Taratunes (タラチュネス) is the theme of the giant spider boss. The song is pretty much the same between the NES and MSX versions.
The title is translated from Japanese on the official MSX soundtrack.
Legacy of the Wizard (NES)
In the NES version of the game, the song plays for each of the four main bosses, Taratunes, Archwinger, Erebone, and Rockgaea, unlike the MSX version where each boss has their own unique theme. The song for NES has a slightly richer sound then the MSX version. The song is track 12 in the NSF file and plays on the RP2A03.
Dragon Slayer IV: Drasle Family (MSX)
Unlike the NES version which uses this song as a generic boss theme, Taratunes is used only for the giant spider boss. The song is track 12 in the KSS file and is played on the AY-3-8910 on the MSX and the identical-sounding YM2149 on the MSX2.