement of tentacles. Cubozoans have muscular pads called pedalia at the corners of the square bell canopy, with one or more tentacles attached to each pedalium. In some cases, the digestive system may extend into the pedalia. Cubozoans typically exist in a polyp form that develops from a larva. The polyps may bud to form more polyps and then transform into the medusoid forms.

CONCEPT IN ACTION

Watch this video to learn more about the deadly toxins of the box jellyfish.

Hydrozoa includes nearly 3,500 species,1 most of which are marine. Most species in this class have both polyp and medusa forms in their life cycle. Many hydrozoans form colonies composed of branches of specialized polyps that share a gastrovascular cavity. Colonies may also be free-floating and contain both medusa and polyp individuals in the colony, as in the Portuguese Man O’War (Physalia) or By-the-Wind Sailor (Velella). Other species are solitary polyps or solitary medusae. The characteristic shared by all of these species is that their gonads are derived from epidermal tissue, whereas in all other cnidarians, they are derived from gastrodermal tissue (Figure 15.2.7ab).

Section Summary

Animals included in phylum Porifera are parazoans and do not possess true tissues. Sponges have multiple cell types that are geared toward executing various metabolic functions.

Cnidarians have outer and inner tissue layers sandwiching a noncellular mesoglea. Cnidarians possess a well-formed digestive system and carry out extracellular digestion. The cnidocyte is a specialized cell for delivering toxins to prey and predators. Cnidarians have separate sexes. They have a life cycle that involves morphologically distinct forms—medusoid and polypoid—at various stages in their life cycle.

Review Questions

The large central opening in the poriferan body is called the _____.

A. emmule
B. picule
C. stia
D. osculum

D

Cnidocytes are found in _____.

A. phylum Porifera
B. phylum Nemertea
C. phylum Nematoda
D. phylum Cnidaria

D

Cubozoans are ________.

A. polyps
B. medusoids
C. polymorphs
D. sponges

B

Free Response

Describe the feeding mechanism of sponges and identify how it is different from other animals.

The sponges draw water carrying food particles into the spongocoel using the beating of flagella in the choanocytes. The food particles are caught by the collar of the choanocyte and brought into the cell by phagocytosis. Digestion of the food particle takes place inside the cell. The difference between this and the mechanisms of other animals is that digestion takes place within cells rather than outside of cells. It means that the organism can feed only on particles smaller than the cells themselves.

Compare the structural differences between Porifera and Cnidaria.

Poriferans do not possess true tissues, whereas cnidarians do have tissues. Because of this difference, poriferans do not have a nerve net or muscle cells for locomotion, which cnidarians have.

Glossary

amoebocyte
an amoeba-like cell of sponges whose functions include distribution of nutrients to other cells in the sponge
budding
a form of asexual reproduction that occurs through the growth of a new organism as a branch on an adult organism that breaks off and becomes independent; found in plants, sponges, cnidarians, and some other invertebrates
choanocyte
a cell type unique to sponges with a flagellum surrounded by a collar used to maintain water flow through the sponge, and capture and digest food particles
Cnidaria
a phylum of animals that are diploblastic and have radial symmetry and stinging cells
cnidocyte
a specialized stinging cell found in Cnidaria
epidermis
the layer of cells that lines the outer surface of an animal
extracellular digestion
a form of digestion, the breakdown of food, which occurs outside of cells with the aid of enzymes released by cells
fragmentation
a form of asexual reproduction in which a portion of the body of an organism breaks off and develops into a living independent organism; found in plants, sponges, and some other invertebrates
gastrodermis
the layer of cells that lines the gastrovascular cavity of cnidarians
gastrovascular cavity
the central cavity bounded by the gastrodermis in cnidarians
gemmule
a structure produced by asexual reproduction in freshwater sponges that is able to survive harsh conditions
intracellular digestion
the digestion of matter brought into a cell by phagocytosis
medusa
a free-floating cnidarian body plan with a mouth on the underside and tentacles hanging down from a bell
mesoglea
the non-living, gel-like matrix present in between ectoderm and endoderm in cnidarians
mesohyl
the collagen-like gel containing suspended cells that perform various functions in sponges
monoecious
having both sexes in one body, hermaphroditic
nematocyst
the harpoon-like organelle within a cnidocyte with a pointed projectile and poison to stun and entangle prey
osculum
the large opening in a sponge body through which water leaves
polyp
the stalk-like, sessile life form of a cnidarians with mouth and tentacles facing upward, usually sessile but may be able to glide along a surface
Porifera
a phylum of animals with no true tissues, but a porous body with a rudimentary endoskeleton
spicule
a short sliver or spike-like structure, in sponges, they are formed of silicon dioxide, calcium carbonate, or protein, and are found in the mesohyl

