| P number: | P550289 |
|---|---|
| Caption: | Pleurotomaria gigantea, a gastropod from the Cretaceous. |
| Description: | Pleurotomaria gigantea is an archaeogastropod from the early Cretaceous of southern England. Modern species of Pleurotomaria show that this species belongs to this more primitive group of gastropods which have paired gills. Pleurotomaria gigantea has a large, conical shell (trochiform) with the surface of each whorl flattened. The outer surface of the shell is ornamented with thin, spiral ribs or cords. A slight notch in the aperture means that, as the gastropod grew and increased the number of whorls, the notch left a trace in the growth lines (called slit-band or selenizone). Gastropods are molluscs with a muscular foot, eyes, tentacles, and a rasp-like feeding organ (a radula), although only the coiled or conical shell is fossilised. The earliest Cambrian species were marine, but gastropods now colonise fresh water and the land. Classification is based mainly on soft body parts, which are not fossilised, and although there is uncertainty, most fossils appear to fall into one of three groups: 1. Archaeogastropods which have two auricles in the heart, two gills and two kidneys. 2. Caenogastropods which have one gill, auricle and kidney and sometimes a siphon. 3. Pulmonates which have a lung. |
| Photographer: | Unknown |
| Copyright statement: | Unknown |
| Orientation: | Landscape |
| Size: | 425.93 KB; 1000 x 911 pixels; 85 x 77 mm (print at 300 DPI); 265 x 241 mm (screen at 96 DPI); |
| Average Rating: | Not yet rated |
| Categories: | Best of BGS Images/ Fossils |
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