Giant Deep-sea Isopod (Nature Techni Colour by Kitan Club)

Review of the Kitan Club Nature Techni Colour Giant Isopod, Bathynomus giganteus, Milne-Edwards, 1879. The figure was released in late December 2014. Bathynomus giganteus is the largest known species of isopods although it has been considered that other species within the same genus may rival it in size. The remarkable size, roughly that of a loaf of bread at usually between 190 and 350 mm (though some specimens may get considerably larger), is what sets it apart from the majority of isopods. Like the Colossal Squid, Mesonychoteuthis hamiltoni, and the Giant Squid, Architeuthis dux, the giant isopod is often mentioned as an example of deep-sea gigantism. However, this term may lead to a misconception of what size deep-sea organisms usually attain (and it is dependent on how deep sea is defined), actually many of them are smaller on average than their shallow-water relatives. On the other hand species of some invertebrate groups tend to attain very large sizes especially in cold waters – which is why in these groups giant species can also occur e.g. on the Antarctic continental shelf.

Bathynomus species belong to the Cirolanidae, a family of carnivorous isopods which are usually scavengers but are also known to attack fishing trawls. And while B. giganteus is generally regarded as a typical deep-sea organism it should be noted that it lives in the shallowest parts of what we usually define as deep sea and it has been recorded from depths between 310 and 2140 m – with a majority of records between 365 and 730 m. So this is a species which usually lives on the upper continental slopes, the seafloor that connects the shallow continental shelf with the much deeper abyssal plains. There is still some light reaching the seafloor at the upper continental slopes and B. giganteus has very large, reflective (they have a silvery shine in life) compound eyes with thousands of ommatidia (while most isopods of the deeper abyssal plains are actually eyeless). Although not regularly sampled, the giant isopod may actually be quite an abundant species but population estimates and even their densities are difficult to evaluate. So it’s understandable that the species has also not been evaluated (“NE”) by IUCN. Live specimens of Bathynomus species are currently displayed in several aquaria in Japan [editor’s note: in the US too; I have seen them in Chicago and we have them here in Utah as well].

The figure itself is about the size of an average mature specimen at 287 mm length and is made of hollow PVC. Despite its size the weight is merely 346 g. It is about as accurate as a plastic figure can be, i.e. it rivals scientific models in quality and accuracy: All but the first pereonite (thoracic segments that carry the walking legs) show lateral coxal plates, the number and shape of leg segments is correct, each of the five pleonites (rear thoracic segments behind the pereonites) bears a pair of (simplified) biramous leaf-shaped limbs, the pleopods (which are used for respiration and swimming), and the pleotelson (the shield-like terminal “segment”, actually it’s a fusion of two segments) has a correct number of spines. The head shows a small antenna 1 (often named “antennule”) and a larger antenna 2, as well as very detailed mouthparts.

Much attention was given to reflect a correct morphology, something still many arthropod figures get completely wrong, but in this respect the figure is flawless. However, on a large, high quality (and expensive) figure even more and sharper details on the legs, e.g. fringes of setae, would not have been impossible to achieve while other parts, e.g. those leaf-like pleopods, are just too much simplified for a figure of this size. Sadly, the eyes are plain black instead of metallic silver. Other than that it is an impressive figure which (at least for me) justifies its high price, although I have to admit that I am particularly biased towards deep-water isopods.

Editor’s epilogue: This figure was promptly retired and became very expensive very fast on eBay. Luckily, after Ikimon took over the Nature Techni Colour line, they released this figure again in 2018 (when I got mine).