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Invertebrates > The deuterostomes > Flashcards

The deuterostomes Flashcards

1
Q

Evolutionary branch of deuterostomes

A
  • Bilateria
  • Chordata (all invert chordates are marine)
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2
Q

Body layers

A
  • Mesoderm
  • Two layers
  • Coelomates
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3
Q

Examples of Echinoderms?

A
  • Starfish
  • Sea Urchins
  • Sea Cucumber
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4
Q

Echinoderm features

A
  • Pentamerous radial symmetry
  • Body divided into 5 parts
  • Not related to other radially symmetrical groups
  • Variation in groups

Odd one out = sea cucumber - e.g. ‘burnt sausage’ - secondarily bilaterally symmetrical

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5
Q

Mouth location on echinoderms

A
  • Mouth on top: oral surface
  • Anus on top: aboral surface

Some variation:

  • Starfish & Sea urchins - aboral surface -mouth underneath
  • Sea lilies & Feather stars - oral surface - mouth on top

Irregular urchins: mouth has moved to underneath at one end - moving towards bilateral symmetry

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6
Q

Echinoderm larval stages symmetry

A

Bilateral symmetry

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7
Q

Larvae stages show convergent evolution

Echinoderms

A

Although not closely related:

  • Sea cucumber and starfish have similar larval stages
  • Sea urchins and brittle stars have similar larval stage
  • Some groups have lost the planktonic larval stage (also shows convergent evolution)
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8
Q

How do Echinoderms go from bilateral symmetrical larvae to radially symmetrical adults?

A
  • Adult arises from cells set aside in the larval stage (maximal indirect development)
  • Anterior-posterior body axis shifts, body twists around new axis (aboral-oral axis)
  • Coelomic cavities undergoes reorganisation
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9
Q

Ossicle features

A
  • Each calcareous ossicle separated by living tissue
  • Increase size without moutling
  • Unlike arthropods, does not need to shed
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9
Q

How can ossicles be modified?

A
  • Ossicles can fuse together, are hinged (e.g. urchins)
  • Aristotle’s lantern - used for feeding(grinds away at algae). Are modified ossicles
  • Sea cucumber ossicles are either very minute or absent
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9
Q

Echinoderm internal skeleton

A

Ossicles

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10
Q

Echinoderms tube feed

A

Podia

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11
Q

Podia modifications

A
  • Can be large - used for locomotion and feeding
  • Starfish with long legs use podia for latching onto prey - can pry open bivalves and inverts stomach into shell to digest prey by releasing enzymes.
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12
Q

How Brittle Stars uses their Podia

A
  • Don’t use podia for locomotion
  • Use podia for feeding
  • Secrete mucus which created sticky surface that food gets stuck to
  • Moves around by thrashing legs
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13
Q

How Sea cucumber use their Podia

A

Deposit feeder or suspension feeder using modified podia

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14
Q

Echinoderm: Water vascular system that controls the podia

A
  • Modified coelom
  • Sea water is circulated around the animal
  • Podia can contract and relax via water circulating and entering the body and ampulla
15
Q

Echinoderm: Mutable connective tissue

A
  • Able to change their connective tissue
  • Able to change how stiff it is
  • Change in viscosity of collagen fibres
  • Under nervous control so doesn’t use much energy
  • Very rapid
  • Defence mechanism
16
Q

Echinoderm: Mutable connective tissue (Examples)

A
  • Sea cucumbers can release their guts out of their back end
  • Sea urchins spines can change rigidity for movement
17
Q

Echinoderm: Nervous System

A

Nerve net

  • Central ring with branches going down legs (in starfish)
  • Part can take on a temporary brain function
18
Q

What are Hemichordates?

A
  • “Half chordates”
  • They lack a true notochord
19
Q

Two groups of Hemichordates

A
  • Enteropnuets: Acorn worms
  • Pterobranchs: Sea angels
20
Q

Enteropnuets: Acorn worms

Hemichordates

A
  • Solitary
  • Vary in length long
  • Body made up of 3 regions (proboscis, collar and trunk)
  • Proboscis collects food, gills slits used to respiration
  • Stomochord - supports heart and excretory organ
  • Larval stage (toraria) - similar to echinoderms
  • Nerve net (concentrated in collar and can be hollow)
21
Q

Pterobranchs: Sea angels

A
  • Lophophores
  • Still same structure as acorn worms
  • Very small 1-5mm long
  • Sessile
  • Colonial
  • Some have gill slits
  • Simple nerve net
  • Stomochord - supports oral shield
  • Can be traced back to the graptolites (cambrian - devonian)
22
Q

Three groups of Chordates

A
  1. Urochordates: Tunicates
  2. Cephalochordates: Lancelets
  3. Vertebrates
23
Q

Chordate features

A

Chordates have the following at some point in their lives:

  • Notochord - stiffening rod used as support
  • Dorsal, hollow nerve cord
  • Pharyngeal (gill slits)
  • Post-anal tail
24
Q

Invertebrate chordates:
Urochordates (tunicates)

A
  • In larval stage they have all the chordate features (‘Tadpole’ larva)
  • In adults all that is left is pharyngeal slits
  • Covered in ‘tunic’ which contains cellulose
25
Q

Invertebrate chordates:
Urochordates (tunicates) - Larvae to adult metamorphosis

A
  • Larval stages swims, settles on a surface (head down) and undergoes metamorphosis
  • Notochord loses turgor
  • Tail absorbed
  • Rapid growth between buccal syphon & papillae
26
Q

Unusual example of a tunicate: Larvacea

A
  • Retains larval features in adult form
  • Larvacea or Appendicularia (called both names)
27
Q

Ceplalaochordates (amphioxus/lancelet)

A
  • All features of chordates
  • Sirri - tentacles - sensitive to chemicals and also passes water into the mouth over gills - filter feeders.
  • Endostyle - transforms into thyroid gland in vertebrates
28
Q

Phylogentic tree of echinoderms, hemichordates and Chordates

A

Two sister groups within the Deuterostomes

  • Ambulacaria: Echinoderms & Hemichordates
  • Chordates: Urochordates & Vertebrates
  • Gill slits lost in Echinoderms
  • Nerve net lost in Chordates (dorsal nerve chord)
29
Q
A

Invertebrates (13 decks)

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