title for a learn-about section in A SNAIL'S ODYSSEY
  Habitats & ecology

Little research seems to have been done on the physiology of west-coast flatworms and nemerteans. Sections are presented separately for the 2 taxa.

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Physiological & behavioral ecology

  Topics on habitats & ecology of flatworms and nemerteans include physiological & behavioral ecology, considered here, and INTERTIDAL/SEMI-TERRESTRIAL HABITS and NEMERTEAN PARASITES OF CRABS, considered elsewhere.
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Research study 1

Studies on the small, colorful acoel Polychoerus carmelensis at Hopkins Marine Station add much to our knowledge of this little-known group of flatworms.  Polychoerus  inhabits mid-tidal level tidepools on rocky shores.  Theresearch has several parts and summaries for each are presented separately.

Salinity tolerances:  over 2wk exposure to a range of salinities from 25-150% SW, the author determines that 75-125% are tolerable.  All others result in at least some deaths.

Behavioral rhythms: in their tidepools the worms crawl on the upper surfaces of algae or gravel during low tide, and re-burrow into the gravel on return of the tide.  If kept continuously submersed in containers in the laboratory for 2d, the worms appear to be randomly active, and no diurnal or tidal rhythm is apparent.  Further observation of their behaviour in tidepools suggests that they burrow into the substratum when the first waves of the incoming tide begin to agitate the water.

Reaction to light: worms become more slightly active in the laboratory containers as light intensity increases, described as a photokinesis.

photograph of acoel flatworm Polychoerus carmalensis courtesy Gary McDonald, UC Santa CruzFeeding behaviour: live, swimming copepods are readily captured and eaten.  The worm whips its anterior end down over its prey when the latter comes to rest, adopts a cup-like position over its prey, then consumes and digests it. Armitage 1961 Pac Sci 15: 203.Photograph courtesy Gary McDonald, Long Marine Lab, UC Santa Cruz and CALPHOTOS.

NOTE  a kinesis is a change in level of response to a changing intensity of stimulus

Acoel flatworm Polychoerus carmelensis. Anterior end is to the Left.
The light-coloured tissues on either side of the body may be eggs 20X

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Research study 1

histogram showing concentration of heat-shock protein HSP 70 in heat-shocked nemerteans Paranemertes peregrina Intertidal organisms, including nemerteans, may be subject to widely varying temperatures, including daily tidal-related fluctuations and seasonal changes.  High temperatures experienced daily or seasonally may damage protein. Proteins damaged by heat and other agents are “chaparoned” and mended by special heat-shock proteins (HSPs1).  The presence of HSPs in nemerteans has been confirmed for Paranemertes peregrina collected from mudflats at Bodega Bay, California.  After determining that 36oC is lethal to the worms, the authors expose worms to temperatures of 34oC2 for 2h, let them recover in ambient seawater of 15oC for 2h, and monitor their tissues and the tissues of control worms for presence of HSP 703 Although the effect is relatively small, perhaps owing mostly to the presence of a large residual content of HSP 70 in the tissues of control worms, it is statistically significant (see histogram).  The authors suggest that the high HSP levels in the control worms may owe to an especially long tidal-exposure (5-6h) on the day of collection in August, when mud and tidepool temperatures were high.  The authors note that, to the best of their knowledge, this is the first report of HSPs in the phylum Nemertea.  Okasaki et al. 2001 Hydrobiologia 456: 211. Photograph courtesy Rebecca Kordas, Biodiversity Research Centre, University of British Columbia, Vancouver.

NOTE1  HSPs are nearly ubiquitous in intertidal marine invertebrates, and have been identified in many species of cnidarians, molluscs, and crustaceans.  Further information on HSPs in west-coast intertidal invertebrates can be found in the ODYSSEY at:  LEARN ABOUT ABALONES & RELATIVES: HEAT-SHOCK PROTEINS, LEARN ABOUT MUSSELS: LIFE IN THE INTERTIDAL ZONE: HEAT-SHOCK PROTEINS, and LEARN ABOUT LIMPETS: LIFE IN THE INTERTIDAL ZONE: TEMPERATURE STRESS

NOTE2 the authors note that not all worms survive this temperature, and those that do exhibit stress behaviours such as proboscis eversion, mucus secretion, and sluggish movement.  The authors suggest that future experiments on this species and perhaps others should be done at lower stress temperatures and include a longer recovery time

photograph of nemertean worm Paranemertes kordas withdrawing its proboscis after an unsuccessful attack on a nereid worm, courtesy Rebecca Kordas, Biodiversity Research Centre, UBCNOTE3 HSPs are categorised by their molecular mass.  There are many different kinds, with HSP 70 being one of the more common types


Paranemertes peregrina withdrawing
its proboscis following an unsuccessful
attack on a nereid worm 1X

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