Question

Peripatus is an example of an organism belonging to the phylum

• A. Arthropoda
• B. Annelida
• C. Onychophora
• D. Mollusca

Answer 1

Answer:

C. Onychophora

Evolutionary Significance of Peripatus (Velvet Worms)

• Peripatus, commonly known as velvet worms, belongs to the phylum Onychophora. This phylum is also sometimes referred to as 'Proarthropoda' or 'Uniramia' in older classifications, highlighting their primitive arthropod-like features.
• This phylum is of immense evolutionary importance as it represents a "missing link" or transitional form between the Annelida (segmented worms, e.g., earthworms and leeches) and the Arthropoda (insects, crustaceans, spiders).

Key Characteristics and Adaptations

• Habitat: Peripatus are primarily terrestrial, inhabiting humid, damp environments like leaf litter, under logs, and in rotten wood. They are predominantly found in tropical and subtropical regions, including parts of South America, Africa, Australia, and New Zealand.
• Body Structure: Their bodies are caterpillar-like, with a soft, velvety, and unsegmented appearance externally. They possess numerous unjointed, stubby leg-like appendages called lobopods, each ending in a pair of claws.
• Slime Glands: A distinctive and unique feature is the presence of specialized slime glands (or crural glands located near the mouth). When threatened or hunting, they can eject a sticky, proteinaceous fluid (slime) from oral papillae on their heads. This slime quickly hardens upon contact with air, effectively ensnaring prey or deterring predators.
• Respiratory System: Unlike annelids that often respire through their skin or gills, Onychophorans possess a tracheal system for respiration, which is a key characteristic shared with arthropods. This system allows for direct delivery of oxygen to tissues. However, their spiracles (openings to the trachea) cannot be closed, leading to significant water loss, thus restricting them to high-humidity environments.
• Exoskeleton and Molting: While they have a chitinous cuticle, it is thin and flexible, unlike the rigid exoskeleton of most arthropods. They periodically shed their cuticle (a process called ecdysis or molting) throughout their lives, similar to arthropods.
• Nervous System: They have a relatively simple, ladder-like nervous system with a pair of ventral nerve cords, which exhibits some similarities to annelids. They possess a pair of simple eyes (ocelli) and prominent, segmented antennae.
• Reproduction: Reproduction in Onychophora can vary significantly, ranging from oviparous (egg-laying) to ovoviviparous (eggs hatch inside the mother) and viviparous (live birth with maternal nourishment), showcasing diverse reproductive strategies within the phylum.

"Living Fossil" Status

• Peripatus is often referred to as a "living fossil" because their body plan and general morphology have remained largely unchanged for millions of years. Fossil records, particularly from the Cambrian period (e.g., Aysheaia), show striking resemblance to modern velvet worms, making them invaluable for understanding early animal evolution and the diversification of life on Earth.