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Biol321 > Molluscs > Flashcards

Molluscs Flashcards

1
Q

What is the first offshoot of conchifera?

A

Monoplacophora

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2
Q

Describe the class monoplacophora

A
  • single shell valve
  • multiple pairs of ctenidia
  • multiple pairs of dorsal attached ventral muscle
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3
Q

How did the shell evolve as a protective retreat from a
monoplacophoran-like ancestor?

A
  1. Gradual dorsal-ventral visceropallial elongation
  2. Visceropallial coiling

*no modern gastropods have a symmetrical shell

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4
Q

How does assymmetrical coiling work? How has this impacted the shell?

A
  • migrates down the central coiling axis (the column of CaCO3)
  • has transformed shell from dorsal shield to protective retreat
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5
Q

What is the central coiling axis called?

A

The collumella

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6
Q

How do they close the shell opening? What does this do?

A

With an operculum
-provides protections, prevents desiccation

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7
Q

What is the operculum made of?

A

Hard, proteinaceous material, sometimes with CaCO3 salts

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8
Q

How do you get from monoplacophoran to hypothetical intermediate?

A
  1. Reduction of:
    - shell aperture, # shell muscles, # ctenidia
  2. Elongation of shell
  3. Lateral mantle cavities became single one confined to posterior end
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9
Q

How do you get from hypothetical intermediate to gastropod?

A

180 degree rotation of entire visceroapallium relative to cephalopodium

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10
Q

What are two characteristics that support the rotation hypothesis?

A

Cross-over of visceropallial nerve chords (in adults)
Ontogenetic torsion in basal gastropods (larvae themselves exhibit torsion during development, in span of 12-15hrs)

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11
Q

What is the typical larvae of gastropods? What are the two types?

A

veliger
feeding/non-feeding

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12
Q

How do the larvae of gastropods swim?

A

By beating their ciliated velar lobes

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13
Q

What are 3 main body parts of a veliger?

A
  1. Velar lobes
  2. Foot
  3. Shell
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14
Q

Difference of operculum being pulled in before and after torsion

A

Before: foot pulled in first, velum last, no way for operculum to seal aperture
After: velum pulled in first, foot pulled in last, operculum can seal opening

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15
Q

Solutions to fouling in keyhole limpets

A

Water flow in mantle cavity, passes over ctenidia, then over anus and out perforation

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16
Q

Solutions to prevent fouling in coiled gastropods

A
  1. Loss of right ctenidium
  2. Anus moved to right side
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17
Q

Water flow in coiled gastropods

A

Oblique flow pattern

  1. In mantle cavity
  2. Passes over osphradia
  3. Over single monopectinate ctenidia
  4. Out over anus on right side
18
Q

What do some gastropods use to search for prey?

A
  • Their siphon (an outgrowth of mantle epithelium)
  • looks for chemical effluent of prey item
19
Q

What is the alternative hypothesis for a gastropod body plan?

A

Bilateral mantle cavity-> unilateral loss

20
Q

Problems with cross-over of visceropallial nerve connective

A

If torsion evolved as 180 deg rotation, must have occurred rapidly->no functional intermediates

21
Q

Evidence of cephalization in gastropods (general)

A
  1. Labial tentacles
  2. Eyespot
  3. Mouth
22
Q

How do vetigastropoda feed?

A

-herbivorous grazing

23
Q

How do caenogastropoda feed?

A
  • herbivorous grazing
  • some have proboscis and are predatory
24
Q

Where is the proboscis stored when not in use?

A

In the proboscis sac at the anterior end.

25
Q

What does the siphon do?

A

Takes in water, water flows in over osphradia to located prey.

26
Q

Difference between the foregut of caenogastropods with/without a proboscis

A

With proboscis:

  1. head epidermis expanded, formed deep in-pocketing called radular sac where proboscis stored
  2. Anterior esophagus that has elongated to extend down length of proboscis when feeding
27
Q

What pushes the proboscis out?

A
  • Hydrostatic pressure and fluid in the hemocoel
  • circular muscles contract to extend
28
Q

What are shell drills made by? What does this thing look like? How are they made?

A
  • Caenogastropods with a BORING ORGAN at the end of their proboscis
  • Looks like a little mushroom on the ventral side of the proboscis
  • Created by back and forth between radular rasping and chemical dissolution by a calcium chelator
29
Q

How is the foregut of venomous caenogastropods modified?

A
  1. Buccal tube has elongated down length of proboscis
  2. Mid-esophageal gland has become long, convoluted tube. Walls of this gland secrete these toxins
30
Q

What are cone snail toxins called? What are they? What do they target?

A

Conotoxins

  • are small peptides
  • target neural antigens (bind to ion channels and prevent propagation of action potential)
31
Q

Describe the discharge mechanism of the proboscis of a cone snail.

A
  1. Individual harpoon moves to end of proboscis
  2. Becomes charged with neurotoxins
  3. Proboscis elongated
  4. Harpoon exposed and ballistic mechanisms fires it to inject neurotoxin into prey
32
Q

What houses the venomous teeth of a cone snail?

A

The radular sac houses hollow teeth

33
Q

What is a derived feature of marine heterobranchs?

A

-reduction in size or loss of shell in post-metamorphic stage

34
Q

How do heterobranchs defend themselves?

A
  1. Chemical defenses (toxic or unpalatable)
  2. Escape behavior (muscular contractions of ventral and dorsal side gets sea slug up into water currents to be wafted away by current)
  3. Sequester cnidocytes from cnidarian prey
  4. Autotomy (if cerrus (plural: cerrata) grabbed by grab, slug can drop it off and escape)
35
Q

How do heterobranchs sequester cnidocytes?

A
  • immature cnidocytes are carried up digestive gland and individual cnidocytes are phagocytized by cells of digestive tract and mature there.
  • When threatened, these cnidocytes are released from cnidopore
36
Q

How do heterobranchs do gas exchange? What do these structures

A
  • thin walled epithelium called cerrata
  • cerrata contain cells and extensions of digestive gland for gas exchange to occur directly
37
Q

What are the biggest challenges for terrestrial heterobranchs?

A
  1. resisting desiccation
  2. Gas exchange (many marine sp have gill extensions that wouldn’t work in air)
38
Q

How have heterobranchs adapted to life on land?

A
  1. Mantle cavity forms internalized lung with pneumostome to interior
  2. Conversion of ammonia to uric acid (less toxic)
  3. Aestivation when habitat dry
39
Q

What is the penumostome?

A

Opening to heterobranch lung. Only open when breathing to prevent desiccation.

40
Q

What is aestivation?

A
  • Metabolic slow-down
  • tolerance of desiccation
  • ability to rapidly rehydrate

Biol321 (8 decks)

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