As the above source shows, the Venantes are a type of hunting spiders. Off course the name Venantius is not derived from Venantes, but it shares the some origin: venari . I already thought it would come from this word, meaning 'to hunt' or venatio , meaning 'hunter', but this source states it. Your name means thus 'hunter'
About your last name:
it means 'son of Jimen'. Jimen is commonly written as Ximen and another variant is Gimen (note at the lastname Gimenes). People think it is a Spanish form of Simon (according to this site). To see the meaning thus of Ximen, click on the hyperlink of Simon.