Iron metabolic pathways in the processes of sponge plasticity

The ability to regulate oxygen consumption evolved in ancestral animals and is intrinsically linked to iron metabolism. The iron pathways have been intensively studied in mammals, whereas data on distant invertebrates are limited. Sea sponges represent the oldest animal phylum and have unique structural plasticity and capacity to reaggregate after complete dissociation. We studied iron metabolic factors and their expression during reaggregation in the White Sea cold-water sponges Halichondria panicea and Halisarca dujardini. De novo transcriptomes were assembled using RNA-Seq data, and evolutionary trends were analyzed with bioinformatic tools. Differential expression during reaggregation was studied for H. dujardini. Enzymes of the heme biosynthesis pathway and transport globins, neuroglobin (NGB) and androglobin (ADGB), were identified in sponges. The globins mutate at higher evolutionary rates than the heme synthesis enzymes. Highly conserved iron-regulatory protein 1 (IRP1) presumably interacts with the iron-responsive elements (IREs) found in mRNAs of ferritin (FTH1) and a putative transferrin receptor NAALAD2. The reaggregation process is accompanied by increased expression of IRP1, the antiapoptotic factor BCL2, the inflammation factor NFκB (p65), FTH1 and NGB, as well as by an increase in mitochondrial density. Our data indicate a complex mechanism of iron regulation in sponge structural plasticity and help to better understand general mechanisms of morphogenetic processes in multicellular species.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. The specimens of the sponges…

Fig 1. The specimens of the sponges H . dujardini and H . panicea .

Fig 2. Homology features for iron metabolic…

Fig 2. Homology features for iron metabolic proteins of sponges.

Fig 3. The predicted heme biosynthesis pathway…

Fig 3. The predicted heme biosynthesis pathway in sponges (modified from [61]).

Fig 4. Alignments of NGB protein sequences…

Fig 4. Alignments of NGB protein sequences of H . sapiens and three sponges.

Fig 5. Differential gene expression during the…

Fig 5. Differential gene expression during the dissociation/reaggregation processes in sponge H . dujardini .

Fig 6. Expression of ALAD and FTH1…

Fig 6. Expression of ALAD and FTH1 proteins in H . dujardini body tissue, dissociated…

Fig 7. Immune fluorescence of ALAD and…

Fig 7. Immune fluorescence of ALAD and FTH1.

Immune fluorescence of ALAD (red) and FTH1…

Fig 8. Fluorescence intensity of mitochondria in…

Fig 8. Fluorescence intensity of mitochondria in H . dujardini body tissues (A, B), dissociated…

Fig 9. Secondary structures of IREs in…

Fig 9. Secondary structures of IREs in FTH1, NAALAD2 and ACO2 mRNAs of H .…

Fig 10. Changes in gene expression during…

Fig 10. Changes in gene expression during the dissociation and reaggregation processes in H .…


