Warthia zakharovi Kaim, 2009

Foster, William J., Danise, Silvia & Twitchett, Richard J., 2017, A silicified Early Triassic marine assemblage from Svalbard, Journal of Systematic Palaeontology 15 (10), pp. 851-877 : 865-866

Warthia zakharovi Kaim, 2009

( Fig. 10 )

2009 Warthia zakharovi Kaim : 141, figs 132–134.

Material. One hundred and thirty-eight specimens from LD-04 ( NHMUK PI MG 1468–1473 ; NHMUK PI MG 1495–1496 ; NHMUK PI MG 1502–1511 ; NHMUK PE PEI 5478–5482; NHMUK PE PEI 5484–5490; NHMUK PE PEI 5505; NHMUK PE PEI 5507; NHMUK PE PEI 5509–5513; NHMUK PE PEI 5519–5520; NHMUK PE PEI 5522), and 193 specimens from LD-05 ( NHMUK PI MG 1467 ; NHMUK PI MG 1474–1481 ; NHMUK PI MG 1483 ; NHMUK PI MG 1485–1494 ; NHMUK PI MG 1497–1499 ; NHMUK PI MG 1512 ; NHMUK PE PEI 5475–5477; NHMUK PE PEI 5483; NHMUK PE PEI 5491–5504; NHMUK PE PEI 5506; NHMUK PE PEI 5508; NHMUK PE PEI 5514–5518; NHMUK PE PEI 5521) .

Diagnosis. Warthia with wide shell in comparison to its thickness and weakly depressed selenizone.

Description. Shell globular, almost as long as wide. Slit short and broad at base of U-shaped sinus. Weakly depressed selenizone. In well-preserved specimens growth lines can be observed. Aperture is arched around earlier whorls, and curved inwards by the selenizone.

Remarks. The shell of Warthia is usually entirely involute and overgrows the umbilicus. In some of our smaller specimens, the umbilicus is still visible, but in larger specimens it has become overgrown during subsequent growth. Even though our specimens lack an inductural layer and have growth lines that have not previously been recorded in Early Triassic Warthia species, in Permian species of Warthia visible growth lines or wrinkles have been recorded (e.g. W. micromphala and W. stricta ; Waterhouse 1963) and, therefore, we consider our specimens to belong to Warthia .

The question of whether bellerophontids had a planktonic larval stage is unresolved (Nutzel & Mapes 2001). The protoconch in bellerophontids may be very small, less than one whorl, and is succeeded by the teleoconch ( Fryda 1999), and in our specimens the initial whorl is overgrown almost immediately. The small size (<0.05 mm), bilateral symmetry and lack of ornamentation in the initial whorls of Warthia zakharovi recorded in this study ( Fig. 10H ) are comparable to the embryonic shells of Bellerophon from the late Silurian that Fryda (1999) interpreted as indicating planktotrophy. A planktotrophic larval stage is, therefore, inferred for Warthia zakharovi .

Mode of life. Surficial, fully motile, slow, surface deposit feeder ( Linsley 1977).

Figures

Figure 10. Warthia zakharovi Kaim, 2009. A, NHMUK PI MG 1502, apertural view; B, C, NHMUK PI MG 1505; B, apertural view; C, lateral view; D, E, NHMUK PI MG 1509; D, lateral view; E, apertural view; F, NHMUK PI MG 1508, apical view; G, H, NHMUK PI MG 1504; G, apical view; H, protoconch. Scale bars = 500 µm, except H.