New family of copepods discovered in the deep sea of the Atlantic

An international research team, including Dr. Nancy Mercado Salas from the Leibniz Institute for the Analysis of Biodiversity Change (LIB), has described a new family of copepods (Copepoda). The discovery was made at a depth of more than 2,500 metres in the Irminger Basin, south-east of Greenland, and provides new insights into the evolution of a group of animals that has hitherto been poorly understood.

The so-called Monstrilloida are considered one of the most unusual groups of marine copepods. Their larvae live as parasites within other marine organisms, whilst the adults swim freely in the water and do not feed. Due to their distinctive anatomy – they lack, amongst other things, the antennae and mouthparts typical of crustaceans – their phylogenetic classification has long been the subject of scientific debate.

Since 1852, only a single family had been known within the order Monstrilloida: the Monstrillidae. The newly described family Thalassodoridae therefore represents a significant expansion of the known phylogenetic tree of this group of animals. The description was based on both detailed morphological studies and genetic analyses.

The only specimen known to date was collected at a depth of 2,537 metres. It exhibits several characteristics that differ markedly from all previously known Monstrilloids. These include exceptionally long, rear-pointing antennules, as well as previously unknown body structures that could provide new insights into the evolution and lifestyle of these animals.

“The discovery of the new family Thalassodoridae shows that the deep sea still harbours life forms previously unknown to science,” says Dr. Nancy Mercado Salas of the LIB. “It also opens up new perspectives on the biology, morphology and evolution of this extraordinary group of copepods.”

The scientific name also reflects the uniqueness of the find: the newly described species, Thalassodoron bathyale, roughly translates as ‘gift from the deep sea’ – a reference to the unexpected discovery of this extraordinary crustacean.

Researchers from Germany, Italy and Mexico took part in the study. The findings were published in the journal PeerJ.

Publication

Suárez-Morales, E., Martínez, A., Martinez Arbizu, P., Khodami, S., Mercado-Salas, N. F. et al. (2026): A new family of the order Monstrilloida (Copepoda) from deep waters of the North Atlantic supported by morphological and genetic evidence. PeerJ 14. DOI: 10.7717/peerj.21176.