Thirty five species attributed to Serrata Jousseaume, 1875 are recognized from the bathyal zone of New Caledonia. Four of these, S. beatrix (Cossignani, 2001), S. tuii (Cossignani, 2001), S. stylaster (Boyer, 2001) and S. boucheti (Boyer, 2001), were previously described in other genera, and 31 other species are here described as new. This series of 35 Serrata species from New Caledonia increases five-fold the Recent specific diversity recognized in the genus. The diversity of Serrata species from New Caledonia is inferred to be very partially known, based on the fact that 31% of the identified species are represented in the collections by only one specimen and that 51% were collected at only single stations. The important Serrata fauna documented here has an asymmetrical geographical distribution in New Caledonia, the highest diversity of species being found off far southern New Caledonia and on the northern Norfolk Ridge. The Serrata fauna from New Caledonia, the Loyalty Ridge and the Norfolk Ridge appears to be isolated in the southwest Pacific, but it has affinities with several species occurring in the fossil or Recent fauna of Australia and New Zealand. The fossil distribution of Serrata extends from the Eocene of Alabama to the Pliocene of New Zealand. The distribution of the genus in the Recent seems to be restricted mostly to the southern Indo-Pacific latitudes from Cape Agulhas to the Tuamotu Islands, with maximum diversity from the Australian Platform to the Norfolk and New Caledonia Ridges. The fossil genera Euryentome Cossmann,1899 and Conuginella Laseron, 1957 and the Recent genera Deviginella Laseron, 1957 and Serrataginella Coovert & Coovert, 1995 are proposed as junior synonyms of Serrata. Marginella anatina Lea, 1833 is used instead of Euryentome silabra Palmer, 1937 as the valid name for the type species of the genus Euryentome. The fossil genus Strombiginella Laseron, 1957 is placed in synonymy with the recent genus Hydroginella Laseron, 1957. Serrata and Hydroginella do not seem more closely related to each other than they are to Volvarina-Prunum or to the Austroginella and Dentimargo groups. The “Serrata Group” sensu Coovert & Coovert 1995, composed of Hydroginella, Serrata and 3 synonymous genera, is rejected as being a possibly polyphyletic assemblage. The high disparity in the specific shell morphologies of Serrata, the frequent combination of features found as typical in Volvarina and Dentimargo in the Recent, the occurrence of many morphological intergrades between these genera since the Mid-Eocene of the western Tethys sea, and the higher specific frequency of the plesiomorphic character of a radula with numerous cusps, together suggest that the genus Serrata may be situated near the base of the common stem from which most of the Recent groups of the Volvarina-Dentimargo complex have differentiated. |
