zoology practicle 1; basal animals to molluscs

Question 1

describe the functions of the cilia in feeding

Answer 1

the beating flagellum creates a suction current, causing bits of food to get stuck to the microvilli where the food particles are then engulfed

Question 2

describe the functions of the cilia in locomotion

Answer 2

the flagellum whips rapidly driving water upwards

Question 3

describe the relationship of the choanoflagellates to the metazoan(multicellular animals)

Answer 3

choanoflagellates are protists NOT animals. like any other unicellular animals some choanoflagellates form colonies,
which may have been the precursors of the first multicellular organisms

Question 4

draw a diagram of a choanoflagella

Answer 4

theca
microvilli
flagellum
collar
nucleus

Question 5

briefly characterise the phylum porifera

Answer 5

generally marine aquatic organisms, with a few freshwater species. They are diploblastic animals with two layers, the outer dermal layer and the inner gastral layer.

Question 6

Describe the basic organisation of the sponge body.

Answer 6

the sponge body does contain several different cell types.

Sponges are perforated with pores or ostia.Body shape can be cylindrical, vase-like, rounded or sac-like.

Question 7

Explain the skeletal elements of sponges and their composition.

Answer 7

Sponges, like all animals, possess some sort of a skeleton that gives their bodies shape. The fibres they
produce may be sharp spicules or maybe flexible fibres composed of spongin as seen in
bath sponges.Spicules are silicaceous and the long thin ones are like sharp glass needles.

Question 8

Describe the structure and function of a choanocyte in sponges.

Answer 8

Lining the spongocoel, are choanocytes. The flagella of these collar cells trap
food particles which the choanocytes ingest by phagocytosis

Question 9

Differentiate between asconoid, syconoid and leuconoid sponges.

Answer 9

Asconoid sponges are tubular with a central shaft called the spongocoel.
Syconoid sponges are similar to asconoids. They have a tubular body with a single osculum, but the body wall is thicker and more complex than that of asconoids and contains choanocyte-lined radial canals that empty into the spongocoel.
Leuconoid sponges lack a spongocoel and instead have flagellated chambers, containing choanocytes, which are led to and out of via canals.

Question 10

Describe the pattern of water flow in a sponge

Answer 10

Sponges are perforated with pores or ostia. Water is drawn through these pores into an
internal water chamber, the spongocoel and expelled through a larger opening, the
osculum

Question 11

Explain the relationship between sponges and the other metazoan animals.

Answer 11

Sponges are similar to other animals in that they are multicellular, heterotrophic, lack cell walls and produce sperm cells. Unlike other animals, they lack true tissues and organs

Question 12

Describe the basic organisation of the Cnidarian body

Answer 12

Cnidaria is diploblastic and exhibits tissue level of organization. It has two germ layers ectoderm and endoderm. Ectoderm made out covering of animals and endoderm lines the gut. It possesses gastrovascular cavity with a single opening, mouth on hypostome.Their uniting feature is cnidocytes: the specialized
stinging cells they use for capturing their prey.Cnidarians have complex lifecycles and have
two basic body forms: swimming medusae and sessile polyps.Cnidarians are radially symmetrical in both their body forms.

Question 13

Describe the general morphology of Hydra

Answer 13

Hydra is a multicellular organism. Most of the species are marine but the genus Hydra
occurs in freshwater. Individuals cling to the underside of plants and twigs. They reproduce
asexually (budding) and sexually

Question 14

Identify the main morphological features of Hydra on a microscopic slide or illustration

Answer 14

Hydras are small animals with four major body regions: column, hypostome, tentacles, and
basal/pedal disc. The main part of a hydra is the body column, a cylindrical tube that can be
greatly expanded or contracted. The mouth is at the centre of a dome called the
hypostome. The hypostome is surrounded by 4-10 tentacles; these are hollow and can be
extended to more than twice the length of the body. The body is attached to the substratum
by a basal/pedal disc.

Question 15

Explain the structure and function of the nematocyst in Cnidarians.

Answer 15

Cnidarians contain specialized cells known as cnidocytes (“stinging cells”) containing organelles called nematocysts (stingers). These cells are present around the mouth and tentacles, and serve to immobilize prey with toxins contained within the cells. Nematocysts contain coiled threads that may bear barbs.

Question 16

Briefly outline the characteristics of the Phylum Platyhelminthes.

Answer 16

They are triploblastic, acoelomate, and bilaterally symmetrical. They may be free-living or parasites. The body has a soft covering with or without cilia. Their body is dorsoventrally flattened without any segments and appears like a leaf.

