Hyoliths

You have become a Hyolith.  There were many species of hyoliths, but all took the form of a long conical or triangular shell, with a shell cap, and two helens which enabled them to stand up to feed with a crown shaped filter mouth.

You are first found in the early Cambrian period, over 500 million years ago.  However, your numbers appear to dwindle during the Permian period, up to 250 million years ago, possibly due to increasing acidity of the oceans making it hard to make enough shell material for your lifestyle.

At the end of the Permian period is the Permian-Triassic extinction event - the biggest extinction of species in the history of the Earth.  The cause of the P-T extinction is still debated, but we know that 90% of species didn't survive it.

You, already declining, were one of them.