PART 6 of the Burgess Shale Fossils: 

Pikaia gracilens Walcott (1911, pl. 20, figs. 1. 2) is a legless, soft-bodied, ribbon-like animal, up to 2 inches (5 cm) long, whose closest relatives are the sea-lancelet Branchiostoma and the zebrafish. Although Pikaia was originally thought to be an annelid worm, it is not because it is unsegmented. In the 1970s, its remains were restudied and a notochord was discovered = a rod running along its back and resembling a backbone-like structure. In addition, there are markings on the sides of its body, and they resemble myomeres (chordate muscle bundles) found on living chordates (backboned animals). As a result of this discovery, Pikaia is now classified as probably as a basal, or “stem chordate,” ancestral to all back-boned animals (including fish to humans). In the 1970s, it was reported that Pikaia probably swam like an eel, but, in recent years, researchers have concluded that it was probably a slower swimmer and less flexible than an eel.

Key Reference: 

Walcott, C.D. 1911. Cambrian geology and paleontology. II. No. 5. Middle Cambrian annelids. Smithsonian Miscellaneous Collections. 

 PART 5 of the Burgess Shale Fossils:

Anomalocaris canadensis Whiteaves, 1892 is another part of my discussion on “Middle Cambrian Life: Exceptional Fossils” (Lagerstätt), from the Burgess Shale Member of the Stephen Formation, British Columbia, Canada. Genus Anomalocaris Whiteaves, 1892 ranges from the Middle to Late Cambrian (approximately 505 to 520 million years ago) and has been found at various places, but its principal locality is the Burgess Shale.

Please refer to my earlier post [dealing with the fossil Opabinia] for details about the kit of plastic replicas of some of these fossils, including Anomalocaris canadensis.

Anomalocaris (pronounced “ah-NOM-ah-LO-kar-is”) is a Greek word, meaning "unusual shrimp." Anomalocaris belonged to a group of ancestral arthropods, referred to as “stem-group” of arthropods.

Three views are shown below of a plastic replica of Anomalocaris canadensis: dorsal, side, and ventral, in that order. This replica is 5 inches (12 cm) in length. It is just a fraction of the maximum size of Anomalocaris, which was about 3 (one meter) to 4 feet in length.

Anomalocaris was a soft-bodied, bilaterally symmetrical and flattened animal, with lateral
flaps (attached to gills). Its streamlined body was well designed for swimming. The posterior half of its body was segmented and therefore flexible. On the underside of its body, Anomalocaris had a sturdy mouth, with jaws consisting of numerous plates (oval cones). The mouth was next to two large claws. The body also had two stalked compound eyes, which were advantageous for hunting purposes. 

Anomalocaris was an “apex predator” that probably preferred to eat trilobites.

Determining exactly the type of animal that Anomalocaris represented has a complex history, spanning 100 years! This is because only separate parts of its body were originally found, in a piecemeal fashion, at scattered localities. It was not until workers found enough of these disarticularted parts to finally figure out what the whole animal actually looked like. Thus, each part was described originally as a separate animal. For example, its jaws were described as a jelly fish, and one of its claws was identified as a shrimp. Eventually, a complete specimen was found, and that is when “it all came together.” 

“YouTube” has some really excellent animations about Anomalocaris. I strongly encourage you to “Google them.” They are readily available and extremely easy to use, without any  complicated downloads or troublesome links. Just click on the animations. They are worth watching!