Background:

The Gymnosomata is a group of mollusks adapted to pelagic life, which includes about 47 valid species worldwide. Zooplankton tows in the Gulf of California during January 2007 led to the collection of specimens of two different species of Gymnosomata with morphologic characters that did not belong to any species previously described.

Goals:

To describe, based on radular characteristics, two new species of gymnosomatous mollusks collected at the central portion of the Gulf of California, Mexico.

Methods:

Ten specimens of Gymnosomata were obtained with zooplankton tows using a Bongo net system. All the organisms described were identified as adult stages. Three specimens were dissected, and their buccal mass was removed and dissolved in 10% sodium hydroxide until the radula was isolated from the surrounding tissue. Posteriorly the radula was mounted for scanning electron micrographs.

Results:

Two new species were described, Pneumoderma cicimarensis sp. nov. and Pneumodermopsis tacoi sp. nov.

Conclusions:

Pneumoderma cicimarensis sp. nov. has a similar morphology to Pneumoderma pacificum Dall, 1871, but differs in the presence of one lobe on the median portion of the wing, a lack of chromatophores in the body and the shape of the radular teeth. Pneumodermopsis tacoi sp. nov. has a similar radula to Pneumodermopsis ciliata (Gegenbaur, 1855), but differs significantly in the number of rows of the radula and the shape of the central tooth.