Z250 (2005) - Protostomia Clade

Zoology 250 Phylogenetic Trees (2005)

(platyhelminth worm)	(nemertean worm)	BILATERIA (= bilaterally symmetric animals)	(annelid worm)	(pogonophoran worm)
(gastropod mollusc)	(sipunculan worm)	(modified from Tree of Life; traits & tree after Ruppert & Barnes 1994 p. 1052, Eernisse et al. 1992, and Brusca & Brusca 2003 p. 875).	(echiuran worm)	(crustacean arthropod)

            ========================== Platyhelminthes (flatworms, tapeworms,etc.
            |
            |  ===(branch uncertain)== 'pseudoceolomates' (nematodes, rotifers,etc.)
            |  | 
     ===P===|  |      ================ Nemertea (ribbon worms)
     |      |  |      |
     |      =1=|      |        ======= Mollusca (snails, clams, squids, etc.)
     |         |      |   ==3==|
     |         ===C===|   |    ======= Sipuncula (peanut worms)
     |                |   |
<<=B=| B- BILATERIA   |   |         == Annelida (segmented worms)
     |                |   |      =6=|
     | P- PROTOSTOMIA =2==|   =5=|  == Pogonophora (beard worms, vent worms)
     |                 S? |   |  |
     | C- COELOMATE       =4==|  ===== Echiura (proboscis worms)
     |    PROTOSTOMES      S? |
     |                        ==7===== Panarthropoda (velvet worms, insects, spiders, crabs, etc.)
     | S? ORIGIN OF
     |  SEGMENTATION?
     ================================= Deuterostomia (echinoderms, chordates, etc.)

Back to Zool 250 tree for animal phyla

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

P= PROTOSTOMIA: a) spiral, determinate cleavage
b) mesoderm from single (mesentoblast) cell
c) fate of first derm cell set at 5th cleavage
d) mouth (and sometimes anus) from blastopore
e) sheets of sub-epidermal muscles
f) multiciliated cells

1: a) anus present
b) circumpharyngeal ganglia
c) paired gonoducts
d) circular muscle layer lies outside longitudinal muscle layer

C= COELOMATE PROTOSTOMES: a) coelom via schizocoely
b) trochophore-like larva with apical cilia
c) larvae swim with compound cilia

2: a) larvae possess prototrochal cilia
b) entomesoblast cell yields paired coeloms
c) paired ventral nerve bundles
d) contractile dorsal 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

3: a) "molluscan cross" at 64-cell stage
b) scraping buccal organ *
c) muscular creeping foot *

* traits b & c are only present in Sipuncula larvae

4= ARTICULATA: a) segmented coelom
b) pre-oral prostomium
c) anus-bearing pygidium
d) paired ventral nerve cords with segmental ganglia (only in late larva & postlarva of Echiura)

5: a) "annelid cross" in 64-cell embryo
b) protrusible epidermal, chitinous setae in setal sacs

6: a) fully segmented coelom & body wall muscles
(only in opisthoma of pogonophorans)

7= PANARTHROPODA: a) elongate body of multiple similar segments**
b) ventro-lateral legs (lobopods) with hooked tips
c) must molt to grow
d) chemical makeup of cuticle
e) ectodermal cilia lost
f) extensive hemocoel ('open' circulatory system), coeloms reduced
g) heart with openings to hemocoel (ostia)
h) panarthropodan sensilla

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