﻿PROCEEDINGS 
  OF 
  THE 
  UNITED 
  STATES 
  NATIONAL 
  MUSEUM 
  

  

  issued 
  

  

  SMITHSONIAN 
  INSTITUTION 
  

  

  U. 
  S. 
  NATIONAL 
  MUSEUM 
  

  

  Vol. 
  % 
  Wathington: 
  1946 
  Nq. 
  3198 
  

  

  ECHiraOID 
  AVORMS 
  OF 
  THE 
  NORTH 
  PACIFIC 
  OCEAN 
  

  

  By 
  Walter 
  Kenrick 
  Fisher 
  

  

  The 
  echiuroids, 
  sometimes 
  called 
  spoon 
  worms 
  from 
  the 
  shape 
  of 
  the 
  

   contracted 
  prostomium 
  or 
  proboscis, 
  are 
  cigar-shaped 
  or 
  sausage- 
  

   shaped 
  creatures, 
  essentially 
  highly 
  muscular 
  sacs 
  filled 
  with 
  fluid 
  in 
  

   which 
  the 
  long 
  alimentary 
  canal 
  and 
  other 
  organs 
  have 
  great 
  freedom 
  

   of 
  movement. 
  The 
  mouth 
  is 
  anterior, 
  usually 
  at 
  the 
  base 
  of 
  a 
  snout 
  

   or 
  a 
  long 
  proboscis 
  used 
  for 
  gathering 
  food. 
  The 
  skin 
  is 
  highly 
  gland- 
  

   ular 
  and 
  is 
  covered 
  by 
  a 
  very 
  thin 
  cuticle. 
  Typically 
  there 
  are 
  two 
  

   hooked 
  setae 
  behind 
  the 
  mouth, 
  and 
  two 
  genera 
  have 
  either 
  one 
  or 
  two 
  

   circles 
  of 
  setae 
  at 
  the 
  posterior 
  end 
  of 
  the 
  body. 
  The 
  alimentary 
  canal, 
  

   in 
  contrast 
  to 
  that 
  of 
  most 
  annelids, 
  is 
  several 
  times 
  the 
  length 
  of 
  body 
  

   and 
  consists 
  of 
  a 
  long 
  foregut, 
  differc'ntiated 
  into 
  pharyiLX, 
  esoi)hagus, 
  

   giz/.ard, 
  and 
  stomacii, 
  a 
  still 
  longer 
  midgut 
  or 
  intestine, 
  accompanied 
  

   for 
  a 
  considerable 
  part 
  of 
  its 
  length 
  by 
  a 
  collateral 
  intestine, 
  or 
  siphon, 
  

   )ind 
  finally 
  a 
  short 
  hind-gut 
  or 
  cloaca, 
  into 
  which 
  empty 
  two 
  usually 
  

   \<)hiniinc)us, 
  sometimes 
  branched, 
  vesicles, 
  the 
  walls 
  of 
  which 
  are 
  

   studded 
  with 
  minute 
  ciliated 
  funnels. 
  The 
  anterior 
  nephridia, 
  

   tyj)ically 
  elongate, 
  thin-walled 
  sacs, 
  varying 
  from 
  one 
  to 
  many, 
  but 
  

   usually 
  from 
  one 
  to 
  four 
  pairs, 
  hav(! 
  a 
  basal 
  or 
  terminal 
  nephrostome, 
  

   the 
  lips 
  of 
  which 
  may 
  be 
  greatly 
  prolonged 
  and 
  spirally 
  twisted. 
  The 
  

   nephridia 
  vary 
  greatly 
  in 
  size 
  and 
  when 
  filbnl 
  with 
  eggs 
  or 
  sperm 
  ar(^ 
  

   (tftcn 
  very 
  large. 
  The 
  vascular 
  system 
  consists 
  of 
  a 
  ventral 
  vessel 
  

   f(»llowing 
  the 
  nerve 
  cord 
  to 
  form 
  a 
  looj) 
  in 
  the 
  proboscis 
  from 
  the 
  tip 
  of 
  

   u 
  hich 
  a 
  median 
  vessel 
  pa.sses 
  backward 
  in 
  tiie 
  proboscis 
  and 
  along 
  the 
  

   dorsal 
  side 
  of 
  foregut 
  to 
  beginning 
  of 
  midgut, 
  where 
  a 
  neurointestiiuil 
  

   vessel 
  joins 
  it 
  to 
  the 
  ventral 
  vessel. 
  In 
  Urechis 
  there 
  are 
  no 
  blood 
  

   vessels. 
  

  

  215 
  

   •""oaa*— 
  *fl 
  — 
  1 
  

  

  