The Nariscene, described in Matter, are an insectile species, described as a mid-level Involved society, meaning that they are both a mentored species as well as mentoring lesser species in turn.
The Nariscene are described as six-limbed insectiles covered with keratinous shells. Their bodies have five segmentations, and are around a metre and a half long (not counting manipulatory stalks with their mandibles), though sizes change with sub-species, with the lesser individuals in a hierarchy being slightly smaller. They often implant jewelry or tools and weapons straight into their carapaces. They communicate partly via scented gas squirts. They often use 'exoskeletons' with anti-gravity devices.
Their procreation seems to be at least partly based on a 'Queen' spawning new Nariscene. The mate of the queen (who dies in his highly honoured duty) is selected based on the requirements of the 'Imperial Procreational College' which selects the desired genotype according to the current requirements of the species every generation. The clans of the Nariscene may then bid for the honour to go to one of their own.
There is only limited description of the society of the Nariscene in the Banks novels. They are described as being mentors of the Oct, and are in turn mentored by the much more powerful Morthanveld, a relationship which seems reasonably cordial. Their society seems to centre on clans existing in a feudal system with an immortal Queen (though the 'Everlasting' term may be ceremonial)