Questions and Answers
What evolutionary significance do Onychophorans hold in relation to Phylum Annelida and Phylum Arthropoda?
Onychophorans are considered an 'evolutionary link' between Phylum Annelida and Phylum Arthropoda due to possessing characteristics common to both groups.
Describe the geographic distribution and habitat preferences of Onychophorans.
Onychophorans are terrestrial animals found primarily in damp, moist, and dark environments, concentrated in rain forests of the Southern Hemisphere.
List at least three general characteristics of Onychophorans.
Onychophorans exhibit bilateral symmetry, are triploblastic, and possess a segmented coelom.
What are the names derived from Greek for Onychophorans, and what do they signify?
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What is the structure and function of the respiratory system in Onychophorans?
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Study Notes
Evolutionary Significance
- Development of the blastocoel marked a crucial evolutionary event in the Animal Kingdom.
- True coelom led to the emergence of three major coelomate groups:
- Phylum Annelida: Includes earthworms.
- Phylum Arthropoda: Encompasses crayfish and spiders.
- Phylum Mollusca: Features species like octopuses and giant squids.
Lesser Protostomes
- Recognized as less important both economically and ecologically.
- Few or no significant derived species evolved from this group.
Importance of Onychophorans
- Hold prime significance in zoological studies.
- Exhibit characteristics common to both Annelida and Arthropoda.
- Considered an evolutionary link between these two major Eucoelomate phyla.
Name Derivatives of Onychophorans
- Derived from two Greek words:
- Onyx: Means "claws," referring to appendages ending in claws.
- Pherin: Translates to "phora."
- Common names include:
- Walking worms
- Velvet worms
Classification of Onychophorans
- Composed of seventy species organized into twelve genera.
- Divided into two primary families:
- Family Peripatidae: Contains the genus Peripatus.
- Family Peripatopsidae: Encompasses the genus Peripatopsis.
- Commonly found in South Africa.
Geographic Distribution
- Terrestrial onychophorans are primarily located in rainforests.
- Prefer damp, moist, and dark environments, especially in tropical regions of the Southern Hemisphere.
- Active primarily at night when conditions are humid and warm for foraging.
- Restricted to moist habitats due to open spiracles, which become a liability in dry air.
General Characteristics
- Exhibit organ system level organization, following a tube within a tube structure.
- Display bilateral symmetry and are triploblastic, protostomic, segmented coelomates.
- Body structure includes cuticle, epidermis, circular and longitudinal muscles, and tubercles/protruberances.
- Possess parapodia with claws.
- Feature an open circulatory system alongside a hemocele and a dorsal tubular heart with ostia.
- Exhibit paired metanephridia and coxal glands for excretion.
- Utilize a tracheal system for respiration.
- Nervous system is located ventrolaterally.
- Species are sexually dimorphic, exhibiting separate sexes for reproduction.
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Description
Explore the critical evolutionary milestones in the Animal Kingdom, focusing on the development of the blastocoel and the introduction of major coelomate groups like Annelida, Arthropoda, and Mollusca. Understand the significance of lesser protostomes and the importance of onychophorans for zoologists.
