Tutorial Lab 3 - Kingdom Animalia: Invertebrates

Phylum Cnidaria

• The name Cnidaria refers to the specialized cells called cnidocytes that are unique to this phylum.

• Cnidocytes have stinging structures, called nematocysts that are used to immobilize prey.

• The cnidarians are exclusively aquatic animals with the majority of species found in marine habitats.

Phylum Cnidaria

• Members are radially symmetrical characterized by a digestive body cavity known as a gastrovascular cavity (not a coelom), some muscle fibers, nematocysts.

Phylum Cnidaria

• Mature cnidarians are composed of only two cellular layers, an outer epidermis (developed from embryonic ectoderm) and an inner gastrodermis (developed from embryonic endoderm).

• This is why they are diploblastic organisms.

• In cnidarians, these cell layers are thin, making the animals fragile.

• Between these two cellular layers is a gelatinous (non-cellular) layer of mesoglea

Triploblastic Organisms

• Animals above the cnidarians on the evolutionary tree have three germ layers of cells (ectoderm, mesoderm, endoderm)

• This is why they are known as triploblastic organisms (the third layer is between the ectoderm and endoderm and is called the mesoderm).
  

The Forms of Phylum Cnidaria

• The members of Phylum Cnidaria have one of two forms: a polyp or medusa.

• Polyp: A tube-shaped animal that is closed at one end. The other end has a mouth with tentacles around it. (Example: a sea anemone or coral.)

• Medusa: A jellyfish-like animal that looks like an umbrella and floats in the water. Its mouth hangs down from the center on a small stalk called a manubrium. (Example: a jellyfish.)

Hydra sp - Polyp form from Phyla Cnidaria

• The body wall that surrounds the gastrovascular cavity consists of two distinct layers of cells: an outer layer called the epidermis, and an inner layer called the gastrodermis.

• These two layers are held together by a thin, non-cellular layer, the mesoglea

Feeding and Digestion in Cnidaria

• At the upper end of the animal, you can see many elongate and moving tentacles

• Tentacles are used to capture food

• The mouth is at the centre of this circle of tentacles
  

Osmoregulation in Cnidaria

• Cnidarians are small, water-dwelling animals that don’t need special systems for breathing or circulation.

• Their moist bodies allow gases like oxygen to pass directly through their cells.

• Since they have only two cell layers, nutrients and gases can easily move from one cell to another or through the mesoglea

• This simple system works because no cell is far from food or oxygen.

Reproduction in Cnidaria

• Hydra reproduce asexually by budding and sexually through the production of sperm and ova.

• Budding: outgrowth from the body wall.

• The gastrovascular cavity of the bud is at first, continuous with the parent.

• At maturity, the bud will separate from the parent

Reproduction in Cnidaria

• The gametes for sexual reproduction are produced in organs called spermaries: testes and ovaries

• They are protuberances (bumps, lumps, or extensions) that stick out from the body

Obelia sp.

• Obelia is a colonial marine organism that is attached to things in shallow waters.

• They switch between a polyp stage (asexual generation) and a medusa stage (the sexual generation).

Obelia sp.

• At the end of the branches there are two kinds of polyps

• The feeding, or nutritive polyps have tentacles and resemble Hydra.

• The reproductive polyps are club-shaped do not have tentacles

Obelia sp.

• The branches of the colony are covered by a transparent sheath - the perisarc

• The perisarc extends around both polyps as the hydrothecae and the gonothecae

Obelia sp.

• The tentacles have many cnidocytes (with nematocysts inside them) to aid in prey capturing

• Extending into the cavity of the medusa is the manubrium, which has a mouth at the tip and is surrounded by four oral lobes

• The gonads (testes or ovaries) can be seen on the undersurface of the medusa

Phylum Platyhelminthes - FLATWORMS

• In comparison to cnidarians, flatworms are bilaterally symmetrical with distinct anterior and posterior ends and right and left sides.

• Flatworms are triploblastic, with a third cellular layer (parenchyma tissue developed from embryonic mesoderm) between the epidermis and the gastrodermis.

Phylum Platyhelminthes - FLATWORMS

• Flatworms are simple organisms with no body cavity other than the digestive cavity.

• This makes them acoelomate.

• They are much more advanced than cnidarians

Dugesia sp. PHYLUM PLATYHELMINTHES

• They are also called planarians, a common freshwater organism.

• It is often found in ponds and streams.

• Parasitic flatworms like flukes and tapeworms also belong to the Phylum Platyhelminthes.

Dugesia sp.

• Note the extrusion of the pharynx when it is feeding.