Iron metabolic pathways in the processes of sponge plasticity

The ability to regulate oxygen consumption evolved in ancestral animals and is intrinsically linked to iron metabolism. The iron pathways have been intensively studied in mammals, whereas data on distant invertebrates are limited. Sea sponges represent the oldest animal phylum and have unique structural plasticity and capacity to reaggregate after complete dissociation. We studied iron metabolic factors and their expression during reaggregation in the White Sea cold-water sponges Halichondria panicea and Halisarca dujardini. De novo transcriptomes were assembled using RNA-Seq data, and evolutionary trends were analyzed with bioinformatic tools. Differential expression during reaggregation was studied for H. dujardini. Enzymes of the heme biosynthesis pathway and transport globins, neuroglobin (NGB) and androglobin (ADGB), were identified in sponges. The globins mutate at higher evolutionary rates than the heme synthesis enzymes. Highly conserved iron-regulatory protein 1 (IRP1) presumably interacts with the iron-responsive elements (IREs) found in mRNAs of ferritin (FTH1) and a putative transferrin receptor NAALAD2. The reaggregation process is accompanied by increased expression of IRP1, the antiapoptotic factor BCL2, the inflammation factor NFκB (p65), FTH1 and NGB, as well as by an increase in mitochondrial density. Our data indicate a complex mechanism of iron regulation in sponge structural plasticity and help to better understand general mechanisms of morphogenetic processes in multicellular species.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. The specimens of the sponges…

Fig 1. The specimens of the sponges H . dujardini and H . panicea .

Fig 2. Homology features for iron metabolic…

Fig 2. Homology features for iron metabolic proteins of sponges.

Fig 3. The predicted heme biosynthesis pathway…

Fig 3. The predicted heme biosynthesis pathway in sponges (modified from [61]).

Fig 4. Alignments of NGB protein sequences…

Fig 4. Alignments of NGB protein sequences of H . sapiens and three sponges.

Fig 5. Differential gene expression during the…

Fig 5. Differential gene expression during the dissociation/reaggregation processes in sponge H . dujardini .

Fig 6. Expression of ALAD and FTH1…

Fig 6. Expression of ALAD and FTH1 proteins in H . dujardini body tissue, dissociated…

Fig 7. Immune fluorescence of ALAD and…

Fig 7. Immune fluorescence of ALAD and FTH1.

Immune fluorescence of ALAD (red) and FTH1…

Fig 8. Fluorescence intensity of mitochondria in…

Fig 8. Fluorescence intensity of mitochondria in H . dujardini body tissues (A, B), dissociated…

Fig 9. Secondary structures of IREs in…

Fig 9. Secondary structures of IREs in FTH1, NAALAD2 and ACO2 mRNAs of H .…

Fig 10. Changes in gene expression during…

Fig 10. Changes in gene expression during the dissociation and reaggregation processes in H .…


Download Now!

We have made it easy for you to find a PDF Ebooks without any digging. And by having access to our ebooks online or by storing it on your computer, you have convenient answers with Biology Sponges Cnidarians Quiz Answer Key . To get started finding Biology Sponges Cnidarians Quiz Answer Key , you are right to find our website which has a comprehensive collection of manuals listed.
Our library is the biggest of these that have literally hundreds of thousands of different products represented.

Finally I get this ebook, thanks for all these Biology Sponges Cnidarians Quiz Answer Key I can get now!

I did not think that this would work, my best friend showed me this website, and it does! I get my most wanted eBook

wtf this great ebook for free?!

My friends are so mad that they do not know how I have all the high quality ebook which they do not!

It's very easy to get quality ebooks )

so many fake sites. this is the first one which worked! Many thanks

wtffff i do not understand this!

Just select your click then download button, and complete an offer to start downloading the ebook. If there is a survey it only takes 5 minutes, try any survey which works for you.


Sponges and Cnidarians

The kingdom of animals is informally divided into invertebrate animals, those without a backbone, and vertebrate animals, those with a backbone. Although in general we are most familiar with vertebrate animals, the vast majority of animal species, about 95 percent, are invertebrates. Invertebrates include a huge diversity of animals, millions of species in about 32 phyla, which we can just begin to touch on here.

The sponges and the cnidarians represent the simplest of animals. Sponges appear to represent an early stage of multicellularity in the animal clade. Although they have specialized cells for particular functions, they lack true tissues in which specialized cells are organized into functional groups. Sponges are similar to what might have been the ancestor of animals: colonial, flagellated protists. The cnidarians, or the jellyfish and their kin, are the simplest animal group that displays true tissues, although they possess only two tissue layers.

