Search notes:

Oracle: Index Organized Tables

create table tab_iot (
   id    integer,
   col_1 …
   --
   constraint tab_iot_pk primary key(id)
)
organization index
-- nologging
-- pctfree 0
;

Finding index organized tables in the data dictionary

The list of index organized tables can be queried from the data dictionary like so: 
select
   owner,
   table_name
from
   all_tables
where
   iot_type is not null;

Determine size of IOT

select
   seg.blocks,
   round(seg.bytes / 1024/1024/1024, 2) giga_bytes
from
   user_constraints con  join
   user_segments    seg on con.constraint_name = seg.segment_name
where
   con.table_name      = 'TABLE_NAME' and
   con.constraint_type = 'P'
;

See also

$ORACLE_HOME/rdbms/admin/dbmsiotc.sql.
Apparently, the equivalent of IOTs in MySQL are referred to as clustered indexes.

Index