BILATERIAN ANIMALS (modified from WWW Tree of Life; traits & tree after Ruppert & Barnes 1994 p. 1052).

               ===========================  Platyhelminthes (flatworms, tapeworms, etc.)
               |
               |  ====(branch uncertain)==  pseudocoelomates (nematodes, rotifers, etc.)
     ====P=====|  | 
     |         |  |      =================  Nemertea (ribbon worms)
     |         |  |      |
     |         =1=|      |        ========  Sipuncula (peanut worms)
     |            |      |   ==3==|
     |            |      |   |    ==============================  TO MOLLUSCA ===>
     |            ===C===|   |
<<=B=|                   |   |      ======  Echiura (proboscis worms)
     |                   |   |      |
     | B- BILATERIA      =2==|   =5=|  ===  Pogonophora (beard worms, vent worms)
     |                    S? |   |  =6=|
     | P- PROTOSTOMIA        =4==|     ===  Annelida (segmented worms)
     |                        S? |
     | C- COELOMATE PROTOSTOME   |    ====  Onychophora (velvet worms)
     |                           ==7==|
     | S- SEGMENTATION                ====  Arthropoda (insects, spiders, crabs, etc.)
     |
     =====================================  DEUTEROSTOMIA (echinoderms, chordates, etc.)

TRAITS SUPPORTING BRANCH 1: a) circumpharyngeal gangliae b) serial ventral nerve collaterals c) paired gonoducts C: a) larvae swim with compound cilia b) pelagic larvae have apical ciliary tuft 2: a) larvae posess prototrochal cilia b) entomesoblast cell yields paired coeloms c) paired ventral nerve bundles d) contractile dorsal vessel 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: a) segmented coelom b) pre-oral prostomium c) anus-bearing pygidium 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 seen in opisthoma of pogonophorans) 7: a) elongate body of many similar segments** b) ventro-lateral appendages c) must molt to grow d) ectodermal cilia lost e) extensive hemocoel ('open' circulatory system),    coeloms reduced f) heart with openings to hemocoel (ostia) g) tracheal system for respiration h) oblique striated muscles i) larval prototrochal cilia lost j) larval apical ciliary tuft lost

       ======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)

TRAITS SUPPORTING EACH CLADE (** plesiomorphic- a primitive state, not unique to clade): 1: a) muscular, creeping ciliated foot** b) mantle with calcareous spicules produced by single cells, c) posterolateral 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: a) small, elongate, worm-like body b) reduction/loss of foot & head c) reduced # 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: a) 8 unique shell plates (perforated by aesthetes) b) mantle girdle c) calcareous spicules from single cells** 5: CONCHIFERA a) 1 conical or coiled shell b) 3-layered shell (periostracum, prismatic & nacreous calcareous layers) c) crystalline style 6: a) 8 pair pedal retractor muscles** b) monopectinate ctenidia (5-6 pair)

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 9: a) torsion b) operculum attached to foot c) 1 pair ctenidia** 10: 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 11: a) body modified for infaunal life b) burrowing foot c) paired, lateral larval shell plates d) 1 pair ctenidia** 12: a) radula lost b) head lost c) enlarged mantle cavity & ctenidia d) mantle edge fused to shell e) byssal gland 13: a) 2 larval shell plates fuse into tubular adult shell b) ctenidia lost c) captacula

Back to Zool 250 version of tree for animal phyla