• Also, note the position of the pharynx and
  mouth, which is located at the end of the pharynx
  

Feeding and Digestion in Platyhelminthes

• Free-living platyhelminthes are mainly carnivorous and prey on small invertebrates that can be easily captured.

• They can also feed on the remains of dead animals.

• Dugesia sp. has a blind digestive tract (i.e. there is only one opening), but it is very branched and so it is considered more complex in structure than that of the cnidarians

Digestion in Planaria (Dugesia sp.)

• The digestive process in planaria is similar to that in Hydra except that food is brought to the gastrovascular cavity through a muscular protrusible pharynx

Clonorchis Sinensis (Parasitic Platyhelminthes)

• Parasitic platyhelminthes, which have a digestive tract, feed on the tissues and tissue fluids of the host.

• For example, Clonorchis sinensis is a flatworm that lives in the bile ducts of the human liver.
  

Clonorchis Sinensis

• Clonorchis sinensis has a muscular pharynx (not protrusible) which leads into a blind digestive tract

• Instead, Clonorchis sinensis has an anterior mouth located at the bottom of a muscular sucker.

• This oral sucker is used to suck in tissue fluids.

• Other parasitic platyhelminthes do not have a digestive system and absorb simple nutrients directly through the body wall since many internal parasites are often bathed in digested food

Osmoregulation and Excretion in Platyhelminthes

• Freshwater flatworms have a simple excretory system called protonephridia, mainly used to control water balance (osmoregulation) but may also help in excretion

• This system is made of tiny tubes inside the body, with one end opening to the outside and the other ending in flame cells—special cells with cilia that move excess water out.

• Since they are small and live in moist environments, they get oxygen and nutrients through diffusion (direct movement of substances between cells).

• If present, the gut helps distribute nutrients inside the body

Respiration and Circulation in Platyhelminthes

• Platyhelminthes don’t have a respiratory or circulatory system.

• They are small and live in moist environments, whether free-living or parasitic.

• If they have a gastrovascular system (like in Dugesia), it helps transport nutrients.

• Otherwise, nutrients and gases move through their bodies by simple diffusion (spreading directly between cells).

Reproduction in Platyhelminthes

• Planarians are hermaphroditic organisms that have male and female sex organs in the same individual.

• Copulation in flatworms is usually mutual, each partner inseminating the other.

PHYLUM ANNELIDA
External Anatomy of the Earthworm -Lumbricus sp:

• Cuticle: thin external layer

PHYLUM ANNELIDA
External Anatomy of the Earthworm -Lumbricus sp:

• Epidermis: outer cellular layer composed of epithelial cells.

• Try to locate Goblet cells in the epidermis of the earthworm. They appear empty

PHYLUM ANNELIDA
External Anatomy of the Earthworm -Lumbricus sp:

• Circular muscle layer: just beneath the epidermis, with the fibres cut longitudinally in the section.

PHYLUM ANNELIDA
External Anatomy of the Earthworm -Lumbricus sp:

• Longitudinal muscle layer: these fibres are arranged in blocks of feather-like bundles extending toward the center; transversely cut

PHYLUM ANNELIDA
External Anatomy of the Earthworm -Lumbricus sp:

• Peritoneum: a thin epithelial lining which separates the body cavity from the body wall. (epidermis and muscles)

PHYLUM ANNELIDA
External Anatomy of the Earthworm -Lumbricus sp:

• Coelom: the body cavity (fluid-filled in the living worm)

PHYLUM ANNELIDA
External Anatomy of the Earthworm -Lumbricus sp:

• Intestine: note the infolding of the dorsal surface of the intestine.

• This infolding is called the typhlosole.

• The cells surrounding the intestine are called chloragogue cells.

• These function as: an accessory digestive gland; the site of glycogen synthesis, deamination of proteins, and production of ammonia and urea

PHYLUM ANNELIDA
External Anatomy of the Earthworm -Lumbricus sp:

• Dorsal blood vessel: just above the intestine.

• Ventral blood vessel: just below the intestine.

PHYLUM ANNELIDA
External Anatomy of the Earthworm -Lumbricus sp:

• Nephridia: within the coelom, between the intestine and the body wall.

• In these sections, only incomplete portions of nephridia can be seen, usually appearing as wavy lines

PHYLUM ANNELIDA
External Anatomy of the Earthworm -Lumbricus sp:

• Setae: two pairs ventrally and two pairs ventro-laterally projecting from the body wall.

PHYLUM ARTHROPODA
Respiratory and Circulatory Systems of the Grasshopper

• Terrestrial arthropods breathe using a tracheal system, where air enters through spiracles (small body openings) and travels through trachea

• Trachea divide into tiny tracheoles, which deliver oxygen directly to cells.

• This system provides a large surface area for gas exchange.