28. Hemichordata & Chordata Flashcards
T/F
Phylogenetic placement of Hemichordata is very clear; it is sister to Echinodermata
False
It’s not clear, but molecular evidence does suggest it’s sister to Echinodermata
Are Hemichordata and Chordata Protostomia or Deuterostomia?
Deuterostomia
T/F
Pharyngeal slits and a 3-part body coelom are both shown in Hemichordata
true!
Acorn worms and pterobranchs are from which phylum?
Phylum Hemichordata
How many extant described species of Hemichordata are there?
~140
T/F
Hemichordata are entirely terrestrial
false
they are entirely marine
Most Hemichordata have one or more pharyngeal slits. Are these used for gas exchange?
No, they’re used for feeding rather than gas exchange
Hemichordata have a __-partite body with eucoeloms
3-part body coelom
Do Hemichordata have brains? Eyes?
No, neither
T/F
Most hemichordata have dorsal and ventral nerve cords (and nerve nets)
true
Explain the circulatory system of Hemichordata
Their circulatory system includes a heart and dorsal + ventral vessels, but the system is not completely closed
Are hemichordata hermaphroditic?
Do they use sexual or asexual reproduction?
No, they have separate sexes.
They use both sexual and asexual reproduction
Name the two classes of Hemichordata.
Which one has the majority of the phylum’s extant species?
- Enteropneusta: most extant spp
- Pterobranchia
Which class of Hemichordata are acorn worms in?
Enteropneusta
T/F
Acorn worms (Enteropneusta) are solitary, sediment-dwelling worms with a clear tripartite body plan
true
Describe the 3 parts of an acorn worm body plan
- Proboscis: acorn-shaped usually
- Collar: mouth at base of the collar
- Truck: long & squiggly with numerous perforations called “GILL SLITS” & a terminal anal opening
T/F
Each of the 3 body regions in acorn worms has its own eucoelomic cavity (or pair of cavities)
true
The protocoel (one of the eucoelomic cavities in acorn worms) has a single coelomopore on the left side. What’s the function of this?
It connects the coelom to the water outside
A pharyngeal chamber with slits is present in Acorn worms.
It’s very similar to the one in _______, and may be truly homologous with chordate branchial slits
Cephalochordata
Cilia are present on the slits of the Acorn worm’s pharyngeal chamber. What is the function of these cilia?
These cilia generate a current that sucks water through the mouth and expels it through holes running from the pharynx to the outside of the body
In acorn worms, the proboscis is covered with cilia and mucus. What is this proboscis used for?
feeding
How do most Enteropneusta feed?
Most deposit-feed by selectively ingesting organic matter from sediments
- Some are non-selective deposit feeders that create large casts of undigested sediment
How are food particles sorted by acorn worms? What happens to the desirable ones?
Particles are sorted at the base of the proboscis. Desirable ones are added to an iodine-rich mucus cord that’s constantly generated and slurped into the mouth
Where do acorn worms live?
They are all marine
- some live in burrows
- others can’t burrow, so live on the surface of sediments
