Xenacoelomorpha and Acoelomorpha

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Questions and Answers

Which feature distinguishes Xenacoelomorpha from more complex animal phyla?

  • Ability to reproduce sexually.
  • Presence of three true tissue layers. (correct)
  • Presence of a complete digestive system.
  • Lack of excretory systems.

What is the primary function of the statocyst in Acoelomorpha?

  • Excretion of waste.
  • Reproduction.
  • Sensory organ for localization and movement. (correct)
  • Digestion of food.

What structural feature classifies Acoelomorpha as acoelomates?

  • Presence of a coelom.
  • Absence of a digestive system.
  • Lack of an internal body cavity, possessing only a gastral cavity. (correct)
  • Presence of testes and ovaries.

How do 'mint sauce worms' acquire their green color?

<p>By harvesting symbiotic algae transmitted from mothers to juveniles. (D)</p> Signup and view all the answers

What adaptation do free-living Platyhelminthes possess for enhanced cephalization?

<p>Auricles for sensory perception. (C)</p> Signup and view all the answers

What role does the mesoderm play in the body plan of Bilateria?

<p>It provides structural support through the development of muscles. (B)</p> Signup and view all the answers

How do free-living flatworms typically acquire their nutrition?

<p>By predation, using enzymes to dissolve prey. (D)</p> Signup and view all the answers

What is the primary difference in the body wall structure between free-living and parasitic flatworms?

<p>Free-living forms have a ciliated epidermis, while parasites have a non-ciliated tegument. (C)</p> Signup and view all the answers

How do parasitic flatworms, specifically Neodermata, obtain nutrients?

<p>By absorbing nutrients through the tegument from their surrounding environment. (B)</p> Signup and view all the answers

What is the role of microtriches in parasitic flatworms?

<p>To increase the surface area for nutrient absorption. (B)</p> Signup and view all the answers

How do tapeworm segments reproduce and disperse?

<p>Segments grow and detach, releasing into the environment when the host defecates. (C)</p> Signup and view all the answers

What is a common method of asexual reproduction observed in free-living flatworms like Dugesia?

<p>Fragmentation followed by regeneration (transverse fission). (D)</p> Signup and view all the answers

What reproductive strategy is commonly observed in flatworms, given their hermaphroditic nature?

<p>Cross-fertilization between two individuals. (C)</p> Signup and view all the answers

What is the typical life cycle of a parasite found in cows, after the cow eats contaminated grass?

<p>Embryos are released, larvae enter blood vessels, and end up in the muscles. (B)</p> Signup and view all the answers

What accounts for the widespread dispersal of nematodes across various environments?

<p>Dispersal via wind, rain, animals, and insect vectors. (D)</p> Signup and view all the answers

What anatomical feature is absent in nematodes, influencing their physiological processes?

<p>Gas exchange system. (D)</p> Signup and view all the answers

What feature defines nematodes in terms of their body cavity?

<p>Pseudocoelomates with a pseudocoelom between the ectoderm and endoderm. (A)</p> Signup and view all the answers

What is the significance of C. elegans as a model organism in biological research?

<p>Its simple anatomy and ease of study make it valuable for developmental biology and genetics. (C)</p> Signup and view all the answers

What unique reproductive characteristic is found in C. elegans?

<p>Hermaphroditism with ovaries that also function as testes. (A)</p> Signup and view all the answers

What is the function of dauer larvae in nematodes?

<p>To colonize new environments through phoresy. (A)</p> Signup and view all the answers

What type of sperm is unique to certain nematodes and some vertebrates like elephant fish?

<p>Amoeboid sperm. (D)</p> Signup and view all the answers

What is the term for the point of connection between a nerve and muscle in nematodes?

<p>Myoneural junction. (D)</p> Signup and view all the answers

What is meant by 'eutely' in the context of nematode biology?

<p>Constant cell number within an organism. (A)</p> Signup and view all the answers

What is the significance of chromosome diminution in nematodes?

<p>It maintains the original chromosome number in the germline while reducing it in somatic cells. (C)</p> Signup and view all the answers

What is the function of protonephridia in Platyhelminthes?

<p>Excretion and osmoregulation. (D)</p> Signup and view all the answers

Which feature allows flatworms to move substances throughout their body without a circulatory or respiratory system?

<p>Flattened body shape. (D)</p> Signup and view all the answers

What is the role of the pharynx in free-living flatworms during feeding?

<p>Ejecting outwards to secrete enzymes and dissolve prey. (A)</p> Signup and view all the answers

How does the tegument of parasitic flatworms aid in their survival?

<p>By protecting against the host's immune system and facilitating nutrient absorption. (D)</p> Signup and view all the answers

What is the primary function of the hook-bearing rostellum and suckers in parasitic flatworms?

