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The Shieldback evolved from a population of lituslugs that migrated into the sunlight zone. They settled into the cold waters of Hydro and Barlowe. In order for them to survive in these predator-infested waters, the shieldback evolved a large, shield-like shell that covers the majority of its body. The shell consists of red hematite, allowing it to blend in with the red sediments of Hydro and Barlowe. The shell grows from a mantle that is located on an extension of the cephalon. Three simple eyes are located on the cephalon, and protrude from the shell.

The organ systems have also undergone some change. The body cavity that evolved in its ancestor has differentiated into a digestive and circulatory system. Both systems are closely intertwined and form a bundle of tracts. Most of the circulatory system is capable of exchanging nutrients and wastes with the digestive system. Each isomer has a small heart that pumps blood through its respective isomer. Like its ancestor, if an isomer is severed from the body, the exposed parts of its digestive and circulatory system will close off in order to prevent the parent or daughter organism from bleeding out.

The nerve net found in the lituslug has become more centralized, with each isomer having a ganglion. Most of the ganglia are small and are only used when an isomer is severed. When an isomer is severed, the smaller ganglion takes over and begins transforming the isomer into a cephalon. The ganglion in the cephalon is far larger than those of the isomers and is responsible for the regulation of behavior throughout the shieldback.

When a segment is severed from the body either through budding or fragmentation, the isomer will immediately begin to metamorphose into a cephalon. This is done by the ganglion, which sends out signals that encourage the production and release of hormones that encourage the restructuring of the organ systems. Once the metamorphosis concludes with the ganglion transforming into a fully-fledged brain, the signals cease. From there, the cephalon will produce isomers and elongate to form the mantle, which in turn forms the shell. Once the shieldback reaches its maximum size, it will begin reproducing via budding.