Interchangeability of nominative and genitive forms of Spanish patronymics?

I’m thinking of examples like Álvarez/Álvaro, Alves/ Alves, Benítez/Benito, Díaz/Diego, Domínguez/Domingo, Fernández/Fernando, Giménez/Ximeno, Gómez/Guillermo, González/Gonzalo, Gutiérrez/Gutierre, Henríquez/Henrique, Ibáñez/Juan, Juánez/Juan, López/Lope, Márquez/Marco, Martínez/Martín, Menéndez/Menendo, Muñoz/Muño, Núñez/Nuño, Ordóñez/Ordoño, Ortiz/Ortún, Peláez/Pelayo, Pérez/Pere, Ramírez/Ramiro, Rodríguez/Rodrigo, Ruiz/Ruy, Sánchez/Sancho, Suárez/Suero, Vázquez/Vasco, Velázquez/Velasco.

Langston Hughes in Spain

Idealism vs realism as a Stalinist hack copes with the Italian bombing of Barcelona but struggles to explain why Moorish peasants are slaughtering Spanish workers in the battle for Madrid.

Langston Hughes in 1936.

Castells, for real

A mad, mad Japanese video, and a human ladder at the Muslim siege of Aleppo in 637.

Roman double testudo, from Potter <em>Archaeologia graeca</em>. I'm told that the optimal shagging angle for turtles is 30º, so this counts as deviant.