The new Alfa Romeo Spider will blend lightweight engineering and modern styling with an accessible chassis and a power output of 168bhp when it goes on sale in late 2015.

Based on the next-generation Mazda MX-5 platform and to be built in Japan, the new Spider’s styling is close to final sign-off.

The work is that of Marco Tencone, design chief at Alfa Romeo and Maserati, and his team at Fiat’s Centro Stile and a satellite studio in Japan.

Tencone’s most recent cars are the Alfa 4C sports car and the new Maserati Quattroporte and Ghibli saloons. Pininfarina, which designed the original boat-tail ‘Duetto’ in the mid-1960s, is understood not to be involved in the design of the new Spider, despite creating the striking 2010 Duettotanta concept.

The Duettotanta blended the slender boat-tail proportions of the original with contemporary body surfacing. Insiders say Centro Stile strived for months to make the design work on a production car.

It is likely that Tencone will take a similar approach for the new Spider, looking at historic design themes but with a very modern interpretation, just as the 33 Stradale has been reimagined for the 4C.

“The new Spider definitely won’t be retro in design,” said a well placed source. “The Spider has to be contemporary and must fit into the range with the modern 4C.”

Another source added: “It would have been easy to go for a retro, boat-tail design, but how would that fit in with the 4C and today’s Alfa designs?”

Among the design features that are understood to feature on the new Spider are conventional headlamp clusters, which will help to give the roadster wider appeal than the hardcore, mid-engined 4C, which is set to go on sale later this year.

The 4C features a single-projector headlight, five circular LED running lights and an indicator bulb set in a contrast-coloured moulding.

The Spider’s front end will be characterised by an Alfa ‘shield’ grille flanked by lower air intake ‘whiskers’, but the execution will be more subtle than that employed on the 4C.

The Alfa and Mazda will share windscreens, windscreen structure, front bulkhead, engine compartments and front and rear axles. Although both cars will be about four metres long and 1.7 metres wide, the Alfa’s styling is said to make it a few centimetres longer than the more minimalist Mazda. Both cars will be lightweight, tipping the scales at 1000-1100kg, thanks to a large proportion of high-strength steel in the body structure.

Although the inner structures of the two sports cars will be shared to keep costs down, sources say they won’t have any external panels in common. “They’ll have different bodies,” said one.