Eyes Under Puget Sound: Critter of the Month — The "Unicorn" Shrimp

June’s tiny crustacean critter doesn’t have a common name, but it does have a fascinating projection on its head, so we’re informally referring to it as the Unicorn Shrimp!

Move over, narwhal — there’s a new Unicorn of the Sea

Nebalia pugettensis is part of a group of animals called benthos, because they live on or below the seafloor, also known as the benthic zone. N. pugettensis is a unicorn in more ways than one — besides the unicorn-like rostrum or snout, it is also a rarity in our benthic samples, although we know it occurs in all areas of Puget Sound. This might be because it can move around and avoid our grab of samples or because it just doesn’t exist in high abundances. Either way, its appearance is cause for excitement here in the benthic lab. 

Critter with transluscent clamshell-shaped body has fuzzy shrimp-like legs, a pointy lobster-like tail, beady eye, walrus moustache, and fea

Nebalia pugettensis specimen from Padilla Bay, Wash.

N. pugettensis is fairly tiny, maxing out at about 7 mm. Its body consists of three sections: 

  • Head (front)
  • Thorax (middle) 
  • Abdomen (back)

Closeup of critter indicating with printing the "carapace," body; "rostrum," horn; the eye, the "antennae," walrus mustache and front leg; a

N. pugettensis carapace, lateral (side) view.

A bivalved carapace (almost like a clam shell) covers the head, thorax, and eight short appendages called thoracopods. Interestingly, the thoracopods function like a set of lungs, each with a gill to facilitate gas exchange. The carapace pitches in as an additional large respiratory membrane, and also pulls double duty as a brood pouch for developing embryos, which hatch out looking like adorable mini-adults.

Ancient history

N. pugettensis belongs to a primitive group of crustaceans called leptostracans (pronounced “LEP-tow-STRA-cans”). These shrimp-like marine critters date back millions of years, with about 40 species alive today. 

Some leptostracans can withstand extreme habitats, making their homes in places like deep sea hydrothermal vents and marine caves. Some can also tolerate low oxygen, nutrient enrichment, and other conditions that are characteristic of poor environmental quality. 

Words indicate, "thoracopods" and "pleopods." The thoracopods are diaphanous membranes, and the pleopods look like snail legs.

N. pugettensis thorax and abdomen with the carapace and head removed, lateral (side) view.

Stirring up trouble

Arising from the leptostracan abdomen are six pairs of feathery pleopods, used to stir up bottom sediments and suspend food particles in the water. Pleopods also come in handy for nighttime swims, which must be a relief after long days spent buried face-first in the mud. Leptostracans swim by beating their pleopods and telson (tail), with its spiny paddles, or caudal furcae

Closeup view of tail end with words indicating a "telson" appearing like the ferrule of a paintbrush, and "caudal furca," coming from the te

The tail end of N. pugettensis, dorsal (top) view.

Naked news

Unfortunately, the Puget Sound Nebalia isn’t currently counted as a true species. Nebalia pugettensis has been declared a nomen nudum, or “naked name”, meaning that a complete description of the species has yet to be published. Some taxonomists call it a species complex, meaning that it might actually be more than one species. Sounds like more work is needed to iron out the taxonomic wrinkles within this group — and to give the little nameless crustacean a permanent moniker! 

 

Critter of the Month

Our benthic taxonomists, Dany and Angela, are scientists who identify and count the benthic (sediment-dwelling) organisms in our samples as part of our Marine Sediment Monitoring Program. We track the numbers and types of species we see in order to understand the health of Puget Sound and detect changes over time.

Dany and Angela share their discoveries by bringing us a Benthic Critter of the Month. These posts will give you a peek into the life of Puget Sound’s least-known inhabitants. We’ll share details on identification, habitat, life history, and the role each critter plays in the sediment community. Can't get enough benthos? See photos from our Eyes Under Puget Sound collection on Flickr.