Sponges

Animals in subkingdom Parazoa represent the simplest animals and include the sponges, or phylum Porifera ([link]). All sponges are aquatic and the majority of species are marine. Sponges live in intimate contact with water, which plays a role in their feeding, gas exchange, and excretion. Much of the body structure of the sponge is dedicated to moving water through the body so it can filter out food, absorb dissolved oxygen, and eliminate wastes.

The body of the simplest sponges takes the shape of a cylinder with a large central cavity, the spongocoel. Water enters the spongocoel from numerous pores in the body wall. Water flows out through a large opening called the osculum ([link]). However, sponges exhibit a diversity of body forms, which vary in the size and branching of the spongocoel, the number of osculi, and where the cells that filter food from the water are located.

Sponges consist of an outer layer of flattened cells and an inner layer of cells called choanocytes separated by a jelly-like substance called mesohyl. The mesohyl contains embedded amoeboid cells that secrete tiny needles called spicules or protein fibers that help give the sponge its structural strength. The cell body of the choanocyte is embedded in mesohyl but protruding into the spongocoel is a mesh-like collar surrounding a single flagellum. The beating of flagella from all choanocytes moves water through the sponge. Food particles are trapped in mucus produced by the sieve-like collar of the choanocytes and are ingested by phagocytosis. This process is called intracellular digestion. Amoebocytes take up nutrients repackaged in food vacuoles of the choanocytes and deliver them to other cells within the sponge.

Physiological Processes in Sponges

Despite their lack of complexity, sponges are clearly successful organisms, having persisted on Earth for more than half a billion years. Lacking a true digestive system, sponges depend on the intracellular digestive processes of their choanocytes for their energy intake. The limit of this type of digestion is that food particles must be smaller than individual cells. Gas exchange, circulation, and excretion occur by diffusion between cells and the water.

Sponges reproduce both sexually and asexually. Asexual reproduction is either by fragmentation (in which a piece of the sponge breaks off and develops into a new individual), or budding (an outgrowth from the parent that eventually detaches). A type of asexual reproduction found only in freshwater sponges occurs through the formation of gemmules, clusters of cells surrounded by a tough outer layer. Gemmules survive hostile environments and can attach to a substrate and grow into a new sponge.

Sponges are monoecious (or hermaphroditic), meaning one individual can produce both eggs and sperm. Sponges may be sequentially hermaphroditic, producing eggs first and sperm later. Eggs arise from amoebocytes and are retained within the spongocoel, whereas sperm arise from choanocytes and are ejected through the osculum. Sperm carried by water currents fertilize the eggs of other sponges. Early larval development occurs within the sponge, and free-swimming larvae are then released through the osculum. This is the only time that sponges exhibit mobility. Sponges are sessile as adults and spend their lives attached to a fixed substrate.

Watch this video that demonstrates the feeding of sponges.

Cnidarians

The phylum Cnidaria includes animals that show radial or biradial symmetry and are diploblastic. Nearly all (about 99 percent) cnidarians are marine species. Cnidarians have specialized cells known as cnidocytes (“stinging cells”) containing organelles called nematocysts. These cells are concentrated around the mouth and tentacles of the animal and can immobilize prey with toxins. Nematocysts contain coiled threads that may bear barbs. The outer wall of the cell has a hairlike projection that is sensitive to touch. When touched, the cells fire the toxin-containing coiled threads that can penetrate and stun the predator or prey (see [link]).

Cnidarians display two distinct body plans: polyp or “stalk” and medusa or “bell” ([link]). Examples of the polyp form are freshwater species of the genus Hydra perhaps the best-known medusoid animals are the jellies (jellyfish). Polyps are sessile as adults, with a single opening to the digestive system (the mouth) facing up with tentacles surrounding it. Medusae are motile, with the mouth and tentacles hanging from the bell-shaped body. In other cnidarians, both a polyp and medusa form exist, and the life cycle alternates between these forms.

