Isopod crustaceans, including members of the deep-sea genus Bathynomus, are distantly related to their better-known decapod relatives: the crabs, shrimp, and lobsters.
Bathynomus yucatanensis, body length 26 cm: (a) dorsal view, (b) ventral view. Each square is 1 cm on a side. Image credit: Huang et al., doi: 10.1080/00222933.2022.2086835.
Bathynomus is the dominant scavenging isopod genus in the tropical and temperate deep sea.
First described in 1879 by the French zoologist Alphonse Milne-Edwards, the genus includes almost 20 living and four fossil species.
These isopods are abundant in the cold, deep waters of the Atlantic, Pacific and Indian Oceans.
They are well known because of their gigantism, with some species reaching large sizes in excess of 30 cm (11.8 inches) length.
They are noted for their resemblance to the much smaller common woodlouse, to which they are related.
And, just like woodlouse, although they perhaps look a little scary, they are completely harmless to humans.
“In the 1970s, a deep seabed trawl fishery emerged in Taiwan,” said National University of Tainan’s Dr. Ming-Chih Huanga and colleagues.
“Fishermen in what is now the Ruifang District of New Taipei City on Taiwan’s north-eastern coast began to eat Bathynomus, prepared by steaming them like lobsters or crabs and calling them ‘Tua Hay-Shi’ (‘big sea lice’ in Taiwanese).”
According to scientists, Bathynomus can be divided into ‘giant’ species where the adults generally are between 8 and 15 cm (3.1-5.9 inches) long and ‘supergiants’ where the adults are up to 50 cm (19.7 inches) long.
One of the supergiant species, Bathynomus giganteus, measures between 19 and 36 cm (7.5-14.2 inches). An individual claimed to be 76 cm (30 inches) long has been reported in the media, but the largest confirmed was 50 cm (20 inches) in length.
The newly-discovered giant Bathynomus species, named Bathynomus yucatanensis, is around 26 cm (10.2 inches) long.
“Bathynomus yucatanensis was initially thought to be a variation of Bathynomus giganteus,” the researchers said.
“But closer examination of the specimen, which was captured in a baited trap in 2017 in the Gulf of Mexico off the Yucatán Peninsula at around 600 to 800 m (1,969-2,625 feet) down, revealed an array of unique features.”
“Bathynomus yucatanensis is morphologically distinct from both Bathynomus giganteus and Bathynomus maxeyorum,” they added.
“Compared to Bathynomus giganteus, Bathynomus yucatanensis has more slender body proportions and is shorter in total length and the pereopods (thoracic limbs) are more slender. It also has longer antennae.”
“The two species have the same number of pleotelson spines. These spines protrude from the tail end of the crustacean.”
“Compared with Bathynomus maxeyorum, the most distinctive feature is the number of pleotelson spines — 11 spines in Bathynomus yucatanensis versus 7 in Bathynomus maxeyorum.”
“The blotchy, creamy yellow coloration of the shell further distinguished it from its grayer relatives.”
The discovery of Bathynomus yucatanensis is described in a paper published this week in the Journal of Natural History.
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Ming-Chih Huang et al. 2022. A new species of Bathynomus Milne-Edwards, 1879 (Isopoda: Cirolanidae) from the southern Gulf of Mexico with a redescription of Bathynomus jamesi Kou, Chen and Li, 2017 from off Pratas Island, Taiwan. Journal of Natural History 56: 13-16; doi: 10.1080/00222933.2022.2086835
