Description
Read pages 3-5 and 8-12 in chapter 15 Phylum Mollusca of Unit II of the Study Guide to answer the Clam Dissection Questions. Then read pages 5-8 Cephalopoda in Unit III of the Study guide attached below and watch the videos below to answer the Squid Dissection Questions.https://docs.google.com/presentation/d/1_u38Omi_um…https://www.youtube.com/watch?v=ADGkuX8IL9chttps://www.youtube.com/watch?v=qaNrQrwlCQ4
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Phylum Mollusca Clam Dissection Questions
Name _________________________
Detailed Clam (bivalve, molluscs or mollusks Dissection (Jr. High, High School and
College Review)
Steven Rokusek
Dr. Dale Droge
Dakota State University
10 points each
1. What does the term bivalve mean? Identify the three layers of the shell. Identify
the umbo by giving its location and describing its structure. How do the rings on the
shell form? What can we determine from the series of rings?
2. Explain how to pry open the shells of the clam so that the internal structures can be
dissected and identified. Two large muscles that close the shells of the clam and
hold them together must be cut to pry open the shell. Name these muscles.
3. Name the fleshy membrane that lines the inside of the shell, and give three
functions of it. Explain how this structure is used by the clam to produce a pearl.
4. Describe the structure of the gills and tell what the distinguishing features are that
allow you to identify them in dissection. What are two functions performed by the
gills? Explain the process of gaseous exchange that is carried out by the gills.
What is the importance of the large surface area of the gills in carrying out this
function?
5. Give the term for the type of feeding clams have and explain what this term means.
How do the gills help in this process?
6. Describe the position, appearance, and structure of the foot and explain its function.
7. Describe the structure of the labial palps. What is their function?
8. Describe and define the visceral mass. Identify the structures that are visible in a
dissected visceral mass. What is the greenish structure identified in the dissection?
What is its function? What is the yellowish material? Describe the appearance of
the intestines in the tissue of the visceral mass and explain how you would you
identify them.
9. What kind of circulatory system do clams have? Describe it. Compare it to the type
of system we have by explaining the difference in how ours works. Describe the
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location and chambers of the heart. What structure passes through the cavity in
which the heart is found?
10. Was a brain visible in the dissection? Describe the nervous system of the clam.
(Use the study guide)
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UNIT II
Diversity of Invertebrates
Phylum Porifera to Platyhelminthes and Nemertea
CHAPTER 11
Introduction to the Animal Kingdom
Objectives:
1. To learn the characteristics of animals that distinguish them from other kingdoms of
organisms.
2. To recognize that animals are classified into groups based upon their evolutionary
relatedness.
3. To understand the importance of major characteristics, such as type of body
symmetry, type of body cavity, and type of embryological development in the
classification of animals.
4. To learn the types of body symmetry found in animals, and to become aware of the
practical importance of planes and directional terms in dissection and anatomical
identification
5. To learn the types of body cavities found in animals, and to become aware of the
significance of this characteristic is the classification of animals.
6. To learn how embryological development is used to divide animals into two groups:
protostomes and deuterostomes.
7. To gain an overview of the evolution of the major groups of animals by examining an
“evolutionary tree”, which shows animals separated into “branches” according to key
features of structure and development.
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Definition
Animals are defined as multicellular, ingestive, heterotrophic, eukaryotes.
Characteristics of Animals
1.
Animals have heterotrophic nutrition; they ingest food and digest it within a
digestive system. Carbohydrate food is stored in the form of glycogen.
2.
In animals, the body form is rather constant, the organs are mostly internal.
3.
Animals stop growing when they reach maturity.
4.
Animals are multicellular; their bodies are composed of many cells.
5.
The cells of animals are eukaryotic; a well-formed nucleus is present.
6.
The cells of animals lack cell walls and chloroplasts. Plant cell have cell walls and
chloroplasts. Animal cells have centrioles. Centrioles are lacking in plant cells.
However, they have another structure called the microtubule organizing center that
forms spindle fibers. During division, animal cells have astral rays. Astral rays are
lacking in plant cells. Animal cells divide by constriction of cytoplasm. Plant cells
divide by cell-plate formation.
