Echiejile has played just twice since been loaned to Cercle Brugge in January but is set for a second World Cup after playing for Nigeria at the 2010 finals in South Africa. He was an unused substitute against England in the 2-1 loss at Wembley on Saturday, having been brought back into the squad last month.
The 30-year-old, previously on the books of Monaco, was injured in a warm-up friendly before the 2014 tournament and missed out on the last finals in Brazil.
Forward Nwankwo made his debut for Nigeria last Monday in their friendly against the Democratic Republic of Congo but was left on the bench at Wembley on Saturday.
The 26-year-old gets the berth vacated because of the knee injury to Belgian-based attacker Moses Simon.
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Five players –- John Obi Mikel, Victor Moses, Ahmed Musa, Kenneth Omeruo, Ogenyi Onazi –- were also in the squad for the 2014 World Cup.
Nigeria open their World Cup Group D campaign against Croatia in Kaliningrad on June 16.
Squad:
Goalkeepers: Daniel Akpeyi (Chippa United), Ikechukwu Ezenwa (Enyimba), Francis Uzoho (Deportivo Coruna)
Defenders: Chidozie Awaziem (Nantes), Leon Balogun (Brighton & Hove Albion), Tyronne Ebuehi (ADO Den Haag), Elderson Echiejiole (Cercle Brugge), Brian Idowu (Amkar Perm), Kenneth Omeruo (Kasimpasa), Abdullahi Shehu, William Ekong Troost (both Bursaspor)
Midfielders: Oghenekaro Etebo (Las Palmas), John Obi Mikel (Tianjin Teda), Wilfred Ndidi (Leicester City), Joel Obi (Torino), John Ogu (Hapoel Be'er Sheva), Ogenyi Onazi (Trabzonspor)
Forwards: Odion Ighalo (Changchun Yatai), Kelechi Iheanacho (Leicester City), Alex Iwobi (Arsenal), Victor Moses (Chelsea), Ahmed Musa (CSKA Moscow), Simeon Nwankwo (Crotone).
(Reporting by Mark Gleeson in Cape Town; Editing by Clare Fallon)