<p>To attach to the host. (B)</p> Signup and view all the answers

How do free-living flatworms move?

<p>By gliding using cilia or swimming via muscular movement. (D)</p> Signup and view all the answers

What is the feeding strategy of free-living flatworms?

<p>Predators, carnivores, or scavengers. (D)</p> Signup and view all the answers

What is the significance of the 'sinus' in flatworms?

<p>It is a thin space that facilitates the movement of substances. (B)</p> Signup and view all the answers

What role does the frontal gland play in flatworms?

<p>Sensory perception. (C)</p> Signup and view all the answers

How does the abundance of nematodes compare to other animal groups?

<p>They are the most abundant animal group. (B)</p> Signup and view all the answers

What type of skeleton do nematodes possess?

<p>Hydroelastic skeleton. (D)</p> Signup and view all the answers

How do nematodes achieve locomotion?

<p>Circular and longitudinal muscles. (B)</p> Signup and view all the answers

What systems are absent in most nematodes?

<p>Gas exchange and circulatory systems. (B)</p> Signup and view all the answers

What is the epicuticle of nematodes primarily composed of?

<p>Lipids (A)</p> Signup and view all the answers

What are muscle arms also called in nematodes?

<p>Myoneural junction (D)</p> Signup and view all the answers

Which of the following correctly describes the lifestyle of free-living flatworms?

<p>They capture and consume other animals. (B)</p> Signup and view all the answers

Flashcards

Xenacoelomorpha

Basic animal phyla with three true tissues; includes Aceolomorpha and Xenoturbellida.

Acoelomorpha/Xenoturbellida

Flattened worms lacking an excretory system, found in shallow or deep sea environments.

Statocyst

Sensory organ located in the anterior part of the body in flattened worms.

Acoelomates

Condition of lacking an internal body cavity, as seen in flattened worms.

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Photosymbiotic

Symbiotic relationship where an animal hosts algae or protists within its tissues.

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Platyhelminthes

Flattened worms with auricles, indicating advanced cephalization.

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Triploblastic Condition

Having three germ layers or tissues: ectoderm, mesoderm, and endoderm.

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Bilateria

Animals with three germ layers, bilateral symmetry, and cephalization.

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Protonephridia

Excretory organs in Platyhelminthes, aid in osmoregulation and waste removal.

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Cephalization

The concentration of sensory and neural organs in the anterior region of an animal.

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Sinus

A thin sinus in the flatworm that allows for movement of substances.

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Sagittal plane

The plane that divides an animal into left and right halves.

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Pharynx

Ejected from the body to secrete enzymes to dissolve prey.

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Neodermata

Non-ciliated tegument with microtriches for nutrient absorption in parasitic flatworms.

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Hook-bearing rostellum

Hook-bearing structures used by parasites for attachment to hosts.

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Segments

Distal segments of tapeworms that detach and are released into the environment.

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Free living flatworms

Free-living flatworms that are predators, carnivores, or scavengers.

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Dugesia

A type of free-living flatworm known for its regenerative abilities.

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Transverse fission

Asexual reproduction in flatworms where the body divides into two or more pieces.

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Hermaphrodites

Condition of having both male and female reproductive organs in one individual.

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Nematodes

Extremely abundant, free-living or parasitic worms with a triploblastic, bilateral body plan.

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Pseudocoelom

Body cavity between the ectoderm and endoderm in nematodes.

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C. elegans

A nematode species widely studied for genetics and developmental biology.

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Dauer larvae

A larval stage in nematodes that uses phoresy to colonize new environments.

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Amoeboid sperm

A type of sperm that moves with amoeboid movements rather than flagella.

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Eutely

Constant cell number in an organism or a specific tissue.

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Chromosome diminution

Process where chromosomes are eliminated from somatic cells but retained in the germline.

