Pseudochama radians ( Lamarck, 1819 )

Simone, Luiz Ricardo L., 2024, New species, misidentifications and problematic taxonomy of some Atlantic South American marine mollusks: a review, Papéis Avulsos de Zoologia 64, pp. 1-104 : 89-90

Pseudochama radians ( Lamarck, 1819) revalidated

Chama radians Lamarck, 1819: 96 .

Chama cristella Lamarck, 1819: 96 (l′Océan de grandes Indes).

Type locality: "l′Océan de grandes Indes?"

Remarks: In the case of Pseudochama radians , the species has a notably problematic taxonomic history. Consequently, our approach to this species differs from the conventional method applied to other species. Instead of adhering strictly to the orthodox approach, we opt for a chronological explanation.

Currently, P. radians has been considered a synonym of P. cristella , both of which were described in the same paper, on the same page, and share the same type locality. It is worth noting that although P. radians precedes P. cristella (being species 12 and 13, respectively), this chronological order does not hold significance according to the International Code of Zoological Nomenclature (ICZN). The resolution of simultaneously published names is guided by the Principle of First Reviser (Art. 24.2).

Accordingly, Reeve (1847) was the first reviser, but he covered both species:

C. radians – pl. 4, fig. 19, local: -----? (Lamarck described for "Ocean des grades Indes?");

C. cristella – pl. 8, fig. 42, local "Batavia" (?) (Lamarck described it for"grades Indes").

Reeve (1847) included both species, rendering the paper unsuitable for resolving the priority of names. Notably, the author modified the locality information for both species. In the case of C. radians , he retained only the original designation′s question mark. Conversely, for C. cristella , the location changed from the initially stated ‘undoubtful grandes Indes′ to ‘Batavia.′ Notably, Batavia appears to have been a region in the Netherlands, existing from 1795 to 1806.

The second reviser was Clessin, 1889, who also studied both species:

C. cristella (sp. 18, pg. 17, for Portorico);

C. radians (sp. 50, pg. 36, for Indischer Ocean, with the remark: "Reeve gibt keinen Fundort an." – means Reeve does not provide a location, but Lamarck did… see above).

The examination of both species by Clessin (1889) also fails to resolve the priority of names. Nevertheless, the author did relocate C. cristella to the Caribbean (specifically Puerto Rico), associating it with C. radians .

Subsequent to these studies, C. cristella seemingly vanished from the literature on the Western Atlantic, with only occasional citations, such as those by Steyn & Lussi (1998) for South Africa and other papers in the Indo-Pacific region. In contrast, C. radians continued to be extensively mentioned,with approximately 40 papers citing the species. Notably, Huber (2010) resurrected an Atlantic C. cristella , designating it as the valid name and providing justification on page 678:

"Against page priority the type species Pseudochama, SD Gardner, 1926 P. cristella is here selected to represent this well known Caribbean species. The type locality of Pseudochama cristella ( Lamarck, 1819) is corrected to the P.radians type locality Virgin Islands, St. Croix. There also the closest matching specimen has been found.″

Consulting Gardner (1926: 92), in the supposed "subsequent designation" of the type of Pseudochama there is:

" Type: Pseudochama cristella (Lamarck) . (Recent from the Gulf of Siam to Java, the Molluccas, and Australia.)″

An apparent anomaly arises when considering Gardner′s concept of P. cristella , which pertains to the Indo-Pacific region. In contrast, Huber (2010) replaces the Western Atlantic P.radians with this very entity. However, there are additional complexities:

Upon consulting the original description of the genus Pseudochama by Odhner (1917: 30), the following details emerge:

"LYNGE (1908) gives a satisfactory criticism of CLESSIN′s opinion as to the Chama cristella of Reeve, which, according to the last-named author, is specifically distinct from the type of Lamarck, a view that cannot be maintained. The species is distributed from the Gulf of Siam to Java, the Moluccas, and Australia ( Lynge, 1909). It is at once recognized by its orange colour and raised crista-shaped form, due to its attachment with the front half of the right valve, while its hind part is sharply bent from the substratum. I have referred this species to a new genus, Pseudochama , which comprises the so-called "inverse" Chamas, opposite to the normal or dextrally…" [my bold for emphasis].

These concluding paragraphs lead us to three key observations:

1) Pseudochama cristella does not emerge as a subsequent designation by Gardner in 1926. Odhner (1917) distinctly established it as the type species of the genus through original designation and monotypy.

2) There is a possibility that the Indo-Pacific ‘ Chama cristella of Reeve′ mentioned by Odhner (1917: 30) does not correspond to Lamarck′s (1819) species from the Caribbean. It appears to be a misidentification, as Odhner seems to have had a different species in hand, distinct from the true C. cristella . Despite labeling it as the ‘ C. cristella of Reeve,′ the author acknowledged and discussed the observed differences.

3) The alteration of the type locality of Chama cristella to ‘ Virgin Islands, St. Croix′ by Huber (2010) seems inappropriate. This information lacks support in any published source, and the justification provided concerning P.radians type locality lacks clarity.

The priority dilemma finds resolution in the work of Pilsbry & McGinty (1938), the third reviser. In their comprehensive study, the authors addressed P. radians (pg. 77-78), establishing the species, along with some subspecies, for the Florida-West Indies region. Notably, P. cristella was seemingly overlooked, suggesting it may have been considered a non-regional species.

In summary, applying the Principle of First Reviser (ICZN Art. 24.2), and considering that the first two detect- ed revisers (Reeve, 1847; Clessin, 1889) addressed both species without resolving priority, the ultimate determination came from the third reviser – Pilsbry & McGinty (1938), favoring P. radians .

Anything documented about C. or P.cristella between Clessin (1889) and Pilsbry & McGinty (1938) appears to be the result of misidentifications.These errors were rooted in the inclusion of Indo-Pacific populations, which represent distinct species. This is evident in Huber′s (2010) justification for considering P. cristella as valid (indirectly influenced by Odhner, 1917), wherein he referred to the ‘ Chama cristella of Reeve,′ implying a species distinct from Lamarck′s description.