Question 17

Identify the major advances in organisation of the Platyhelminthes over the Cnidaria.

Answer 17

Flatworms are more complex than cnidarians. Cnidarians have two layers of cells, the ectoderm and the endoderm; flatworms have a middle layer called the mesoderm between the other two layers (Fig. 3.16). This extra layer is important because its cells specialize into a muscular system that enables an animal to move around

Question 18

Describe the general morphology of the Flukes (Class Trematoda)

Answer 18

s a parasitic
flatworm that infects the liver of various mammals, including humans. The adult
worms live in the bile passages of the liver.

Question 19

Identify the major structures of the Fluke Fasciola hepatica as seem in a whole mount
of the specimen

Answer 19

The life cycle of flukes follows a typical pattern. The eggs pass out of the host and hatch
into a free-swimming stage called a miracidium. This only survives in moist conditions for a
short period and must encounter a snail to complete the next stage. This stage enters or is
consumed by a snail and it divides to become a sporocyst. This is a sac filled with small
individuals, each of which may give rise to further sporocysts or else develop into a larval
stage called a redia. The rediae enter the various tissues of the snail and develop into
cercaria larvae with tails. These leave the snail and usually encyst. When the cyst is eaten
by the final host, it hatches out and migrates to its final destination in the host to become
an adult fluke.

Question 20

List and briefly characterise the four main classes of Molluscs

Answer 20

There are eight classes of mollusc
Class bivalves. As their name suggests, bivalves have two
halves, or ‘valves’ to their shell, joined by a hinge. Bivalves
include most of the shelled species that you eat including
clams, oysters and mussels. In this practical, you will dissect
the edible mussel Mytilus edulis.

Class Gastropoda: the gastropods. Characterised by a long,
flat foot; a distinct head with eyes and tentacles and a dorsal
visceral mass usually housed in a spiral shell. These are the
snails, but the class also includes some animals that
externally look a little different, although their internal
anatomy has many shared features. Hence slugs, sea slugs,
sea hares and limpets are all gastropods. The gastropods
account for about 80% of mollusc species

Class Polyplacophora: the chitons. Chitons are found on
rocky shores worldwide and down to depths of more than 3
km in the world’s oceans. In Ireland, the chitons that you
find on rocky shores are rarely bigger than 1-2 cm long, but
in other countries (e.g. the pacific coast of USA) they may
be the size of your hand or bigger.

Class Cephalopoda: the cephalopods. Cephalopod molluscs
such as squid, cuttlefish and octopus are among the most
neurologically advanced invertebrates. They have large
eyes, and complex nervous systems that allow them to
undergo rapid colour changes. The giant squid is the largest
known species of invertebrate. In contrast, the pygmy squid
is only 1 cm long.

Question 21

Identify the external and internal features of the mussel Mytilus edulis

Answer 21

It is a bivalve. Mussels live attached to hard substrates
(e.g. rocks or piers) by means of byssus threads. They are filter feeders, extracting plankton
from the water currents. The sexes are separate, ripe gametes are released into the sea
where fertilization occurs.
The paired valves are joined by a tough hinge ligament. Concentric lines are visible which
usually represent yearly growth.
The posterior end of the shell is rounded; the umbo is the oldest part of the shell and lies to
the anterior.
Byssus threads are used for attachment to the substratum and are may be visible
protruding from the ventral surface of the shell.
Internally, the anterior adductor muscle is reduced and is much smaller than the posterior
adductor muscle. The pallial line marks the outer margin where the mantle was attached to
the shell.

Question 22

Identify the principle internal organs in a specimen of the edible mussel Mytilus edulis.

Answer 22

Internally, the anterior adductor muscle is reduced and is much smaller than the posterior
adductor muscle. The pallial line marks the outer margin where the mantle was attached to
the shell.

Question 23

Explain the pattern of water flow through the mussel.

Answer 23

Water enters via the incurrent
siphon carrying oxygen and food particles while wastes and dissolved CO2 leave via the
excurrent siphon.

Question 24

Identify the following:
 The paired valves and the hinge ligament.
 The umbo (oldest part of the shell)
 The right, left, dorsal, ventral, anterior and posterior surfaces
 Growth lines
 Byssus threads.
Examine the external shell of Mytilus and label the following 3 features: (i) hinge ligament,
(ii) growth rings, (iii) byssus threads.
Internal features
On the inside of the valve note the muscle scars where the adductor muscles were
attached. Locate the pallial line.

Answer 24

see diagrams