Aperioptus pictorius, Richardson, 1848

Kottelat, Maurice, 2020, Nomenclatural status and possible identity of Aperioptus pictorius (Teleostei Gonorynchidae [?] and Cobitidae), Zootaxa 4763 (2), pp. 294-300 : 294-297

The

usages of the name Ap. pictorius are few and it has never been treated as an unambiguously valid species. Günther (1868: 371) mentioned the name at the end of his account of the family Cobitidae and merely commented “The fish has the form of a Lepidocephalus , the dorsal being placed far backwards, nearly opposite to the ventrals. But the mouth is represented as transverse, curiously lobed, and without barbels”. Vaillant (1902: 145) mentioned Ap. pictorius when he tentatively placed his new Ap. megalomycter in the same genus (it is now Ellopostoma megalomycter , in Ellopostomatidae ; Bohlen & Šlechtová, 2009; Kottelat, 2012). Popta (1906) mentioned the name in various lists, while Weber & de Beaufort (1916: 238) reproduced Richardson’s description and commented that its systematic position was doubtful. Roberts (1972: 2–3) commented “its identity may never be resolved” and “if they were freshwater they may have been cobitids”. Kottelat (2012: 22, 2013: 177) listed the name, with a question mark, as a possible junior synonym of Acantopsis dialuzona (erroneously influenced by its placement in Cobitidae by Günther, Vaillant, Popta, Weber & de Beaufort, and Roberts). Until that time, Ap. pictorius was merely a nomen dubium, threatening no existing name and not a concern for any ichthyologist. Recently, however, Page & Tangjitjaroen (2015) argued that Ap. pictorius is a synonym of Acanthopsoides molobrion Siebert, 1991 ( Fig. 1c ), a freshwater fish from Borneo, Sumatra and the Malay Peninsula.

Page & Tangjitjaroen (2015) displayed side-by-side the original figure of Richardson (1848) and a photograph of a fresh specimen of Acanthopsoides molobrion . They pointed to differences (number of dorsal-fin rays, respective positions of the dorsal- and pelvic-fin origins) which, however, they dismissed. Page & Tangjitjaroen (2015) did not mention or discuss the many other important differences between Richardson’s illustration of Ap. pictorius and Ac. molobrion .

The most obvious differences are shown on Fig. 1 b–c:

(1) the dorsal and pelvic fins are at about two-thirds the distance from the tip of the snout to the base of the caudal fin (vs. at about midlength);

(2) the dorsal-fin origin is distinctly behind the vertical through the pelvic-fin origin (vs. above or slightly in front).

After the head and the caudal fin, the dorsal, pelvic and anal fins are the first landmarks when drawing a fish, especially a very slender fish, and it is hard to imagine that an experienced artist would not have displayed correctly the location and relative positions of the dorsal and pelvic fins (compare Figs. 1a and 1b ). This rules out the possibility that Aperioptus could be an Acanthopsoides .

Richardson’s description does not mention the presence of the main external diagnostic characters of the family Cobitidae , the suborbital spine and the 6 barbels; nor are these characters indicated in the figure. The spine is sharp and difficult to ignore when handling the fish, and both Richardson and the artist would likely have noted it, if present. Although Richardson observed the mouth and commented that it “is restricted on the sides by membranous processes”, he did not mention barbels and the drawing does not show any structures identifiable as barbels. Thus, there is no external character to support identification of Ap. pictorius as a member of Cobitidae .

Richardson had experience of other species of Cobitidae (e.g., in Richardson, 1846): they are a well known component of the European ichthyofauna. If the specimens of Ap. pictorius had been a cobitid, he would have recognised the unmistakable mouth of a cobitid and the suborbital spine, which characters are all present in Acanthopsoides .