7.
The cells of an animal exhibit division of labor. This means that the cells are
specialized to perform specific functions.
8.
Animals have a unique family of connective tissue proteins called collagens.
9.
Most animals are capable of locomotion or movement from place to place. Animals
move by means of contraction of muscle cells.
10. Animals have an acetylcholine/cholinesterase-based nervous system with special
types of cell-cell junctions. Most animals have a pronounced response to stimuli,
and neural cells that coordinate the action of the muscles.
11. Most animals reproduce sexually with large, nonmotile eggs, and small, flagellated
sperm. Most animals are diploid with gametes the only haploid stage in the life
cycle.
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The Animal Kingdom includes over a million known species, but it is believed that there
are many more species that remain undiscovered. Estimates of the number of species
believed to exist range from lows of 10-30 million to highs of 100-200 million. Animals
are traditionally divided into two large groups, the invertebrates, or those that do not
possess a backbone and the vertebrates, or those species that possess a backbone. The
invertebrates are by far the largest group, constituting over 96% of all described species
of animals.
Comparison of Plant Cells and Animal Cells
Characteristic
Cell Walls
Presence of Chloroplasts
Presence of Centrioles
Plant Cells
Have cell wall composed
of cellulose
Plants are photosynthetic.
The photosynthetic
pigments are concentrated
in chloroplasts.
Plant cells lack centrioles.
Storage of Food
Food is stored in the form
of starch within plastids.
Cell Division
(Cytokinesis)
Plant cell divide by cellplate formation.
Vacuoles
Plant cells have a large
central vacuole
Animal Cells
Lack cell walls
Animal cells are not
photosynthetic. Animal
cells lack chloroplasts.
Animal cells have
centrioles.
Food is stored in the form
of glycogen. Plastids are
lacking.
Animal cells divide by
constriction of cytoplasm.
( a cleavage furrow)
Animal cells have many
smaller vesicles
Features of the Body Used to Classify Animals
Animal Symmetry
Symmetry is present in an animal if it can be divided by a median plane into equivalent
halves with corresponding parts on opposite sides of the plane.
Terms Describing Symmetry
Asymmetry is a lack of symmetry. Examples are certain sponges.
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Types of Symmetry
Radial symmetry is a type of symmetry in which the organism can be divided into
similar halves by any longitudinal plane passing through the center. The animal body has
the form of a cylinder with body parts arranged regularly around the longitudinal axis.
Examples of animals that have radial symmetry are hydra, jellyfish, and sea anemones.
Oral side- the surface on which the mouth is located.
Aboral side – the surface opposite the mouth.
Biradial symmetry is a variation of radial symmetry. Because of some part that is single
or paired rather than radial, only one or two planes through the longitudinal axis divide
the organism into equivalent halves. Examples are the members of phylum Ctenophora
(comb jellies).
Bilateral Symmetry is a type of symmetry in which a midsagittal plane divides the
organism into halves that are mirror images of one another. In a bilaterally symmetrical
animal, three planes (flat surfaces) are used to divide the organism into specific parts:
1) Sagittal plane, a lengthwise vertical plane that divides the animal into right and left
portions.
1a) Midsagittal plane, a lengthwise vertical plane through the midline that
divides the organism into halves that are mirror images of one another.
Note: An ordinary sagittal plane can be off center to the left or right, dividing the
animal into unequal left and right portions.
2) Frontal plane, a lengthwise plane at a right angle to the sagittal plane; divides the
organism into dorsal and ventral portions.
3) Transverse plane, a plane at right angles to both the sagittal and frontal planes;
divides the body into anterior and posterior portions.
In a bilaterally symmetrical animal, there is a definite head end and a definite tail end.
Bilateral symmetry is also associated with cephalization, the concentration of nerve
tissue in the head end of the organism. Bilateral symmetry is also associated with
directed movement. The animal moves in the direction of the head or anterior end, the
tail follows.
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Terms Used to Indicate Direction or Regions of an Animal’s Body
1) Anterior – toward the head end. (In the direction of forward motion)
2) Posterior – toward the tail end.
