The shell and body structure of the plesiomorphic pulmonate false-limpet Siphonaria pectinata (Linnaeus) from the south coast of Portugal is presented in detail. All the systems are described and discussed, in order to create a phenotypic database, since the siphonariid relationships are controversial, and most of the recent attempts at their resolution have been molecular. Most siphonariids show several morphological peculiarities (e.g., flap-like head without tentacles, interrupted shell

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... e, anterior portion of genitalia surrounding shell muscle) compared to the remaining pulmonates or even to heterobranchs. On the other hand, the odontophore structure, and the genital system, including the penis retractor muscle connected with the shell muscle, place them close to higher pulmonates. The siphonariids present a new mode of limpetisation, with the visceral structures placed inside the haemocoel instead of being located below the shell apex.