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Zoology 375 > Phylum Cnidaria > Flashcards

Phylum Cnidaria Flashcards

1
Q

Cnidarians

A 
11,200 spp in 6 classes
Radially symmetrical
Diploblastic
Polyp and Medusa forms
Gelatinous mesoglea
2-way digestive tract
Apomorphies:
- Cnidae
- Planula larvae
(Have tissues, muscles, NS, DS, morphs)
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2
Q

Cnidae

A

Organelle in a cnidocyte (cnidoblast, hematoblast)
Explosive discharge
30 kinds
Capsule - one open end, usually with lid (operculum)
• coiled thread - inside-out sock
• cluster of cilia at edge of opening
Cnidocil - trigger

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3
Q

Osmotic hypothesis

A

Water rushes into the organelle

Pressure increases and capsule opens

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4
Q

Tension hypothesis

A

Capsule pressure always high

Pressure released when lid is triggered

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5
Q

Contractile hypothesis

A

Contractile units squeeze capsule

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6
Q

Types of cnidae

A

Sticky
Wrap
Penetrate
Toxic

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7
Q

Functions of cnidae

A

Food collection (paralyze/hold prey)
Defense
Locomotory? Attachment?

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8
Q

Location of cnidae

A

Feeding tentacles
Epidermis
Gastrodermis (not in Hydra)

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9
Q

Problems with a 2-way digestive tract

A

Can’t ingest when egesting
GVC distorts with movement
Gametes and gonads take up space (in some)

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10
Q

Nervous system

A

Diffuse nerve net (no brain, spinal cord, longitudinal major nerve)

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11
Q

Slow nerve network

A

Multiple synapses; multiple direction for transmission

Nerve signal spreads from site of stimulation

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12
Q

Fast nerve network

A 
Fewer branches in neurons
Less “net-like”
Transmission more directional 
Larger cell process diameter
Just under epithelium
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13
Q

Food processing

A
  • cnidae on tentacles
  • “mouth” to gastrovascular cavity
  • digestive enzymes in gastrovascular cavity
  • food into cells of gastrodermis
  • waste out through mouth
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14
Q

Muscles

A 
Not mesodermally derived (no mesoderm)
Epitheliomuscular (from ectoderm)
Nutritive muscular (from endoderm)
Layers:
longitudinal - shortening
circular - squeezing for extension (with hydrostatic skeleton)
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15
Q

Gas exchange

A

Lack gills or other specialized gas exchange structures

Gases diffuse across exposed epidermal and gastrodermal surfaces

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16
Q

Sexual Reproduction

A

Medusae usually gonochoristic (separate sexes)

  • reproduce sexually (external and internal fertilization)
  • planktonic, ciliated planula larva produced
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17
Q

Asexual reproduction

A

produce genetically identical medusae and polyps

18
Q

Class Anthozoa

A

(anemones, corals, sea whips, sea pens, sea fans, and sea pansies)
• ~ 6,000 species, ~ 70 % of Cnidaria
• polyp only, no medusa stage
• absence (not loss!) of operculum on cnidae
• ciliated grooves (siphonoglyphs) in pharyngeal wall leading from mouth
• mitochondrial DNA is circular (as most eukaryotes)
not linear like other cnidarians

19
Q

Siphonoglyph

A

A ciliated groove at one or both ends of the mouth of sea anemones and some corals. The siphonoglyph extends into a pharynx and is used to create currents of water into the pharynx. These water currents are important for respiration and maintenance of internal pressure.

20
Q

Mesentries

A

Infoldings (septa) of gastroderm and mesoglea which greatly increase the SA available for secreting digestive enzymes and absorbing nutrients

21
Q

Acontia

A

Thin filaments loaded with nematocysts and secretory cells
Used offensively and defensively and may function in digestion
Extended outside body wall (openings)

22
Q

Cnidarian Evolution

A

Most of the recent evidence appears to reject Hydrozoa as basal lineage
• Supports Anthozoa as basal lineage
– suggests medusa was not present in common
ancestor of Cnidaria
– Also a good lesson that basal (primitive) does not mean “simple, less complex”

23
Q

Corals

A

Some reef-building
• skeleton external to animal - sits on top
• can retract within
• polyps connected by thin layer of tissue
• zooxanthellae (symbiotic dinoflagellates) provide energy via photosynthesis

24
Q

Infoldings (septa) of gastroderm and mesoglea which greatly increase the SA available for secreting digestive enzymes and absorbing nutrients

A

Mesenteries

25
Q

A ciliated groove at one or both ends of the mouth of sea anemones and some corals. The siphonoglyph extends into a pharynx and is used to create currents of water into the pharynx. These water currents are important for respiration and maintenance of internal pressure.

