I sincerely doubt that the one species was intermixing because it was meeting
a friend. I am not sure about this habit,  but during my work in St. Croix I
found T.rustica in moderate numbers. ( about 10 per Meter ^2) I always found
this particular species  in close proximity to herbivorous gastropods ( mainly
Diadora, lucapina, and tegula). I never found carnivorous gastropods ( such as
Cymatium....I am doing this with out looking at my data sheet) other than
members of the same species in a I
40cm region. ( I am betting that this species is carnivorious because it is a
member of the family muricadae  but would an expert confirm  or deny that
please?)  I never found Thais is groups more than 3 or 4.  but there were
several groups in one section ( meter^2) This may be just that region.
This species is part of my research down there. I am mapping the diversity of
gastropods and a corrolation with diversty of algae. I need to go back and
take massive amounts of data but I won't be able to have time or money until
March again.
Sarah
http://www.geocities.com/southbeach/tidepool/8845