Microcalyculus

"This descendant of Hurdia has shrunk to much smaller sizes, occupying a similar niche to our krill and shrimp today. Most species of Microcalyculus can be found together in large swarms during the bloom seasons feeding on algae and plankton, while simultaneously being feasted on by larger carnivorous Cambrian creatures. These have completely gave up their arms, instead grabbing food and sucking it in with their elongated mouths. Their tails have also shortened in some species, as those will take advantage of the ocean currents, using those as their primary traveling methods."

-DinoCoat

The Microcalyculus has a very similar body plan to the original Hurdia and is depicted in the coloration of a krill shrimp. It has a shortened tail and a singular, elongated mouth with filters behind it.

Trivia

 * Microcalyculus evolves into Ausculumanus in Gen 2.