﻿216 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.96 
  

  

  Echiuroids 
  are 
  burrowers 
  in 
  mud 
  or 
  sand, 
  where 
  they 
  fashion 
  more 
  

   or 
  less 
  permanent 
  tunnels. 
  Sometimes 
  they 
  live 
  under 
  rocks; 
  some- 
  

   times 
  in 
  mud-filled 
  mollusk 
  shells 
  or 
  sand-dollar 
  tests, 
  which 
  afford 
  

   some 
  protection; 
  or 
  they 
  inhabit 
  the 
  rock 
  galleries 
  excavated 
  by 
  boring 
  

   clams. 
  Their 
  food 
  consists 
  of 
  organic 
  material 
  contained 
  in 
  the 
  mud 
  

   which 
  they 
  swallow 
  in 
  large 
  quantities, 
  or 
  of 
  lighter 
  organic 
  detritus 
  

   selected 
  by 
  the 
  usually 
  long 
  proboscis. 
  In 
  the 
  same 
  species 
  from 
  dif- 
  

   ferent 
  locaUties 
  the 
  intestinal 
  pellets 
  vary 
  with 
  the 
  character 
  of 
  the 
  

   bottom. 
  One 
  genus 
  (Urechis) 
  has 
  very 
  specialized 
  feeding 
  habits 
  and 
  

   uses 
  only 
  finely 
  divided 
  material, 
  including 
  bacteria. 
  It 
  is 
  probable 
  

   that 
  any 
  small 
  organisms 
  living 
  in 
  the 
  surface 
  film 
  of 
  mud 
  will 
  be 
  

   eaten 
  by 
  echiuroids. 
  Gislen 
  (1940, 
  p. 
  30) 
  found 
  the 
  intestinal 
  pellets 
  

   of 
  Echiurus 
  echiurus 
  "to 
  consist 
  of 
  the 
  same 
  stuff 
  as 
  that 
  which 
  is 
  

   formed 
  by 
  the 
  detritus-film 
  growing 
  on 
  the 
  aquarium 
  bottom. 
  There 
  

   are 
  thus 
  plenty 
  of 
  sand 
  grains; 
  further 
  the 
  pellets 
  consist 
  of 
  diatoms, 
  

   algal 
  threads, 
  debris 
  of 
  leaves 
  of 
  phanerogams 
  (Zostera 
  et 
  al.), 
  

   Infusoria, 
  Bacteria, 
  occasional 
  Nematodes 
  and 
  Rotatoria 
  and, 
  to 
  a 
  

   large 
  extent, 
  of 
  amorphous 
  brown 
  stuff 
  which 
  emanates 
  from 
  

   decomposed 
  organic 
  substance." 
  

  

  The 
  smallest 
  sexually 
  mature 
  echiuroid 
  I 
  have 
  ever 
  seen 
  is 
  a 
  

   Listriolobus 
  pelodes 
  7 
  mm. 
  long 
  (0.275 
  of 
  an 
  inch), 
  and 
  the 
  largest 
  is 
  

   Urechis 
  caupo, 
  470 
  mm. 
  long 
  preserved, 
  or 
  18.5 
  inches. 
  I 
  have 
  seen 
  

   a 
  relaxed 
  living 
  Urechis 
  caupo 
  19.75 
  inches 
  long. 
  The 
  Japanese 
  

   Ikeda 
  taenioides, 
  a 
  remarkable 
  and 
  isolated 
  form, 
  attains 
  a 
  body 
  

   length 
  of 
  16 
  inches 
  with 
  a 
  proboscis 
  of 
  58 
  inches, 
  or 
  a 
  total 
  length 
  of 
  

   6 
  feet 
  2 
  inches 
  (Ikeda, 
  1907, 
  p. 
  20). 
  

  

  More 
  helpless, 
  unprotected 
  animals 
  can 
  scarcely 
  be 
  imagined. 
  The 
  

   immature 
  stages 
  are 
  prey 
  for 
  every 
  predaceous 
  inhabitant 
  of 
  the 
  

   sea 
  bottom. 
  The 
  adults 
  are 
  regularly 
  eaten 
  by 
  fishes, 
  especially 
  

   flatfishes 
  and 
  rays, 
  as 
  well 
  as 
  by 
  the 
  Indians 
  of 
  Chiloe 
  Island, 
  Chile 
  

   (Gay, 
  1854, 
  p. 
  475). 
  In 
  Japan 
  and 
  Korea 
  Urechis 
  unicinctus 
  is 
  

   extensively 
  used 
  as 
  bait. 
  Sato 
  (1939, 
  p. 
  319) 
  states 
  that 
  in 
  Korea 
  

   the 
  natives 
  catch 
  it 
  by 
  means 
  of 
  iron 
  hooks 
  and 
  dry 
  it 
  for 
  food. 
  

  

  Systematics 
  of 
  the 
  Echiuroidea 
  present 
  the 
  usual 
  problems 
  in 
  

   addition 
  to 
  others 
  inherent 
  to 
  the 
  group. 
  The 
  principal 
  diSiculty 
  is 
  

   the 
  lack 
  of 
  structures 
  having 
  a 
  permanent 
  form. 
  The 
  setae 
  are 
  of 
  

   very 
  limited 
  use; 
  everything 
  else 
  is 
  soft 
  and 
  capable 
  of 
  distortion. 
  

   The 
  practical 
  difficulties 
  encountered 
  are 
  those 
  which 
  would 
  confront 
  

   the 
  student 
  of 
  holothurians 
  if 
  these 
  creatures 
  did 
  not 
  carry 
  embedded 
  

   in 
  the 
  skin 
  a 
  species 
  label 
  in 
  the 
  guise 
  of 
  characteristic 
  calcareous 
  

   deposits. 
  Most 
  of 
  the 
  generic 
  and 
  specific 
  characters 
  of 
  echiuroids 
  

   must 
  be 
  sought 
  by 
  careful 
  dissection 
  of 
  the 
  internal 
  organs, 
  which 
  

   arc 
  susceptible 
  to 
  variation 
  arising 
  from 
  accidents 
  of 
  fixation. 
  Never- 
  

   theless, 
  a 
  fairly 
  satisfactory 
  system 
  of 
  genera 
  can 
  be 
  constructed. 
  

   But 
  it 
  is 
  obvious 
  that 
  closely 
  related 
  species 
  may 
  not 
  be 
  recognized, 
  

  

  