Marcus started collecting shells as a kid, back in 1976. In the 80's he met several collectors in Brazil, and in 1989 he founded his company Femorale Shells, which supplies specimen shells to collectors, biologists and Museums all over the world. He was co-founder of Conquiliologistas do Brasil, the main shell club in Brazil, and served as its President from 1995 to 1999.

He and his brother Jose have discovered more than 100 new species in Brazil in the past years, some named after them (Chicoreus coltrorum (E.Vokes, 1991); Favartia coltrorum Houart, 2005; Fusinus coltrorum Hadorn & Rogers, 2000; Fusinus marcusi Hadorn & Rogers, 2000; Muricopsis josei Vokes, 1994; Muricopsis marcusi Vokes, 1994; Perotrochus amabile coltrorum Rios, 2004; Polystira coltrorum Petuch, 1993; Prunum coltrorum Cossignani, 2005; Strictispira coltrorum Tippett, 2006).

Marcus travels all over the world to look for shells and takes many pictures, including underwater.

Carlos Henckes is a shell collector, and has worked with computers for many years. In 1999 he was hired by Femorale Shells, where he now works as webmaster and photographer. He has been the President of Conquiliologistas do Brasil since 2005. He also has a shell named after him: Conus henckesi Coltro, 2004