What type of alien is Lt. Jadzia Dax?

Answer 1

Lt. Jadzia Dax is a Trill. This unique "joined race" whose humanoid members have provided host bodies for small soft-bodied entities in a symbiotic relationship; Among the humanoid Trill joined species, apparently at least two races of hosts are used to house a symbiont: those of the ridged forehead and those like Jadzia with a narrow speckled band running along the hairline to the sides of the neck, then down along the body. If a host is weak, the personality of the symbiont will overwhelm it. Unless its current Joined Host objects, a prospective Host may request a specific symbiont.

The symbiont body is a foot-long purplish lump of cranial and exoskeletal tissue, some are susceptible to damage by transporter beam. Thousands of symbionts live on Trill.

Since the symbiont integrates each new host's personality with its own after joining, Trill relationships are often hard for single-unit species to deal with and sometimes don't survive the change.

The symbiont does carry memories of time shared with each of its hosts, and each new combination - aside from gender, height and weight - carries a different blood type, metabolism, nervous system, and brain wave pattern.

Only one Trill in ten is chosen to be joined to the "thousands" of symbionts, but those not joined still lead normal, productive lives. If the truth were known that half the population could be hosts, rather than the 1-in-1,000 ratio officially quoted and the reason behind the rigorous selection and training program, some at the Symbiosis Commission worry that the symbionts would be bartered as commodities.

A Trill's lineal or family name follows the given name, as is done on Earth, but a host drops his lineal name in favor of the symbiont's. Social role equality seems apparent among the population, at least in medicine, with doctors and nurses of both genders.