This is certainly one of the most overlooked animals in the ocean, and the reason is that frankly, they aren’t much to look at. It’s pretty easy to ignore vague, almost microscopic spheres of organized debris with wing-like structures in the center. However, there’s a tiny animal living inside this bubble of schmutz. Enter the larvacean, a tadpole-shaped tunicate also known as an appendicularian.

Yet another version of the ocean’s many grazers, its job is to filter and consume phytoplankton, protists, bacteria, detritus, and perhaps even colloidal dissolved organic carbon.

How small can you get? Less than two millimeters long, a larvacean is no more than a trunk and a tail. The trunk houses both male and female sex organs together, glands for producing its mucous house, a mouth, and other standard issue organs. The muscular tail has a flexible rod for support and a nerve cord.

A naked larvacean.

Photo taken from http://palaeos.com/vertebrates/chordata/chordata.html#Oikopleuridae

From glands on its head, larvaceans secrete a feeding house of protein and cellulose, which contains a complex mucous net. As the tail undulates, water is drawn first onto mesh prefilters, which exclude large particles. Beyond the incurrent filters, an even finer mucus network sieves and concentrates food particles smaller than a micron, smaller than 1/1000th of a millimeter! Besides being a wonder of nature, the net is possibly the only attractive thing about the animal.

This drawing shows the direction of the water currents. The mouth of the animal is connected to the mucous net by a thin feeding tube.

Phil and I found ourselves in a storm of these last Sunday. There had to be millions. How wide was the swath? From where did they originate? Are they concentrated into dense swarms by currents and/or shear layers?

Note the blue larvacean trunk. Within the external mucous sheet are 2 sets of feeding filters.

Larvaceans periodically discard their feeding houses, abandoning anywhere from 3 to 12+ houses per day. Opinions differ as to the reason for this. It was commonly thought that houses are vacated only after clogging or wearing out, but studies show that the tiny animals are always in production mode. They have a spare house secreted and ready to go; all they have to do is inflate it with water.

Larvaceans have a tremendous impact on the marine environment. Their feeding houses trap bacteria, cyanobacteria, ciliates, and flagellates. Particulates remain embedded in discarded structures, which provide a habitat or food source for other organisms. Billions and billions of cast-off houses contribute to marine snow and provide vertical transport of organic matter to the abyssal depths, where it can be utilized by other organisms.

It's a sticky little house!

The shape of the feeding net appears to differ between species.

This is probably an Oikopleura that sports a festive yellow and blue trunk, and pale blue tail.

Fritillaria sp., perhaps.

An ellipsoidal or ovoid house belonging to a different species.

Although larvaceans aren’t the most glamorous photo subjects, scientific interest in them is keen because of their important role in the ocean carbon cycle.

This link will take you to larvaceans in action.

• Living larvaceans up close.

• Re: A very, very, very fine house. Gabriel Gorsky 02:55:59 08/20/20 (0)
• Re: A very, very, very fine house. Linda Blanchard 09:13:18 02/21/13 (0)
• Re: A very, very, very fine house. Scott S. 07:41:26 02/21/13 (0)
• A Wonderful Presentation Patrick 19:36:33 02/20/13 (0)
• Re: A very, very, very fine house. Dr. Bill Bushing 22:23:30 02/19/13 (0)