Lecture 6

Question 1

Neurosecretory cells

Answer 1

Specialized neurons that produce chemical messengers that are released into the bloodstream and affect distant target tissue

Question 2

Myoepithelial cells

Answer 2

Cells usually found in glandular epithelium as a thin layer above the basement membrane but generally beneath the luminal cells

Question 3

Luminal cells

Answer 3

Line the lumen and produce secretory proteins such as prostate-specific-antigen (PSA)

Question 4

Velum (muscular ring)

Answer 4

• Constricts, forcing greater amounts fo water to propel animal at higher speeds
• Only in cubozoan and some hydrozoan medusae

Question 5

Usually two distinct nets

Answer 5

1.) Ectoderm; mesenchyme
2.) Gastroderm; mesenchyme

Question 6

Mechanoreceptors

Answer 6

Type of somatosensory receptors which relay extracellular stimulus to intracellular signal transduction through mechanically gated ion channels

Question 7

Chemoreceptors

Answer 7

Special nerve cells that detect changes in the chemical composition of the blood and send information to the brain to regulate cardiovascular and respiratory functions

Question 8

Polyps (sensory features)

Answer 8

• Few sensory features
• Most nerve nets concentrated at pharynx, oral cavity, mesenteries abd tentacle tips
  
  • Somewhat oral-aboral centralised
• Mechanoreceptors and some chemoreceptors on tentacles

Question 9

Medusae (sensory features)

Answer 9

• Many sensor features
• Epidermal: mesenchymal nerve net condenses into inner/outer nerve rings
  
  • Innervations connect these rings to the tentacles, muscles and sense organs
• Inner ring: swimming pacemaker
• Statocysts trigger to inhibit adjacent muscles and activate opposing muscle contractions
  
  • Maintain swimming orientation

Question 10

Medusae outer rings (rhopalia and vision)

Answer 10

• Outer nerve rings involves photo-sensation
  
  • Photosensor axons form ‘optic nerves’
  • Photosensor systems highly variable, exceptionally sensitive in cunozoans

Question 11

Cnidarian weapons (Cnidae)
Three major types

Answer 11

• Concentrated on oral arms, tentacles and mouth
• Anthozoan and cubozoans also have internal gastrodermal cnidae

1.) Nematocystes - spines, venom
2.) Sporocytes - adhesive, hexacorallia
3.) Ptychocyst - adhesive, ceriantharians

Question 12

Polar capsules

Answer 12

Structures found in the valves of myxosporean parasites which contain the polar filament

Question 13

Complex intracellular reorganisation

Answer 13

• Large vacuole forms
• Golgi secretes proteins, vacuole grows
• Collagen matrices from capsule
• Hollow tubule forms at apical edge of capsule
• Tubule invaginate and coils, capsule hardens
• ‘Lid’ covered by operculum, capsule pressurises
• Spines added after coiling
• Maturę cnidocyte separate from syncytium

Question 14

Operculum

Answer 14

A comeous or calcareous anatomical structure like a trapdoor that exists in many groups of snails

Question 15

Nematocyst batteries

Answer 15

Maturę cnidocytes migrate after separating forming cnidae clusters called nematocyst batteries
- Wart-like structures

Question 16

The osmotic hypothesis

Answer 16

• Hypothesised pressurised firing mechanism
• Highly supported
• Poly-y-glutamate synthesised and collected within capsule
  
  • Negatively charged amino-acid side-chain attracts cation
  • Water diffusively follows ion movement
  • Osmotic pressures reach about 150 bars
• Operculum opens upon stimulus, unleashing osmotic pressure trapped within capsule, ejecting the tubule; single-firing per cnidocyte

Question 17

The tension hypothesis

Answer 17

• Hypothesised pressurised firing mechanism
• Stimulus releases intrinsic tension from cnidogenesis ejecting the tubule

Question 18

The contractile hypothesis

Answer 18

• Hypothesised pressurised firing mechanism
• Nearby supporting cells squeeze and pop the capsule, ejecting the tubule

Question 19

Musculature feeding (medusozoans)

Answer 19

• Oral tentacles rely on my-epithelial cells and a nerve net to reach mouth
• Myonemes form longitudinal and circular synapses
• Nerve net communicates to my-epithelial cells via chemical synapses
• Longitudinal muscle contractions apply pressure to hydrostatic skeleton go arms
• Some scyphozoans contact food directly on their ciliated bells instead

Question 20

Gastrovascular cavity (GVC)

Answer 20

• Prey swallowed whole by mouth
• Gland cells within gastroderm secrete enzymes into GVC
  
  • Extracellular digestion occurs first
  • Cells then absorb partially digested prey via phagocytosis for intracellular digestion
• Ciliated cells mix GVC contents
  
  • Gastric filaments in cubozoa and Scyphozoa mix and secrete enzymes
• Undigested material exits mouth (incomplete gut)

Question 21

Oral disc

Answer 21

Has a central mouth, usually slit-shaped , surrounded by one or more whorls of tentacles

Question 22

Mucous net suspension feeding

Answer 22

• Mostly observed in stony corals
• Excess mucous feed fish

Question 23

Polyp GVC (digestion and distribution)

Answer 23

• Food is passed through the pharynx
  
  • Muscular with ciliated grooves called siphonoglyphs that draw in water
  • Water influx maintains hydrostatic skeleton while body contractions help move food via peristalsis
  • Waste diffuses into water

Question 24

Peristalsis

Answer 24

The involuntary contraction and relaxation of longitudinal and circular muscles throughout the digestive tract

Question 25

Mesenteries subdivide GVC

Answer 25

• Increased surface area
• Increased structural support
• Absent in Hydrozoan polyps