Ñāṇa writes clearly in this subject:
Joy (pīti) and pleasure (sukha) born of seclusion (vivekajaṃ pītisukhaṃ)
The discourses differentiate between carnal joy and pleasure (sāmisā pīti and sukha) and non-carnal joy and pleasure (nirāmisā pīti and sukha). SN 36.31 Nirāmisa Sutta tells us that carnal joy and pleasure arise in dependence on the five strands of sensual pleasure, while non-carnal joy arises in the first two jhānas and non-carnal pleasure arises in the first three jhānas.
SN 48.40 Uppaṭipāṭika Sutta states that the pain faculty (dukkhindriya) ceases completely in the first jhāna, the unhappiness faculty (domanassindriya) ceases completely in the second jhāna, the pleasure faculty (sukhindriya) ceases completely in the third jhāna, and the happiness faculty (somanassindriya) ceases completely in the fourth jhāna.
SN 48.37 Dutiyavibhaṅga Sutta informs us that the pleasure and pain faculties are born of body contact (kāyasamphassaja), whereas the happiness and unhappiness faculties are born of mind contact (manosamphassaja).
Taking all of the above passages into consideration we can deduce that the non-carnal joy of the first jhāna is mental pleasure (cetasika sukha, i.e. somanassa) born of mind contact, and the non-carnal pleasure of the first jhāna is bodily pleasure (kāyika sukha) born of body contact.
This reading of these sutta sources accords with Peṭakopadesa 7.72:
The twofold bodily and mental pain does not arise in one steadied in directed thought and evaluation, and the twofold bodily and mental pleasure does arise. The mental pleasure thus produced from directed thought is joy, while the bodily pleasure is bodily feeling.
This understanding is also supported by the Vimuttimagga. The author of the Vimuttimagga was knowledgeable of and quotes from the Uppaṭipāṭika Sutta, the Paṭisambhidāmagga, the Vibhaṅga, and the Peṭakopadesa. And when commenting on the bathman simile for the first jhāna (e.g. DN 2, MN 119, etc.) he explains: Just as the bath-powder when inside and outside saturated with moisture, adheres and does not scatter, so the body of the meditator in the first jhāna is permeated with joy and pleasure from top to bottom, from the skullcap to the feet and from the feet to the skullcap, skin and hair, inside and outside. And he dwells without falling back. Thus he dwells like a Brahma god.
[Q.] Joy (pīti) and pleasure (sukha) are said to be formless phenomena (arūpa-dhamma). How then can they stay permeating the body?
[A.] Name (nāma) depends on form (rūpa). Form depends on name. Therefore, if name has joy, form also has joy. If name has pleasure, form also has pleasure.
Again, form born from joy causes tranquility of body, and when the entire body is tranquillized there is pleasure due to the tranquility of form. Therefore there is no contradiction.
To this we can add a couple of more points. First, due to the presence of directed thought and evaluation in the first jhāna, intermittent occurrences of mental unhappiness can still arise, as indicated in SN 48.40. Thus the singleness of mind of the first jhāna isn’t necessarily as unified as in the higher jhānas. Secondly, when the meditator is steadied in the first jhāna, all of the jhāna factors work together to maintain what DN 9 calls an actual refined recognition of joy and pleasure born of seclusion (vivekajapītisukhasukhumasaccasaññā). Thus, while the singleness of mind of the first jhāna may not be as unified as in the higher jhānas, it is still a very refined samādhi. It takes considerable mental development in order to be able to successfully induce and maintain this level of heightened mind (adhicitta).http://measurelessmind.ca/jhana.html