3) Dorsal – toward the back.
4) Ventral – front or belly side.
5) Medial – toward the midline of the body.
6) Lateral – toward the side of the body.
7) Proximal – toward the point of attachment of a part.
8) Distal – away from the point of attachment of a part.
9) Pectoral – refers to the chest region or the area supporting the forelegs.
10) Pelvic – refers to the hip region or the area supporting the hind legs.
Special Use of Directional Terms in Man
The directional terms are used differently in man, because man is bipedal. The terms
anterior and ventral are synonymous. Anterior is toward the front of the body in the
direction of forward motion. This is also the ventral or abdominal surface. Posterior is
the opposite direction, toward the back. This is also the dorsal surface. Which direction
is toward the head in man? To refer to this direction, the term cranial is used in man.
The opposite direction is caudal.
Type of Body Cavity
Body cavity – a cavity that is located between the body wall and the wall of the digestive
tract. Cavities are considered to be Body Cavities only if they enclose organs.
Animals may be divided into three types based upon which type of body cavity they
have:
1) Acoelomate – an animal that does not have a body cavity. In this type, the
space between the epidermal body covering and the wall of the digestive tract
is filled in with solid tissue. Examples of animals with this type of body cavity
are flatworms and nemertean worms.
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2) Pseudocoelomate –an animal that has a body cavity located between the body
wall and the wall of the digestive tract, but it is either unlined or only partially
lined by peritoneum. The peritoneum is a membrane that lines the inside of
the body cavity. Examples of pseudocoelomate animals are nematode worms
or rotifers.
3) Coelomate – an animal that has a true body cavity; a body cavity that is lined
by peritoneum. The peritoneum is a membrane that lines the inside of the
coelom. Examples: molluscs, annelids, arthropods, echinoderms, chordates.
Segmentation
Segmentation is the division of the body into a longitudinal series of sections variously
known as segments, somites, or metameres. Segmentation or metamerism is found in
Phylum Annelida, Phylum Arthropoda, and Phylum Chordata.
Embryological Development
The development of an animal from the zygote to the adult is its ontogeny. All animals
develop from a single fertilized egg, or zygote. The egg divides into two cells, then again
to form four cells, eight cells, and so on. This process of mitotic division is known as
cleavage. The embryo does not increase in size during cleavage; its mass is successively
subdivided into smaller and smaller cells. Cleavage results in the formation of a solid
ball of cells known as a morula. This develops into a hollow ball of perhaps several
hundred cells known as a blastula. The cellular layer usually surrounds a cavity called
the blastocoel. Next, one side of the blastula buckles inward and forms a pore known as
the blastopore. This embryonic stage is known as a gastrula.
The fate of the blastopore can be used to separate animals into two groups, based upon
their embryological development:
1) Protostome – an animal in which the blastopore opening of the embryo
develops into the mouth. Examples: Molluscs, Annelids, Arthropods.
2) Deuterostome – an animal in which the anus forms from the blastopore. The
mouth develops as a secondary opening. Includes: Echinoderms, Chordates.
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Depending upon the animal, the embryo may contain either none, two, or three germ
layers. Sponges have no germ layers. In most cnidarians, there are two germ layers, an
outer layer called the ectoderm and an inner layer called the endoderm. An animal with
two germ layers is called diploblastic. Some cnidarians in the Class Anthozoa and the
more evolutionarily derived animals have three germ layers. Animals with three germ
layers are known as triploblastic. The outer layer is ectoderm; it will give rise to the
epithelium of the body surface and to the nervous system. The middle layer or
mesoderm will form the muscular system, reproductive system, and peritoneum (lining
of the coelomic compartments). The inner layer, the endoderm will give rise to the
epithelial lining of the digestive tube.
Genetic Analysis
Studies carried out in the new field of molecular phylogenetics have resulted in magor
changes in the classification of animals. The ability to sequence the DNA comprising the
genome of animals has provided biologists with a powerful new tool for analyzing the
phylogenetic relationships of animals.
The first molecular phylogenies were constructed from analyses of ribosomal genes,
which code for RNA that forms the large subunit 28S, and small subunit 18S of
ribosomes. This work established the new field of molecular phylogenetics.
