Phylum Porifera: Sponges and Parazoa

Sponges

• Pinacocytes are cellular components responsible for the outer epithelial layer of sponges.
• Choanocytes (also known as collar cells) are responsible for exhibiting flagella and the filter feeding system in sponges.
• Amoebocytes are responsible for various functions, including digestion, nutrient transport, and spicule formation in sponges.
• Grey cells are presumed to be responsible for the transmission of nervous impulses in sponges.
• The skeleton of sponges is composed of spicules, which can be made of silica or calcium carbonate.
• Sponges primarily obtain oxygen for respiration through diffusion.

General Phyla Characteristics

• Phylum Cnidaria exhibits both polymorphism and alternation of generation in their life cycle.
• Phylum Platyhelminthes has an incomplete digestive cavity and one opening in the body that serves both for food ingestion and egestion.
• Class Trematoda of Platyhelminthes consists of non-ciliated parasitic flatworms or flukes.
• Phylum Cnidaria is characterized by having a central gastrovascular cavity communicating to the exterior by the mouth and tentacles provided with nematocysts for food capture and defense.
• Phylum Platyhelminthes has a blind-sac body plan and possesses a ladder-like nervous system comprising the brain and two main longitudinal nerve cords connected at intervals by transverse commissures.
• Phylum Cnidaria exhibits radial or biradial symmetry and a phenomenon of polymorphism, including both polyps and medusae.
• Phylum Cnidaria is mostly marine but also includes a few freshwater forms like Hydra.

Nervous and Excretory Systems

• In Phylum Platyhelminthes, the nervous system and excretory system are described as one or more network of nerve cells and neurites located in the ectoderm and endoderm, and flame cells leading into tubules that open out by one or more excretory pores.

Cnidaria

• Class Cubozoa of Cnidaria consists of free-swimming and sexual zooids.

Protozoa

• The term 'Protozoa' was coined by scientist Georg Goldfuss.
• The size range of protozoa is from 10-50 μm to several millimeters.
• Protozoa is considered to be a connecting link between the Animal and Plant Kingdoms.
• Protozoa exhibit holophytic and saprozoic nutrition.
• The body of protozoa can be covered by pellicle or shells.
• The primary form of organization of protozoa is unicellular.
• Subphylum Mastigophora of protozoans does not contain any organelles for locomotion.
• The primary mode of reproduction in protozoans is binary fission.
• Superclass Sarcodina of protozoans includes organisms with bodies covered by plasmalemma or pellicle and are mostly free-living or some are parasitic.
• Subclass Opalinata of protozoans exhibits numerous cilia-like organelles on their entire body and engage in syngamy with flagellated anisogamete.
• Phylum Rhizopoda is characterized by having a blind-sac body plan, pseudopodia locomotory organelles, and forms gametes and flagellates young once.
• Superclass Ciliophora of protozoans primarily consists of organisms with bodies covered by plasmalemma or pellicle and engage in binary fission.
• Class Phytomastigophora of protozoans possesses chromatophores and one to two flagella, and are mostly free-living.
• Subclass Rhizopoda of protozoans has amoeboid forms with some having half shells but do not form spores.
• Phylum Amoeba of protozoans is primarily characterized by the absence of organelles for locomotion in adults.