Animal Kingdom: Diploblastic Classification

• The slides cover animal biology, focusing on the animal kingdom and the classification of different animal groups based on embryonic development and body plans.

Règne des animaux (Animal Kingdom)

• Animals are multicellular, heterotrophic organisms, synonymous with Metazoa.
• Metazoa is a monophyletic group, sharing a common ancestor.
• Embryonic development patterns define the organizational plans of major animal groups.
• Animals are classified based on the number of embryonic layers: diploblastic (two layers) and triploblastic (three layers).

LES DIPLOBLASTIQUES (Diploblastic Animals)

• Diploblastic animals have two embryonic layers: ectoderm and endoderm.
• Ectoderm forms the epidermis and nervous system.
• Endoderm forms the digestive system.
• Examples include Porifera (sponges) and Cnidaria (jellyfish, corals).

E/ Spongiaires (Sponges)

• Sponges (Porifera) are the basal branch of Metazoa, lacking differentiated organs.
• They are diploblastic, with ectoderm and endoderm separated by a pluricellular layer called the mesoglea.
• Porifera have pores for water intake and excurrent openings.
• They exist as massive or shrub-like colonies.
• Sponges are found in marine, freshwater, and brackish environments across all climates.
• They exhibit variable forms: erect or branched in calm waters, encrusting in flowing waters.
• Approximately 5500 sponge species have been described.
• Sponges are sessile, attached to a substrate.

Sponge Cellular Components

• Ectoderm:
  • Pinacocytes consist of flattened, joined cells,
  • Porocytes contain inhalant pores.
• Endoderm:
  • Choanocytes are flagellated cells.
  • The beating of flagella creates water currents, drawing water through inhalant pores, delivering oxygen and microorganisms.
  • Waste products pass through the osculum.
• Mesoglea:
  • Scleroblasts produce spicules.
  • Amoebocytes digest food particles.
  • Gonocytes are the sexual cells and they produce female and male gametes.

Sponge Nutrition and Reproduction

• Nutrition:
  • Sponges feed through phagocytosis, consuming bacteria, organic debris, and unicellular algae.
• Reproduction:
  • Sexual reproduction: Some sponges are gonochoric (separate sexes), while others are hermaphroditic.
  • Asexual reproduction: Occurs when undifferentiated cells develop asexually through external budding or via internal budding.

E/ Cnidaires (Cnidarians)

• Cnidarians are metazoans with diploblastic structure (ectoderm + endoderm + mesoglea).
• 99% are marine, 1% are freshwater species.
• Their architecture features radial symmetry.
• Having no respiratory, excretory, or circulatory systems, their primitive nervous system is rudimentary.
• The life cycle includes polyp and medusa forms.
  • Cnidoblasts are venomous cells.
• A single opening serves as both mouth and anus, surrounded by a ring of stinging tentacles.

Cnidarian Anatomy and Cells

• Ectoderm:
  • Myoepithelial cells cover the animal's surface, aiding in contraction and retraction.
  • Interstitial cells are embryonic cells that can develop into other ectodermal cells (gametes).
  • Sensory cells or nerve cells have sensory cilia for external stimuli.
  • Cnidoblasts release stinging liquid to capture or kill prey.
• Mesoglea:
  • Proto-neurons form a primitive nervous system.
• Endoderm:
  • Sensory cells are present
  • Interstitial cells are present
  • Glandular cells secrete digestive enzymes (diastases) to help in extracellular digestion.
  • Digestive cells carry out phagocytosis for intracellular digestion.

Cnidarian Nutrition and Reproduction

• Animals are carnivorous they feed on prey captured by tentacles, like plankton, protists, worms, crabs, and small fish.
• Prey are captured and brought to the mouth, where digestive enzymes perform extracellular digestion.
  • Pinocytosis then leads to digestion inside the gastric cavity.
• Reproduction:
  • Residue of digestion exits through the mouth.
• Asexual and sexual reproduction alternate.
  • Polyps reproduce asexually through budding.
  • Medusae reproduce sexually
  • Gametes get released in the water
  • External fertilization occurs.
  • The fertilized egg develops into a larva and settles to become a young polyp.