In 1997, Anna Marie Aguinaldo and colleagues published a paper, that divided the
Protostomia into two distinct clades, a nonmolting clade and a “molting clade” called
Ecdysozoa. Classification was revised on this basis to remove Nematoda from their
grouping with other pseudocoel groups and place it next to Arthropods and other groups
characterized by ecdysis or shedding of the exoskeleton.
As the field of molecular genomics developed, it became possible to sequence larger
numbers of genes including genes coding for nuclear and mitochondrial proteins. With
newer DNA sequencing technology, it is now possible to sequence tens of thousands of
genes. Methods are available for sequencing specific regions of the genome giving
investigators the ability to target genes of phylogenetic significance.
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Evolutionary Relationships
The classification of animals is based on their evolutionary relationships, which are
established by identifying similarities in the groups. The evolutionary history of a group
of organisms is called its phylogeny, and is depicted using a phylogenetic tree (or
cladogram).
It is believed that animals evolved approximately 700 million years ago from a
flagellated Protist ancestor. Based upon the similarity between collar cells found in
sponges and collar cells found in protozoans known as choanoflagellates,
choanoflagellates have been identified as the likely ancestor. Zoologists envision that the
ancestral protozoan consisted of a small spherical colony with a layer of flagellated collar
cells lining its surface that functioned in locomotion and feeding.
Multicellular organisms that are recognized as animals are referred to as Metazoa. They
constitute the Animal Kingdom or Kingdom Animalia. The animal kingdom may be
divided into two large groups of subkingdoms:
1) Subkingdom Parazoa, which consists of the sponges, with no digestive cavity and
with body wall pierced by pores, and
2) Subkingdom Eumetazoa, which includes all other animals
Eumetazoa are classified on the basis of body symmetry into:
1) Radiata, which are radially symmetrical. This group includes the cnidarians
(jellyfish and their relatives) and the ctenophores (comb jellies).
2) The second group is the Bilateria or bilaterally symmetrical animals. This group
includes all of the other animals.
The Bilateria may be classified on the basis of the type of body cavity they have into:
1) Acoelomates – animals that do not have a body cavity. Examples are flatworms
and nemertean worms.
2) Pseudocoelomates –animals that have an unlined body cavity. Examples are
rotifers and nematodes.
3) Coelomates – animals that possess a true coelom, a body cavity lined by
peritoneum. Examples: all other bilateral animals and the echinoderms.
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Coelomates may be divided into two large groups based on the pattern of embryological
development:
1) Protostomes –a major division of the animal kingdom in which the blastopore
develops into the mouth and the anus forms secondarily. Protostomes include
the annelids, arthropods, and molluscs.
2) Deuterostomes – a division of coelomate animals in which the anus develops
from the blastopore; includes the echinoderms and chordates.
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KEY TERMS
Acoelomate
Anterior
Asymmetry
Bilateral symmetry
Biradial symmetry
Blastopore
Blastula
Body cavity
Caudal
Cephalization
Cleavage
Coelomate
Cranial
Deuterostome
Distal
Division of labor
Dorsal
Ectoderm
Endoderm
Eumetazoa
Eukaryotic
Frontal plane
Gastrula
Germ layers
Heterotrophic
Invertebrates
Locomotion
Medial
Mesoderm
Metazoa
Midsagittal plane
Multicellular
Lateral
Morula
Ontogeny
Parazoa
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Pectoral
Phylogeny
Phylogenetic tree
Pelvic
Posterior
Protostome
Proximal
Pseudocoelomate
Radial symmetry
Radiata
Sagittal plane
Segmentation
Symmetry
Tetrapod
Transverse plane
Vertebrates
Ventral
Zygote
Questions for Chapter 11, Introduction to the Animal Kingdom
1) Give the definition of an animal.
