Other contributors have said "What is the external features of sea cucumber?" is the same question as "What is the scientific name for the sea cucumber?" If you believe that these are not asking the same thing and should be answered differently, click here
Isostichopus fuscus, Stichopus horrens, and Holothuria Ref: Charles Darwin Research Station Fact Sheet 2006 Charles Darwin Foundation for the Galapagos Islands (AISBL), Galapagos, poo
The sea cucumbers scientific name is Holothuroidea.
although it depends on what type. Another scientific name for the sea cucumber is also Parastichopus californicus.