Zoology 250 Phylogenetic Trees (2014)


(aplacophoran)

(polyplacophoran)
PHYLUM MOLLUSCA

(Tree and traits from
Ruppert et al. 2004 p. 406, and
Brusca and Brusca 1990 p. 762)


(heterodont bivalve)

(scaphopods)

(prosobranch gastropod)

(nautiloid cephalopod)


       ======2================== Aplacophora (shell-less, worm-like molluscs)
       |
<<=1===|    ====4=============== Polyplacophora (chitons)
       |    |
       ==3==|   ====6=========== Monoplacophora (primitive limpet-like molluscs)
            |   |
            =5==|         ===9== Gastropoda (snails, slugs, etc.)
                |    ==8==|
                |    |    ==10== Cephalopoda (nautiloids, cuttlefish, squids, octopus)
                ==7==|
 5="CONCHIFERA"      |    ==12== Bivalvia (mussels, clams, scallops, etc.)
                     ==11=|
                          ==13== Scaphopoda (tusk shells)

Back to Zool 250 tree for animal phyla or Protostomia


TRAITS SUPPORTING EACH CLADE (** plesiomorphic- a primitive state, not unique to clade) AND HIGHER TAXA:
1:
a) muscular, creeping ciliated foot**
b) mantle with calcareous spicules produced by single cells
c) ventrolateral mantle cavity with multiple bipectinate gills (ctenidia)
d) radula
e) larval/adult body with traces of eight segments
f) trochophore larvae**
g) coelom via schizocoely**
h) 'open' circulatory system (hemocoel) with pumping heart
i) circumpharyngeal nerve-ring (brain) with ladder-like ventrolateral nerves**
2= APLACOPHORA:
a) 2 taxa with small, elongate, worm-like body
b) reduction/loss of foot & head
c) reduced number of ctenidia (two or fewer)
3:
a) large muscular foot
b) one or more dorsal, solid shell plates
c) 8 pair pedal 'retractor' muscles
d) mobile radular membrane & odontophore
4= POLYPLACOPHORA:
a) 8 unique shell plates (perforated by aesthetes)
b) mantle girdle
c) calcareous spicules from single cells**
5= CONCHIFERA:
a) single conical or coiled shell
b) 3-lobed mangle margin
c) 3-layered shell (periostracum, prismatic & nacreous calcareous layers)
d) crystalline style
e) diplosome lost (2001 Invert Biol 120:342)
6= MONOPLACOPHORA:
a) 8 pair pedal retractor muscles**
b) 5 - 6 pairs of monopectinate ctenidia
7:
a) 2 pair pedal retractor muscles
b) 1 or 2 pair ctenidia
c) veliger larva (absent in Cephalopoda)
8:
a) coiled, tubular shell**
b) dorsoventrally expanded body with large, dorsal viscera
c) 1 pair pedal retractor muscles
d) posterior mantle cavity
9= GASTROPODA:
a) torsion (yields anterior mantle cavity & twisted nervous system)
b) operculum attached to foot
c) 1 pair ctenidia**
10= CEPHALOPODA:
a) foot modified as siphon
b) shell with gas-filled chambers & siphuncle
c) ink gland
d) beak-like jaws
e) large, circumoral tentacles/arms
f) 'closed' circulatory system (vessels lined by epithelium)
g) image-forming eyes & large brain
h) active predators; crystalline style lost
i) large, yolky eggs; direct development (no larva)
11:
a) body modified for infaunal life
b) burrowing foot
c) paired, lateral larval shell plates
d) 1 pair ctenidia**
12= BIVALVIA:
a) radula lost
b) head lost
c) enlarged mantle cavity & ctenidia
d) mantle edge fused to shell
e) byssal gland
13= SCAPHOPODA:
a) 2 larval shell plates fuse into tubular adult shell
b) ctenidia lost
c) captacula


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Copyright (c) 2014 by A. Richard Palmer. All rights reserved.
(revised Jan. 1, 2014)