Euspira sirenkoi, Pedriali & Sosso & Dell’Angelo, 2019

Pedriali, Luca, Sosso, Maurizio & Dell’Angelo, Bruno, 2019, Naticid gastropods from the middle Miocene of western Ukraine, Zootaxa 4700 (2), pp. 151-195 : 175-177

Euspira sirenkoi sp. nov.

(Fig. 28.1−4)

Type material. Holotype and 4 paratypes ( Table 12 ).

Type locality. Varovtsi , Ukraine .

Type stage. Middle Miocene (Upper Badenian) .

Etymology. The species is named after Dr. Boris Sirenko, Russian Academy of Sciences, Moscow, who provided material relevant to the present study.

Other material. Varovtsi: MZB 50519 (1 shell, Fig. 28.3); BD 167 (2 shells); MS 106 (1 shell).

Diagnosis. Small, oval shell with rather elevated spire and broadly oval last whorl. Protoconch I sculptured with spiral threads. Umbilicus deep, narrowly bean-shaped, largely covered by parietal callus (a narrow chink in most specimens); funicle small, depressed. Parietal callus thick, covering adapical part of umbilicus. Basal fasciole narrow, prominent. Colour pattern of uneven, whitish-brown collabral stripes over uniform, light brown background.

Description. Protoconch small, turbiniform, of 1.9−2.1 convex whorls, tip very small; protoconch I sculptured with unevenly noded, evenly spaced spiral threads. Teleoconch small, oval, higher than wide, thick. Spire conical, rather elevated, whorls gently convex; suture fine, adpressed. Last whorl broadly oval, narrowing abapically; subsutural shelf indistinct; periphery above midline. Aperture D-shaped in slightly prosocline plane; outer lip semicircular, inner lip nearly straight. Parietal callus thick, with straight to sligtly convex abapertural outline, ending with rounded, scarcely distinct anterior lobe, reaching basal fasciole. Umbilicus deep, very small, largely covered by parietal callus (a narrow chink in most specimens). Umbilical wall steep, narrowly arched and bounded abapically by basal fasciole. Funicle small, depressed, separated from umbilical wall by narrow, moderately deep spiral furrow and merging into anterior lobe of parietal callus. Basal fasciole narrow, prominent and bounded abapically by rounded step. Outer surface with fine growth lines; microscopic spiral striation present on last whorl. One specimen retains remnants of uniform, light brown background with pattern of uneven whitish-brown collabral stripes.

Remarks. Euspira sirenkoi sp. nov. is very similar to the Burdigalian to late Pliocene subspecies E. helicina helicina (Figs 27.9−11) in teleoconch shape, but differs from it by having: 1) a protoconch of about 0.5 fewer whorls, with smaller diameter (average values 0.634 mm and 0.937 mm, respectively) and smaller diameter of the first half-whorl (average values 0.088 mm and 0.122 mm, respectively), 2) a higher spire, which grows much faster with increasing shell height ( Fig. 10 ), 3) a slight to indistinct anterior lobe (well-developed in E. helicina helicina ), 4) an umbilical callus with straight abapertural outline (convex in E. helicina helicina ), 5) a larger umbilicus (see Fig. 16 ), 6) a narrowly prominent basal fasciole (indistinct in E. helicina helicina ), and 7) a smaller size.

The early Miocene to late Pliocene northwestern Italian species Euspira subobturata (Figs 28.5, 28.6) is also similar, but can be readily distinguished from E. sirenkoi sp. nov. in having a protoconch with larger diameter (average values 1.155 mm and 0.634 mm, respectively) and larger diameter of the first half-whorl (average values 0.194 mm and 0.088 mm, respectively), a more globose teleoconch, a distinct, rounded anterior lobe of the parietal callus, a wider, depressed basal fasciole, and a larger size.

The early Miocene French species Euspira benoisti (see Fig. 28.7, 28.8) is morphologically similar to E. sirenkoi sp. nov. and the values of the characteristic elements of its protoconch are basically identical to those measured for E. sirenkoi sp. nov. However, E. benoisti is readily differentiated from E. sirenkoi sp. nov. in that it has: 1) protoconch I sculptured with undulating, interconnected spiral cordlets forming an irregular somewhat reticulated pattern; 2) a more globose teleoconch with more convex whorls; 3) a rounded and wide anterior lobe of the parietal callus; 4) a wider, depressed basal fasciole; and 5) a larger size.

Finally, E. sirenkoi sp. nov. differs from E. protracta (Fig. 27.1−27.8) by having a protoconch with smaller di- ameter (average values 0.634 mm and 0.844 mm, respectively) and diameter of the first half-whorl (average values 0.088 mm and 0.164 mm, respectively, about half the size), protoconch I sculptured with coarser and less numerous spiral threads, a higher spire (see Fig. 10 ), a wider umbilicus (see Fig. 16 ) and a large size.

Distribution. Middle Miocene: Central Paratethys (upper Badenian) in Ukraine (this paper).

Figures

FIGURES 4–11. FIGURE 4. Relationship between the diameter of the first half-whorl of the protoconch and the protoconch diameter in the naticine taxa studied. FIGURE 5. Relationship between the diameter of the first half-whorl of the protoconch and the protoconch diameter in the poliniceine and sinine taxa studied. FIGURE 6. Relationship between the diameter of the first half-whorl of the protoconch and the protoconch whorls in the naticine taxa studied. FIGURE 7. Relationship between the diameter of the first half-whorl of the protoconch and the protoconch whorls in the poliniceine and sinine taxa studied. FIG- URE 8. Relationship between the protoconch diameter/diameter of the first half-whorl ratio and the protoconch whorls in the naticine taxa studied. FIGURE 9. Relationship between the protoconch diameter/diameter of the first half-whorl ratio and the protoconch whorls in the poliniceine and sinine taxa studied. FIGURE 10. Relationship between the spire height and the shell height for species of Euspira Agassiz in J. Sowerby, 1837 studied herein. FIGURE 11. Relationship between the spire height and the shell height for species of Payraudeautia Bucquoy, Dautzenberg & Dolfuss, 1883 studied herein.

FIGURES 12–19. FIGURE 12. Relationship between the spire height and the shell height for species of Polinices Monfort, 1810 studied herein. FIGURE 13. Relationship between the aperture width and the aperture height for species of Cochlis Röding, 1798 studied herein. FIGURE 14. Relationship between the aperture width and the aperture height for species of Payraudeautia Bucquoy, Dautzenberg & Dolfuss, 1883 studied herein. FIGURE 15. Relationship between the aperture width and the maximum diameter for species of Payraudeautia Bucquoy, Dautzenberg & Dolfuss, 1883 studied herein. FIGURE 16. Relationship between the umbilicus width and the maximum diameter for species of Euspira Agassiz in J. Sowerby, 1837 studied herein. FIGURE 17. Relationship between the umbilicus width and the maximum diameter for species of Payraudeautia Bucquoy, Dautzenberg & Dolfuss, 1883 studied herein. FIGURE 18. Relationship between the width of the umbilical callus and the maximum diameter for species of Cochlis Röding, 1798 studied herein. FIGURE 19. Relationship between the width of the umbilical callus and the maximum diameter for species of Tectonatica Sacco, 1890 studied herein.