Rhynchocinetidae

The Rhynchocinetidae are a family of small, reclusive shrimp. They are often called hinge-beak shrimps. This name comes from their unique rostrum. A rostrum is a beak-like part on the head. In this family, the rostrum is hinged. It is partially or completely articulated with the carapace. This means the beak can move in several ways. This physical trait is the basis for their scientific name. Rhynchocinetidae means movable beak.

These crustaceans are very colorful. Most members show red and white patterns or bands. Their bodies have several specialized parts. The first pair of chelipeds, or claws, are quite robust. The second pair of chelipeds is smaller. The carpus of this second pair is undivided. Both pairs of claws have a special feature. They have a bundle of spines at the tips. When the shrimp retracts these spines, they form a basket-like cage.

In many species, males look different from females. This is especially true in larger, older individuals. In these males, certain parts grow much larger. The first pair of chelipeds becomes exceptionally large. The third pair of maxillipeds also grows significantly. These parts are much bigger in proportion to the rest of the body than in females. This specialized growth is a distinct feature of the males in this family.

Scientists divide the Rhynchocinetidae into two distinct genera. These are Cinetorhynchus and Rhynchocinetes. They can be told apart by looking at their shells. Members of Rhynchocinetes have two acute teeth. These teeth sit on the central carina of the carapace. They also possess a supraorbital spine. They do not have spines on the fourth and fifth abdominal somites.

Cinetorhynchus has a different set of physical traits. This genus has three teeth on the carapace. It does not have a supraorbital spine. Instead, it has a single spine on the margins of the fourth and fifth abdominal somites. These specific anatomical details allow scientists to classify them correctly. The hinged rostrum may also help them survive. It might allow them to wedge into crevices. This could prevent predators from dislodging them.

The way we classify these shrimp has changed over time. Historically, scientists thought there was only one genus. They believed there was only Rhynchocinetes. This genus was divided into two sub-genera. However, a scientist named Holthuis changed this in 1995. He elevated the subgenus Cinetorhynchus to a full genus. He made this decision based on morphology, which is the study of the shape of organisms.

These shrimp live in many different environments. They inhabit both tropical and some temperate waters. They can be found in the littoral zone near the shore. They also live down on the continental shelf. You can find them in coral reefs and rocky reefs. One specific species is Cinetorhynchus rigens. This species lives in Bermuda. It is a nocturnal animal. This means it hides in crevices during the day.

We are still discovering much about their biology. The study of their ecology is quite limited. In Bermuda, researchers used baited traps to study Cinetorhynchus rigens. They found the shrimp were not attracted to the bait. However, they learned what the shrimp eat by looking at faecal pellets. These pellets contained algae and sponge spicules. They also contained fragments of mollusc shells. This shows they feed on a variety of reef materials at night.