Skeleton Shrimps: The Bizarre ‘Ghost’ Amphipods Hiding in Plain Sight

Lawson Wood takes a closer look at one of the more-bizarre denizens of the deep – skeleton shrimps 

What Are Skeleton Shrimps?

Skeleton shrimps are often referred to as ‘ghost shrimps’ and although they are arthropods and members of the crustacean super family, they are not actually shrimps, rather they are a very select group of entirely marine amphipods.

Common Skeleton Shrimp Species Found Around Our Shores

There are some 15 or so different species found around our shores and apart from close scientific study under a microscope, they are quite difficult to tell apart. The two main species found locally and on most dives at all times of the year are the linear skeleton shrimp (Pseudoprotella phasma) and the stick skeleton shrimp (Caprella linearis). Both are very similar and grow to around the same maximum size of 25mm-30mm long.

Life Cycle, Reproduction and Behaviour

The species are sexually dimorphic (males are larger than females), both have two pairs of antenna and the males are able to detect the females’ pheromones with these antenna. Once they get together, the male will either ride on the female’s back or certainly clasp it tight until the female moults. Once she moults then the male is able to pass its sperm package to the marsupium in the female and, once this has been achieved, he releases her!

After a few hours, the female passes her eggs into the marsupium, where they can be fertilised. The eggs will hatch into tiny versions of the parent and will stay in the marsupium where they are brooded for a few days, before being released.

Habitat and Predators

Like other similar species, the young often clamber onto the adults’ back, before making their way onto a suitable habitat such as dead man’s fingers (Alcyonium digitatum) and various types of hydroid.

They live for around one year and during that time will moult around 20 times. They are active predators of passing plankton and are, in turn, predated upon by pollock and various species of wrasse. The northern species can be found from temperate to polar regions in the northern hemisphere, but they are found as far away as New Zealand and in the eastern Mediterranean.

Linear Skeleton Shrimp (Pseudoprotella phasma)

The linear skeleton shrimp (Pseudoprotella phasma) was first described and identified by the naturalist George Montagu in 1804 and is the easier skeleton shrimp to identify. Being that much larger in general terms, it has a noticeable spine at the back of the head, as well as on the first body segment and three spines on the next body segment. It has small gills under the third and fourth segments and prefers large hydroids such as the sea beard (Nemertesia antennina), which live on substrate in more-active water movement areas, with plenty of plankton floating by to eat.

Stick Skeleton Shrimp (Caprella linearis)

First described by Carl Linnaeus in 1767, the stick skeleton shrimp (Caprella linearis) tends to be smaller with an average of only 15mm long and can often be found in huge numbers covering dead man’s fingers, where they may actually resemble the feeding polyps of this soft coral, thus helping with its camouflage against predators. This species is usually more colourful, with cream or pale orange or brown predominating.

Being so small undoubtedly helps them to hide away from predators and underwater photographers, but if you just slow down a little bit more and look closely among the hydroids and soft corals, you will be rewarded by these wonderful little critters.

Frequently Asked Questions