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Family Mathildidae Mathildids
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The Mathildidae is a group of deep-water molluscs, reported by Rüdiger Bieler (1995) to contain about 130 species, occurring in both the Atlantic Ocean and the Indo-Pacific region. The group has an extensive fossil record, with many of the genera being based on fossil types. The dominant shell character of the family is the heterostrophic protoconch, where the protoconch axis is offset markedly from the teleoconch axis. The family in NSW was revised by Charles Laseron in 1951, published as a section in his revision of the NSW Pramidellidae (Laseron, 1951). Working entirely from empty shells, and with limited microscope magnification, Laseron assigned six NSW species to the family, four of them described as new. The next work on the group was by Bieler, in 1995, when he described shells of the family from deep-water dredging off New Caledonia and the Loyalty Islands. Being the first work on the family for 40 years, Bieler conducted "a housekeeping" and reassigned most of Laseron's species to other families, leaving just one species in the NSW fauna. For reference, the species of Mathildidae that had been included in the family by Laseron, (1951) that were reassigned by Bieler (1995) were: Eucharilda elegantula Angas, 1871. Bieler examined the type and placed this in the Pyramidellidae. Eucharilda pleurorbis Laseron, 1951. Belongs in the Triphoridae. Opimilda protolineata Laseron, 1951. Belongs in the Triphoridae. Opimilda porrigata Laseron, 1951. Possibly belongs in the Cerithiopsidae. Opimilda fastigia Laseron, 1951. Removed from Mathildidae, but placement uncertain. Family References Bieler, R. 1995. Mathildidae from New Caledonia and the Loyalty Islands (Gastropoda: Heterobranchia). In P. Bouchet (ed.), Résultats des Campagnes MUSORSTOM, Volume 14. Mém. Mus. natn. Hist. nat.,167: 595–641 Laseron, C. 1951. The New South Wales Pyramidellidae and the genus Mathilda. Records of the Australian Museum 22(4): 298–334. Coverage Following the work of Bieler (1995) there is now only one NSW species, Mathilda decorata Hedley, 1903, placed in this family. Identification Notes The single NSW species is recognised by an elongate shell elaborately sculptured with spiral and axial elements, with a prominent heterostrophic protoconch.
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