Friday, August 28, 2020

Protostomes -- The Ancester's Tale, Richard Dawkins

 Rendezvous 26: 590 mya +/- large moe -- protostomes

The biggest of all rendezvouses
Protostomes: the great bulk of of the pilgrimage of animals
Less and less hard support of fossils
Now: molecular rangefinding
Animal kingdom divided into two great subkingdoms
Deuterostomia
Protostomia
Deuterostomia (all pilgrims, including us, so far)
Protostomia: joined us at Rendezvous 26
Has to do with gastrulation (embryology)
Protostome: mouth first
Deuterostome: mouth second

Protostomes: over a million species
Deuterostomes: 60,000 species

Protosomes: an embryological term, not a classical Linnaeus classification based on pattern observation.

There are "classically" five phyla that are protostomes.

  • three worm phyla
  • molluscs
  • arthopods

Put the molluscs between the worm phyla and the arthropods because the molluscs are more closely related to the annelid worms than the worms are related to the arthropods.

  • to the far left, round worms, and flat worms (two separate phyla)
  • toward the middle, the annelid worms
  • in the middle, the fourth phylum, the molluscs
  • to the far right, the fifth phylum, the arthopods

Some would group these into three super-phyla:

  • Ecdysozoa: molting animals
  • Lophotrochozoa: crest/wheel animals
  • Platyzoa: flat animals

Ecdysozoa:

  • more than 34th of the entire animal kingdom
  • insects, crustaceans, spiders, millipedes, centipedes, trilobites, others
  • land and sea; includes the giant Eurypterids, p. 381

Lophotrochozoa:

  • outnumber deuterostomes, but in turn they themselves are greatly outnumbered by Ecdysozoa
  • molluscs, annelid worms
  • bivalves, brachiopads

Platyzoa:

  • flat animals

*******************************
From Here, 590 MYA, To About 560 MYA: Chordates
In Round Numbers: about a half million years ago: fish

But not "recognizable" until about 530 mya when lampreys and hagfish showed up. It took "forever" to get to this point, but once things started, "we" go to fish pretty quickly -- and then a long time before amphibians.

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