Coosella Trilobite with Selkirkia Worm

Description: This trilobite is a rare member of the family Crecicephalidae known as Coosella It has not as yet been scientifically described, so the species has not yet been named. There are 2 types known from the region, commonly called Type 1 and Type 2 that differ in that Type 1 has a straighter thoracic profile and a wider pygidium. The tapering profile may indicate that this one is what is termed Type 2 or that the body morphology changed with ontogeny. This is a diminutive example, seen here in association with the shell of Selkirkia. In the Burgess Shale, only about 20% of the shells of Selkirkia have been preserved with the animal within. A portion of the empty shells are found preserved with Agnostid trilobites present. Is the association here happenstance or the result of juvenile Coosella imitating the habits of their Agnostid cousins?.