Anguilla Aceti or Turbatrix Aceti. The vinegar eel, as the name suggests, lives in acidic vinegar however is not an eel but a nematode.
Vinegar eels can be seen with the naked eye when light is shone through their jar, the close up image illustrates this.
To culture, decant the vinegar eels into a larger jar containing apple cider vinegar (with the 'mother'), water and a slice of apple, leave the lid loose to allow airflow.