Historical development of nomenclature and taxonomy of Cyprideis torosa (Ostracoda)

The historical development of the complex nomenclature and taxonomy of the ostracod species Cyprideis torosa(Jones, 1850) is reviewed. Based on published volumes of the Kempf Database Ostracoda, the long span of time in which nomenclatural and taxonomic uncertainty existed is also documented.


Nomenclatural steps and their meaning
This section provides an overview of the historical development of the different kinds of naming (nomenclature) of the species torosa and its meaning (taxonomy).

Candona torosa Jones, 1850
In July 1850, under the binomen Candona torosa, the first description of the species was published by Thomas Rupert Jones (Jones 1850). Although he received Recent, though dead, specimens of this interesting species through the kindness of Mr Pickering from ditches at Gravesend, he only described and figured fossil shells from the non-marine Pleistocene deposits of the locality Grays. Detailed information on that type locality and the original specimens is provided by Frogley & Whittaker (2016).
A reason might have been the fact that the fossil valves showed tubercles or nodes while the Recent specimens presumably were smooth. However, it is more likely that Jones confined himself to the study of the fossil specimens and left the Recent material to the zoologists, because later in the great number of studies he published during his lifetime he exclusively described fossil Ostracoda.
Another peculiarity is the assignment of this new species to the genus Candona. In his description Jones mentioned the considerably developed hinge-margin of the valves, a fact that should exclude the species from the genus Candona. Until that time, however, no information had been given on the characteristics of the inside of the valves by the author of that genus (Baird 1845(Baird , 1846(Baird , 1850. We find an answer to Jones's decision in his monograph on the Entomostraca of marine Cretaceous deposits of England (Jones 1849), in which (on p. 5) he mentioned the fossil species of Candona from Grays, then thought to be Pliocene in age. As until 1845 there were only two useful genera named within the Recent Ostracoda, Cypris (freshwater) and Cythere (marine), the genus Candona (fresh and brackish waters) was thought by Jones to be ecologically intermediate.

Cyprideis
Jones, 1857 (a subgenus?) Cyprideis torosa (Jones, 1850) Jones, 1857 In his monograph of the Tertiary Entomostraca of England (Jones 1857) the generic-level name Cyprideis is coined for the monotypic species Cyprideis torosa (Jones, 1850). However, there is some uncertainty regarding the generic assignment. According to a tabular scheme on p. 9, Cyprideis is regarded with a question mark as a subgenus of Candona within the Cyprididae. But also on p. 9 in a footnote, Jones mentions the possibility that Cyprideis could prove to be a fresh-or brackish-water Cythere, while on p. 21 he mentions that, according to its hinge, Cyprideis closely resembles the marine genus Cytheridea. Cyprideis was used throughout this publication formally, like the name of a genus. The formal expression Candona (Cyprideis) is not given, although it was later cited by Sandberg (1964).
Cyprideis Jones, 1857 (a subgenus!) In a short publication (Brady 1864), living specimens of Cyprideis torosa (Jones, 1850) were reported from several places in Britain. A short description of the animal revealed that it differs only very slightly from that of the genus Cythere. Characteristics of the valves are reported to be quite variable. Following the description of Candona albicans, Cyprideis is treated informally as a subgenus.
Cyprideis Jones, 1857 (a genus!) On p. 49 of his survey of the marine Ostracoda of Norway (Sars 1866), the generic status of Cyprideis with clear differentiation from the genus Cythere was expressed based on the detailed description of the animal of the Recent brackish-water Cyprideis torosa.
Cytheridea torosa (Jones, 1850) Brady, 1867 On p. 122 of his 'Synopsis of the Recent British Ostracoda' (Brady 1867), the genus Cyprideis was considered to be a synonym of the genus Cytheridea. That led to a new combination of the species.
Cytheridea torosa (Jones, 1850) Brady, 1867 Cytheridea lacustris (Sars, 1863) Brady, 1867 Some confusion arose through the monograph of the Recent British Ostracoda (Brady 1868) in which detailed information was given for the 1867 combination with the genus Cytheridea. As a consequence, the typical freshwater shells of Cyprideis torosa with nodes (figured by Jones 1850, but also in 1857 as figs 1a-1i on pl. II) were considered to be synonymous with Cythere lacustris of Sars (1863) and referred to as Cytheridea lacustris. Only the sexually dimorphic Recent specimens with smooth shells from brackish waters were described under Cytheridea torosa (Jones, 1850).

