Zoology 250 Phylogenetic Trees (2017)

(platyhelminth worm)

(nemertean worm)
(= bilaterally symmetric animals)

(annelid worm)

(pogonophoran worm)

(gastropod mollusc)

(sipunculan worm)
(modified from Tree of Life after
Ruppert et al. 2004 p. 220, 420
Eernisse et al. 1992, and
Brusca et al. 2016 p. 1049).

(echiuran worm)

(crustacean arthropod)

            ========================== Platyhelminthes (flatworms, tapeworms, etc.)
            |  ===(branch uncertain)== 'pseudoceolomates' (nematodes, rotifers, etc.)
            |  | 
     ===P*==|  |      ================ Nemertea (ribbon worms)
     |      |  |      |
     |      =1=|      |   ============ Mollusca (snails, clams, squids, etc.)
     |         |      |   |
     |         ===C*==|   |      ===== Annelida (segmented worms)
     |                |   |      |
<<=B=| B- BILATERIA   |   |      |==== Sipuncula (peanut worms) $$
     |                |   |   =4=|
     | P- PROTOSTOMIA =2==|   |  |==== Pogonophora(beard worms, vent worms) $$
     |                 S? |   |  |
     | C- COELOMATE       =3*=|  ===== Echiura (proboscis worms) $$
     |    PROTOSTOMES      S? |
     |                        ==5===== Panarthropoda (velvet worms, insects, spiders, crabs, etc.)
     | S? ORIGIN OF
     ================================= DEUTEROSTOMIA (echinoderms, chordates, etc.)

   $$ all three of these phyla are now considered to be taxa within polychaete annelids (Struck et al. 2011. Nature 471:95-98, Andrade et al. 2015)!

Back to Zool 250 tree for animal phyla

TRAITS SUPPORTING EACH CLADE(** plesiomorphic- a primitive state, not unique to clade) AND HIGHER TAXA:
a) spiral, determinate cleavage
b) mesoderm from single (mesentoblast) cell
c) fate of first germ cell set at 5th cleavage
d) mouth (and sometimes anus) from blastopore
e) sheets of sub-epidermal muscles
f) multiciliated cells
a) anus present
b) circumpharyngeal ganglia
c) paired gonoducts
d) circular muscle layer lies outside longitudinal muscle layer
a) coelom via schizocoely
b) trochophore-like larva with apical cilia
c) larvae swim with compound cilia
a) larvae possess prototrochal cilia
b) entomesoblast cell yields paired coeloms (mesoderm)
c) paired ventral nerve bundles
d) dorsal contractile vessel or heart
e) gonads lie in coeloms
f) heart lies in coelomic pericardium
g) metanephridial funnel opens in coelomic sac
h) dorsal heart pumps anteriorly
a) pre-oral prostomium/acron
b) anus-bearing pygidium/telson
c) paired: ventral nerve cords, segmental ganglia, coelomic cavities, metanephrida, & gonads
d) engrailed expression at posterior segment margins
4= ANNELIDA & relatives:
a) protrusible epidermal, chitinous setae in setal sacs (lost in Sipuncula)
b) fully segmented coelom & body wall muscles (only in larva of Echiura, opisthoma of pogonophorans; lost in Sipuncula)
a) elongate body of multiple similar segments**
b) ventro-lateral legs (lobopods) with hooked tips
c) must molt cuticle to grow
d) similar chemical makeup of cuticle
e) epidermal cilia lost
f) extensive hemocoel ('open' circulatory system), coeloms reduced
g) heart with openings to hemocoel (ostia)
h) panarthropodan sensilla
i) superficial cleavage, no trochophore-like larva

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Copyright (c) 2017 by A. Richard Palmer. All rights reserved.
(revised Dec. 19, 2016)