Parasitism by dicyemids in the vampire squid

What is it?

The vampire squid (Vampyroteuthis infernalis) is a small, enigmatic cephalopod living in the dark, oxygen-poor zones of the deep ocean. Like many other cephalopods, it frequently harbours tiny parasites called dicyemids in its kidneys. Scientists have studied this host-parasite relationship for a long time, but it remains mysterious because observing this species in its natural environment is difficult. This infestation is generally considered a discreet association with no obvious visible impact on the animal's health.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Causes and risk factors

The condition is caused by dicyemids (also called rhombozoans), tiny primitive parasites whose taxonomic classification is still debated by scientists—somewhere between simple animals and complex single-celled organisms. These microscopic thread-like worms make their home in the vampire squid's kidneys, where they feed and reproduce using the host's nitrogenous waste as a nutrient source.

All vampire squid appear to be potentially affected, as this parasitic relationship is considered by scientists to be very widespread, even nearly universal, among many deep-sea cephalopod species. No individual risk factors have been clearly identified to date, owing to insufficient studies of wild populations.

Transmission

The exact mode of transmission between cephalopods remains incompletely understood by scientists. It is thought that free larval forms dispersed in seawater may be capable of infesting a new host, but the precise details of the dicyemid life cycle in the vampire squid remain unclear because specimens for study are rare.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

Treatment

No veterinary treatment has been described or is applicable for this infestation in the vampire squid. This deep-sea species cannot be maintained in captivity long-term, and infestation by dicyemids is in any case not considered to require therapeutic intervention given its apparently low pathogenic nature.

Prevention

Possible complications

In most cephalopods studied, dicyemid infestation is considered relatively well tolerated and does not cause visible severe disease. No solid scientific evidence exists for mortality directly attributable to these parasites in the vampire squid. However, a very high parasitic burden could theoretically disrupt normal kidney function and thus waste elimination from the body, an aspect still poorly documented in this deep-sea species.

When to see a veterinarian

Prognosis

The prognosis is generally considered favourable, as dicyemid infestation appears to be part of the normal biology of many cephalopods, with no major demonstrated effects on the survival or reproduction of the vampire squid. However, many unknowns remain, as this deep-sea species is extremely difficult to study in its living state.

Frequently asked questions

References

WOAH — Organisation mondiale de la santé animale (ex-OIE)

Content reviewed by the TunisieVet editorial team · Updated 07 September 2026