Riedelia is a genus of alga known from the fossil record, comprising approximately eight species. Many of the species were originally described under the closely allied genus Hemiaulus. Paleontologists Hans-Joachim Schrader and Juliane Fenner, working with fossil specimens obtained from Leg 38 of the Deep Sea Drilling Program

Deep Sea Drilling Program

The Deep Sea Drilling Project was an ocean drilling project operated from 1968 to 1983. The program was considered to be successful as evidenced by the data and publications that have resulted from it and is now supported by Texas A&M University, although for the years of its operations these were...

 in the Norwegian

Norwegian Sea

The Norwegian Sea is a marginal sea in the North Atlantic Ocean, northwest of Norway. It is located between the North Sea and the Greenland Sea and adjoins the North Atlantic Ocean to the west and the Barents Sea to the northeast. In the southwest, it is separated from the Atlantic Ocean by a...

 and Greenland Sea

Greenland Sea

The Greenland Sea is a body of water that borders Greenland to the west, the Svalbard archipelago to the east, Fram Strait and the Arctic Ocean to the north, and the Norwegian Sea and Iceland to the south. The Greenland Sea is often defined as part of the Arctic Ocean, sometimes as part of the...

s, decided that several previous descriptions of diatoms belonging to Hemiaulus were rightfully placed on Riedelia. Schrader and Fenner note that while Hemiaulus diatoms have polygonal areolated valves, Riedelia valves are punctate with isolated punctae. Additionally, Riedelia typically have two spines, while Hemiaulus have only one. These characteristics were used to justify the placement of these species in Riedelia.

Riedelia clavigera is known from fossils dating from the early Eocene

Eocene

The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

 to the middle Oligocene

Oligocene

The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...

.

Species

The valid species currently considered to belong to this genus are:

• R. alata (Greville) H.J.Schrader & J.Fenner
• R. altar (J.Brun) H.J.Schrader & J.Fenner
• R. clavigera (A.Schmidt) H.J.Schrader & J.Fenner
• R. longicornis (Greville) H.J.Schrader & J.Fenner
• R. lyriformis (Greville) H.J.Schrader & J.Fenner
• R. mirabilis Jousé
• R. sublevata J.Fenner
• R. tenuicornis (Greville) H.J.Schrader & J.Fenner