Further differences between the figure of Ap. pictorius and Ac. molobrion are:

(3) the eye is relatively much larger in Ap. pictorius , about 1.8 times in snout length (vs. about 3 times in Ac. molobrion );

(4) the eye is centred distinctly anterior to the middle of head length (vs. approximately at the middle);

(5) the eye is directed laterally (vs. dorsolaterally), its upper margin below the dorsal profile in lateral view (vs. flush with the dorsal profile);

(6) the lower rim of the eye is level with (vs. conspicuously above) the tip of the snout;

(7) the pectoral fin is slightly falcate, inserted laterally; its base is vertical, the upper extremity of the base being about level with the upper extremity of the gill opening, its lower extremity clearly above the ventral profile of the body (vs. the pectoral fin is rounded, inserted ventrally, extending laterally, its base situated entirely at the level of the lower extremity of the gill opening; in lateral view, the fin usually protrudes below the ventral profile);

(8) the outline of the dorsal fin is approximately squarish (vs. distinctly rounded) and the length of the dorsal-fin base is about half (vs. about one third) the distance between the origins of the dorsal and anal fins and 1.8 (vs. about 2.5) times in the distance from the origin of the anal fin and the base of the caudal fin;

(9) the anal fin has a longer base and 11 rays according to the text (vs. short, with 3 unbranched and 5 branched rays [in the descriptions of other small cypriniforms, Richardson did not distinguished between unbranched and branched rays, and he often counted the unbranched rays only as 1, so that the actual number in Ap. pictorius was probably more than 11; e.g., compare data on Squalius cii in Richardson, 1857: 377 and Stoumboudi et al., 2006: 137]);

(10) there is no colour mark at the base of the caudal fin (vs. a conspicuous black spot at the upper extremity of the base of the caudal fin) [in most genera and species of the suborder Cobitoidei , the presence and shape of the black pattern at the base of the caudal fin is a diagnostic feature; it is the most conspicuously marked element of the colour pattern, and it persists even in poorly preserved and old museum specimens];

(11) there is no suborbital spine and Richardson did not mention its presence (vs. present, and obvious when specimens are manipulated);

(12) there are no barbels and Richardson did not mention their presence (vs. three pairs of barbels).

Page & Tangjitjaroen (2015) argued that some of the differences between the drawing published by Richardson and actual specimens of Ac. molobrion might owe to a lack of accuracy of the figure. I cannot agree. All the drawings on the 10 plates in Richardson (1848) are excellent and were evidently executed by an experienced illustrator. Why then, would just the drawing of Ap. pictorius be unreliable? Also, if the model before him were in fact an Acanthopsoides , it is difficult to imagine that even a less experienced artist would deliver a sketch containing such major differences as thoses enumerated above.

Richardson’s figure also shows a close-up of the mouth. This means that he had examined the specimens with sufficient attention to notice what he considered to be an important feature, justifying a close-up figure, a description, and the creation of a new genus. It seems unlikely that the artist would take the trouble and time to make this drawing without having been asked by Richardson. However, given that this was merely a sketch, not checked by Richardson against the specimens, not much importance can be given to the details.

Page & Tangjitjaroen (2015) commented that «the number of [dorsal-fin] rays drawn by the artist could have been incorrect». But the number could just as well have been correct… They counted about 9–10 rays in the figure, Richardson reported 13. Species of Acanthopsoides have 3 unbranched and 7 or 8 branched dorsal-fin rays ( Siebert, 1991). The fact that Richardson’s count possibly differs from the illustration may suggest that he made the count before the artist executed the drawing. However, this is only a speculation. I count about 11 or 12 branched and 3 unbranched rays in the figure. Richardson possibly did not count the minute unbranched rays at dorsal-fin origin; if he had counted the rays on an Acanthopsoides in a similar way, he could have missed the two minute anterior unbranched rays and hence given a count of 8 or 9. See also discussion of the count of anal-fin rays above.

Page & Tangjitjaroen (2015) justified their decision to identify Ap. pictorius as an Acanthopsoides as follows: “The figured specimen is long and slender with a somewhat elongated snout and many small black spots on the upper side of the head to the caudal peduncle. All these characters are consistent with those of species now assigned to the genus Acanthopsoides ” and “other characteristics of Acanthopsoides […] that are consistent with the drawing of A. pictorius , include a terete body, slender caudal peduncle, moderately long snout—2 to 2.5 times in head length, and a symmetrical and emarginated caudal fin”. They also commented on characters “that appear inconsistent with those of A. molobrion and all other species of Acanthopsoides include the number of dorsal rays [… however …] the number of rays drawn by the artist could have been incorrect. Also [… in Acanthopsoides …] the origin of the dorsal fin is slightly before to over the origin of the pelvic fin, but the figure of A. pictorius shows the origin of the dorsal fin behind the origin of the pelvic fin”. The number of dorsal-fin rays and the respective positions of the dorsal- and pelvic-fin origins are discussed above.

