Abstract
Abstract. The genus Axelheibergella is established for cladocopid ostracods with well-developed, radially aligned septa between the outer lamella and the relatively wide, free-margin infold parts of the shell. Two deep-water species of the genus are described from the Holocene of the Alpha Ridge rise and Axel Heiberg slope, central Arctic Ocean (CAO). Two other species are present in the warmer, shallower waters of the Mediterranean region. Presumably the septa are designed to strengthen the free margin of the shell. The relationship of the camerae (interseptal chambers) to marginal pore canals in extant ostracods, including the Punciacopina, and to the marginal shell glands of cladocopids and halocypridid myodocopids is discussed. Cladocopid and podocopid (podocopine) shell ultrastructure is discussed, and new terms are defined. The septate frill and its function in the enigmatic Punciacopina are discussed in the light of recent discoveries of the radically different lifestyle of Manawa, and presumably of Puncia and Promanawa, from other non-punciacean ostracods. It is suggested that the frill of the Punciacopina is homologous to the ala of some cytheracean (cytherurid) podocopid ostracods. Two unnamed species of Puncia from the New Zealand Pleistocene are illustrated, and complement the discussion of septa and camerae in Axelheibergella.
Highlights
This study is based on an examination of the ostracods present in the top CL1 cm section of two bottom sediment samples from the central Arctic Ocean CAO (Fig. 1), one from the Alpha Ridge (CESAR 83-211, at a present-day water depth (PDWD) of 1730m) and the other from the continental margin off Axel Heiberg Island (AH 87200-009, 1150m PDWD)
CESAR 83-21 1 is the 0-1cm section from the top of a 46 cm-long Benthos gravity core retrieved from the Alpha Ridge graben, 1730m PDWD, at 85'43.9'N, 108'51.9' W. (Jackson et al, 1985).Axel Heiberg AH 87200-009is the 0-1 cm section from the top surface of sediment retrieved by a Dietz-LaFond grab from the upper slope, 1150 m PDWD, at 82'09.62", 102'33.87'W
More research on the nature and extent of sensilla and exocrine types of marginal pore canals in cladocopids is needed, but the limited data available indicate the presence of one or the other or both types of pore canals in some taxa, these structures are not known in any great detail
Summary
This study is based on an examination of the ostracods present in the top CL1 cm section of two bottom sediment samples from the central Arctic Ocean CAO (Fig. 1), one from the Alpha Ridge (CESAR 83-211, at a present-day water depth (PDWD) of 1730m) and the other from the continental margin off Axel Heiberg Island (AH 87200-009, 1150m PDWD). Several intermediate-depth to deeper-water ostracod species that are common in the assemblages of the Amerasian and Eurasian Basins have been described as new by Whatley & Eynon (1996) from deep-water sites in the Greenland Sea area of the North Atlantic Ocean Two of these taxa are present in assemblages containing Axelheibergella from the CESAR and Axel Heiberg sites (Table 1).
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