At Paris fashion week, "going back to the DNA of the brand" is code for "get lost, upstart designers – we are a blue-chip name and we're not going to let anyone forget it". Although, naturally, Karl Lagerfeld makes the point rather more elegantly than that.

Of all the codes of the great house of Chanel, the pearl is the most enduring. The classic images of Coco show her in a little black dress, toying with a string of pearls; over the 29 years Karl Lagerfeld has helmed the label he has kept the pearl front and centre of its image. He has designed shoes with pearls around the platform and the heel, and once kick-started a high-street craze for multiple strings of pearls when he featured the look on his catwalk.

For this Paris fashion week, he took the idea one step further, going back to the roots of this most potent symbol of Chanel. In other words, Chanel went underwater. The vast Grand Palais, where Chanel's biannual catwalk extravaganzas are staged, was transformed for the event into a seabed dreamscape. Glossy white sculptures of coral the size of oak trees loomed above a catwalk covered in white sand, while the high iron walls were draped in undulating sheets of glossy polythene, so that the light had the refracted quality of sunlight underwater.

This was a dazzling display by Lagerfeld. In lesser hands, the pearl conceit might quickly wear thin, but his 360-degree talent in ensuring every detail is executed to perfection, every idea pursued to its conclusion, is second to none. To help the spectacle fill the stadium-sized venue, he enlisted Florence Welch, who sang live during the show and accompanied the designer on his lap of honour.

There were pearls pinned into the models' chignons, pearls as the pull on the zipper of cardigans, pearl belts around cocktail dresses and pearl buttons on boucle jackets.

Tiny stick-on pearls dotted onto noses and bottom lips, and tracing vertical lines from the napes of necks, were a very Lagerfeld-ish joke, poking fun at the piercings and tattoos which have become as much a cliché of models at Paris fashion week as pearl chokers once were among Parisian ladies of a certain age. Handbags in the shape of conch shells, encrusted with palest pink seed pearls, were worn with dresses decorated with clouds of fine black ribbon, shredded and tangled as seaweed. After last season's hard-edged, goth-influenced collection this was a soft, pretty summer look which seems a surefire commercial hit.

Boucle tweed suits and dresses came in the sleek, collarless shapes fashion currently adores. Soft, puffed-out volume at the back - along the shoulders of a tweed jacket, or above the gathers at the hip of a silk dress – served to show off the superb quality of fabric and workmanship at Chanel. This was a show which, as it was intended to, reminded the fashion world that Chanel is pure class.