Phylum Rotifera Flashcards

Overview of Rotifera

• Rotifers are small aquatic invertebrates, averaging 50 micrometers to over 2 millimeters in size, characterized by a ring of cilia around the mouth that resembles a spinning wheel.
• Commonly referred to as "wheel animals" due to their distinct head structure known as the corona, which aids in locomotion and feeding.

Anatomy of Rotifers

• Head: Features a semicircular, wheel-like appearance covered with cilia that assist in digestion and sensory functions. The cilia collectively referred to as the corona, resemble a crown.
• Neck: Contains the trophi, the only rigid part of the rotifer's body, which can fossilize when replaced by minerals post-mortem.
• Trunk: A tube-like, extendable body made of concentric tubular portions for flexibility and movement, covered by a transparent cuticle.
• Foot: Used for propulsion and attaching to surfaces, essential for rotifers that form colonies for survival; over twenty species live in colonies.

Habitat and Diet

• Rotifers primarily inhabit aquatic environments and can be found as parasites on other aquatic animals.
• They predominantly feed on microscopic organisms, aligning their size and hunting strategy with their prey.

Reproduction and Development

• Reproduction: Primarily through parthenogenesis (asexual) where embryos develop without fertilization; both male and female forms exist, but males are rare or not observed in many species.
• Embryo Development: Eggs can be carried externally or internally, hatching typically within 12 hours, with development stages influenced by environmental factors.
• Adult Life Span: Generally short, ranging from 5 to 45 days, with their eggs and adults being preyed upon by various organisms.

Specific Class: Bdelloid Rotifers

• Comprising 450 species, bdelloid rotifers are resilient and primarily found in freshwater, feeding on bacteria and algae.
• Known for unique survival mechanisms, they undergo anhidrosis to withstand dry conditions by dehydrating and entering a dormant state until moisture returns.

Key Biological Processes

• Cilia are crucial for guiding food to the rotifer's mouth and aiding in efficient feeding.
• Digestion and absorption mainly occur in the stomach, where food is processed after being gathered by cilia.
• The trophi structure is the only part of a rotifer that can become fossilized, highlighting its significance in paleontological studies.

Notes on Life Cycle

• Many microscopic animals, including rotifers, exhibit short life cycles, a common trait that enhances species survival in fluctuating environments.