Page & Tangjitjaroen (2015) discounted the substantial difference in the respective positions of the dorsal and pelvic fins, they ignored the absence of the characters diagnostic for the family Cobitidae , they did not pay attention to the many differences mentioned above, and they speculated that the difference in the number of dorsal-fin rays was a result of the number not being clear in the figure or that the artist might have made an error.

Of the similaries between Aperioptus and Acanthopsoides , only the following remain: the slender body, the slender caudal peduncle, the somewhat elongated snout, the black dots on the body, and the emarginate caudal fin. This combination of features is shared by many fish species in many families. How much weight can these be given, against the several gross differences involving anatomical features easily seen on the drawing, as detailed above? The identification of Ap. pictorius as an Acanthopsoides was not based on the more informative taxonomic characters; indeed, the authors do not even mention those diagnostic of the family Cobitidae or of the genus. It is certain that the fish figured by Richardson is not an Acanthopsoides .

The identification of Ap. pictorius at the species level as Ac. molobrion is not based on characters but solely on the type locality “Borneo”, and the conjectures that this means the Sarawak River, that it is a freshwater fish, and that there is only a single species of Acanthopsoides known from Sarawak, and that this is A. molobrion . See Appendix 1 for information on the type locality. See Appendix 2 for information on the possible identity of Ap. pictorius .

Page & Tangjitjaroen (2015) concluded: “the name seems to be a senior synonym of A. molobrion [...], and the holotype of A. molobrion [...] is here designated as the neotype of A. pictorius ”. Nowhere did they mention a possible need for the neotype and what would be the consequences of not designating a neotype.

This neotype designation is invalid, however, because it does not satisfy the conditions set by the International Code of Zoological Nomenclature , art. 75.3, which states that “a neotype is validly designated when there is an exceptional need and only when that need is stated expressly and when the designation is published with the following particulars:” These particulars must all be satisfied for the designation to be valid. They include :

“75.3.1. a statement that it is designated with the express purpose of clarifying the taxonomic status [....] of a nominal taxon”. There is no such statement in Page & Tangjitjaroen (2015). Further, since they identified Ap. pictorius as a species of Acanthopsoides and since they asserted that there is only one species of Acanthopsoides in Sarawak, then it means there was no confusion at the moment the synonymy was accepted, then the “exceptional need” did not exist.

“75.3.5. evidence that the neotype is consistent with what is known of the former name-bearing type from the original description [...];” The differences stated by Page & Tangjitjaroen (2015), as well the many listed above, show that this was not the case.

In conclusion:

(1) the neotype designation does not satisfy art. 75.3.1 (absence of need, absence of statement) and 75.3.5 (not consistent with original description), thus art. 75.3 is not satisfied and the neotype designation is invalid;

(2) Aperioptus pictorius is not a species of Acanthopsoides and hence [since the neotype designation is shown here to be invalid] cannot be a senior synonym of Ac. molobrion (corollary: Aperioptus is therefore not a senior synonym of Acanthopsoides );

(3) the names of the taxa Acanthopsoides and A. molobrion remain.

Figures

FIG. 1. a. Gonorynchus abbreviatus, KAUM-I 53441, 68.0 mm SL; Japan: Kagoshima: Kawajiri (photograph by H. Motomura); b, Aperioptus pictorius, about 65 mm SL, from Richardson (1848: pl. 10 fig. 4); c, Acanthopsoides molobrion, CMK 21740, 44.0 mm SL; Borneo: Mahakam drainage; d, mouth of Ap. pictorius, from Richardson (1848: pl. 10 fig. 5). Vertical lines show the position of the origin of the pelvic, dorsal and anal-fin origins, and of the base of the last dorsal-fin ray.