Lecture 5 – Porifera & Placozoa

Phylum Porifera: Sponges

• Sponges are known as "pore-bearing" organisms.
• Classified as parazoans; they lack true embryological germ layers.
• Multicellular, with totipotent cells, but true tissues are absent.
• They are sessile, functioning as suspension feeders with a specialized water canal system.

Characteristics of Sponges

• Exhibit asymmetrical or +/- radial symmetry.
• Unique cells called choanocytes create water currents for feeding.

Sponge Skeleton & Taxonomy

• Skeleton comprises spicules:
  • Calcium carbonate spicules belong to Class Calcarea.
  • Hexactinellida features siliceous, 6-rayed spicules.
  • Class Demospongiae has siliceous spicules that are not 6-rayed or may consist of collagen (spongin).

Class Calcarea

• Characterized by calcium carbonate spicules, all marine.
• Includes species such as Leucosolenia eleanor.

Class Hexactinellida

• Identified by 6-rayed siliceous spicules, predominantly found in deep marine waters.
• Commonly referred to as glass sponges.

Structural Design of Glass Sponges

• Structural designs inspired civil and mechanical engineering breakthroughs.
• Known for light transducing properties, allowing photosynthetic symbionts to thrive in dark environments.

Class Demospongiae

• Comprises sponges with siliceous spicules, not 6-rayed.
• Can have a collagenous network replacing spicules.
• Habitat ranges include marine, brackish, and freshwater environments at varying depths.

Sponge Body Plans

• Asconoid: Simple structure, choanoderm one cell thick, small in size.
• Syconoid: Features folded choanoderm, typical of calcareous sponges.
• Leuconoid: Divided choanoderm into distinct chambers, most common in demosponges.

Feeding Mechanism

• Filter feeders; water enters through ostia, controlled by porocyte cells.
• Water movement is partly passive; choanocytes actively help in water propulsion.
• Sponges can filter high volumes of water, with some able to filter an entire sea volume in one day.

Nutrition

• Food particles are captured by choanocytes and transferred to amebocytes for digestion.
• Phagocytosis occurs on the surface of choanocytes.

Reproductive Strategies

• Asexual reproduction via fragmentation, budding, or gemmules, which are survival pods for freshwater sponges.
• Most sponges are monoecious, with sperm from choanocytes and eggs from archeocytes.
• Mass spawning occurs during reproduction.

Sponge Larvae

• Produce two types of larvae: parenchymella (solid) and amphiblastula (hollow), both are ciliated.

Ecological Success & Importance

• Sponges are prevalent in unpolluted freshwater and abundant in marine environments.
• They support various symbiotic relationships, provide camouflage, and contribute to bioerosion via specialized cells.

Economic Importance

• Bath sponges are harvested commercially, notably in the Mediterranean and Tarpon Springs, Florida.

Este quiz explora os Phylum Porifera e Placozoa, discutindo as características dos esponjas e outros filo mesozoan. Aprenda sobre a estrutura, a alimentação e a classificação destes organismos unicelulares. Teste seu conhecimento sobre estas fascinantes criaturas aquáticas.