Clade diagram so far:
Soleneidea
from Ancient Greek: σωλήν/solen "tube", eiδἠς "species"
While the fossil record is unclear, evidence suggests that the solenids, or tube worms, are best classified with the thiophiles as opposed to the bastrovites, due to the active transport channels present that maintain sulfur homeostasis in environments where no
environmental sulfur is present, and tight linkages seen between solenid cells--all features characteristic of protothiophiles. Furthermore, cellular differentiation along a sulfur gradient can already be seen in certain well-preserved fossils.
The lack of methanol dehydrogenase present in even the earliest bastrovites, but not in thiophiles, indicates an earlier point of divergence, perhaps as far back as Archaeoblobus. This would seem to indicate that tube worms evolved from tubular colonies of protothiophiles.
Morphologically, the earliest soleneids are extremely simple, though surprisingly sophisticated in their chemistry. Solenids are characterized by their
tubular structure, with a largely undifferentiated mesenchymal layer between well-differentiated exterior and interior cells.
The digestive mechanism of tube worms is extremely primitive: water, containing prey cells primarily of unicellular protothiophiles and bastrovites, is taken in through the mouth opening, with the anal opening closed. Cells in the digestive layer secrete small amounts of sulfuric acid (H2SO4), formed from a catalyzed reaction of biosynthesized sulfur dioxide (SO2) with hydrogen peroxide (H2O2, a metabolic byproduct of glycolysis). The resulting acidic environment inside the digestive tract denatures the cell membranes of prey, and the resulting nutrients are absorbed by the cells of the digestive lining. The water is then expelled through the anal opening; this peristalsis, though inefficient, provided a measure of motility for the earliest tube worms.
Additions:
* Cell differentiation
* Acid tolerance
* Sulfuric acid-based 'digestive tract'
* Free-floating
Subtraction:
* Unicellular independence
* Non-motile colonies (anchored to rocks, etc)