Description

Opabinia regalis, an extinct arthropod belonging to the stem group, was uncovered in the Middle Cambrian Burgess Shale Lagerstätte of British Columbia, dating back around 505 million years.

Opabinia was a soft-bodied creature, reaching lengths of up to 7 cm, characterized by a segmented trunk with flaps along its sides and a tail resembling a fan. Its head displayed unique attributes: five eyes, a mouth situated beneath the head and facing rearwards, and a clawed proboscis believed to have transferred food to the mouth. Opabinia likely inhabited the ocean floor, utilizing its proboscis to locate small, soft prey. Only a limited number of well-preserved specimens, fewer than twenty, have been documented. Among them, three Opabinia specimens originate from the Greater Phyllopod bed, constituting less than 0.1% of the community.

Classification and specimen challenges

Opabinia is classified as a lobopod due to its segmented body configuration referred to as "lobes." However, despite sharing some surface-level similarities with later organisms such as trilobites, the lobes of Opabinia appear to have lacked the firm exoskeleton characteristic of arthropods. This pliable body structure has often undergone distortion during the preservation process, resulting in slightly varied reconstructions depending on the specific specimen under examination. Furthermore, owing to the soft nature of its body, impressions of Opabinia sometimes unveil its internal organs. This implies that recognizing and distinguishing these organs from external features demands a keen expertise.

Feeding habits and lifestyle

The manner in which the Burgess Shale organisms were entombed, either by a mudslide or a sediment-laden current akin to a sandstorm, implies that they inhabited the seafloor's surface. Opabinia likely employed its proboscis to sift through the sediment in search of food particles, then transferring them to its mouth. Since no structures resembling jaws are evident, it's presumed that its diet consisted of small, soft creatures. The presence of paired gut diverticula could have potentially enhanced the efficiency of digestion and nutrient absorption. Whittington (1975), while suggesting that Opabinia lacked legs, proposed that it moved by crawling on its lobes and could have potentially achieved slow swimming by undulating these lobes, particularly if it synchronized the motions with the metachronal wave of its lobes. Conversely, he opined that the body's flexibility might not have been sufficient for fish-like undulations of the entire body.