title for a learn-about section in A SNAIL'S ODYSSEY
  Locomotion
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  Flatworm
  Studies on locomotion of flatworms are presented here. No research appears to have been done specifically on locomotion in west-coast nemerteans.
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Research study 0
 

photograph of acoel flatworm Polychoerus carmelensis courtesy Gary McDonald, Long Marine Lab, CaliforniaInvestigations at the University of California Davis on locomotory responses of acoel flatworms Polychoerus carmelensis to different temperatures reveal the following.  Of a range of treatment temperatures from 3-38oC, locomotion is fastest at 17oC (mean rate: 9cm . min-1).   The worm’s locomotory posture changes with temperature, from a U-shaped one at 5oC with propulsion largely effected by cilia on the dorsal surface (about 2cm . min-1) to a more “usual…position” at a temperature of 29oC where the “posterior portion of the body is drawn up under the more anterior portion” and with propulsion being effected by action of cilia on the anterior/ventral surface yielding a locomotory rate of about 5cm . min-1.  The author does not describe locomotory posture at all intermediate temperatures, but does note that at 8oC they begin to move in the U-shaped posture just described, but soon re-orient to “typical flatworm posture).  The author postulates that a curled position during temperature stress, especially at higher levels, may enhance oxygen uptake owing to greater surface area being exposed to gas diffusion.  Were a worm to adopt a normal crawling position, the epidermal tissues for diffusion would be effectively halved.  Schwab 1967 Pac Sci 21: 85. Photograph courtesy Gary McDonald, Long Marine Lab, UC Santa Cruz and CALPHOTOS.

NOTE  test temperatures are separated by 3-4oC

NOTE  locomotion does not last long at this temperature as tissue disintegration quickly ensues and the worms die.  At temperatures above 29oC the worms likewise disintegrate

 

Acoel flatworm Polychoerus carmelensis. The anterior end is
pointing downwards. The small "tails" within the posterior
lappets have no known function but are likely to be sensory 30X

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Research study 1
 

photograph of flatworm Notocomplana acticola courtesay Kevin Lee Fullerton CaliforniaLocomotion of the marine flatworm Notocomplana acticola consists of waves of extension and contraction on either side of the body, a pattern known as ditaxic locomotion.  The waves begin at the anterior end and pass posteriorly along the length of the body, with left and right sides being out of phase with one another.  Maintenance of this ditaxic pattern even after a series of cuts have been made, suggests a net-like type of nervous-system construction. Koopowitz 1973 Biol Bull 145: 352. Photograph courtesy Kevin Lee, Fullerton, California www.diverkevin.

NOTE  the author uses worms collected at Corona del Mar, California

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photograph of flatworms Notocomplana freemania crawling on a piece of kelp taken from a video

CLICK HERE to see a video of two flatworms Notoocomplana freemania crawling on a piece of kelp. Note the branched structure of the gut (polycladid) when the darker-coloured individual crawls upside-down on the kelp frond.

NOTE video replays automatically

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Research study 2
 

electro micrograph of rhabdite packets in the acoel flatworm Polychoerus carmelensisAcoel flatworms commonly locomote by ciliary gliding.   A researcher at the University of California, Berkeley describes the role of rhabdites in locomotion of the small acoel flatworm Polychoerus carmelensis.  The rhabdites in Polychoerus are rod-shaped, pointy-ended granules, 2-3µm in length, that are gathered into packets of about 125 rhabdites and secreted from cells scattered over the ventral, crawling surface of the worm.  On contact with seawater, the rhabdites swell and form a sticky mucous sheet that instantly attaches to the substratum. The worm is actually adhered to some extent to the substratum by its mucus, but it is the viscosity of the mucus that enables locomotion by offering resistance to the effective or power stroke of each beating cilum.  The force generated by the cilia propels the worm forwards.  At the beginning of the recovery stroke, the tip of each cilum pulls away from the mucous layer and returns to the starting position for the next power stroke.  A 4mm worm can locomote at about one-half a body length per second.  The mucus remains attached to the substratum and is left behind the moving worm as a slime trail.  Martin 1978 Zoomorphology 91 (3): 249; Martin 1978 Zoomorphology 91 (3): 235.

NOTE  other functions described for rhabdites in turbellarian flatworms include repelling predators and territorial markers

 

Two rhabdite packets in the acoel Polychoerus carmelensis opening
onto the epidermis of the ventral crawling surface. Note the
proximity of the rhabdites to the ventral ciliary layer 5000X

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