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ZOOLOGY 300 > Week 5 > Flashcards

Week 5 Flashcards

1
Q

Eight Molluscan classes

A
  • Gastropoda
  • Bivalvia
  • Cephalopoda
  • Scaphopoda
  • Solenogastres
  • Polyplacophora
  • Caudofoveate
    -Monoplacophora
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2
Q

How many mollusk classes have shells

A

6

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3
Q

What differs between the shells of the molluscan classes

A

Number and arrangement of shells

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4
Q

Radulla

A

A feeding structure unique to mollusks

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5
Q

Innovations of radula

A
  • Magnetite in the radula of some chitons (makes them strong)
  • Radula of squids (Tongue that can scrape flesh inside of beak structure)
  • Radula of Conus snails (Radula modified as harpoon, tipped with venom)
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6
Q

Aplacophoran mollusks

A
  • Mollusks that lack shells
  • Caduofoveata and Solenogastres
  • Calcareous spicules cover the skin of both groups
  • Caudofoveata lacks muscular foot
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7
Q

Monoplacophora

A
  • Single, cap-like shell
  • Few species, mostly restricted to deep waters
  • First appear in fossil record in early Cambrian
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8
Q

Polyplacophora (“chitons”)

A
  • Eight shell plates (“valves”)
  • Ventral foot
  • Some chitons have hundreds of eyes in the valves
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9
Q

Cephalopoda

A
  • Mantle edge is clamped around the head to form a funnel or siphon
  • The foot is modified into tentacles, sometimes with suckers
  • Internal shell (except in Nautilida)
    -Direct development (no trochophore/veliger larval stage)
  • Foot is anterior
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10
Q

Nautiloida

A

Sister group of the remaining Cephalopoda

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11
Q

Squids

A

-Not monophyletic
- Octopus and cuttlefish are derived squid

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12
Q

Scaphopoda (“tusk shells”)

A
  • Shell open at both ends
  • Lacking gills (ctenidia) and heart
  • Gas exchange occurs directly across mantle cavity
  • Benthic, burrowing
  • SCAPHOPOD FOOT IS VENTRAL
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13
Q

Bivalvia (mussels, clams, scallops)

A

-Infaunal bivalves burrow from the anterior end
- The incurrent and excurrent siphons (sometimes fused) enable filter feeding and gas exchange
- Highly asymmetrical bivalve shells are capable of rapid burrowing
- In some groups, byssal threads secreted by the byssal gland enable adhesion to substrate

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14
Q

Gastropoda (snails, limpets, cowries, slugs, and nudibranchs)

A
  • Asymmetrical mollusks with single, usually spirally coiled shell
  • Shell lost of reduced in many groups
  • During development there is torsion in visceral mass and mantle cavity lies anteriorly or on right side and gut and nervous system are twisted
  • Some taxa have partly or totally reversed rotation (detorsion)
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15
Q

Torsion

A

90-180 degree rotation on foot

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16
Q

Why does mollusk phylogeny remain contentious

A

-Various groupings have been proposed because morphological characters are in conflict

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17
Q

Based on recent reconstructions of Ordovician mollusk fossils, is it thought that the molluscan common ancestor likely had a shell?

A

Yes

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18
Q

Mollusk development

A
  • In three groups, the trochophore larva metamorphoses into the veliger larva
  • Veliger larve unique to mollusca
  • The velum of the veliger is a feeding and swimming organ consisting of two large ciliated lobes
    -Torsion, two steps: contraction of velar foot causing larval shell and viscera to rotate 90 degrees counterclockwise, second 90 degree counterclockwise twist via differential tissue growth (result: viscera are pulled from above toward the left)
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19
Q

In gastropods, what states of torsion can occur

A

dextral and sinistral torsion

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20
Q

Dextral torsion

A

Clockwise

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21
Q

Sinistral torsion

A

Counterclockwise

22
Q

When is the direction of spiraling established in gastropods

A

Early cleavage

23
Q

Nodal signalling controls what in vertebrates

A

Left-right asymmetry

24
Q

L. gigantea

A

Dextral torsion with nodal expression domain on the right side

25
Q

B. glabrata

A

Sinistral torsion with nodal expression domain on the left side

26
Q

Where is Hedgehog expressed

A

Expressed in the ventral midline, helpful for orienting left and right

27
Q

What gene does Nodal activate in vertebrates

A

Pitx. Nodal is upstream of Pitx and activates its expression

28
Q

When is asymmetry established

A

-Nodal is detected in the 32-cell stage
- Pitx is detected in the blastula
- Both are asymmetrically expressed at these points

29
Q

What happens to the shell if Nodal signaling is disrupted

A

Uncoiled shells

30
Q

What happens to Pitx expression when Nodal signaling is disrupted

A

Pitx expression disappears in the shell growth margin

31
Q

What establishes the torsion of the gastropod shell

A

Nodal

32
Q

What establishes the direction of the spiral

A

Early expression of nodal and its downstream target Pitx

33
Q

What establishes the direction of the spiral

A

Early expression of nodal and its downstream target Pitx

34
Q

Knockdown of Nodal signaling causes what

A

Loss of torsion and leads to a symmetrical shell (no asymmetry)

35
Q

Limbs have evolved repeatedly in the bilaterian tree of life

A
  • Vertebrates
  • Arthropods
  • Annelids
  • Cephalopods
36
Q

What is responsible for establishing the axes of the limb

A

Key signaling pathways such as:
-Sp8
-Shh

37
Q

Sp8

A

Gene necessary for limb outgrowth

38
Q

Shh (Sonic hedgehog)

A

Necessary for posterior appendage gate

39
Q

Ectopic expression

A

Expressing a gene where it is not normally expressed

40
Q

Two techniques of ectopic expression

A

Graft and bead implant

41
Q

Sp8/9

A

Necessary for limb outgrowth in arthropods

42
Q

Expression patterns of limb patterning genes are what

A

Highly conserved across vertebrates, arthropods and cephalopods
- Cephalopods use some ancient genes to pattern new structures too

43
Q

Expression boundaries of Exd/Hth correlate with

A

the point where suckers are formed

44
Q

Arms Exd and Hth expression

A

Restricted proximally

45
Q

Tentacle Exd and Hth expression

A

Expressed more distally

46
Q

BMP is required for

A

specification of dorsal appendage fate

47
Q

Noggin

A

Disrupts BMP expression

48
Q

Repression of BMP in tentacle results in

A

Ectopic suckers on the dorsal part of the limb

49
Q

Ectoptic expression of hedgehog (Hh) in the posterior side of the appendage using a graft results in

A

A mirror image duplication (new AP axis)

50
Q

Cyclopamine

A

Disrupts Hh signaling

51
Q

Knockdown of Hh signaling using cyclopamine results in

A

Disruption of ventral fate

ZOOLOGY 300 (5 decks)

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