Polycope sanctacatherineae Whatley & Downing 1983

Warne, Mark T., Jones, Peter J. & Kornicker, Louis S., 2006, Referral of the Halocypridina Thaumatocypris (Miocene, Australia) to the Cladocopina (Ostracoda, Halocyprida), Zootaxa 1260, pp. 47-55 : 50-53

Polycope sanctacatherineae Whatley & Downing 1983

Figs. 2 B–D

1955 Thaumatocypris ; Nadeau, 93

1972 Thaumatocypris Nadeau ; McKenzie, 179 1974 Polycope sp. McKenzie, 160, pl. 1, fig. 1

1978 Thaumatocypris Nadeau, De Deckker & Jones , 173

1983 Polycope sanctacatherineae Whatley & Downing , 387–388, pl. 8, figs. 20–21 1987 Polycope sanctacatherineae Whatley & Downing ; Warne, 441, pl. 1, fig. A 1990 Polycope sanctacatherineae Whatley & Downing ; Warne, 60–62, pl. 2, figs. 1A, 2A–D

Nadeau material. Five disarticulated valves (3 complete adults and 2 fragmented juvenile? specimens) from the mid­Miocene (Balcombian) Glenample Clay, 1.6–2.4 km southeast of Princetown, Otway Basin, Victoria. Figured specimens are housed in the invertebrate palaeontological collections of the Museum of Victoria under the registered number NMV P109502 (i.e. all 5 specimens are housed on this assemblage slide).

Description. RV, NMV P109502 (specimen 1; Fig. 2 D) 1: L = 0.42 mm, H = 0.34 mm; LV, NMV P109502 (specimen 2; Fig. 2 C): L = 0.41 mm, H = 0.33 mm; RV, NMV P109502 (specimen 3): L = 0.36 mm, H = 0.33 mm; NMV P109502 (specimen 4; fragment): L & H = not determined; NMV P109502 (specimen 5; fragment): L & H = not determined.

Carapace is relatively small, opaque or semi­translucent, well calcified, subcircular in lateral view, compressed in dorsal view. Externally, the valves possess strongly expressed concentric ribs and reticulate ornamentation as well as conspicuous, although delicate, marginal spines (often broken). Typical of all adult specimens of this species, material from the Glenample Clay here illustrated possesses two strong concentric ribs subparallel to the anterior and ventral margins of valves. In some (but not all) particularly strongly calcified adult specimens (i.e. Figure 2 C), some muri in the center of the valves align to form a third small, poorly defined rib or ridge. Right valve slightly overlaps left valve. One strong marginal spine extends from the anterior margin above mid height. Three to four generally smaller spines extend from the anterodorsal margin adjacent to the external manifestation of the carapace hinge. One strong spine also extends from the posterior margin at about mid height. Internally, inner lamella is narrow and the hinge adont. Adductor muscle scars are a cluster of three tightly interlocking, centrally located scars. Normal pore canals are scattered. Shadows of external reticulate ornaments are visible from an internal perspective. Other internal features are not visible.

Remarks. Polycope sanctacatherinae , P.? favus Brady 1880, Polycope demulderi Sissingh 1972 and Polycope sp. 1 Whatley & Downing 1983 all possess similar carapace morphologies. However, Polycope sanctacatherinae lacks the broad, relatively thick peripheral exterior carapace rim of P.? favus; and Polycope demulderi and Polycope sp. 1 Whatley & Downing 1983 both possess one subconcentric rib, while Polycope sanctacatherinae possesses at least two subconcentric ribs. The best preserved adult specimens of Polycope sanctacatherinae from the Glenample Clay present on Betty Nadeau’s slide P109502 have slightly stronger ornamentation than the type material illustrated by Whatley & Downing (1983) from the Balcombe Clay, although the reticulation pattern in specimens from both lithostratigraphic units is the same. Those of Nadeau's specimens illustrated here (well preserved) appear to have slightly stronger (higher) muri and subconcentric ribs compared to Whatley & Downing's illustrated holotype, which is also slightly smaller (length 0.38 mm), and other well preserved specimens that one of us (MTW) has examined from the type locality. We interpret this difference as morphological (ecophenotypic) variation within Polycope sanctacatherinae , with slight variations in the degree of aggradation (i.e., calcification) of the muri and subconcentric ribs being a consequence of ostracod physiological responses to geochemical fluctuations at the sediment­sea water interface. However, we cannot completely exclude taphonomic factors being responsible for this particular variation. Of additional note, various poorly preserved specimens of this species (not illustrated here) from Betty Nadeau's Glenample Clay collection clearly exhibit the effects of secondary (diagenetic) accretion of mineral material or abrasion.

The Balcombian Polycope sp. illustrated by McKenzie (1974: pl. 1: fig. 1; refigured here as Fig. 2 B) bears the highly sculptured pattern characteristic of an adult specimen of Polycope sanctacatherinae . There is an apparent discrepancy in the magnification of x246 given by McKenzie, which results in a length of 0.24 mm (including spines), whereas the length of the adult holotype of P. sanctacatherinae is 0.38 mm. A magnification of x146 would be more appropriate for McKenzie’s specimen. We were unable to locate the specimen (not at the Australian Museum, Museum of Victoria, Natural History Museum (London), National Museum of Natural History (Washington, D.C.)). Many specimens that McKenzie had retained in his home laboratory were deposited in the Australian Museum, Sydney after his demise. One of us (PJJ) examined the collection, which at present is roughly sorted and packed in temporary boxes, but it did not contain the sought after Polycope sp. or other specimens illustrated in the McKenzie 1974 paper. At present we regard the length of this specimen as unknown.

Figures

FIGURE 2. A, Thaumatocypris (= Pokornyopsis) feifeli Triebel l 941, holotype, left valve, length 1.02 mm, Oxfordian, Malm, Late Jurassic (figure from Triebel 1941: pl. 13: fig. 140 a). B – D, Polycope sanctacatherinae Whatley & Downing 1983: B, right valve, length unknown, Balcombian, Miocene (figure from McKenzie 1974: pl. 1: fig. 1); C, D, left (length 0.41 mm) and right (length 0.42 mm) valves, Glenample Clay, Miocene, from Nadeau slide P 10952.