2) Animals have _________________________ nutrition; they ingest food and digest it
within a digestive system. Carbohydrate food is stored in the form of
_________________________.
3) The cells of an animal are eukaryotic. Eukaryotic cells have a true
____________________ and membranous _________________________.
4) Compare animal cells and plant cells by completing the following table:
Comparison of Animal and Plant Cells
Animal Cells
Plant Cells
Presence of Cell Walls
Presence of Chloroplasts
Presence of Centrioles
Presence of Astral Rays
Method of Division of
Cytoplasm
5) The phrase _________________________ of ____________________ means that
the cells are specialized to perform specific functions.
6) Compare invertebrates and vertebrates.
7) _________________________ is present in an animal if it can by divided by a
median plane into equivalent halves with corresponding parts on opposite sides of
the plane.
_________________________ is a lack of symmetry.
____________________ symmetry is a type of symmetry in which the organism can
be divided into similar halves by any longitudinal plane passing through the center.
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_________________________ symmetry is a variation of radial symmetry. Because
of some part that is single or paired rather than radial, only one or two planes through
the longitudinal axis divide the organism into equivalent halves.
__________________________ symmetry is a type of symmetry in which a
midsagittal plane divides the organism into halves that are mirror images of one
another.
8) Give the type of symmetry present in each of the following animals:
Jellyfish
______________________________
Cat
______________________________
Comb Jelly
______________________________
Hydra
______________________________
Earthworm
______________________________
Clam
______________________________
9) The following planes are used to divide an organism with bilateral symmetry:
A _________________________ plane is a lengthwise vertical plane that divides the
animal into right and left portions.
A _________________________ plane is a lengthwise vertical plane through the
midline that divides the organism into halves that are mirror images of one another.
A _________________________ plane is a lengthwise plane at a right angle to the
sagittal plane; divides the organism into dorsal and ventral portions.
A _________________________ plane is a plane at right angles to both the sagittal
and frontal planes; divides the body into anterior and posterior portions.
10) What does the term mirror image mean?
11) Explain the advantage of radial symmetry to the animals that have it and how it fits
their lifestyle. What group of animals is characterized by radial symmetry?
12) What group of animals is characterized by biradial symmetry?
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13) Using the example of a cat, use directional terms to identify regions and directions
on the body. Directional terms are applied differently in man as compared to a fourfooted animal. Explain.
14) A veterinarian performing an operation on a cat makes an incision in the middle of
the abdomen below the sternum. Using anatomical terminology, explain where this
cut is.
____________________________________________________________________
____________________________________________________________________
15) A surgeon performs an operation to repair the attachment of a muscle to the proximal
portion of the upper arm bone. Which direction is proximal?
____________________________________________________________________
____________________________________________________________________
16) In the frog, the ovaries are attached to the dorsal wall of the coelom. Which
direction is dorsal?
____________________________________________________________________
____________________________________________________________________
17) In a four-footed animal, the stermum is _________________________ to the heart.
The heart is _________________________ to the lungs. The knee is
_________________________ to the thigh.
18) Bilateral symmetry is associated with cephalization and directed movement.
Explain. What is the significance of cephalization?
19) What is a body cavity? _________________________________________________
____________________________________________________________________
20) Draw diagrams of animals that are acoelomates, pseudocoelomates, and coelomates.
Label the body wall, type of body cavity, and peritoneum if present.
21) What is segmentation? In which phyla is it found?
22) A _________________________ is an animal in which the blastopore opening
develops into the mouth. A __________________________ is an animal in which
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the blastopore opening develops into the anus and the mouth develops from a
secondary opening. What is the significance of embryological development in
classification? Give examples of protostome and deuterostome animals.
Multiple Choice
1)
____
The type of nutrition found in animals is
A) autotrophic
B) heterotrophic
2)
____
C) saprophytic
D) chemosynthetic
The cells of animals
A) are surrounded by cell walls
B) have large central vacuoles
3)
____
Which of the following is a type of symmetry in which the organism can
be divided into similar halves by any longitudinal plane passing through
the center?
A) spherical
B) radial
4)
____
C) biradial
D) bilateral
Which of the following is a lengthwise plane that divides the organism
into dorsal and ventral portions?
A) sagittal
B) frontal
5)
____
C) midsagittal
D) transverse
Which of the following terms means toward the back surface?
