Tyrrhenocythere transitivum, Pipík, 2007

Pipík, Radovan, 2007, Phylogeny, palaeoecology, and invasion of non-marine waters by the late Miocene hemicytherid ostracod Tyrrhenocythere from Lake Pannon, Acta Palaeontologica Polonica 52 (2), pp. 351-368 : 360-361

Tyrrhenocythere transitivum sp. nov.

Figs. 4N–R, 5A–C, I 1 , I 2 , L, 6E .

Derivation of the name: After intermediate arrangement of the anterior marginal pore canals between those of the genera Hemicytheria and Tyrrhenocythere .

Type material: Holotype: SNM RP27−16 , a complete LV ♀ and 7 paratypes: SNM RP26−4 − 4 , LV ♀; SNM RP27−17 , LV ♀; SNM RP27−19 , LV ♀; SNM RP27−18 , LV ♂; SNM RP27−20 , RV ♀; SNM RP27−21 , RV ♂; SNM RP27−22 , RV ♀.

Type locality: Pezinok, clay pit, Danube Basin; co−ordinates—48 ° 16’720’’ N and 17 ° 16’340’’ E.

Type horizon: Pannonian, zone E, late Miocene, Neogene.

Material.— 42 adult valves, 52 juvenile valves.

Diagnosis.— Tyrrhenocythere transitivum sp. nov. differs of other Tyrrhenocythere in having incompletely developed “brushes” on AM. T. transitivum sp. nov. differs from Hemicytheria folliculosa , H. marginata , and H. dubokensis by having the MPC on AM divides into 2–4 canals, which subsequently bifurcate into 2–3 canals.

Description.—LV ♀ (holotype): anterior curved; DM straight and sloping toward posterior, only the posterior angle is visible; PM straight to slightly curved; PVM strongly rounded with posterior process; VM straight; outline sub−rectangular; maximum height at anterior, behind the eye spot.

RV ♀ : AM symmetrically rounded; ADM slightly rounded to straight; DM straight and sloping toward posterior; anterior and dorsal angles rounded; PM straight to curved; PVM strongly rounded with distinctive posterior process; VM curved in the first third then straight; outline sub−rectangular; maximum height at anterior, behind the eye spot.

Sexual dimorphism:males longer with rectangular valves.

Muscle scars: consisting of a vertical row of 6–8 scars (the first and second from the top divided in two, the third can be thin and elongate or divided into two smaller elongate scars), with three additional scars anteriorly ( Fig. 5I 1 ).

Normal pore canals: open, rare at the centre, more frequent toward outer margin.

Hinge (amphidont): the hinge ( Fig. 5I 2 , J) of the LV is composed of a large, elongate and divided anterior socket; an elliptical tooth that continues into a thin, smooth bar; an elongated posterior socket with slight crenulations (3 elements) on the dorsal side that opens into the interior; a tiny tooth in middle of posterior socket. The hinge of the RV has a tooth divided into two lobes; an elongated socket, a straight, smooth groove; a kidney−shaped elongated posterior tooth, dorsally delicately crenulated with 3 elements.

Ornamentation: prominent; central area with circular to semicircular pits; toward outer margin, the pits connect and form polygonal fossae with reticulation of second order; polygonal fossae on outer margin with smooth solum; a strong ventral rib along the PM terminating on PDM; an anterior rib starting in ADM and extending along the entire AM, terminating on centro−ventral margin below ventral rib; tiny riblets visible between anterior rib and external AM; similar ribblets developed on PVM; two−three parallel ribs on dorsal and one−two weak ventral ribs above ventral rib; three spines on PVM; five weak anterior spines; eye tubercle smooth; pore conuli on anterior and posterior.

Marginal zone: inner lamella large with a series of parallel striae; inner margin parallel with outer margin; large anterior MPC on AM divides into 2–4 canals which subsequently bifurcate into 2–3 canals ( Fig. 6E ); individuals with straight MPC are also observed; MPC on VM right, short and thin, some fused at the base; large zone of fusion; drop−like space between the anterior MPC; irregular, slightly sinusoidal line of concrescence on AM which become straight posteriorly.

Discussion.—A surface covered with circular to semicircular pits in combination with polygonal fossae is a very common feature in Pannonian Hemicytheria . H. folliculosa from the Pannonian of the Vienna Basin has a surface densely covered with circular pits and a slightly concave DM on the LV ( Pokorný 1952: 289). Female LVs of Hemicytheria dubokensis and H. marginata each have a very high anterior and a low posterior connected by a long and straight DM ( Sokać 1972: pl. 38: 3, pl. 36: 8; Krstić 1985: 139).

Stratigraphical and geographical range.—This species is known only from the Pannonian deposits in Pezinok.

Figures

Fig. 5. Late Miocene hemicytherid ostracods from the layer 36+37A in Pezinok, Slovakia. A–C, I, L. Tyrrhenocythere transitivum sp. nov. A. RV♂, paratype, SNM RP27−21, external lateral view. B. LV♂, paratype, SNM RP27−18, external lateral view. C. LV♀, paratype, SNM RP26−4−4, external lateral view. I. LV♀, paratype, SNM RP27−19, internal lateral view; I1, central muscle scars; I2, detail of hinge. L. RV♀, paratype, SNM RP27−22, internal lateral view, detail of hinge. D. Tyrrhenocythere sp. 1, RV, SNM RP27−2, external lateral view; D1, SEM photo; D2, valve in transparent light. F. Tyrrhenocythere sp. 2, RV♀, SNM RP28−2, external lateral view. G, J. Tyrrhenocythere pezinokensis (Jiříček, 1985). G. LV♀, SNM RP27−8, internal lateral view, G1, central muscle scars; G2, detail of hinge. J. RV♀, paratype, SNM RP27−5, internal lateral view, detail of hinge. E, H, K. Tyrrhenocythere rastislavi sp. nov. E. RV♂, paratype, SNM RP26−16−1, external lateral view. H. RV♀, paratype, SNM RP27−15, internal lateral view; H1, central muscle scars; H2, detail of hinge. K. LV♀, paratype, SNM RP27−12, internal lateral view, detail of hinge.

Fig. 1. A. Palaeogeographical map of Europe in the upper Miocene (9.5 Ma) (after Steininger and Rögl 1985). B. Lake Pannon in a time of maximum flooding surface in Pannonian zone E (Spiniferites paradoxus Biochron) (after Kováč 2000).

Fig. 2. Geographical sketch (A) and lithological col− umn (B) of Pezinok clay pit (Pipík 1998). C. Detail of the sequence with Tyrrhenocythere mirror swamps and shallow water sedimentation on the bord of freshwater− /miohaline lake (Baráth et al. 1999).

Fig. 6. Marginal pore canals on anterior margin and their transformation from straight Hemicytheria arrangement to brush−like Tyrrhenocythere one. A. Hemicytheria reniformis (Reuss, 1850), Hemicytheria folliculosa (Reuss, 1850), Hemicytheria omphalodes (Reuss, 1850), original by author. B. Hemicytheria biornata (Zalányi, 1944), original by author, Hemicytheria maeotica Olteanu 1989 after Olteanu and Vekua (1989). C. Hemicytheria major Sokač, 1972. D. Hemicytheria marginata Sokač, 1972 after Sokać (1972). E. Tyrrhenocythere transitivum sp. nov. F. Tyrrhenocythere pezinokensis (Jiříček, 1985). G. Tyrrhenocythere rastislavi sp. nov. original by author.