Les triploblastiques (Triploblastic Animals)

• The presence or absence of a cavity within the mesoderm (coelom) helps classify triploblastic animals:
  • Acoelomates lack an internal cavity.
  • Coelomates have a mesoderm that develops into coelomic sacs.
  • Pseudocoelomates have a body cavity that is not lined by mesoderm.

Les triploblastiques coelomates (Triploblastic Coelomates)

• Protostomes: the mouth develops first during gastrulation.
• Deuterostomes: the mouth develops later.
• Nerve cord position relative to the digestive tube:
  • Hyponeurians: ventral nerve cord.
  • Epineurians: dorsal nerve cord.
  • Epithelioneurians: A diffuse, dorsal nervous system is located under the epidermis.

Plathelminthe (Flatworms)

• Flatworms (Plathelminthes) are primarily elongated animals that lack a distinct head and appendages.
• They consist of 4 classes:
  • Turbellarians: free-living in marine and freshwater (eg. planarians)
  • Cestodes: endoparasites (eg. tapeworms)
  • Trematodes: endoparasites (eg. flukes and schistosomes)
  • Monogeneans: ectoparasites of aquatic organisms (mainly fish)

CI/ TURBELLARIES (Turbellarians)

• They are free-living.
• They are small in size, approximately 10 cm.
• They are aquatic, found in marine environments (some terresterial).
• Movement is facilitated by cilia, creating swirling movements in water.

Planarian Anatomy

• Flatworm that is 3 cm long.
• Leaf shaped with wavy edges.
• They have 2 sensory tentacles and eye spots.
• They move via cilia.

CI/ TREMATODES (Trematodes)

• The body covering has scales and spines facilitating growth because the covering is discontinuous.
• Equipped with attachment and fixation organs (hooks and suckers), they are parasites.
• Ectoparasites monoxenes: they only have one host.
• Endoparasites heteroxenes: They inhabit multiple hosts.
• Hôte principal: the main host experiences manifestations of the disease.
• Hôtes intermédiaires: secondary hosts

The Molt

• The presence and rigidity of the exoskeleton imposes on a particular mode of discontinuous growth: moult or exuviation.
• Molting is preceded by intense mitoses followed by the secretion of epidermal cell proteases, ensuring that lysis of the endocuticle and peeling superficial parts. Simultaneously, a new coating is formed below the previous one.

Corps (Body)

• Leaf-shaped, between 2 and 3 cm long.
• Features a cephalic extension with a perforated oral sucker.
• Ventral Side:
  • Contains the hermaphroditic genital opening.
  • It has a non-perforated sucker called the acetabulum for attachment to bile ducts of the host.

Flatworm Reproduction

• Exhibit hermaphroditism with protandry (male first, then female).
• Sexual Reproduction:
  • A reciprocal copulation that contains:flagellated sperm, male and female gametes, and vitelline cells.
  • Fertilization occurs.
  • This leads to an egg rich in vitellus, then direct development to become a planarian adult.
• Asexual Reproduction through Regeneration:
  • The animal fixes itself to a surface by its rear.
  • It divides its portions
  • The front which has the head will directly regenerate the portion behind it.
  • the rear will fully reorganize and turn into new planarians.

Némathelminthe (Nematodes)

• Roundworms feature an unsegmented body and possess a cuticle.
• Adults are differentiated by sex.
• Cylindrical Roundworms are nonsegmented.
  • Thick, non-ciliated cuticles
• Nematodes exhibit discontinuous growth with molting.
• They are free-living or parasites to plants and animals.
• They are divided into two classes: Gordians and Nematodes.
  • Nematodes are further divided in to two groups.
  • Nématodes ovipares: lay eggs (Oxyure, Ascaris, Ankylostomes, Anguillules)
  • Nématodes vivipares: lay embryos (Trichines, Onchocerques, Filaires)

Nematodes

• These are cylindrical worms with effilated white bodies.
  • They have 3 cutting jaws, one dorsal and two ventrolateral.
• Sexual Dimorphism exists in the species.
  • Taille 30: Females are 30cm
    • Their posterior end is thinner
    • The Genital opening shows a ring shaped depression in the first third of the worm.
  • Taille 15cm: Males are 15cm
    • The posterior end is coiled
    • The Genital opening has copulatory spicules to help them be closer to the anus.