Southend boss Steve Tilson has signed Brighton striker Alex Revell for £150,000 - and turned down a bid from Motherwell for defender Steven Hammell.
Revell is moving to Southend, while Hammell is staying at Roots Hall
Revell, 24, has joined on a two-and-a-half-year contract.
The Shrimpers also signed Reading forward Hal Robson-Kanu, 18, on loan for the rest of the season.
Hammell, 25, joined Southend from Motherwell in 2006, but they have no intention of letting him return to the Scottish Premier League side.
"We have no interest in selling Steve, who is an important part of our side," said Southend chairman Ron Martin.
Revell began his career at Cambridge United, but moved to Brighton in July 2006 via a prolific spell at non-league Braintree Town.
He scored 18 goals in 71 league and cup appearances for the Seagulls, including a hat-trick against Bournemouth earlier this month.
Brighton replenished their striking ranks earlier in the day by signing Aldershot front man Jonny Dixon for £56,000.
Robson-Kanu is an England Under-19 international who can play up front or on the left.
Motherwell manager Mark McGhee was still hopeful of signing Hammell and has also targeted Derby midfielder Bob Malcolm.
"We have not signed anyone yet, but we are expecting a couple of phone calls and we still hope to make some signings," he said.
"Steven Hammell is a possibility. We are close to that one."