(platyhelminth worm) |
(nemertean worm) |
BILATERIA
|
(annelid worm) |
(pogonophoran worm) |
(gastropod mollusc) |
(sipunculan worm) |
(modified from WWW 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)== Aschelminthes (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.)
|
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 b) circumpharyngeal ganglia c) serial ventral nerve collaterals d) paired gonoducts b) trochophore-like larva with apical cilia c) larvae swim with compound cilia b) entomesoblast cell yields paired coeloms c) paired ventral nerve bundles d) contractile dorsal vessel b) scraping buccal organ * c) muscular creeping foot * * traits b & c are only present in Sipuncula larvae |
b) pre-oral prostomium c) anus-bearing pygidium b) protrusible epidermal, chitinous setae in setal sacs c) paired, ventral segmental nerves in larva (only seen in opisthoma of pogonophorans) 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 |