﻿218 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  96 
  

  

  Neither 
  is 
  Poeobius 
  meseres 
  Heath 
  (1930) 
  included. 
  This 
  remarkable 
  

   pelagic 
  transparent 
  worm 
  was 
  first 
  taken 
  in 
  350 
  meters, 
  Monterey 
  

   Bay, 
  Calif., 
  and 
  was 
  later 
  found 
  to 
  be 
  abundant 
  off 
  southern 
  Alaska. 
  

   Its 
  anatomy 
  has 
  been 
  fully 
  described 
  by 
  Professor 
  Heath. 
  Sub- 
  

   sequently 
  the 
  writer 
  observed 
  and 
  sketched 
  a 
  living 
  animal. 
  The 
  

   blood 
  vessels 
  are 
  clearly 
  visible 
  and 
  contain 
  a 
  dull 
  green 
  fluid, 
  but 
  the 
  

   enlargement 
  of 
  the 
  dorsal 
  vessel 
  is 
  dull 
  red. 
  Blood 
  vessels 
  extend 
  to 
  

   tip 
  of 
  the 
  2 
  prostomial 
  palps 
  and 
  the 
  10 
  (possibly 
  peristomial) 
  cirri. 
  

  

  The 
  creature 
  has 
  no 
  paired 
  appendages, 
  no 
  somatic 
  segmentation, 
  

   and 
  no 
  setae. 
  "The 
  nervous 
  system 
  conforms 
  to 
  the 
  usual 
  annelidan 
  

   type, 
  with 
  supra-oesophageal 
  ganglion, 
  circum-oesophageal 
  connec- 
  

   tives, 
  and 
  a 
  ventral 
  nerve 
  chain 
  comprising 
  11 
  pairs 
  of 
  ganglia 
  with 
  

   the 
  usual 
  commissures 
  and 
  connectives. 
  The 
  somatic 
  musculature 
  

   comprises 
  four 
  great 
  longitudinal 
  bands, 
  extending 
  throughout 
  the 
  

   length 
  of 
  the 
  body, 
  and 
  a 
  more 
  delicate 
  external 
  sheath 
  of 
  circular 
  

   fibres." 
  This 
  is 
  the 
  annelid 
  pattern 
  and 
  distinctly 
  not 
  the 
  echiuroid. 
  

   The 
  head 
  is 
  unlike 
  that 
  of 
  any 
  known 
  echiuroid 
  but 
  resembles 
  

   that 
  of 
  some 
  polychaete 
  annelids. 
  The 
  alimentary 
  canal 
  and 
  

   nephridia 
  seem 
  to 
  the 
  writer 
  to 
  be 
  specialized 
  m 
  much 
  the 
  same 
  way 
  as 
  

   in 
  the 
  case 
  of 
  Sternaspis, 
  which 
  in 
  one 
  species 
  {S. 
  spinosus 
  Sluiter) 
  has 
  

   the 
  prostomium 
  prolonged 
  outward 
  on 
  each 
  side 
  to 
  form 
  a 
  grooved 
  

   palplike 
  organ. 
  The 
  Scoleciformia, 
  however, 
  have 
  definite 
  mesoder- 
  

   mal 
  segmentation. 
  

  

  The 
  difficulty 
  in 
  finding 
  a 
  place 
  for 
  Poeobius 
  may 
  well 
  mean 
  that 
  it 
  

   is 
  not 
  an 
  annelid 
  or 
  a 
  echiuroid 
  or 
  a 
  link 
  between 
  the 
  two. 
  Although 
  

   nothing 
  whatever 
  is 
  known 
  of 
  the 
  development 
  of 
  Poeobius, 
  we 
  have 
  

   to 
  assume 
  that 
  mesodermal 
  segmentation 
  is 
  absent; 
  therefore 
  it 
  is 
  not 
  

   an 
  annelid. 
  Its 
  nerve 
  cord 
  is 
  segmented 
  (implying 
  pseudometamer- 
  

   ism). 
  The 
  nerve 
  cord 
  of 
  larval 
  echiuroids 
  is 
  segmented, 
  but 
  this 
  is 
  

   lost 
  in 
  the 
  adult, 
  suggesting 
  that 
  the 
  ancestors, 
  while 
  deprived 
  of 
  

   mesodermal 
  metamerism, 
  still 
  had 
  a 
  pseudometamerism 
  of 
  the 
  nerve 
  

   cord. 
  A 
  tenable 
  hypothesis 
  is 
  that 
  the 
  echiuroids 
  and 
  Poeobius 
  

   stemmed 
  from 
  a 
  common 
  group 
  that 
  was 
  as 
  fundamentally 
  un- 
  

   segmented 
  as 
  the 
  Amphineura 
  among 
  mollusks. 
  According 
  to 
  this 
  

   view 
  Poeobius 
  is 
  the 
  survivor 
  of 
  a 
  lesser 
  phylum, 
  comparable 
  to 
  the 
  

   Phoronidea 
  and 
  Priapuloidea. 
  As 
  the 
  genus 
  now 
  floats 
  in 
  a 
  sort 
  of 
  

   taxonomic 
  limbo, 
  it 
  may 
  be 
  provisionally 
  assigned 
  to 
  a 
  new 
  phylum, 
  

  

  POEOBIOIDEA. 
  

  

  The 
  region 
  covered 
  by 
  this 
  report 
  includes 
  all 
  the 
  water 
  north 
  of 
  a 
  

   line 
  drawn 
  from 
  Cape 
  San 
  Lucas, 
  Baja 
  California, 
  to 
  the 
  southern 
  

   end 
  of 
  Sakhalin 
  Island 
  on 
  the 
  east 
  Asiatic 
  coast. 
  The 
  Gulf 
  of 
  Cali- 
  

   fornia 
  has 
  been 
  included, 
  and 
  a 
  species 
  long 
  ago 
  dredged 
  by 
  the 
  

   Albatross 
  in 
  Japanese 
  waters 
  has 
  been 
  added, 
  as 
  it 
  modifies 
  the 
  

   concept 
  of 
  Acanthohamingia, 
  which 
  I 
  wished 
  to 
  include 
  in 
  the 
  key. 
  

  

  