Zoology 250

Clade for ASCHELMINTHES=PSEUDOCOELOMATES


The ASCHELMINTHES. A grouping of convenience; probably not monophyletic; tree & most characters from Nielson 1994 p. 62, 235, 262.


        ==T=======(placement uncertain)== Tardigrada (water bears)
        |
        |             ===3=============== Rotifera (rotifers= "wheel bearers")
        |====2========|
<<==1===|            ===4=============== Acanthocephala (spiny headed worms)
        |
        |   =============6=============== Gastrotricha (gastrotrichs, hairy-belly worms)
        |   |
        =5==|         ===9=============== Nematoda (round worms)
            |   ===8==|
            |   |     ==10=============== Nematomorpha (horsehair worms)
            |   |
            =7==|     ==12==(uncertain)== Priapula (penis worms)
                |     |
                ==11==|     ===14======== Kinorhyncha (spiny-snout propelled worms)
                      ==13==|
                            ===15======== Loricifera (corset-bearer worms)

TRAITS SUPPORTING EACH CLADE
(** plesiomorphic- a primitive state, not unique to clade):

T (aschelminth-like):
a) pseudocoel
b) tri-radiate, myo-epithelial sucking pharynx
c) cleavage not spiral or radial
1:
a) triploblastic**
b) pseudocoelom
c) bilaterally asymmetrical, determinate cleavage
d) mesoderm from blastopore rim
e) direct development without ciliated primary larva
f) protonephridia**
2:
a) trunk with intracellular skeletal lamina (extracellular cuticle absent)
b) sperm structure
3:
a) toes with adhesive glands
b) one ventral nerve cord
4:
a) loss of gut
b) apical proboscis with intracellular hooks
c) two lateral nerve cords
5:
a) terminal mouth
b) radial pharynx
c) tripartite epipharyngeal brain
6:
a) myo-epithelial sucking pharynx
b) pseudocoelom lost
c) two lateral nerve cords
7:
a) no locomotory cilia
b) cuticle molted
c) introvert with cuticular spines, teeth or scalids
8:
a) collagenous cuticle
b) protonephridia lost
c) circular trunk muscles lost
d) non-ciliated sperm
9:
a) 6+6+4 sensillae and amphids
b) four nerve cords (dorsal, ventral, 2 lateral)
10:
a) gut rudimentary or absent in adults
b) no amphids
c) one ventral nerve cord
11:
a) conspicuous introvert
b) rings of scalids on introvert
c) chitinous cuticle
d) one ventral nerve cord
12:
a) large body cavity with amoebocytes and erythrocytes
13:
a) mouth cone with cuticular ridges and spines
b) circular trunk muscles lost
14:
a) segmented body (13 segments)
15:
a) scalids with muscles
b) tri-radiate, myo-epithelial sucking pharynx

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Copyright © 2002 by A. Richard Palmer. All rights reserved.
(revised April 3, 2002)