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Marine Invertebrates > Lecture 9 > Flashcards

Lecture 9 Flashcards

Bilateria and xenacoelomorpha

1
Q

General features

A
  • (Most) bilateral symmetry
    • Dorsal (ventral)
    • Anterior (posterior)
  • ‘Heads’ for feeding and cephalisation often appear
  • Homeobox (hox) genes and proteins; directors of bilateral body plan arrangements
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2
Q

Hox proteins

A

Developmentally-linked transcription factors
* Binds to DNA to regulate the expression of developmentally-linked genes
* Anterior, central, and posterior hox genes help determine where specific features develop

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3
Q

Bilateria germ layers

A
  • Tripoblastic
  • Ectoderm, mesoderm, endoderm
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4
Q

Cnidaria germ layers

A
  • Dipoblastic
  • Ctenophora and placozoa
  • Ectoderm and endoderm
  • Mesoglea does not form from germ layer
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5
Q

Tripoblastic

A

A body derived from three embryonic cell layers; ectoderm, mesoderm, endoderm

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6
Q

Dipoblastic

A

A body derived from only two embryonic cell layers; ectoderm, endoderm

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7
Q

Ectoderm

A

Outer epithelium and simple nerves

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8
Q

Endoderm

A

Digestive cells

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9
Q

Epitheliomuscular

A

Muscle-like cells, not true muscles

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10
Q

Xenacoelomorpha

A
  • Originally misunderstood as secondarily simplified platytrochozoa, Platyhelminthes
  • Acoelomate, flat, unsegmented body, incomplete gut, similar nervous system
  • Unlike Platyhelminthes, no excretory system; rely on diffusion
  • Mouth do not develop at blastopore
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11
Q

Locomotory ciliated epidermal cells

A
  • ‘Gliding’ through multi-ciliated outer epidermal cells
    • Upon degeneration, these cells are reabsorbed, and the cilia ‘pulsate’ AKA “pulsatile bodies”
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12
Q

Epidermal rhaboid cells

A

Mucous glands which lubricate the body to improve the gliding efficiency

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13
Q

Mesoderm derived musculature

A

Gives the animal high degrees of flexibility to aid in movement

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14
Q

Frontal organ/pores

A
  • Function poorly understood
  • May have sensory functions
    • Chemo/mechanoreceptors
  • Mucous secretion
    • Prey trapping, protecting ‘head’
    • May also help track chemicals
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15
Q

Anterior ‘brain’ (nervous system)

A

Connects to the body via multiple longitudinal nerve cords

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16
Q

Sensory receptors

A

Anterior statocyst capsules surrounded by retractile statolith for geotactic control

17
Q

Light

A
  • Acoels have simple ‘eyes’
  • Light sensitive photoreceptors innervated by peripheral neurons
18
Q

Statolith

A

A calcareous particle in the statocysts of invertebrates that stimulates sensory receptors in response to gravity, enabling balance and orientation

19
Q

Feeding and digestion

A
  • Incomplete gut
  • Mouth position varies wildly across species
  • Extra and intracellular digestion occurs
  • Xenacoelomorph glides onto prey, like placozoa
  • Gastric cavity is everted onto prey for digestion
  • Prey is grasped by the body, covered in mucous and pushed towards the mouth
  • Pharynx or circular muscles near the mouth constrict to trap prey
20
Q

Symsagittifera roscofensis

A
  • Marine ‘sun-bathing’ green worms
  • Members of the acoels
  • Symbiotic relationship with algae ingested within the xenacoelomorph gastric cavity
21
Q

Sexual reproduction (acoels and possibly nemertodermatida)

A
  • Simultaneously hermaphroditic animals ‘nip’ each other before larger individual initiates mating
  • Animals ball together and undergo mutual copulation (well develop copulatory organs)
  • Fertilisation is always internal
  • Zygotes released from the mouth, gonopore, or body rupturing
  • Direct development, no larval phase
22
Q

Sexual reproduction (xenoturbellida)

A
  • Simultaneously hermaphroditic animals; lack well-developed testes/ovaries of acoelomorpha
    • Disorganised cells near gut appear to produce gametes
    • No copulatory organs, spawning is through mucous-gamete extrusion
  • Zygotes released from the mouth or body rupturing
  • Direct development, no larval phase
    • Juveniles do not seem to have mouths
23
Q

Asexual reproduction (fission and regeneration)

A
  • Mesodermally-derived neoblasts replace damaged or missing body components
    • Gives strong regenerative action to the phyla
  • Acoelomorpha can reproduce via fission and budding
  • Xenoturbellida may not reproduce asexually

Marine Invertebrates (17 decks)

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