﻿FRESH-WATER 
  TRICLADS 
  OF 
  ALASKA 
  — 
  KENK 
  173 
  

  

  undoubtedly 
  very 
  closely 
  related; 
  whether 
  some 
  of 
  them 
  are 
  identical 
  

   or 
  are 
  the 
  same 
  as 
  the 
  Alaskan 
  form 
  cannot 
  be 
  established 
  on 
  the 
  basis 
  

   of 
  present 
  knowledge. 
  The 
  Alaskan 
  Poly 
  cells, 
  therefore, 
  is 
  described 
  

   as 
  a 
  new 
  species, 
  

  

  Holotype. 
  — 
  On 
  three 
  slides, 
  USNM 
  22333, 
  clear 
  spring 
  on 
  the 
  road 
  

   from 
  Palmer 
  to 
  Willow, 
  20.1 
  mUes 
  from 
  Palmer, 
  altitude 
  3,800 
  feet, 
  

   Aug. 
  9, 
  1950. 
  

  

  Distribution 
  and 
  ecology. 
  — 
  Polycelis 
  borealis 
  is 
  a 
  very 
  common 
  species 
  

   occurring 
  in 
  mountain 
  streams 
  in 
  the 
  southern 
  part 
  of 
  Alaska 
  (Alaska 
  

   Range, 
  Talkeetna 
  Mountains, 
  Chugach 
  Range). 
  Typically 
  it 
  

   inhabits 
  clear, 
  cold, 
  fast-running 
  waters. 
  It 
  has 
  also 
  been 
  found, 
  

   however, 
  in 
  several 
  small 
  mountain 
  lakes 
  which 
  connect 
  with 
  streams 
  

   in 
  which 
  the 
  species 
  lives. 
  It 
  has 
  not 
  been 
  observed 
  in 
  sUt-bearing 
  

   glacier 
  streams. 
  

  

  The 
  typical 
  temperature 
  range 
  of 
  the 
  habitats 
  was 
  between 
  3.0° 
  

   and 
  about 
  15° 
  C. 
  (August 
  1950). 
  Temperatures 
  above 
  15° 
  C. 
  (up 
  

   to 
  22.4° 
  C.) 
  were 
  encountered 
  only 
  rarely 
  and 
  only 
  in 
  habitats 
  which 
  

   presumably 
  have 
  great 
  diurnal 
  temperature 
  amplitudes 
  (shallow 
  lakes, 
  

   small 
  exposed 
  streams). 
  

  

  The 
  great 
  majority 
  of 
  the 
  specimens 
  collected 
  was 
  asexual. 
  Sexually 
  

   mature 
  animals 
  were 
  seen 
  in 
  only 
  6 
  of 
  the 
  31 
  localities 
  in 
  which 
  the 
  

   species 
  was 
  found. 
  In 
  some 
  localities, 
  a 
  large 
  percentage 
  of 
  the 
  speci- 
  

   mens 
  exhibited 
  freshly 
  regenerated 
  heads 
  or 
  posterior 
  ends, 
  indicating 
  

   that 
  vivid 
  asexual 
  reproduction 
  was 
  taking 
  place. 
  

  

  Clear 
  springs 
  on 
  the 
  road 
  from 
  Palmer 
  to 
  Willow, 
  20.1 
  miles 
  from 
  Palmer, 
  

   altitude 
  3,800 
  feet, 
  Aug. 
  9, 
  1950, 
  water 
  temperature 
  3.0° 
  C, 
  numerous 
  specimens, 
  

   five 
  mature 
  (holotype). 
  

  

  Clear, 
  fast 
  mountain 
  stream 
  crossing 
  Mount 
  McKinley 
  Park 
  road, 
  5.5 
  miles 
  

   from 
  the 
  railroad 
  station; 
  Aug. 
  5, 
  1950. 
  

  

  Streams 
  on 
  road 
  from 
  Palmer 
  to 
  Willow 
  11.9, 
  18.0, 
  19.2, 
  20.2, 
  21.6, 
  22.1, 
  22.8, 
  

   and 
  34.0 
  miles 
  from 
  Palmer, 
  and 
  Ice 
  Lake, 
  20.4 
  miles 
  from 
  Palmer, 
  Aug. 
  9, 
  1950. 
  

  

  Streams 
  on 
  Glenn 
  Highway 
  (Anchorage 
  to 
  junction 
  with 
  Richardson 
  Highway 
  

   near 
  Glenallen) 
  at 
  mileposts 
  33.1, 
  33.9, 
  43.5, 
  64.8, 
  89.4, 
  98.8, 
  and 
  117.1; 
  Aug. 
  11 
  

   and 
  13, 
  1950. 
  

  

  Streams 
  on 
  road 
  from 
  Anchorage 
  to 
  Potter 
  2.9 
  (Campbell 
  Creek), 
  10.3, 
  and 
  10.6 
  

   miles 
  from 
  the 
  city 
  limits 
  of 
  Anchorage, 
  Aug. 
  12, 
  1950. 
  

  

  Streams 
  on 
  Richardson 
  Highway 
  (section 
  between 
  Valdez 
  and 
  Glenallen) 
  at 
  

   mileposts 
  20.5, 
  25.5 
  (22.4° 
  C), 
  26.3 
  (see 
  pi. 
  7), 
  29.0, 
  37.3, 
  54.7, 
  62.6 
  (see 
  pi. 
  7), 
  

   81.0 
  (Squirrel 
  Creek), 
  and 
  87.5 
  (Rock 
  Creek), 
  and 
  lake 
  at 
  milepost 
  27.3 
  (22.1° 
  C), 
  

   Aug. 
  15, 
  1950. 
  

  

  Polycelis 
  borealis 
  was 
  also 
  identified 
  in 
  samples 
  of 
  triclads 
  collected 
  

   by 
  Dr. 
  Reece 
  I. 
  Sailer 
  in 
  July 
  and 
  September 
  1948. 
  The 
  following 
  

   localities 
  were 
  represented: 
  Richardson 
  Highway, 
  mileposts 
  8.3, 
  187.5, 
  

   192.9, 
  209.7, 
  223.6 
  and 
  239.9, 
  and 
  Glenn 
  Highway, 
  milepost 
  117.1. 
  

  

  