Physiological Processes of Cnidarians

All cnidarians have two tissue layers. The outer layer is called the epidermis, whereas the inner layer is called the gastrodermis and lines the digestive cavity. Between these two layers is a non-living, jelly-like mesoglea. There are differentiated cell types in each tissue layer, such as nerve cells, enzyme-secreting cells, and nutrient-absorbing cells, as well as intercellular connections between the cells. However, organs and organ systems are not present in this phylum.

The nervous system is primitive, with nerve cells scattered across the body in a network. The function of the nerve cells is to carry signals from sensory cells and to contractile cells. Groups of cells in the nerve net form nerve cords that may be essential for more rapid transmission. Cnidarians perform extracellular digestion, with digestion completed by intracellular digestive processes. Food is taken into the gastrovascular cavity, enzymes are secreted into the cavity, and the cells lining the cavity absorb the nutrient products of the extracellular digestive process. The gastrovascular cavity has only one opening that serves as both a mouth and an anus (an incomplete digestive system). Like the sponges, Cnidarian cells exchange oxygen, carbon dioxide, and nitrogenous wastes by diffusion between cells in the epidermis and gastrodermis with water.

Cnidarian Diversity

The phylum Cnidaria contains about 10,000 described species divided into four classes: Anthozoa, Scyphozoa, Cubozoa, and Hydrozoa.

The class Anthozoa includes all cnidarians that exhibit a sessile polyp body plan only in other words, there is no medusa stage within their life cycle. Examples include sea anemones, sea pens, and corals, with an estimated number of 6,100 described species. Sea anemones are usually brightly colored and can attain a size of 1.8 to 10 cm in diameter. These animals are usually cylindrical in shape and are attached to a substrate. A mouth opening is surrounded by tentacles bearing cnidocytes ([link]).

Scyphozoans include all the jellies and are motile and exclusively marine with about 200 described species. The medusa is the dominant stage in the life cycle, although there is also a polyp stage. Species range from 2 cm in length to the largest scyphozoan species, Cyanea capillata, at 2 m across. Jellies display a characteristic bell-like body shape ([link]).

Use this video to identify the life cycle stages of jellies.

The class Cubozoa includes jellies that are square in cross-section and so are known as “box jellyfish.” These species may achieve sizes of 15–25 cm. Cubozoans are anatomically similar to the jellyfish. A prominent difference between the two classes is the arrangement of tentacles. Cubozoans have muscular pads called pedalia at the corners of the square bell canopy, with one or more tentacles attached to each pedalium. In some cases, the digestive system may extend into the pedalia. Cubozoans typically exist in a polyp form that develops from a larva. The polyps may bud to form more polyps and then transform into the medusoid forms.

Watch this video to learn more about the deadly toxins of the box jellyfish.

Hydrozoa includes nearly 3,500 species, 1 most of which are marine. Most species in this class have both polyp and medusa forms in their life cycle. Many hydrozoans form colonies composed of branches of specialized polyps that share a gastrovascular cavity. Colonies may also be free-floating and contain both medusa and polyp individuals in the colony, as in the Portuguese Man O’War (Physalia) or By-the-Wind Sailor (Velella). Other species are solitary polyps or solitary medusae. The characteristic shared by all of these species is that their gonads are derived from epidermal tissue, whereas in all other cnidarians, they are derived from gastrodermal tissue ([link]ab).

Section Summary

Animals included in phylum Porifera are parazoans and do not possess true tissues. These organisms show a simple organization. Sponges have multiple cell types that are geared toward executing various metabolic functions.

Cnidarians have outer and inner tissue layers sandwiching a noncellular mesoglea. Cnidarians possess a well-formed digestive system and carry out extracellular digestion. The cnidocyte is a specialized cell for delivering toxins to prey and predators. Cnidarians have separate sexes. They have a life cycle that involves morphologically distinct forms—medusoid and polypoid—at various stages in their life cycle.


Cnidarian Anatomy

Anemone and coral are shaped with one end attached to something solid and the other end with tentacles moving out into the water. The shape is generally called a polyp form. Yes, even coral have that going on. When you think of a coral, you are probably thinking of a hard thing. That hard exoskeleton is what is left of the coral after it dies. When it is alive, hundreds of thousands of cells are alive and waiting for food to come by.