A) anterior
B) ventral
6)
____
C) proximal
D) dorsal
Which of the following is a body cavity not lined with peritoneum and not
a part of the blood or digestive systems?
A) coelom
B) gastrovascular cavity
7)
____
C) have chloroplasts
D) are eukaryotic
C) spongocoel
D) pseudocoelom
Animals in which the blastopore develops into the mouth and the anus
forms secondarily are known as:
A) Protists
B) deuterostomes
C) protostomes
D) acoelomates
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CHAPTER 12
PHYLUM PORIFERA
Objectives:
1. To learn the characteristics of sponges.
2. To distinguish the types of canal systems found in sponges
3. To learn the types of skeletons found in sponges.
4. To examine the structure and function of a representative sponge.
5. To understand the dependence of sponges upon currents of water drawn into their body
and the role of the cell known as a choanocyte in creating these currents.
6. To understand how sponges reproduce and carry out their life cycle.
Phylum Porifera
Phylum Porifera is made up of the sponges. The name Porifera means “pore bearing”
and refers to the many tiny pores or ostia that open to the surface of the sponge. Sponges
are defined as aquatic, sessile, filter-feeding, animals that utilize flagellated collar cells to
draw in water through external pores and circulate it through a system of internal water
canals and chambers. Sponges are sessile, that is, attached to the bottom and cannot
pursue their food. Therefore, they depend upon the water drawn in through these tiny
pores and canals for obtaining food and oxygen and eliminating waste. The type of
feeding employed by sponges is known as filter feeding, a process in which minute food
particles are extracted from the water as it passes through tiny canals and chambers that
act as strainers.
Most species of sponges are marine, but there are 150 species of freshwater
sponges. Sponges exist in a variety of forms including erect, branching, and encrusting.
They are abundant in littoral and tropical reef habitats, where they attach to rocks,
timbers, shells, or corals. Although they are most common in shallow water some, such
as the glass sponges, live in deep water. Many sponges display bright colors, including
red, purple, green, yellow, or orange, although some are brown or gray.
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Characteristics
1) Sponges are all aquatic, mostly marine.
2) Adult sponges are attached (sessile). Most form colonies; some live as separate
individuals.
3) Most sponges are asymmetrical; some have radial symmetry.
4) Multicellular at the cellular grade of construction; body a loose aggregation of cells
in a gelatinous matrix. No true tissues or organs. The body wall is composed of an
outer epidermis, a lining of choanocytes on most internal chambers and canals, and a
gelatinous protein matrix called mesohyl (mesoglea) in between that contains
amoebocytes and spicules.
5) Cells totipotent.
6) The body of the sponge is pierced by many pores or ostia.
7) The canals and chambers within the sponge are lined by flagellated collar cells or
choanocytes.
8) The skeleton of sponges consists of calcareous or siliceous spicules or of protein
spongin.
9) Muscular system with true muscle cells is absent. Contractile cells are present that
regulate the size of the openings into the canals that penetrate the body.
10) Adults are sessile filter feeders (suspension feeders). Sponges have no digestive
cavity. Digestion is intracellular; excretion and respiration by diffusion.
11) Nervous system and sense organs lacking; response to stimuli localized and
independent.
12) Asexual reproduction by buds or gemmules and sexual reproduction by eggs and
sperm; free-swimming ciliated larvae.
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Classes of Sponges
There are three classes of sponges:
1) Calcarea (with calcareous spicules). Canal systems of asconoid, syconoid, or
leuconoid design.
2) Hexactinellida (six-rayed siliceous spicules). Glass sponges. Syconoid and
leuconoid canal systems.
3) Demospongiae (with a skeleton of siliceous spicules and/or spongin). Leuconoid
canal system.
Structure and Function
Sponges are sessile; they are attached to the bottom. The body can occur in various
forms, including vertical and erect, branched or lobed, and flat and encrusting. Sponges
are organized at the cellular level, with no organs or true tissues. Most of the body cells
are totipotent, retaining the ability to differentiate into other types of specialized cells.
