Porifera (Sponges) and Hydra

• The text discusses the structure, types, reproduction, and significance of Porifera (sponges) and Hydra

Sponge Body Structure

• Sponges are classified into three types based on the arrangement of their body structure: Asconoid, Syconoid, and Leuconoid

Asconoid Type

• Simplest type of sponge
• Has a vase-like shape with a central cavity (spongocoel) that opens to the outside through an osculum
• The body wall consists of an outer epithelium (Outer epithelium) and an inner epithelium (Inner epithelium)
• Mesoglea, a gelatinous substance, lies between these two epithelial layers
• The outer layer (pinacocytes) consists of flat cells, while the inner layer consists of flagellated collar cells (choanocytes)
• The mesoglea contains skeletal spicules and various types of amoeboid cells
• The body wall is perforated by numerous microscopic pores called incurrent pores or ostia
• Each pore is a canal that extends between the spongocoel and the outside environment through a tubular cell or porocyte
• Water, along with oxygen and nutrients, enters the spongocoel due to the movement of the flagella of choanocytes
• Waste products are carried out through the osculum
• Leucosolenia is a common example

Syconoid Type

• Similar layers to Asconoid but the body wall folds outward to form finger-like projections
• Each projection contains a radial canal
• Radial canals are lined with choanocytes and connect to the spongocoel via internal pores or apopyles
• In some syconoid sponges, the radial canals are separate, while in others, they fuse, leaving tubular spaces called inhalant pores
• Inhalant pores connect to the outside environment through dermal ostia or pores
• Radial canals connect to the incurrent canals via prosopyles
• Unlike asconoid sponges, where porocytes extend through cells, prosopyles extend between cells
• Water flow: dermal ostia → incurrent canals → prosopyles → radial canals → apopyles → spongocoel → osculum
• Two main differences from Asconoid are the thickness of the wall, and the presence of incurrent and radial canals arranged alternately; choanocytes are found in radial canals instead of lining the spongocoel

Leuconoid Type

• Most complex structure
• Radial canals branch extensively
• Forming chambers or rounded pockets lined with choanocytes called flagellated chambers
• The body wall is very thick and penetrated by a network of complex canals that converge and open to the outside through the osculum
• Spongocoel is reduced or absent

Sponge Regeneration

• Sponges have a high capacity for regeneration
• If a sponge is broken into small pieces or its cells are separated, the fragments can reorganize and form a new sponge
• Amoeboid cells can form the outer epithelium of the new sponge

Sponge Reproduction

• Sponges reproduce asexually and sexually

Asexual Reproduction Types

• Budding: portions of the sponge body pinch off and develop into new individuals
• Reduction Bodies: in unfavorable conditions, the sponge body may shrink, leaving behind small, spherical masses called reduction bodies
• Gemmules: internal buds consisting of amoebocytes surrounded by a protective layer
• Gemmules can survive harsh conditions and develop into new sponges when conditions become favorable
• Freshwater sponges form gemmules containing archeocytes that accumulate nutrients from trophocytes; gemmules are surrounded by a thick layer including amphidisc spicules

Sponge Significance

• Sponges have several unique characteristics
• The first three cell divisions of the fertilized egg are longitudinal, unlike other animals where the third division is transverse
• Inversion occurs in sponge embryos
• Sponges have multiple small pores for water and food intake
• Sponges have limited cell specialization

Sponge Economic Importance

• Some sponges have commercial value
• Used for bathing and other purposes
• Structural fibers made of spongin
• Used in hospitals in New Zealand to help heal wounds due to their anti-inflammatory compounds
• Some sponges are harmful, producing toxins or causing irritations
• Some bore into shells of mollusks, causing damage
• Cliona sponges can damage pearl oyster shells

Hydra Examples

• Chlorohydra viridissima (green)
• Hydra vulgaris (gray)
• Pilmatohydra oligactis (brown)
• Hydra gangetica (white or pink)

Hydra

• Hydra is a solitary freshwater polyp that attaches to submerged objects
• Can also float or swim freely
• Hollow
• 1-3 cm long
• Attaches to surfaces via a basal disc that secretes an adhesive substance, forming gas bubbles for flotation
• The free end has a conical hypostome with a mouth
• 4-12 hollow tentacles surround the mouth
• Contraction and extension abilities
• The stalk connects the foot and the hypostome
• Asexual and sexual reproductive structures can form on the stalk
• Five types of Hydra based on stalk structure:
  • Hydra plain: smooth stalk without structures
  • Hydra male: stalk with conical testes near the mouth -Hydra female: stalk with ovaries near the base -Hydra hermaphrodite: stalk with both testes and ovaries -Hydra budding: stalk with buds

Hydra Reproduction

• Hydra reproduces both asexually and sexually

Hydra Asexual Reproduction

• Budding: buds develop on the body surface, grow tentacles, and detach to form new individuals

Hydra Sexual Reproduction

• Some Hydra species are dioecious (separate sexes), while others are monoecious (hermaphroditic)
• Gametes arise from interstitial cells
• A single egg develops in the ovary, while other interstitial cells provide nourishment
• The fertilized egg undergoes cleavage to form a blastula, which then transforms into a solid gastrula
• The outer cells of the gastrula secrete two layers: a thick chitinous outer layer and a thin gelatinous inner layer
• The embryo detaches from the parent and settles to the bottom, hatching into a new hydra under favorable conditions