Well this is confusing...I googled to see what the difference was.
OVERVIEW:
It is easy to see why the Scarlet Reef Hermit Crab is one of the most popular reef maintenance animals. Paguristes cadenati is very hardy and requires minimal care in a well-established system. More importantly, however, these small hermit crabs have a voracious appetite for detritus and algae. In fact, they are particularly fond of nuisance algae of the filamentous, hair, and slime varieties, as well as cyanobacteria. Finally, unlike some hermit crabs, most Scarlet Reef Hermit Crabs are very peaceful towards their tankmates.
Also known as the Red Reef or Red Legged Hermit Crab, the Scarlet Reef Hermit Crab is named for its bright red legs, which are contrasted by their yellow face. Native to the reef faces and coral rubble of the Caribbean and Western Atlantic, these active scavengers can consume large amounts of animal matter and algae. Despite their large appetites and constant feeding habits, the Scarlet Reef only grows to an adult size of 1-1/2" in length.
In the home aquarium, Paguristes cadenati is best kept in an established reef system with ample algae supplies. However, they will eat almost anything, including fish food and invertebrate diets. If algae levels are insufficient, supplement their diet with dried seaweed and other marine foods.
Adding to the confusion, another site says this..I notice the latin names are not the same:
Clibinarius diguetti "Red Leg Hermit Crab"
The Red Leg Hermit Crab is an excellent algae eater for any aquarium. They are one of the few hermit crabs that may eat cyanobacteria red slime algae and are considered one of the staples of marine aquarium "clean-up crews".
Most hermit crabs are scavengers. Some smaller hermit crabs will feed on algaes like nuisance hair algae while larger hermit crabs are scavengers and carnivores. Most hermit crabs are opportunistic - they will not actively hunt for a fish or active invertebrates but will prey on sick, dead, or dying individuals. Only the larger hermits like those from the genuses Aniculus, Dardanus, Peguristes, and Petrochirus are a real threat to healthy, larger tankmates or to corals. Calcinus, Clibinarius, and Paguristes are some of the most common "clean-up crew" hermit crabs for algae control and to eat leftover foods and detritus. Hermit crabs that are underfed are also a greater threat to tankmates like snails and other invertebrates.
Hermit Crabs have soft abdomens and use empty snail shells to protect their bodies. As with other crustaceans, hermit crabs must molt to grow. When they molt, they crawl out of their shell homes and shed their own hard shell to grow larger. As they grow larger, they need to find new, larger shells in which to live. Provide extra larger shells in the aquarium for the hermit crabs to move into. Hermit crabs without homes may sometimes make their own by killing the snail inside, or they may molt before they have a new shell, leaving them extremely vulnerable to predators.