how many molluscas are there whose families are theodore dru alison cockerell and theodore dru alison cockerell ?
SELECT DISTINCT COUNT attr_open var_uri attr_close where brack_open var_uri dbo_family dbr_Theodore_Dru_Alison_Cockerell sep_dot var_uri dbo_family dbr_Theodore_Dru_Alison_Cockerell brack_close