Rhodon provides this information about the disciples of Marcion:

Therefore they (the followers of Marcion, the Marcionites) have ceased to agree among themselves, maintaining inconsistent opinions. One of their herd is Apelles, who is reverenced for his life and old age. He admits that there is one Principle but says that the prophecies are of an opposing spirit, and he was persuaded by the utterances of a possessed maiden named Philoumena. But others, such as the captain himself (Marcion), introduced two Principles. To them belong Potitus and Basilicus. These followed the wolf of Pontus (Marcion), not perceiving the division of things, any more than he, and, turning to a simple solution, announced two Principles boldly and without proof. Others again, passing into worse error, supposed that there are not only two but even three natures. Of them the chief and the leader is Syneros, as those state who represent his school. (Eusebius, H. E. 5.13.2-4)

Rhodon offers this account of a discussion with Apelles:

For the old man Apelles, when he consorted with us, was proved to make many false statements. Hence also he used to say that it is not necessary to investigate the argument fully, but that each should remain in his own belief, for he asserted that those who place their hope in the Crucified would be saved, if they persisted in good works. But as we have said, the most obscure part of all the doctrines which he put forward were about God. For he kept on saying that there is only one Principle just as our doctrine states. . . . And when I said to him, ‘where is this proof of yours, or how can you say that there is one Principle? Tell us’, he said that the prophecies refute themselves by not having spoken the truth at all for they are inconsistent and false and contradict themselves, but as to how there is one Principle he said that he did not know it, but merely inclined to that view. Then when I adjured him to speak the truth he swore that he was speaking the truth, when he said that he did not know how the unbegotten God is one, but that he believed it. But I laughed at him and condemned him, because though he called himself a teacher he did not know how to establish what he taught. (Eusebius, H. E. 5.13.5-7)
J. Quasten writes (Patrology, vol. 1, pp. 273-274):

From this account it appears that Apelles disagreed with Marcion in most important questions. First of all, he rejected his teacher’s avowed dualism and endeavored to get back to a single first Principle. Consequently he presented the demiurge as a creature of God, as an angel who created the world. Secondly, Apelles eliminated Marcion’s Docetism. Jesus Christ was no phantom; he had a realy body although he did not receive it from the Virgin Mary but borrowed it from the four elements of the stars. When he ascended he restored his body to the elements.

On the other hand apelles went much father than Marcion in his rejection of the Old Testament. Marcion regarded the Old Testament as a document of purely historical value without any religious significance. To Apelles it was a lying book, full of contradictions and fables and entirely unreliable. In order to prove the worthlessness of the Old Testament Apelles composed a book entitled The Syllogisms which comprised at least thirty-eight books. Ambrose has preserved a large number of passages from this work in his treatise De Paradiso. Nothing is extant from the book of Manifestations (φανερωσεις) of Apelles in which he published the visions of the prophetess Philoumena.
Thus, though Apelles was a disciple of Marcion, he was in several respects his own thinker.
Founder of a Gnostic sect; died at an advanced age late in the second century. What little is known of his life is gleaned chiefly from fragments of the writings of his antagonist Rhodon, preserved by Eusebius (Hist. Eccl., V, xii), and from Tertullian’s “Prescription against Heretics” (xxx). At Rome he separated from Marcion, whose most famous pupil he was, and went to Alexandria, where he met the visionary Philumene, whose utterances he regarded as inspired. Besides collecting her oracles in a book entitled “Manifestations”, he wrote an extensive work, Eullogismoi, an attack on Mosaic theology. The moral character of Apelles is differently estimated according as one is influenced either by Rhodon’s uncoloured picture of the aged heresiarch, or by the stories of scandals in his early life to which Tertullian, not without exaggeration, refers.