Back to the anatomy of the cnidarians. Anemone and coral are an improvement on sponges. One big improvement is that they have a nervous system. That doesn't mean that they are thinking and planning how to catch food. It does mean that the whole organism can have a coordinated response. That response means if something happens in one part of the anemone, the rest of the anemone can act in a certain way. Maybe a fish is captured on the left side. The right side would then move over to help hold the fish so that it can't escape. They aren't thinking yet. They are acting based on a stimulus.


What are Sponges?

Sponges are aquatic animals with a simple hollow asymmetrical body and categorized under Phylum Porifera. Phylum Porifera includes about 7000 identified species. Some examples for sponges include barrel sponges, boring sponges, basket sponges, bath sponges, etc. Most species are marine and very few live in freshwater. Adults are sessile and have an asymmetrical bodies. Sponge body is composed of two layers outer flattened cell layer and inner flagellated collar cell line, which opens to its internal cavity. In between these two cell layers, there is a gel-like extracellular matrix. In most sponges, this matrix secretes fibrous protein that acts like an exoskeleton. Unlike other animals, sponges have intracellular digestion. Sponges feed on planktons by filtering water. Sponges are hermaphrodites. Their sperms are released into the water and eggs are stored in their body. The larva is free-living and motile. Sponges are harvested from the sea by humans and used for bathing and cleaning.


Polymorphism: Definition, Causes and Significance | Cnidarians

Polymorphism may be defined as the “phenom­enon of existence of different physiological and morphological forms represented by an extensive range of variation within a single species”.

It may be defined in another way, poly­morphism means “the existence of indi­viduals (zooids) of a single species in more than one forms and functions.”

Causes of Polymorphism:

Polymorphism is due to the division of labour, diversifica­tion of forms and specialization. Two general types of interactions, viz., co-operation and disoperation are exhibited by the members of an animal association.

In the colonial forms, disoperation ceases gradually and is replaced by co-operation. Finally the whole colony appears as a single individual, and the zooids function collectively for the inter­est of the colony (Barrington 1979).

Basic Units of Polymorphism:

All forms of zooids can be divided into two fundamen­tal forms which can be derived from each other.

(A) Polyp form (L. Polypus = polyp) (Fig. 12.32A):

(i) Sedentary tubular form with one end closed.

(ii) Free conical end (preoral end) bear­ing hypostome, mouth and tentacles.

(iv) Mouth situated on hypostome lead­ing to coelenteron.

(v) Un-branched elongated tentacles sur­rounding the mouth.

(vi) The polyp may be encased by a trans­parent covering, the hydrotheca (e.g., Hydra).

(B) Medusoid form (Gk. Medousa = one who rules) (Fig. 12.32B):

(i) Umbrella-shaped with convex exumbrella and ventral concave subumbrellar surface.

(ii) Subumbrellar surface with mouth and manubrium.

(iii) Radial and circular canals present.

(iv) Marginal tentacles are present.

(vi) A velum is often present.

Polyps and medusae are consid­ered as homologous structures and can be theoretically derived from a sac-like body. Possessing of manubrium and mouth points to the basic similarity (Hyman, 1940).

These two forms alternate with each other in the life history of a typical cnidarian—the polyp pro­ducing medusa asexually and the medusa producing polyp sexually.

Origin of Polymorphism:

Polymorphism in cnidarians is virtually regarded to be the division of labour, where different zooids perform diverse functions.

As regards the origin of polymorphism in cnidarians, the following theories have been advanced:

The main support­ers of the theory are Huxley, Metschnikoff and Eschscholtz. They regard that each poly­morphic colony is an individual and the polyps or medusae, which are budded off from it, are the organs.

The supporters of this theory are Vogt, Leuckart, Gegenbaur, Cuhn and Kukenthal. This theory suggests that cnidarian colony is constituted of inde­pendent and separate individuals which re­main in organic connection with one another. According to this view each zooid is a sepa­rate individual, where some portions may be either lost or obliterated in course of time.

