It is called the fat innkeeper worm, although in social networks it is known as the ‘penis fish’, given its peculiar elongated structure and with its domed head.
This type of worm is awakening great interest, especially after last December 6, thousands of specimens of this ‘penis fish’ appeared stranded on a Costa Rican beach : a prospect that has been unpleasant for many.
What do we know about this marine worm? Where does it live and how does it behave?
Image: holding a ‘penis fish’ specimen at Bodega Bay in June 2019./Kate Montana
Habitat
The fat perch worm (Urechis caupo ) lives in large U-shaped burrows in sand, mud, and other soft sediments. Their underground homes date back 300 million years. In addition to being old, they are quite long-lived, since they can live up to 25 years.
The perch worm’s shape, which reminds us so much of that part of the male anatomy, has an explanation: it is perfectly designed to glide under wet lands.
Feeding
The innkeeper worm has an interesting way of feeding: it produces a mucous web that captures small pieces of food that float in the water. After a while, it reabsorbs this network again, also swallowing the food that has been trapped in it.
Predators
And who feeds on this repulsive marine worm? It is a delight for bat rays, leopard sharks, and even some marine mammals of a certain size, such as otters , which absorb them to remove them from their burrows. As if it were a snack!
One of the problems that the perch worm has is that the food, shelter, and running water pumped by it attract hosts to its burrow, such as goby fish ( Pholidichthys leucotaenia ) , scaly worms ( Polynoidae ), or some types of crab, with whom he is forced to share space.
Reproduction
Urechis caupo has offspring through sexual reproduction : males and females respectively deposit the sperm and egg in the water, where fertilization occurs. Once the egg is fertilized, it grows into a free-swimming larva until it begins to build its own U-shaped burrow.
Thousands of fat perching worms washed up on Drake Beach in Costa Rica / David Ford.
The invasion of the ‘penis fish’
As we explained at the beginning of the article, thousands of ‘penis fish’ were found stranded on a Costa Rican beach on December 6; but it has not been the only case. Scenes similar to the one in the image above have been seen in other areas, such as Dunas de Pájaro, Moss Landing, Bodega Bay and Princeton Harbor, in recent years.
What is causing this barrage of worms stranded on the beaches? As the photographer and biologist Ivan Parr reports on the baynature.org page, it is very possible that they are the consequences of strong storms , such as those that occurred during the El Niño years: “These storms are perfectly capable of besieging the intertidal zone, break up the sediments and leave their contents stranded on the coast ”, he explains.
Where do we find the ‘penis fish’?
U. caupo is endemic to North America . It usually populates the area it occupies from southern Oregon to Baja California; and most of the sightings have occurred between Bodega Bay, in California, and Monterey, in Mexico.
