TWO 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; have extreme sexual dimorphism: females may be up to 2 m including the proboscis, but males are only 1 - 2mm and live as a commensal inside the female's genital sac!
d) linked to annelids by: annelid cross, paired setae in setal sacs, highly segmented nervous system in late larvae and early juveniles
a) reach large size (> 2 m) 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) larvae of some Vestemintifera have a complete gut like an annelid worm; adults lack a gut but possess symbiotic bacteria in tentacles or trophosome
d) separate sexes, method of fertilization unknown; early cleavage is "irregular" spiral
e) linked to polychaete annelids by: features of opisthosoma (segmentation, setae in setal sacs), trochophore-type larva, fully segmented juvenile with setae (some)
f) now considered to be an order or family (!) of polychaetes (Pogonophoridae) closely related to feather-duster worms (Sabellidae)
Copyright (c) 2013 by A. Richard Palmer. All rights reserved.
(revised Jan. 3, 2013)