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Study Notes

  • Flattened worms are less complex than rounded worms.
  • Xenacoelomorpha is comprised of the most basic animal phyla, and has three true tissues.
  • Xenacoelomorpha includes both Aceolomorpha and Xenoturbellida.
  • Acoelomorpha inhabits shallow and brackish waters while Xenoturbellida resides in deep sea environments.
  • Excretory systems are absent in both Acoelomorpha and Xenoturbellida.
  • Acoelomorpha and Xenoturbellida feature a simple internal structure with just one opening that functions as both mouth and anus.
  • They possess a statocyst in the anterior part of their body, which is a sensory organ used for localization and movement.
  • The body structure consists of an external tissue layer, an internal layer, and some cells in the mesoderm.
  • These organisms are acoelomates because they lack an internal cavity and only have a gastral cavity.
  • They produce eggs without ovaries and sperm without testes.
  • Flattened worms often have other organisms like algae or protists associated with their mesodermal layer, leading to photosymbiosis.
  • Mint sauce worm is common in the UK, and it harvests symbiotic algae that are transmitted from mothers to juveniles, giving the worm a green color.
  • Xenacoelomorpa has a more developed cephalic end and are known to carry brown algae.
  • Some claim Xenacoelomorpa can be used to produce instant noodles in Southeast Asia.
  • Platyhelminthes are found in both freshwater and ocean water and possess auricles.
  • Platyhelminthes exhibit a more advanced cephalization.
  • Platyhelminthes show a triploblastic condition with more developed systems, such as excretory organs with protonephridia, and have bilateral symmetry.
  • Bilateria have three germ layers or tissues.
  • The body plan organization includes organs and systems with internal plumbing that allows movement in coordination with a triploblastic condition, bilateria, and cephalization.
  • The mesoderm provides structural support through muscle development, which allows animal movement.
  • The digestive system consists of a gastric cavity with one opening for both excretion and feeding.
  • Cephalic ganglia act as a brain, along with a nervous system, excretory system, and sensorial system.
  • Most flattened worms are hermaphrodites.
  • Cilia on the base of the body facilitates movement.
  • Flattened shape allows gas movement inside the mesoderm to any part of the animal.
  • Sinus being very thin allows movement of substances without a circulatory or respiratory system.
  • Sagittal plane includes a brain associated with a statocyst.
  • The frontal gland has sensorial uses.
  • The pharynx can be ejected outwards to act as a mouth, secreting enzymes to dissolve prey since free-living forms are predators.
  • Cross-fertilization is common among flattened worms.
  • Body wall differs between parasites and free-living forms.
  • Free-living forms have an epidermis composed of ciliated syncytial epithelium.
  • Parasites (Neodermata) possess a non-ciliated tegument with organelles called microtriches.
  • Parasites absorb nutrients from their environment and release waste through the tegument.
  • Free-living forms move by gliding on cilia or swimming with muscular movements.
  • Parasite attachment devices include hook-bearing rostellum suckers that attach to a host.
  • Each segment contains reproductive organs in tapeworms.
  • Tapeworm segments grow and detach from the distal end of the animal during host defecation, releasing them into the environment.
  • Feeding occurs through both the pharynx and the tegument.
  • Free-living forms are predators, carnivores, or scavengers, and have eyes to chase prey.
  • They typically have a lobed gut.
  • Dugesia feeds on other flatworms.
  • Reproduction can be sexual or asexual.
  • Dugesia can regenerate through transverse fission if chopped.
  • Sexual reproduction involves releasing an egg capsule that requires cross-fertilization since most are hermaphrodites.
  • Parasites can undergo cross-fertilization of segments or self-fertilization within the same animal.
  • Parasites in the cow end up in the intestine after the cow eats grass, and the released embryos become larvae that migrate to blood vessels and muscles.
  • Roundworms and threadworms are highly abundant and live freely in freshwater, marine, soil, and parasitic in invertebrates, vertebrates, and plants.
  • Life patterns of roundworms and threadworms are triploblastic, bilateral, vermiform, unsegmented, blastocoelomates, with high fecundity, for example, Ascaris produces 200,000 eggs per day and are dispersed by wind, rain, animals, or insect vectors.
  • One rotten apple can contain up to 90,000 nematodes.
  • Nematodes are the most abundant animal group, with the highest populations found in temperate areas towards the Equator and the southern hemisphere.
  • Nematodes have four larval stages and can be dioecious, trioecious, or hermaphrodites that reproduce through parthenogenetic females.
  • Nematodes have a simple anatomy consisting of three cuticle layers: an epicuticle with lipids, a proteinaceous exocuticle, and an endocuticle with chitin or collagen, forming a hydroelastic skeleton.
  • Nematodes lack circular muscles, but possess a complete digestive system with a mouth and anus.
  • Nematodes lack gas exchange, circulatory, and excretory systems, as well as a fat body or liver, but some have ocelli.
  • The pseudocoelom is located between the ectoderm and endoderm.
  • C. elegans has been genetically studied and are called spitting worms because they spit when disturbed.
  • C. elegans is a soil nematode that is easy to study, making it ideal for developmental biology and genetics.
  • C. elegans characteristics include being hermaphrodites with ovaries that function as testes, enabling self-fertilization.
  • C. elegans produce dauer larvae that use phoresy to colonize new environments.
  • Nematodes feature amoeboid sperm that moves like amoebas, sometimes with flagellated with a and big head, found in nematodes and elephant fish.
  • Nematodes have varied nervous systems with myoneural junctions known as muscle arms.
  • Eutely refers to constant cell numbers.
  • Chromosome diminution involves keeping the germline of an animal with the original chromosomes to pass onto the next generation, but during division, most cells accept germline, although is not present in all nematodes.
  • Cleavage of the egg involves a sector preserving all chromosomes while others are eliminated.

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