A

Siphonoglyph

26
Q

Thin filaments loaded with nematocysts and secretory cells
Used offensively and defensively and may function in digestion
Extended outside body wall (openings)

A

Acontia

27
Q

Pharynx

A

Tubular

Leads to GVC

28
Q

Class Scyphozoa

A

• ~ 200 species (~ 2.3 % of Cnidaria)
• medusoid stage dominates, often large (polyps small or absent)
• asexual replication by strobilation - apomorphy
• 100% marine
Gut of medusa 4 -chambered
• Mesoglea acts as skeleton, stretching muscles • When muscles relax, bell “pops” back into shape

29
Q

Scyphozoa Sensory Organs

A

• balance organs: statocysts
– Hold weighted statoliths (see fig. 6.8b)
• light receptors: ocelli (not image forming)
• touch receptors (some spp): sensory lappets • held in rhopalia (singular = rhopalium)

30
Q

Scyphozoan reproduction

A

Planula larva becomes a scyphistoma
This grows & buds off new scyphistomae & strobilates, producing genetically identical ephyras, which are juvenile medusae

31
Q

Class Cubozoa

A 
(Box Jellyfish, Cubomedusae, Sea Wasps)
20 species
• medusa box-like, 4 corners each with tentacles 
• complex, lensed eyes (but no brain!?)
• medusae small, usually only a few cm
• highly virulent cnidal toxin
• each polyp => 1 medusa
• rhopalia hold statocysts & ocelli
• rhopalia in Scyphozoa & Cubozoa
• Cubozoa lensed eyes are among the most complex in the invertebrates
32
Q

Class Hydrozoa

A

(Hydras, men-o’-war, hydrocorals)
~ 2,700 species
• gastrodermal tissue without cnidae, epidermis only
• mesoglea without cells
• freshwater but mostly marine
• hydrocorals - convergent
• velum - shelf of tissue around inner edge of bell of the medusa
Velum - shelf of tissue around inner edge of bell of the medusa (increases velocity of ejected water)
• polyp predominates
• hydromedusae smaller than scyphomedusae
• most colonial (e.g. Obelia)
• - each polyp a zooid
• connected - share gastrovascular cavity
• often with protective perisarc -

33
Q

Colonial polymorphism

A
  • gastrozooids (hydranths): feeding
  • gonozooids: reproduction
  • dactylozooid - with cnidae for prey capture & defense
34
Q

Genus Hydra

A

Atypical Hydrozoan

  1. Not colonial
  2. Not marine
  3. No medusa
35
Q

Siphonophores

A

Genus Physalia
Genus Praya
- colony of both polyp-zooids & medusa-zooids
- all from 1 planula

36
Q

Myxozoa

A 
Spore-forming protozoa
• parasitize fish and aquatic annelids 
• degenerate multicellular animals
• molecular data - Cnidaria
• strange polar capsules
37
Q

Coral reefs

A
  • reef-building corals (hermatypic) restricted to clear, warm waters
  • usually shallow tropical - <90 m - need sunlight
  • diverse ecosystem:
  • algae, protozoans (foraminifera), shelled molluscs, tube-dwelling polychaete annelids, bryozoans give structure
  • most from corals
  • calcification - additional 10 kg calcium carbonate per m2 annually
  • carnivorous
  • live in areas with low productivity of plankton
38
Q

Zooxanthellae

A

• endosymbiotic dinoflagellates
• photosynthesize - provide corals with energy-
rich organic compounds
• 20-95% of products of photosynthesis released to host
• zooxanthellae use metabolic wastes of coral - carbon dioxide and nitrogenous wastes
• protected from predators
NEGATIVES
• toxic forms of oxygen build up (hydrogen peroxide, oxyradicals)
• coral tissue counteract with high levels of enzymes to detoxify oxygen toxins

39
Q

Coral bleaching

A
  • Loss of zooxanthellae
  • high water temperatures
  • adaptation to allow colonization by more appropriate zooxanthellae?
40
Q

Genus Chironex

A

Cubozoa
• 3 - 60 m long tentacles
• ~ 1 human death per year in N. Australia
• death in 3 minutes

Zoology 375 (7 decks)

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