Neptunian society is fully transhuman, with all concerns of biology and morphology rendered irrelevant by sufficiently-advanced technology. Neptunians exhibit a wide variety of forms, though they’re generally centered around ease of use underwater first, and on land as only a secondary concern. Indeed, cephalopoid and cetaceoid are two of the most common general body plans.
Though no single form has a majority, some have a strong enough plurality to be worthy of mention. The foremost among these, the largest plurality (and indeed the most likely image to come to a galactic citizen’s mind when the word ‘Neptunian’ is used), is the Lutrineptunian, or Neptunian Otter. This is a general body plan spec, not a mass-produced morphology, since it can be found implemented on many substrates (the most common being biomorph and smartgel-filled nanoprene) The style itself is distinctive though, being a sleek anthromorphic otter form, androgynous and usually brightly-colored, with webbed paws and a fluked tail. Streamlining is held in utmost importance, so fur, if present, is generally short, and the head is usually left bare or decorated with sleek tendril-like dreadlocks. Tentacles, rooted in the back, are a common accessory, though not considered part of the standard template.
Streamlining is also one of the main reasons behind another iconic Neptunian morphological feature, this one not limited to the lutrineptunian template: The adaptive sexual differentiator. Most Neptunian biomorph templates are not created with any sort of sexual differentiation. These default bodies are smooth both in the chest and the groin, with a level of curviness intermediate between standard masculine and feminine, tuned for hydrodynamic performance rather than gender. These forms are also equipped with the standard capability for erogenous zones and orgasm, even though there’s no specific physical correspondent to the latter.
Many Neptunians use these bodies as-is, androgynous and undifferentiated, but many others do have a desire to manifest some sort of sexually differentiated features, on either a short- or long-term basis. This is where the differentiator comes in. The differentiator is essentially a modified subset of the endocrine and reproductive systems, augmented by biotech and nanotech to allow for adjustment of primary and secondary sexual characteristics to any desired combination, as specified by mindlink commands. Male and female genitalia can both be manifested, individually or together, fertile or infertile. Other genital forms can be produced as well, with the most popular commonly called the anemone: a set of dozens of small motile tendrils surrounding a soft sensitive patch between legs. Breast tissue can be generated at any level desired, though most Neptunians don’t go far with it, since it tends to interfere significantly with underwater movement. Muscle mass can be similarly increased, though this is also not a popular adjustment, for the same reason.
The sexual differentiation adjustments happen quickly in biological terms, but can still take several hours to complete, particularly in the case of a significant genital change. (Going from one set of differentiated genitalia to another takes significantly longer than going from undifferentiated to either, which is another reason many Neptunians chose full-androgyne as their default). The changes also come at a significant metabolic cost; someone in the middle of differentiation tends to be lethargic and ravenously hungry. Many food delivery services have quick and easy ordering options for a ‘differentiation snack;’ actually a large, easily-devoured carbohydrate-rich meal.