The 23-year-old was born in Edinburgh and has represented England at U21 and U18 levels, playing alongside such international luminaries as Jonny Wilkinson, Iain Balshaw and Mike Tindall, as well as appearing in three Varsity Matches for Oxford University.
At a shade under 16 stone, Danielli is one of the new breed of big wingers, but also possesses plenty of pace and has made 13 starting appearances for Bath in their current Zurich Premiership campaign.
"We've been aware of Simon for quite some time and his call-up is reward for some impressive performances in his last few games," said McGeechan.
Absent from the squad are Allister Hogg of Edinburgh and Borders wing Nikki Walker, who drop down to Scotland's U21 side for their upcoming shadow 'Six Nations' tournament.
McGeechan said: "Ally and Nikki have both done well with Scotland on our tour to North America last summer and have continued their development this season.
"At this stage of their development I believe they will both benefit from being involved with the national U21 team."
Scotland squad: G Beveridge (Glasgow), M Blair (Edinburgh), A Craig (Orrell), S Danielli (Bath), B Hinshelwood (Worcester), B Laney (Edinburgh), G Metcalfe (Glasgow), S Moffat (Glasgow), C Paterson (Edinburgh), B Redpath (Sale Sharks), G Ross (Leeds Tykes), G Townsend (Borders), K Utterson (Borders), S Webster (Edinburgh) R Beattie (Bristol Shoguns), G Bulloch (Glasgow), B Douglas (Borders), S Grimes (Newcastle Falcons), A Hall (Glasgow), D Hall (Edinburgh), D Hilton (Glasgow), N Hines (Edinburgh), A Jacobsen (Edinburgh), S Lawson (Melrose), M Leslie (Edinburgh), A Mower (Newcastle Falcons), S Murray (Edinburgh), J Petrie (Glasgow), B Pountney (Northampton Saints), A Rennick (Borders), S Scott (Borders), T Smith (Northampton Saints), M Stewart (Northampton Saints), S Taylor (Edinburgh), J White (Glasgow).