Phylum Porifera: Characteristics of Sponges

Study Notes

Phylum Porifera (Sponges)

Also known as pore-bearing animals, they are commonly called sponges
They are aquatic, mostly marine, and a few species live in freshwaters
They are primitive, multicellular, and sessile with a cellular level of organization
Their cells are loosely arranged and they possess a water transport system (canal system)
Water enters through minute pores called ostia, passes through a central cavity (spongocoel), and exits through the osculum
This water transport system helps in food gathering, circulation, respiration, and waste removal
Choanocytes or collar cells are special flagellated cells lining the spongocoel and canals
Their body is supported by a skeleton made up of calcareous and siliceous spicules or spongin or both
Nutrition is holozoic and intracellular
All sponges are hermaphrodites, producing both ova and sperms
They reproduce asexually by fragmentation or gemmule formation and sexually by gamete formation
Development is indirect with different types of larval stages, such as parenchymula and amphiblastula

Phylum Cnidaria

Also known as Cnidarians (previously called Coelenterata)
They are aquatic, sessile or free-swimming, solitary or colonial forms with radial symmetry
The name Cnidaria comes from cnidocytes or cnidoblasts with stinging cells or nematocysts on tentacles
Cnidoblasts are used for anchorage, defense, and capturing prey
They exhibit tissue-level organization and are diploblastic
They have a central vascular cavity or coelenteron, which serves both digestive and circulatory functions
The coelenteron has a single opening called the mouth or hypostome, which serves both ingestion and egestion
Digestion is both extracellular and intracellular
Their nervous system is primitive and consists of a diffused nerve net
Cnidarians like corals have a skeleton made up of calcium carbonate
They exhibit two basic body forms: polyp and medusa
Polyp forms are sessile and cylindrical (e.g., Hydra, Adamsia), while medusa forms are umbrella-shaped and free-swimming
Cnidarians that exist in both forms exhibit alternation of generations in their life cycle (Metagenesis)
The polyp represents the asexual generation, and the medusa represents the sexual generation
Polyps produce medusa asexually, and medusa forms polyps sexually
Development is indirect and includes a free-swimming ciliated planula larva

Description

Learn about the characteristics of sponges, including their aquatic habitat, asymmetrical shape, and primitive multicellular structure. Discover their unique features such as the water transport system and canal system.