title for sandworms & relatives section of A SNAIL'S ODYSSEY
  Physiological ecology
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Research study 1
 

graph comparing salt loss in 3 species of nereid polychaetesA researcher at the University of California, Berkeley compares rates of salt loss in 3 species of commonly occurring nereid polychaetes Neanthes diversicolor, N. limnicola, and N. succinea.  The author approaches the study from a standpoint of strict comparative physiology, and there is little to interest students of ecology.  All 3 species inhabit brackish and estuarine waters and are adapted to, or tolerant of,  exposure to dilute salinities.  The main experiment involves immersing the worms for 1h in a measured quantity of distilled water and measuring the salt content of the bathing water afterwards.  Results show that salt loss is greatest in N. succinea and least in N. limnicola, and that loss scales with body mass (M) to a logarithmic exponent of 0.68-0.89, as would be expected from the three-quarters “surface rule”.   Other data not shown here includes loss rates in media such as sugar and urea solutions.  Smith 1963 Biol Bull 125 (2): 332.

NOTE  at the time of the study all 3 species were nominally classified in the genus Nereis, but have since been moved to Neanthes 

NOTE  the study is a preliminary one and, in the words of the author, is aimed at “evaluating the separate roles of body wall, nephridia, and gut” in the process of salt loss

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Research study 2
  photograph of scaleworm Halosydna brevisetosa courtesy Lovell & Libbie Langstroth, Californiadrawing of water flow in a scalewormPolynoid polychaetes or scaleworms bear a double row of overlapping scales or elytra on their dorsal surfaces.  The elytra are held in erect position to create a continuous roof along each side of the body.  Theories as to their function include sensory, protection, gas-exchange, luminescence, and egg-protection, depending upon the species in question.  For Halosydna brevisetosa, research at the Hopkins Marine Station, Pacific Grove, California confirms that the elytra are positioned to contain and direct water flow posteriorly, presumably for gas exchange.  The elytra themselves are not ciliated nor do they exhibit any fanning or pumping motions; rather, it is cilia on the dorsal epithelium and parapodial lobes that generate the water flow.  Water enters the sub-elytral area at the front and along the sides of the animal (see drawing).  If selected elytra are removed, the otherwise continuous anterior-posterior current is disrupted, and water escapes at the break.  Coelomic fluid just beneath the skin apparently moves counter-current with the ciliary-generated flow above.  Although not measured directly by the author, this counter-current arrangement would maximise gas exchange between the 2 fluids.  The author opines that the elytra would permit the currents to operate effectively even when the worms are wedged into crevices and other hideaways during daylight hours.  Lwebuga-Mukasa 1970 Bull So Calif Acad Sci 69: 154. Photograph courtesy Lovell & Libbie Langstroth, California.
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Research study 3
 

Pileworms Neanthes succinea in the Salton Sea, California are accustomed to living in salinities ranging from 36-40‰, but localised or seasonal conditions may lead to even higher salinities than this.  To assess effects of high salinities on survival and reproduction, researchers at Pomona graph showing survival of pileworms Neanthes succinea in different salinitiesCollege, Claremont, California expose worms to salinities up to 90‰ at a normal Sea temperatures of 22oC, but in some cases as high as summer temperatures of 34oC.  Results show that 50% survival is possible in salinities of about 60-65‰, but only for about 6d (see graph).  Survival in salinities above 70‰ is only  a day or less.  Reproduction occurs year-round, but is less in summer perhaps owing to higher water temperatures.  The authors present information on heteronereid development, and spawning and development in relation to salinity in laboratory experiments, but in view of the uncertain hygeine in culture, these results are not presented here.  Kuhl & Oglesby 1979 Biol Bull 157: 153.

NOTE  high salinities are made by evaporating Salton Sea water to 90‰, then diluting with Salton Sea water of 36‰ to obtain the desired treatment salinities

NOTE  this median survival time of 6d relates to survival in “normal” 36‰ Salton Sea water.  However, since this salinity is about average for the Sea, one wonders why survival in it shouldn’t be 100% (see on the graph that survival time in 36‰ is only about 12d).  Conditions in this “control” treatment are obviously sub-optimal, and it turns out that several worms are being tested simultaneously in single small containers. The authors note that death of one worm in these multi-worm experiments was often followed by death of all, “presumably because of the accumulation of toxic materials before the medium was changed”.  Thus, more than one stressful factor is being tested: salinity and death/degradation substances

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