The Ghost Shrimp, Pestarella tyrrhena is a species of thalassinidean crustacean that dwells in shallow, sandy tunnels of the ocean floor in the Mediterranean Sea and northern Atlantic Ocean. Initially, the crustacean derived its name from the Tyrrhenian Sea where it inhabited. The crustacean was called formerly Callianassa tyrrhena, but current common terminology for the species is Ghost Shrimp or Mud Shrimp. Fishermen in the Mediterranean have used it as bait for at least 200 years because it is the most prevalent thalassinidean.
The crustacean is small in size, measuring up to 3 inches long with a whitish or greenish-grey soft exoskeleton with pink or blue spots on it. It has beady eyes on short stalks and two large, incongruent claws. On the head of the crustacean are several maxillipeds arranged to form an operculum. The terminal segment is very short, and the rostrum is so tiny it is almost non-existent.
Rapid development with few distinguishing stages takes place during the larval state. After eggs hatch, they enter into a zoeal stage, followed by a second zoea and then into megalopa stage just before transforming into adulthood. Planktonic larvae develop at such a fast rate so that they do not have to remain exposed too long before settling down in their secure muddy substrates of their adult habitat. Low salinities slow down larval development, which is why this species avoids estuaries and the Baltic Sea. Warmer temperatures are favorable to growth, resulting in shorter seasons of reproductive activity in northern areas of its range, and longer seasons in warmer places of the south.
The burrow system in which the crustacean comprises is quite complex. They tunnel down into the sediment about 2 feet deep, and then dig spiraling central shafts about an inch wide, along with one or more shallow U-shaped, 0.5 inch shafts that direct up to the surface of the sediment as funnel-shaped indentions. Numerous seagrass filled side-chambers have been found linking these various shafts. The crustacean is always busy creating new tunnels and letting the old ones fill in. They receive their nutrition from the foraminiferans and algae that reside on the walls of the tunnels, as well as remnants of organic matter collected on the sediment and inside debris chambers. The activity within the tunnels causes the walls to become enriched with three times the ambient number of nematodes and more than 100 times the number of foraminiferans than what is in the encircling sediments.
The species is a parasitic host to the isopod lone thoracica and the barnacle Parthenopea subterranean.