Comments on: Graptolites Have Tentacles Too

By: Jennifer Frazer

Jennifer Frazer — Thu, 21 Apr 2011 12:37:15 +0000

Excellent. This will get changed post-haste. Thanks for weighing in! Convergent evolution strikes again, it seems . . .

By: dwbapst

dwbapst — Thu, 21 Apr 2011 04:26:45 +0000

They are definitely not actual lophophores. The similarity is striking (Halanych, 1993) but recent molecular phylogenies strongly suggest that the ancestral hemichordate was an enteropneust-like animal, not a pterobranch-like animal (for example, Cannon et al., 2009). I guess it just means that if you want to feed on little particles flowing past, there is pretty much one way to do it.

By the way, thanks for writing this article! I’m a graptolite worker and this exciting new find just sailed right past me with out me noticing.
-Dave Bapst, UChicago

Cannon, J. T., A. L. Rychel, H. Eccleston, K. M. Halanych, and B. J. Swalla. 2009. Molecular phylogeny of hemichordata, with updated status of deep-sea enteropneusts. Molecular Phylogenetics and Evolution 52(1):17-24.

Halanych, K. M. 1993. Suspension Feeding by the Lophophore-like Apparatus of the Pterobranch Hemichordate Rhabdopleura normanni. Biological Bulletin 185:417-427.

By: Bombardier Beetles, Bee Purple, and the Sirens of the Night

Bombardier Beetles, Bee Purple, and the Sirens of the Night — Tue, 19 Apr 2011 15:20:54 +0000

[…] Indeed, they have also done so to my graptolites post. They linked to my blog post as “proof of biological stasis”. Unfortunately, […]

By: Jennifer Frazer

Jennifer Frazer — Thu, 07 Apr 2011 03:32:32 +0000

Good points. I really don’t know, so that’s why I asked! I’ve qualifed it and I’ll change the text if someone can come up with evidence they’re definitely not lophophores. : )

By: Ben

Ben — Tue, 05 Apr 2011 03:47:57 +0000

I dunno, a lot of sessile filter-feeders have a u-shaped gut. Clams and tunicates, to name one example each from protostomes and deuterostomes. It can imagine a long series of selective pressures favoring putting both the input and output ends of the digestive tract next to the cilia that are powering the flow of water and food and waste. And bilateral symmetry seems more useful for a worm than a sessile feeder.

you asked!

cool news about pterobranchs, though. It’s pretty neat to imagine a world ocean full of frondy zooplankton colonies!

By: Jennifer Frazer

Jennifer Frazer — Sat, 02 Apr 2011 05:56:58 +0000

Excellent question. I was suprised too, but this is what my biology text says, “Innovations in Feeding. Evolution in one lineage of deuterostomes resulted in several modifications of the lophophore and the coelomic cavity within it. These modifications provided new ways of capturing and handling food. All living representatives of this lineage (Hemichordates) are wormlike animals that live buried in marine sands or muds, under rocks, or attached to algae […] The ten living species of pterobranchs seem to have changed relatively little from the ancestors of their lineage […] In the other hemichordate lineage (the enteropneusts, or acorn worms — jf), the lophophore was apparently lost and the proboscis grew larger and became a digging organ . . . ” — Purves, Orians, and Heller. Life: The Science of Biology, Fourth edition.

It is possible they misinterpreted the structure and it is convergent (homoplasy), but the overall body plan *does* look a heck of a lot like a bryozoan (complete with u-shaped digestive track with anus opening near the mouth), even though these are deuterostomes and they are protostomes. Based on this and my book, I’d guess the common ancestor (the ancestral bilaterian) must have had it, and it was lost in all deuterostomes but the ones who have changed the least.

Anyone else want to weigh in? Thoughts welcome.

By: Vasha

Vasha — Sat, 02 Apr 2011 00:40:26 +0000

Wait, pterobranchs are deuterostomes and they have a lophophore? Is this homologous to the protostome lophophore (and would the ancestral bilaterian have had one)?