Cytheridea littoralis Brady, 1869
In a publication on the Crustacea of the salt-marshes of Northumberland and Durham (Brady 1869), the new name Cytheridea littoralis was introduced for the Recent brackish-water species with smooth shells that Brady had described in his monograph under the name Cytheridea torosa (Jones, 1850).
Cytheridea torosa (Jones, 1850) Brady, 1867 Cytheridea torosa teres Brady & Robertson, 1870 The publication on 'The Ostracoda and Foraminifera of tidal rivers' (Brady & Robertson 1870) is of special significance. For the first time, besides the typical smooth forms, shells with nodes were also reported from collections of living specimens of Cytheridea torosa from Norfolk and Suffolk. A typical example was figured on plate VIII: 6 and 7. It was further reported, if both forms were found living together, that gradual transitions from smooth to forms with nodes were observable. As a consequence, in footnotes on pp. 21 and 22, Brady withdraws his recently established Cytheridea littoralis for the smooth forms and returns to Cytheridea torosa (Jones, 1850) of his 1868 monograph, but with the original meaning of T. R. Jones. From now on, the smooth forms should be regarded as variety teres. In fact, both Cytheridea littoralis as well as Cytheridea torosa teres were falling into the synonymy of Cytheridea torosa (Jones, 1850).
Cytheridea torosa torosa (Jones, 1850) Brady, 1867 Cytheridea torosa littoralis (Brady, 1869) Müller, 1912 On p. 326 of his manual on Ostracoda (Müller 1912), the freshwater form with nodes described by Jones in the fossil state is listed as Cytheridea torosa (Jones, 1850). It is no longer seen as a synonym of Cythere lacustris Sars, but vice versa, Cythere lacustris Sars is considered to be synonymous with Cytheridea torosa. Due to intermediate forms that had become known in the meantime, Cytheridea littoralis Brady, 1869 is treated only as a subspecies of Cytheridea torosa.
Evidence for the separation of the genera Cythere, Cyprideis, Cytherissa and Cytheridea was presented.

Gradual acceptance of the facts
With the publication of Sars (1925), Cyprideis finally became confirmed as a genus. In addition, with the detailed statement of Brady in his footnotes in Brady & Robertson (1870), it was also explained as a fact that the specific name Cyprideis torosa was valid for both noded and smooth forms of that species. In more recent years, an excellent example of this was studied and figured by Keyser & Aladin (2004).
As a consequence, from 1925 onwards Cyprideis torosa (Jones, 1850) Jones, 1857 should have been accepted and referred to by the community of ostracod researchers. However, looking at the literature dealing with Ostracoda it can be stated that those facts were accepted only gradually. On the contrary, for a very long time the splitting into two species, as published by Sars (1925), was followed. In particular, the many researchers dealing solely with the smooth forms used the name Cyprideis littoralis for this species, often using the incorrect subsequent spelling Cyprideis litoralis. Based on the Index D publication of the Kempf Database Ostracoda (Kempf 2006), two lists have been prepared to demonstrate this story (Tables 1 and 2). The detailed literature citations may be consulted in the published bibliographies of the Kempf Database Ostracoda, also known earlier as Cologne Database Ostracoda (Kempf 1980b(Kempf , 1988(Kempf , 1991(Kempf , 1994(Kempf , 1996(Kempf , 1997(Kempf , 2002a(Kempf , b, 2013. Within the two tables, the cited UTIN (Universal Taxonomic Identification Number) Ostracoda, G0147 07714 for Cyprideis torosa and G0147 04245 for Cyprideis littoralis, is based on the numbering of genera and species in the Index B version of the Kempf Database Ostracoda (Kempf 1980a, and supplements). That numbering system is similar to and may be used universally like the ISSN numbers for journals or publication series. For the c. 80 000 named taxa registered in the Kempf Database Ostracoda such UTINs already exist. This novel UTIN system for the Recent and fossil Ostracoda may serve as a model for other groups of named organisms in the future.

Additional problems
Of course, additional problems exist. Collected specimens of Cyprideis torosa, for instance, may have been described under other species names.
A similar example is connected with a species of Cyprideis from Lake Qarun in Egypt. In a publication of Abdel-Malek & Ishak (1980), that species was cited as Cyprideis littoralis. In other publications with the results of detailed studies (Bassiouni et al. 1985(Bassiouni et al. , 1986, that species was reported as Cyprideis sohni Bassiouni, 1979. In more recent years it could be proved through the investigation of newly collected material from Lake Qarun (Wouters 2002) that Cyprideis sohni of Lake Qarun should be regarded as a synonym of Cyprideis torosa.
However, there are also opposite cases in which collected specimens were recorded as Cyprideis torosa, or under the synonym Cyprideis littoralis, but in reality represented different species. Such cases are known from America. Revising studies led to the    17 Development of nomenclature and taxonomy of C. torosa