Altrasian

The Altrasians were a race of amphibious humanoids originating on the planet Dolré. They were known to the Imperium before the end of the First Era and were quickly subjugated. They suffered seriously at the hands of Imperium forces and yet eventually become one of the most Imperium-supportive of the subjugated races, with some of their number nearly achieving citizenship.

Biology and Anatomy
Like the Jatheel (often mistakenly believed to be a related race) the Altrasians are amphibious humanoids with both lungs and gills. Altrasian's lungs were, however, more highly developed and were their primary method of respiration. They were also capable of recognizable speech. They had webbed toes and partially webbed fingers, with the webbing extending from base to middle knuckle. Their basal body temperature was lower than human average (31.1-32.2°C as opposed to 37°C,) but they were basically endothermic.

Respiratory Interchange
While aerial respiration was the primary method of gaseous exchange for Altrasians, they retained fully-functional fetal gills for the entirety of their lives. (TV: Last Best Hope)  Special patches of sensory tissue inside of the nasal passages detected elevated moisture levels indicating submersion. This caused the epiglottis to close and the gills to begin functioning. Due to the involuntary nature of this function, induction without submersion could be potentially fatal.(PROSE: Lacrimosa)

Reproduction
Altrasians were cyclical sequential hermaphrodites. They had a rather androgynous physical appearance in most aspects. The majority of them presented as the human perception of genitally "female" much of the time. Any apparent "male" genital appearance was due simply to periodic extrusion of the clitoropenis as part of the regulation reproductive cycle. There were medications available which allowed for control of the reproductive cycle, with some choosing to maintain themselves as one apparent sex or the other at all times, though of course those presenting as "male" still had internal ovotestes rather than external testicles.

In typical, unaltered cases, two to three standard weeks every four standard months, their genital sex would appear to switch to the opposite of their typical presentation. During this time, their hormones would fluctuate, causing their ovotestes to switch to the appropriate function and severely raising their libido.

Pregnancy caused a cessation of the switch cycle until at least four to eight standard months after the birth. Gestation was close to human average, around nine to nine-and-one-half standard months, and newborn altrasians were nursed mammarialy.

Hybrids
Human-Altrasian crossbreeding was possible, with some hybrids being born shortly after first contact. (PROSE: Shadow of Eden) Hybrids were sometimes born with functional gills, but most had only vestigial slits. They were also by and large profoundly intersexed in various ways.

Most early hybrids, along with their parents, were killed off by the Imperium within the first decade of life (PROSE: Lacrimosa) and the fact that they had ever existed was nearly wiped from all records. (PROSE: A Delicate Condition)  The only currently known living hybrid in the prime universe is Katrina, the offspring of Vanessa Sharpe and Coriola. (TV: Strange Matters)