Transcript:

Today on Animal Fact Files we’re discussing tantulocarida which is a group of tiny parasitic crustaceans. This group doesn't even have a common name, so we'll be referring to them as tantulocaridans throughout this episode, but they're known as tantulocarids, as well. These animals are so small, they almost exclusively must be viewed via microscope, and, unfortunately, there isn't much video of them online. We've compiled what we could find and are allowed to use here.

The smallest known living arthropod is classified in this group of animals. It's only 85 micrometers long. If an inch was divided into a thousand equal parts, this species would only take up three parts. A whole group of them could ride around on the back of an ant! Of course, not all of the approximately 40 known species are this tiny; however, they're all considered minute because they're all less than a millimeter long, at least for most of their life cycle. Some sites suggest a common name for them could be minute parasitic crustaceans for this reason, but this isn't universally used.

Tantulocaridans likely live in marine waters around the world, however their small size makes them easy to overlook. They've been observed in the Atlantic, Pacific, and Arctic oceans as of this recording, and they are most often seen on crustaceans that live on or right above the ocean's floor including isopods, copepods, amphipods, and more. While most frequently associated with deep-sea dwelling creatures living at depths of 6,500 feet (2,000 m) or more, they're also seen in water as shallow as 72 feet (22 m)! Larval tantulocaridans, prior to attaching to their host, can also be found in underwater sediment such as sand.

These parasites utilize their host for nutrients. Like their relatives, the barnacles, tantulocaridans cement themselves to a single place for the remainder of their life. They're sessile animals. Unlike barnacles, however, tantulocaridans position themselves on other crustaceans and take nutrients from their host. After settling, the tantulocaridan pierces the host's shell and creates a hole down to the host's flesh. Through this, the parasite sends out root-like tendrils that remain in place from then after. The roots absorb nutrients from the host in a process not fully understood by science as of this recording. This, in turn, helps develop the parasite's offspring.

Somewhat like jellyfish, tantulocaridans have a double life cycle. There are fully asexual individuals that produce clones of themselves through parthenogenesis– they can reproduce without the need of fertilization; and there are sexually reproducing individuals that are divided into male and female sexes. The sexually reproducing individuals are rare and have not yet been observed alive. Asexual individuals have a sac-like structure that expands to accommodate their offspring. These are the largest of the tantulocaridans and can reach 2 millimeters in length! When fully developed, the larvae simply burst through the mother's body and settle to the seafloor. Like the octopus, tantulocaridans are semelparous– they reproduce only a single time before perishing.

The larvae are free-living for a time until they find a host in which to settle. How this happens is still somewhat of a mystery because tantulocaridan larvae don't have eyes or antennae! What's more, unlike most arthropods who shed their exoskeleton as they develop, tantulocaridan larvae attach to the host and change their body for reproduction without going through an instar. There are times that the attached larva instead forms a sexual offspring that is either male or female. These are grown inside the attached larva's body, but instead hatch as a sexual adult with legs capable of grasping and sensory antennae. In fact, male tantulocaridans are described to be similarly endowed to their barnacle relatives!

There's still a lot to learn about these minute parasitic crustaceans such as how long they live, what kind of threats they face, and even their range and number of living species! This video has been a shallow dive into an otherwise deep pool that is this enigmatic group of arthropods. For more facts on tantulocaridans, check out the links below. Give a thumbs up if you learned something new today. Thank you to our Patrons SpikeSpiegel93, Dad, and everyone else for their support of this channel! And thank you for watching Animal Fact Files!