Dicrogaster perpusilla Looss, 1902 sensu Sarabeev & Balbuena (Digenea: Haploporidae): a note of caution

Abstract

Sarabeev & Balbuena (2003) considered Dicrogaster perpusilla Looss, 1902 and D. contracta Looss, 1902 (Digenea: Haploporidae) synonymous. They designated a neotype for the type-species, D. perpusilla, from a sample of specimens ex Chelon labrosus off West Thurrock, UK. The morphology of the material (three specimen lots) studied by these authors was re-examined in detail and compared with their data. The material labelled 'D. perpusilla' from off West Thurrock, from which the neotype specimen was selected, consists of 14 specimens; of these one might belong to Haploporus Looss, 1902 and one to Haplosplanchnus Looss 1902. A well-developed genital atrium was observed in 11 of the 12 remaining specimens, and they all possess large saccular caeca and a vitellarium consisting of two groups of loosely coalesced follicles rather than two compact masses. These features suggest that the 12 specimens of this lot may belong to Saccocoelium Looss, 1902, but the state of the material does not permit its reliable identification. The specimen designated by Sarabeev & Balbuena (2003) as the neotype of D. perpusilla represents a neogravid dorso-laterally mounted specimen and is unrecognisable. Although five of the six voucher specimens of these authors may represent Dicrogaster spp., the poor state of this material does not allow its accurate identification. The metrical data obtained from this voucher material indicate that juvenile and laterally mounted specimens have been used in the comparisons upon which the synonymy of D. perpusilla and D. contracta was suggested. The overall conclusion of the study is that the synonymy of D. contracta and D. perpusilla proposed by Sarabeev & Balbuena (2003) is based on questionable material. Since the neotype of D. perpusilla is unrecognisable, and a number of qualifying conditions of the ICZN in its designation were not met, the usage of the original conception of the type-species of Dicrogaster given by Looss (1902) is recommended.