'Ist er ein Tier, da Musik ihm so ergriff'. In Kafka's 'die Verwandlung' is Gregor really an animal?

The question of Gregor Samsa's metamorphosis in Kafka's Die Verwandlung is one that has perplexed scholar's for decades. The first page of the novel details Gregor awakening 'aus unruhigen Träumen' to find himself in the body of an 'Ungeziefer', but how far can we accept this transformation? Is Gregor really a beetle?
One might argue, that from a physical perspective Gregor Samsa has unequivocally undergone a transformation into an animal. Gregor has a curved stomach, lots of little 'Beinchen' that flap, a 'panzerartigen harten Rucken' (a armour-hard back) and a 'piepsen' symbolising his animalistic voice - non of which standard features of a human. Gregor has difficulty manoeuvring in his room and must use his jaw to drag a cloth and create a canopy over his beetle body. Kafka leads the reader to believe, furthermore, that his transformation owing to how the other family members react to Gregor's transformation: Gregor's mother faints at the sight of Gregor, which she is unlikely to have done if Gregor was her human son.
However, on the other, Gregor's mental capacity and ability to think in a human manner suggest that his transformation was not complete. Gregor is very much still in the mind set that he is a man and not an animal following his transformation: Gregor is concerned about getting to work the morning he wakes up to discover he is a beetle, worried about how the prokurist will respond if he is late. Furthermore, when Gregor hears his sister Greta playing the violin, Gregor feels moved in a way that no beetle acting based on biological stimuli would ever feel moved.
Whilst there are aspects of Gregor that have for some unknown reason changed, there are elements of Gregor that remain intact following his strange transformation into a beetle.