The Decapodians are a race of aliens who arrived on Earth before the 31st century. (It is impossible for the Decapodians to arrive in the 31st century due to Zoidberg and the professor having an established relationship already at the start of the 31st century. Also, the anchovies went extinct before fry got the last can for pizza in Season 1 Episode 6)
Decapodians seem to be mix of crustacean and primate physiology. They have an exoskeleton shell, claws for hands, four seemingly prehensile appendages above their mouths and no hair. They all speak with Yiddish accents, possibly because of these appendages. They аlso possess a fin-like crest that appears when they are enraged or aroused, as well as an ink gland similar to the Earth octopus. They have been known to use their ink while writing letters that require a personal touch. It appears that Decapodians go through several distinct "stages" in their lives, closely resembling several marine species from Earth, with only the final, adult stage resembling a humanoid in build. At least a some of the Decapodians earlier life stages seem to be very small, as Zoidberg's old "stomping grounds" was a shallow pond, also inhabited by small crabs.
Decapodians also have a strange gland that produces foul odors when they are bored. Upon ingesting dirt, they cough up a kind of pearl, not unlike clams. They must also have gills as they are capable of breathing underwater. Another underwater feature is that of a gas bladder so to not float to the surface. Decapodians are capable of growing barnacles on at least their rear ends and faces. Judging by Zoidberg's comments, barnacles seem to be viewed the same was as humans view acne, and in his case appeared to be an embarrassing problem during his youth.
They also seem capable of eating and digesting almost anything even vaguely organic, from human food, to garbage, all the way to wood. They also have freshwater and saltwater stomachs which they can vomit separately from. They can apparently go for several days without eating. Interestingly, they can still survive and stand upright without their shell, suggesting an endoskeleton as well as a shell intended simply for defensive purposes. "Rebirth" confirms at least the existence of an endoskeleton, albeit one more resembling an aquatic creature, also revealing that Decapodians lack bones in their arms and legs.
Internally, Decapodians are cold blooded and have a number of redundant organs, such as four hearts as they may be able to live without as least one. Apparently, Decapodians are capable of surviving multiple dismemberments, as Zoidberg demonstrated in "Roswell that Ends Well", where he has several of his organs surgically removed after a series of vivisections. He gets them back and reinserts them later with no long-term consequences.
They are also shown being able to survive missile attack in A Taste of Freedom.
They are from Decapod 10 which has the entire planet consists of a series of massive sandbar islands and so as a result, the entire planet is full of beaches. This suggests that although they live on land they mostly dwell in the sea this also supported by thier diet of mostly fish. Thier buildings are made of mud althought they also seem to live in shells under the water so they may choose whether to live on land or underwater therefore.
Life CycleEditDecapodians mature through a long series of larval stages before attaining the humanoid, fully grown form. Apart from this complex life cycle, they have very long lifespans. They begin life as a small immobile creature from which asexually fragmented siblings can separate, each with their own distinct personality. A later stage resembles a parasitic lamprey [this stage seems to need to blood to live suggusting that there might be mammals living on Deapcod 10], followed by a large clam inside which the head is visible. The next oldest form resembles a trilobite. Other stages included an urchin-like state and later a cuttlefish-like appearance. A prominent Decapodian, Dr. Zoidberg, reverted through all of these early "larval" life cycle stages of his species after being exposed to a youth tar. When Decapodians mate, they quickly die off, leaving their young to grow without parents to guide them.
It is implied though, that some Decapodians refrain from mating to help keep their civilization running: they either adopt young into their family or only certain members of families mate so the young do not have to become part of a new family. Zoidberg has revealed during flashbacks to have been raised by a female he calls his mother. It may be that when the Decapodians die, their bodies turn into coral, starting their lives over again and making more of their species.