Is sexual desire an emotion? I see that in the Wikipedia page of emotion classification, sexual desire is only mentioned once (in Parrott's tree-structured list of emotion). It is absent from other kinds of classification. 

What is sexual desire?


  Sexual desire is a motivational state and an interest in “sexual objects or activities, or as a wish, or drive to seek out sexual objects or to engage in sexual activities”. Synonyms for sexual desire are libido, sexual attraction and lust. Sexual desire is an aspect of a person's sexuality, which varies significantly from one person to another, and also varies depending on circumstances at a particular time. Not every person experiences sexual desire; those who do not experience it may be labelled asexual. 


What is emotion?


  Emotions are biological states associated with the nervous system brought on by neurophysiological changes variously associated with thoughts, feelings, behavioural responses, and a degree of pleasure or displeasure. There is currently no scientific consensus on a definition. Emotion is often intertwined with mood, temperament, personality, disposition, creativity and motivation.


So it seems to me that you can consider sexual desire as an emotion. However, the lack of it in other kinds of classification make me question about that. I think sexual desire is common and basic enough to have a consideration in most classifications.
Sexual desire, libido, horniness, titillation, lust and eroticism are all listed as emotions in the Atlas of Personality, Emotion and Behaviour (Mobbs, 2020).  In the atlas taxonomy, emotion is defined the perception of a neurological impulse that initiates behaviour (typically abstract nouns).

The full catalogue is available at: https://doi.org/10.6084/m9.figshare.c.4792323

Mobbs AED (2020) An atlas of personality, emotion and behaviour. PLoS ONE 15(1): e0227877. https://doi.org/10.1371/journal.pone.0227877