The giant deep sea isopod (Bathynomus giganteus) is undoubtedly a unique species. This species belongs to the order Isopoda, that is, they are cousins of the ball bugs that we can find in our gardens. It lives on the seafloor of the cold and deep waters (300-2500 m) of the Western Atlantic Ocean, including the Gulf of Mexico and the Caribbean Sea. Bathynomus giganteus is the first of the described species within the genus Bathynomus, it was described in 1879 by the French zoologist Alphonse Milne Edwards after the isopod was found in fishermen's nets off the coast of the Dry Tortugas in the Gulf of Mexico. Historically it has been described from other oceans beyond the Atlantic, but today these reported species are recognized as other species within the genus Bathynomus.
Bathynomus giganteus is an unusually large species compared to what is usual within the order Isopoda. This is due to an effect known as avisal gigantism, whereby invertebrate animals that inhabit deep, cold waters tend to grow larger and have greater longevity. Its body is divided into three distinct regions: a head (cephalon), a thorax and an abdomen (pleon); and can reach a total length of between 19 and 36 cm, although specimens up to 50-76 cm in length have been reported. The eyes are triangular in shape, widely spaced, large in size and composed of a multitude of facets (up to 4,000 according to some publications). When light bounces off them, they have a highly reflective coating on the back, which causes them to glow brightly. This, together with their unusual gigantism, gives Bathynomus giganteus specimens a frightening appearance, although this is not at all consistent with their calm demeanor.
Bathynomus giganteus uses its 7 pairs of jointed legs to explore the vast and inhospitable expanses of the seafloor. It has two pairs of antennae on its front, one short and the other much longer. These antennae allow them to detect their food at great distances. The diet of Bathynomus giganteus consists mainly of bottom-dwelling debris, although they may occasionally prey on other live and generally slow-moving prey if given the opportunity. Approximately 50-60% of their diet consists of vertebrates remains, followed by 30% cephalopods, 10-20% decapods and 5-10% other smaller isopod species.
Reproduction of Bathynomus giganteus is by egg laying. Mature females develop a pouch known as a marsupium, where the eggs are stored until the young are ready to emerge as miniature adults, known as mancas, skipping a larval stage altogether. Females are many times larger than females of other isopods, yet carry approximately the same number of eggs in their marsupium. The eggs therefore show an increase in size that appears to be almost proportional to the increase in body size.
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