The body may have radial symmetry or asymmetry. The body is a loose organization of
cells, which retain a degree of independence. A skeletal framework of spicules or the
protein spongin supports the body. Sponges are dependent upon currents of water, which
they draw into their bodies through the many pores and canals that penetrate their bodies.
The water brings in food and oxygen and carries away wastes. Flagellated collar cells or
choanocytes create the water currents by the beating action of their flagella and also carry
out feeding and digestion.
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Types of Canal Systems
There are three types of canal systems in sponges: asconoid, syconoid, or leuconoid
1) Asconoid. In the asconoid type of canal system, the canals pass directly from the
ostia to the spongocoel, which is lined with collar cells. Leucosolenia has this type of
canal system.
The asconoid type of canal system is the simplest one. The body of an asconoid
sponge is a hollow cylinder that is attached by its base to the substratum. The body is
pierced by many pores or ostia. Water that enters an ostium passes through a tubular
opening in a cell known as a porocyte and passes directly through the body wall to
enter the central cavity. The cavity within the sponge is known as the spongocoel. It
is lined by a layer of flagellated collar cells. The spongocoel has a large opening at
the top called the osculum. The choanocytes create a water current that enters the
ostia, passes into the spongocoel, and exits the sponge through the osculum.
2) Syconoid. In the syconoid type of canal system, incurrent canals (opening from the
outside) lie alongside radial canals, opening into the spongocoel. Both types of
canals end blindly in the body wall, but are connected by minute pores. Only the
radial canals are lined with collar cells. Syconoid sponges include species in genera
such as Grantia (previously called Scypha).
The flow of water in sponges with a synconoid type of canal system is as follows:
Water enters the sponge through an ostium. The ostium opens into an incurrent canal
that ends blindly in the body wall. The water meets a dead end at the end of this canal.
However, the incurrent canal is connected to another canal lying next to it known as
the radial canal by small openings known as prosopyles. The radial canal opens into
the spongocoel but it also ends blindly in the body wall (does not open to the outside).
The radial canal is lined by flagellated collar cells. The water in the incurrent canal
passes into the prosopyle and then passes into the radial canal. From here, water
passes through an opening called the apopyle, enters the spongocoel and then exits the
sponge through the osculum.
3) Leuconoid. The leuconoid type of canal system is found in the largest sponges and is
the most complex system. The bath sponge has this type of canal system. In the
leuconoid type of canal system, the canals form a complex, branching, network.
Rounded chambers lined with collar cells lie at the intersection of incurrent and
excurrent canals. The spongocoel lacks collar cells. Water enters a leuconoid sponge
through ostia at the surface and flows into an incurrent canal. From the incurrent
canals, water passes through prosopyles into choanocyte chambers. Water exits each
choanocyte chamber through an apopyle (back gate) and then flows through the
excurrent canals. From the excurrent canals, water is discharged to the outside
through one or more oscula.
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The Importance of the Flow of Water through the Body of the Sponge
The flow of water through its canal system is vital to the sponge. The sponge is
dependent upon these water currents for its survival. The canal system accomplishes the
functions of gas exchange, food acquisition, removal of waste, and functions in
reproduction. Sperm and eggs are released through the canal system and enter other
sponges through their canal system; also larvae are released through the canal system.
Skeletons
Sponges have a well-developed skeleton that can support the body in moving water.
Spicules often project through the surface, providing protection. Such projecting spicules
surround and guard the oscula and ostia.
Skeletons may consist of:
1) Spicules of calcium carbonate (calcareous spicules). These are spicules that
are composed of calcium carbonate (CaCO3). Example: Grantia
2) Spicules of siliceous material. These are composed of silicon dioxide (SiO2 ).
Example: glass sponges
3) Spongin, a proteinlike substance. The skeletal framework consists of a
network of protein fibers. Examples: bath sponges, fresh water sponges.
Nutrition
Sponges feed by the process known as filter feeding. This is a process in which minute
food particles are extracted from the water as it flows through the canal system of the
sponge. Their food consists of organisms found in plankton, bacteria, and organic
particles. Food is filtered from the water as it passes through the incurrent canals and
passes over the choanocytes. The incurrent canals progressively decrease in diameter as
they pass inward. Food particles are filtered as the
