Selachian The Selachians were the Ockoran soldiers in the Selachian Empire . They had been specially modified for war , having their lower halves replaced with leg s and being installed in an armoured shell . ( PROSE : " The Final Sanction " ) Technology . The Selachians were distinguished by the Selachian battlesuit s . These battlesuits were large , bulky things that gave the Selachians the appearance of humanoid s . Selachians had to have studs implanted into their nervous system and have their tails removed in order for them to use the battlesuits . They had plasma weapons attached to their arms , which were built for fear rather than power ( though it was still a dangerous weapon ) . Their helmets were shaped and paint ed to look like shark s in order to intimidate their enemies . Later battlesuits were equipped with nanite s to repair damage and to counteract the nanite s of the Terran Security Forces . ( PROSE : " The Final Sanction " ) The Eighth Doctor ' s companion Samantha Jones once wondered if Selachians had the power to melt stone , ( PROSE : " Revolution Man " ) while Polly Wright theorised that the Selachians had a way of communicating with each other without people hearing . ( AUDIO : " The Selachian Gambit " ) Culture . The Ockorans adopted the name " Selachians " after studying other world s and learning that sharks were the most commonly feared marine creatures amongst human s . ( PROSE : " The Murder Game " ) Selachians had a strong sense of pride and would refuse to show weakness or fear . They would rather die than give into their enemies . Conversely , their weaponry , armour and name was specifically chosen to cause fear in the enemy . Selachians hierarchy was shown by stripes painted onto their battlesuits , going from top - left to bottom - right . The Supreme Leader ' s suit had black stripe edged with red , while the next level down had blue stripes . ( PROSE : " The Final Sanction " ) History . At some point before the 22nd century , the Ockoran ' s home - planet of Ockora was discovered by the Kalarian s and chosen as a vacation spot . Though the Kalarians knew of the Ockorans , they believed they weren ' t intelligent and hunted them for sport . ( PROSE : " The Final Sanction " ) The Ockorans eventually developed armour that allowed them to breathe on land , and emerged from the ocean s during a culling festival and took their revenge on the Kalarians . Their homeworld was cordoned off and the Ockorans were eventually forgotten . ( PROSE : " The Murder Game " ) The Ockorans developed space travel and left Ockora . In order to take their revenge on the Kalarians , they followed them to their homewolrld of Kalaya and conquered the planet within the six month s . They then conquered three more neighbouring worlds within a year . The Selachians then formed the Selachian Empire , and soon became a major power on the galactic markets . ( PROSE : " The Final Sanction " ) The Eighth Doctor said that Selachians often tried to sell weapons to less advanced planets , much like 21st century Earth . ( PROSE : " Interference - Book One " ) In an alternative timeline , the Selachians attacked Moonbase in 2044 . ( AUDIO : " The Architects of History " ) In 2054 , the Selachians made contact with humans and sold them weapons . In 2069 , they were featured in the " Eye - Spy Book of Alien Monsters " , which was handed out to UNISYC personnel as potential threats . ( PROSE : " Alien Bodies " ) In 2136 , the Selachians attacked Hotel Galaxian . They were defeated by the Second Doctor , Ben Jackson and Polly Wright . ( PROSE : " The Murder Game " ) In 2191 , the Cybermen stole a Selachian ship . ( PROSE : " Killing Ground " ) At some point before 2211 , the Selachians invaded the Earth colony Rho Priapus . The planet was later taken back by the Space Marines . ( PROSE : " The Janus Conjunction " ) For decades , the Selachians and the humans had traded with each other . Eventually , towards the end of the 22nd century , one deal went particularly bad , causing the humans to declare war on the Selachians . The war went badly for the Selachians and by 2204 they had been pushed back to Ockora . Though they had taken prisoner s on planets they were forced to leave , such as Molinar and Kalaya , this wasn ' t enough to save them and Ockora was destroyed by General Wayne Redfern when he dropped the G - bomb . After the meddling of the Second Doctor , the Supreme Leader and forty Selachian soldiers were able to escape the planet ' s destruction and get on - board the " Triumph " . They killed everyone on the ship , but another G - bomb was accidentally set off , leading to the formation of another black hole and killing the last of the Selachian race . ( PROSE : " The Final Sanction " ) In 2591 , Bernice Summerfield had a Selachian palmtop , which she stole from the body of a Selachian stormtrooper . ( PROSE : " Down " ) In 2775 , Jack Harkness told a story about when he met the Selachians . ( PROSE : " The Stealers of Dreams " )