Water flow for gas exchange
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Research study 1
 
diagram of water flow through the mantle cavity of an abalone

Water flow in abalones is driven primarily by ciliary beating.  Clean water enters via the front-most pair of holes and also under the left edge of drawing of water flow through the shell of an abalonethe shell, and circulates through the mantle cavity where it irrigates the ctenidia (gills).  The flow then picks up urinary discharge from the kidneys and feces from the anus.  The now contaminated water exits from the posterior three holes.  In reproductive season the exhalent water flow also serves to transport gametes to the outside. The 2 flows remain separated in their transit of the mantle cavity: clean inhalent water flows overtop of the head and along the ctenidia to the back of the mantle cavity, then swings up past the anus and paired kidney openings, and out. Drawing on Left modified from Crofts 1929 HALIOTIS  Publ XXIX Liverpool Mar Biol Comm Memoirs, Univ Press Liverpool, 174 pp.

 

 

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Research study 2

  Observations on Haliotis kamtschatkana at Friday Harbor Laboratories, Washington confirm this basic water-flow pattern of water entering the mantle cavity through holes 1 and 2, and exiting through holes 3, 4, and 5.  Interestingly, however, a similar pattern is evident in empty shells diagram showing how Bernoulli effects create passive inflow and outflow via the openings in a shell of an abaloneand in shells of dead but intact animals when placed in a current flow, and occurs regardless of whether the animals are facing upstream or downstream.  This is caused as currents flow past the posterior holes creating a Bernoulli effect, and thus reducing the pressure above the holes and causing water to flow out of them.  As water is sucked out of the posterior holes it flows into the anterior ones. Note that the posterior-most holes are sited towards the side of the shell where the outside water stream around the shell is maximally compressed.  Pressure reduction in these holes relative to the anterior ones creates a passive outflow regardless of current direction.  The shell design thus allows Haliotis to take advantage of induced flow to move water more effectively through the mantle cavity.  Although abalones, like all snails, regularly face into water currents in search of food and mates, and to avoid predators, the 2-way passive-induction capability may be useful in conditions of surge.  In this regard, the author wonders whether abalones position themselves strategically to benefit from these passive water flows.  Voltzow 1982 Am Zool 22: 965; Voltzow 1983 Veliger 26: 18.
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Research study 3
 

photograph of anterior end of black abalone Haliotis cracherodiiA study on shore-level morphological gradients in black abalone Haliotis cracherodii at Laguna Beach, California shows that both size and number of holes in the shell vary with position on the shore.  Thus, in summer and autumn, individuals with relatively fewer smaller holes in their shells are located significantly higher on the shore than ones with relatively more larger holes.  The author credits this with desiccation avoidance. Tissot 1988 J Exp Mar Biol Ecol 117: 71.

NOTE  called tremata (“hole” G.) by the author, a term that seems not to have caught on in the abalone literature

 

 

Black abalone Haliotis cracherodii, showing
portion of foot and mantle edge 2X

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Research study 4
 
drawing showing water flow through the mantle cavity of a black turban snail Chlorostoma funebralis from the left side In related black turban shells Chlorostoma funebralis clean water for gas exchange enters the mantle cavity from the left side and exits from the right side over the head.  On its way, the water initially passes by a chemosensory organ, the osphradium, thought to function in water-quality assessment. The flow then goes past the ctenidium where gas exhange occurs, past the kidney opening and anus, and finally exits the body carrying off the waste products.  Drawings modified from MacDonald & Maine 1964 Veliger 6(Suppl.): 50. drawing showing water flow through the mantle cavity of a black turban snail Chlorostoma funebralis from the right side
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