But they're calling it a third sex because it's due to "normal expression of the species' genes", not because of hermaphroditism.

It is a third (or fourth) phenotype, not a third sex. The abstract of the source article is careful to spell this out; the clickbait site introduced the error.

"Three sex phenotypes in a haploid algal species give insights into the evolutionary transition to a self‐compatible mating system." -- i.e. how might self-pollinating plants have developed?

Like in "the player of games" the third sex was both female and male.

Is that how it was? If my memory serves the third sex was effectively "female", in that you had:

- producer of small gamete (human male)

- producer of large gamete (half of human female)

- incubator of embryo (half of human female)

Sounds like a third sex

I think it depends on how you define sex, or perhaps even gender would be more accurate?

In any case, I think what's being proposed is there are still on 2 unique sexes.

- some of the species have one - some of the species have the other - some have the ability of both.

Technically, yes, that's still only two.

How do you define sex? Because what you just described sure sounds like a third sex to me.

Your description is premised on the assumption that there are only two sexes to begin with, and define the third sex in terms of the two sexes you assume to be the only ones that exist. Instead you could describe them as sexes A, B, and C where any of following pairings are valid for reproducing: A and B, A and C, B and C, or C and C.

Actually. No.

You need two differnt "widgets" to tango, not three.

Unless you say Sex A and Sex B together is a third sex Sex A+B. But that would only make sense if A+Bs were unique in the sense that they can only mate with other A+Bs. Then A+B would be a third sex. That's not the case, is it?

Put another way, sex is a property, not a class.

Are we defining sex by the type of gametes produced by an organism?

> they can produce normal male or female colonies when they reproduce sexually with other P. starrii colonies

Sound the alarms!

Odd, my friend completed their sexual reassignment surgery because they identified so strongly as male-gendered.

I'm going to need to remind them they're actually trying to get rid of gender! Silly them! Let's hope they're never "normalized!"