THREE MINOR PROTOSTOME PHYLA
(click on tree to see full cladogram)
a) body of two distinct parts: a) trunk and b) large flap-like proboscis
b) have one large coelom and coiled gut with terminal mouth and anus
c) separate sexes; extreme sexual dimorphism: females to 2m including proboscis; males 1 - 2mm, live as commensal in female's genital sac!
d) linked to annelids by: paired setae in setal sacs, highly segmented nervous system in late larvae & early juveniles
a) reach large size (> 2 m long, > 4 cm diameter!) in hydrothermal vent communities; make long chitinous tubes
b) 3 body regions: i) forepart (has separate coelom) with tentacles, ii) trunk (has single large coelom), iii) segmented opisthoma (fully segmented coelom; setae in setal sacs)
c) adults lack a gut but possess symbiotic bacteria in tentacles or in internal trophosome; larvae of some Vestemintifera have a complete gut like an annelid worm
d) separate sexes, method of fertilization unknown
e) linked to polychaete annelids by: features of opisthosoma (segmentation, setae in setal sacs), trochophore-type larva, fully segmented juvenile with setae (some)
Copyright (c) 2017 by A. Richard Palmer. All rights reserved.
(revised Dec. 19, 2016)