Subkingdom Protozoa Overview

Subkingdom Protozoa

• The phylum Protozoa includes more than 50,000 species found in almost all habitats with moisture.
• Most are very small (unicellular), only visible with a light microscope; some are only 2-3 µm long.
• Many exist as solitary individuals, but some form colonies.
• Some are free-living (freshwater, saltwater, damp places), others are parasitic (endoparasites).
• Most have a single nucleus with nucleoli (endosomes) in the cytoplasm.
• Cytoplasm is divided into clear ectoplasm (outer) and granular endoplasm (inner).
• Some have a rigid pellicle or non-living external envelopes (gelatinous, cellulose, calcareous).
• Locomotion occurs via temporary cytoplasm protrusions (pseudopodia), whip-like filaments (flagella), or short hair-like filaments (cilia). Some lack locomotory organelles.
• Holozoic nutrition is common (active feeding on other organisms or decaying matter). Some species exhibit holophytic nutrition (plant-like, synthesizing organic material from sunlight).

Subkingdom Parazoa

• Sponges are mostly marine, sessile animals with little or no detectable movement.
• They are considered the most primitive multicellular animals and are placed in a separate subkingdom called Parazoa.
• This subkingdom includes the phylum Porifera.

Subkingdom Metazoa

• Multicellular animals are called Metazoa.

• Metazoa differ from Protozoa in attaining larger sizes and requiring a specialized digestive system due to increased nutritional needs.

• Specialized body cavities for digestion are required for larger food particles

• The larger size necessitates a circulatory system to deliver nourishment and respiratory gases to the tissues, diffusion will not suffice

• Tissues are more developed and organized into organs which form systems in higher phyla

• A nervous system allows coordination between cells and tissues, and communication from receptors to effectors

• Metazoa have developed supportive structures (external/internal skeletal systems) and reproductive organs that produce sexual gametes rather than in cells as in Protozoa

Class Turbellaria

• Free-living flatworms (Platyhelminthes) in freshwater and marine environments.
• Possess a flattened, bilaterally symmetrical body.
• Have a simple digestive system; (Mouth, lacking an anus)
• Excretory system of flame cells

Class Trematoda

• These are parasitic flatworms, which cause fascioliasis in humans.
• They lack a coelom and have complex life cycles, many using intermediate hosts
• The trematodes Fasciola hepatica commonly infect livestock.

Class Cestoda

• These are parasitic ribbon-like flatworms (tapeworms).
• Commonly found in the intestines of vertebrates.
• Their bodies consist of many repeating units called proglottids. Tapeworms lack a digestive system.

Class Nematoda

• These are roundworms with a complete digestive system, with a mouth and anus.
• Most are free-living, some are parasitic (affecting plants and animals).
• Elongate, cylindrical, non-segmented body covered with a cuticle
• Muscles consist of longitudinal fibers

Class Ascaridata

• These are parasitic roundworms living in the intestines of vertebrates
• Oviparous, large and stout nematodes.
• Mouth has 3 prominent lips and a lack of a buccal capsule.
• Males have two copulatory spicules
• The life cycle can be direct or indirect, often involving larval stages

Class Strongylata

• These are parasitic roundworms of vertebrates that lack lips.
• They possess a well-developed buccal capsule with teeth, and males have a copulatory bursa.
• The life cycle usually involves larval stages and may utilize intermediate hosts.

Explore the fascinating world of Protozoa, a diverse phylum comprising over 50,000 species found in various moist habitats. This quiz covers their characteristics, locomotion methods, and nutritional habits, highlighting their significance in ecosystems. Discover the life cycles and survival strategies of these unicellular organisms.