title for a learn-about section in A SNAIL'S ODYSSEY
  Habitats & ecology
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Intertidal/semi-terrestrial habits

  Studies on habitats & ecology of flatworms & nemerteans focus entirely on the latter group, as no comparable work seems to have been done on flatworms. Studies on intertidal/semi-terrestrial habits are considered here, while those on NEMERTEAN PARASITES OF CRABS and PHYSIOLOGICAL ECOLOGY are considered elsewhere.
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Research study 1

A comparison of aspects of the biology of the intertidal nemertean Paranemertes peregrina from Bodega Harbor, California and 3 sites in Puget Sound, Washington reveals several differences in feeding and reproduction.  For example, P. peregrina in California eat a greater variety of polychaetes than ones in Washington.  In California, spionids are the main prey in spring/summer and nereids in autumn/winter, while in Washington spionids are the main prey in autumn/winter.  In California, spawning is in June/July and the worms tend to be nocturnal, while in Washington spawning is in March/June and the worms are less nocturnal.  Notwithstanding these differences, the author notes that these 2 populations separated by 1600km are actually more similar than ones in Washington separated by 100km, especially with respect to diets.  Roe 1979 Pac Sci 33: 281.

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Research study 2

drawing of anterior end of nemertean Paranemertes to show locations of cephalic glands courtesy Stricker et al 1982 Zoologica Scripta 11: 107The high intertidal-inhabiting Pantinonemertes californiensis is distributed from southern California to northern Washington.  Although thought of by some authors as a semiterrestrial species, its distribution in the Tomales Bay and Elkhorn Slough areas of California, at least, is limited to the intertidal zone at 1.3-1.7m, in an area where maximum high tides are around 2.0m. Its principal prey appears to be the semi-terrestrial amphipod Traskorchestia traskiana, and the intertidal distribution of Pantinonemertes tends to follow that of its prey.

Pantinonemertes appears to have no specific adaptations to terrestrial life with respect to life cycle or reproduction.  For example, it sheds its eggs into the sea and produces a typical planktotrophic pilidium larva. It does, however, have some features associated with terrestriality, including relatively large size, cephalic glands strongly developed for secretion of copious amounts of mucus (see accompanying drawing), and a well-developed excretory system, usually associated with an ability to cope with freshwater. However, experiments by the author show that the species is intolerant of freshwater immersion; conversely, it is intolerant of even moderate degrees of drying.  Although adults do not survive for more than a day or two in seawater, juveniles can do so for up to a week. 
Roe 1993 Hydrobiologia 266: 29; see Gibson et al. 1982 J Zool, Lond 196: 463 for the original description of its “semiterrestrial” habit. Drawing courtesy Stricker et al. 1982 Zoologica Scripta 11: 107.

NOTE  1.4m represents the median range of distribution of Pantinonemertes at Tomales Bay, California. The author calculates that at this height the worms would be covered by the tide at least some time during the day during 84% of the days of a year

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Research study 3

drawing of ocelli (eyespots) in intertidal nemertean Paranemertes sanjuanensisThe nemerteans Paranemertes peregrina and P. sanjuanensis live sympatrically in areas of San Juan Island, Washington.  If you need to tell them apart, the following may help.  Externally, the 2 species are distinguished by number and position of ocelli (see accompanying drawing for P. sanjuanensis), and by their differing body coloration:  P. sanjuanensis has a uniform orange-tan colour; P. peregrina hasa light-brown to puple-black dorsal surface and a yellow or tan ventral surface. Stricker et al. 1982 Zoologica Scripta 11: 107.

NOTE the authors do not provide a similar view of P. peregrina for comparison

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