The Vedas refer to not 33 crore Devatas but 33 types

The Vedas refer to not 33 crore Devatas but 33 types (Koti in Sanskrit) of Devatas. 

The number 33 comes from the number of Vedic gods explained by Yajnavalkya in Brhadaranyaka Upanishad – the eight Vasus, the eleven Rudras, the twelve Adityas, Indra and Prajapati. (Chapter I, hymn 9, verse 2)

They are: 8-Vasu, 11-Rudra, and 12-Aaditya, 1-Indra and 1-Prajaapati.

VASUS 

8. Vasus are ~ Earth, Water, Fire, Air, Ether, Moon, Sun, and Star.Elemental gods such as Vayu, Agni, Antariksh and Dyaus, the Sky God. ( Olympian Gods).

They are called Vasus, because they are abode of all that lives, moves or exists. (also mentioned in Mahabharat, 1/66/18).

RUDRAS 

Once, the deities went to sage Kashyapa after being tormented by the demons. They complained to him about the misdeeds of the demons, who also happened to be their step brothers. Sage Kashyapa became extremely furious, when he heard about the misdeeds of his sons - the demons. To protect the deities from his sons, he commenced a penance to please lord Rudra.
Lord Rudra became very pleased by his penance and appeared before him. He asked Kashyapa to demand anything he wished. Kashyapa then requested Lord Rudra to take birth as his son and destroy the demons. Lord Shiva blessed him and said - 'So be it'.
Lord Rudra, later on took birth as eleven Rudras from the womb of his wife Surabhi. The name of these eleven rudras were as follows:-

1) Kapali, 2) Pingal, 3) Bheem, 4) Virupaksha, 5) Vilohit, 6) Shastra, 7) Ajapad, 8)Ahirbudhnya, 9) Shambhu, 10) Chand and 11) Bhav.

These eleven Rudras fought battles with the demons and killed them. The deities were relieved after the death of the demons. They worshipped these eleven rudras to express their gratitude and indebtedness.

 Grown to their perfect strength greatness have they attained; the Rudras have established their abode in heaven. 

Adityas

The 12 Adityas in Hindu mythology explain the evolution of consciousness from its primordial unformed state into energy that transforms into karmic manifestation.

 There are several accounts of the Aditi and the Adityas in the Rig Vedas. Aditi and Kashyapa are referred to as the parents of  the ‘Gods of Light’.

 In each month of the year, it is a different aditya who shines. As Indra, Surya destroys the enemies of the gods. As Dhata, he creates living beings. As Parjanya, he showers down rain. As Tvashta, he lives in the trees and herbs. As Pusha, he makes food grains grow. As Aryama, he is in the wind. As Bhaga, he is in the body of all living beings. As Vivasvana, he is in fire and helps to cook food. As Vishnu, he destroys the enemies of the gods. As Amshumana, he is again in the wind. As Varuna, Surya is in the waters and as Mitra, he is in the moon and in the oceans.

INDRA

The King of Devas and the God of Rain and Thunder. In Rigveda, Indra is described as strong willed, armed with thunderbolt, riding a chariot:

May the strong Heaven make thee the Strong wax stronger: Strong, for thou art borne by thy two strong Bay Horses. So, fair of cheek, with mighty chariot, mighty, uphold us, strong-willed, thunder armed, in battle.

— RigVeda, Book 5, Hymn XXXVI: 

PRAJAPATI

The pro generator of humans of an era. He is in charge of conducting the Yagyas for the Gods. ( Lord Brahma initially )



It has been documented in Brihadaranyaka Upanishad - Chapter 3.)


Śākalya         : "How many gods are there?"
Yājñavalkya  : "Three hundred and three." Then he says, "Three thousand and three."

Śākalya         : "Is this the answer that you give me to my question, how many gods     are there? Three thousand and three; three hundred and three! Have you no other answer to this question?"
Yājñavalkya  : There are thirty-three gods.

Śākalya         : "All right!" (not satisfied with answer) ...Tell me again properly; how many gods are there?"
Yājñavalkya   : "Six are there."

Śākalya         : "How many gods are there. Tell me again. Think properly."
Yājñavalkya   : "Only three gods are there."

Śākalya         : "How many gods are there? Tell again.
Yājñavalkya   : "Two gods are there."

Śākalya         :  "Tell again; how many gods are there?"
Yājñavalkya   :  "One and a half gods"

(Then he was very much upset) 

Śākalya         :  "What is this you say, one and a half gods. Tell again properly; how many gods are there?"
Yājñavalkya  :  "One god is there,"

Śākalya         : "All these numbers that you have mentioned – three thousand and three, three hundred and  three – what are these gods? Give the names of these gods, the deities."
Yājñavalkya  :   "All these three thousand and all that I mentioned – they are not really gods. They are only   manifestations of the thirty-three. The thirty-three are the principal manifestations, and others are only their glories, radiances, manifestations, magnificences or forces, energies,  powers."

Śākalya         : "But what are these thirty-three?"
Yājñavalkya   : "The thirty-three gods are eight Vasus, eleven Rudras, twelve Ādityas, then Indra and Prajāpati – these make thirty-three gods."

Śākalya         : "What are these Vasus which are eight in number?"
Yājñavalkya   : "Fire is one deity; earth is one deity; air is another; the atmosphere is one deity; the sun is one deity; the heaven is one deity; moon is one deity; the stars are one deity. These constitute eight groups"

Śākalya         : "Why do you call them Vasus?"
Yājñavalkya   : "Everything is deposited as it were in these constituent principles. Therefore, they are called Vasus."

Śākalya         : "Who are the Rudras?"
Yājñavalkya  : "The ten senses and the mind make eleven. These are the Rudras."
         
Śākalya         : "What are the twelve Ādityas, the suns?"
Yājñavalkya   : "They are twelve forces of the sun, takes away the vitality of people."

Śākalya         : "Who is Indra? Who is Prajāpati?"
Yājñavalkya   : "The rain cloud can be called Indra. Sacrifice can be called Prajāpati."

Śākalya         : "What do you mean by rain cloud?"
Yājñavalkya   : "By rain cloud I do not actually mean the cloud, but the lightning which is the embodiment of energy."