Ottoia

Ottoia is the most abundant priapulid of the Cambrian Burgess Shale formation of British Columbia and Wheeler Shale formation of Utah dating from the Mid-Cambrian of around 550 million years ago. It is a stem-group priapulid worm.

Morphology
Ottoia specimens are on average 8 centimeters in length. Both length and width show variation with contraction; shorter specimens often being wider than longer ones. The characteristic proboscis of priapulids is present at the anterior, attached to the trunk of the animal, proceeded by the "bursa" at the posterior. The organism's body is bilaterally symmetrical, however, its anterior displays external radial symmetry. Like some other modern invertebrates, a cuticle restricts the size of and protects the animal. The everted proboscis of Ottoia is armed from the distal end by spinules, spines, and hooks. The spinules appear in varying shape and size, classifiable into four types which are comparable to the teeth of modern priapulids. Posterior to the spinules, separated by an unarmed region, are about 40–50 spines. Further posterior are hooks, relatively well spaced from each other and arranged like the five dots on a domino or die. The proboscis most likely would not have been fully everted (turned inside out) when feeding.

The trunk hosts the internal organs of the organism, divided into seventy to a hundred annulations of varying spacing, depending on curvature and contraction. The posterior displays a series of hooks, which likely acted as anchors in burrowing. Muscles support the animal and retract the bursa and proboscis. A gut leading from the anus in the bursa to the mouth in the proboscis runs through the trunk's spacious body cavity, and a concentration of gut muscles serve the function of a gizzard. A nerve chord runs down the organism's length. In addition to the other organs, it is possible Ottoia contained urogenital organs in its trunk. There is no evidence of a respiratory organ, though the bursa may have served this purpose.

Ecology
Ottoia was a burrower that hunted prey with its eversible proboscis.[3] It also appears to have scavenged on dead organisms such as the arthropod Sidneyia.[4]

The spines on the proboscis of Ottoia have been interpreted as teeth used to capture prey. Its mode of life is uncertain, but it is thought to have been an active burrower, moving through the sediment after prey, and is believed to have lived within a U-shaped burrow that it constructed in the substrate. From that place of relative safety, it could extend its proboscis in search of prey. Gut contents show that this worm was a predator, often feasting on the hyolithid Haplophrentis (a shelled animal similar to mollusks), generally swallowed them head-first. They also show evidence of cannibalism, which is common in priapulids today.