Se souvenir is a french third group verb. So, this verb is irregular and do not follow a regular conjugation pattern like first or second group verbs. Follow this link to see all the endings of the conjugation of most of the third group verbs : 
conjugation rules and endings for the second group verbs.
																												
																																					Verbs derived from 
tenir and 
venir form a major group of verbs who gains a 
d in the future and conditional. These verbs are the only verb to have a nasal vowel in the past historic and imperfect subjunctive.																												
																																																																		
The verb 
se souvenir is a reflexive verb which is always reflexive. So it is always conjugated with a reflexive pronoun. Here is the list of the french reflexive pronouns: 
« me », 
« te », 
« se », 
« nous », 
« vous », 
« se ».