This theory is for­warded by Haeckel, Balfour and Sedgwick. The theory advocates that the primitive zo­oid of polymorphic colony was, with all probabilities, a medusa which produced other medusae by the process of budding.

These medusae possess the power of locomotion as well as the power of reproduction. In this view many organs of the colony are nothing more than the parts of such medusoid indi­viduals which have subsequently shifted their attachments from the original medusa.

This concept makes a compro­mise between the two previously de­scribed theories. It agrees with the sec­ond theory in asserting the colonial nature and also admits that asexual re­production and specialisation of certain parts of the colony, as advocated in the first theory.

IV. Theory of neoteny (supported by A. C. Hardy):

Garstang first postulated the idea of the neotenous retention of larval characters and the members of Siphonophora giving rise to polymorphism.

Significance of Polymorphism:

1. Polymorphism is intimately associated with life-history. The life cycle is simple in the monomorphic forms (e.g., Hydra). With the advent of polymorphism reproductive powers are divided. The polyp is capable only of asexual reproduction while sexual reproduction is confined to the gonophores. Thus arises the alternation of generation or metagenesis.

2. Polymorphism is also concerned with the division of labour. So polyp are mainly associated with the function of feeding, test­ing, protection and also asexual reproduc­tion while medusa is concerned with sexual reproduction.


The significance of sponges for comparative studies of developmental evolution

Scott A. Nichols, Department of Biological Sciences, University of Denver, Denver, CO.

Department of Biological Sciences, University of Denver, Denver, Colorado

Department of Biological Sciences, University of Denver, Denver, Colorado

Scott A. Nichols, Department of Biological Sciences, University of Denver, Denver, CO.

Abstract

Sponges, ctenophores, placozoans, and cnidarians have key evolutionary significance in that they bracket the time interval during which organized animal tissues were first assembled, fundamental cell types originated (e.g., neurons and myocytes), and developmental patterning mechanisms evolved. Sponges in particular have often been viewed as living surrogates for early animal ancestors, largely due to similarities between their feeding cells (choanocytes) with choanoflagellates, the unicellular/colony-forming sister group to animals. Here, we evaluate these claims and highlight aspects of sponge biology with comparative value for understanding developmental evolution, irrespective of the purported antiquity of their body plan. Specifically, we argue that sponges strike a different balance between patterning and plasticity than other animals, and that environmental inputs may have prominence over genetically regulated developmental mechanisms. We then present a case study to illustrate how contractile epithelia in sponges can help unravel the complex ancestry of an ancient animal cell type, myocytes, which sponges lack. Sponges represent hundreds of millions of years of largely unexamined evolutionary experimentation within animals. Their phylogenetic placement lends them key significance for learning about the past, and their divergent biology challenges current views about the scope of animal cell and developmental biology.

  • Comparative Development and Evolution > Evolutionary Novelties
  • Comparative Development and Evolution > Body Plan Evolution

Abstract

Reconstructing the earliest events in animal evolution, including the origin of novel cell types and developmental signaling pathways, depends upon comparative research between traditional research models with four understudied lineages: sponges, ctenophores, placozoans, and cnidarians.


Sponge & Cnidarian Study Guide

· Know relatives of the jellyfish
· How are sponges different from other animals
· Know characteristics of all invertebrates
· Know characteristics of sponges
· What is the function of collar cells in sponges
· What are spicules
· Know characteristics of adult sponges
· Be able to explain skeletal support of sponges
· How do sponges obtain their food
· What helps draw water into a sponge
· What is the function of amebocytes in sponges
· How does excess water leave a sponge
· What is the purpose of gemmules in sponges
· What is a hermaphrodite
· How can sponges reproduce
· Know animals that capture prey by using nematocysts
· What are the 2 distinct life stages of cnidarians
· Describe nematocysts
· What organisms have tentacles with stinging cells
· Know examples of cnidarians
· Describe the life of a planula larva
· Know the life stage that is dominant in sea anemones
· What organisms would be anthozoans
· Know the dominant life stage of jellyfish
· Know the main characteristics of ctenophores


Watch the video: Sponges Cnidarians quiz (August 2022).