[ref. ID; 830]
The identification of the various species was done preserved material only and was based on the trophi of the mastax. Hexarthra is characterized by a mastax with malleoramate trophi and the number of teeth on the uncus is used in taxonomy. According to Ruttner-Kolisko (1974) the various morphological characteristics (e.g. size, relation of the ventral arm/body length, number of bristles, number of teeth on the uncus) by which the species of this genus are distinguished show considerable variation in different environmental conditions; there seems to be a tendency towards an increase in the number of teeth on the uncus as salinity increases, and the ratio length ventral arm/body length decreases in warmer climates. Nevertheless, according to Koste (1978), the four species can be identified on the basis of the number of teeth and display clear ecological differences. (ref. ID; 830)

[ref. ID; 1663]
With six stout, muscular, setose appendages. Body conical. With a double ciliary wreath and a ciliated groove between. The "jumping rotifer". Usually in small alkaline lakes and ponds during summer. (ref. ID; 1663)

[ref. ID; 3087]
The object of the present application is to invite the International Commission on Zoological Nomenclature to use its plenary powers to stabilise the name for the genus of the Class Rotifera formerly known as Pedalion Hudson, 1871, or as Pedalia Barrois, 1878, by designating a recognisable species to be the type species of the genus Hexarthra Schmarda, 1854. The facts of this rather complicated case are set out in the following paragraphs.
1. The generic name Pedalion Hudson, 1871 (Mon. microscop. J. 6: 121, pl. 94) was established for a monotypical genus for a new species then made Pedalion mira. The name Pedalion Hudson, 1871, is invalid, because is a junior homonym both of Pedalion Dillwyn, 1817 (Descr. Cat. Shells: 282) and of Pedalion Swainson, 1838 (Nat. Hist. Fishers 1: 199). It will be convenient if, before considering whether there is any subjectively identical nominal genus, the name of which should replace the invalid name Pedalion Hudson, 1871, we examine briefly the subsequent history of Hudson's name Pedalion.
2. In 1877 Barrois gave a paper at the Sixth Session of the "Association francaise pour l'Advancement des Sciences" held at Le Havre, entitled: "Sur l'anatomie et le developpement du Pedalia mira". This paper was published in 1878. Although, as noted above, the generic name was written in the form Pedalia in the title of Barrois' paper, that name appeared in the form Pedalion at ever point at which it appeared in the body of that paper. Rousselet, in 1914 (Association francaise pour l'Advancement des Sciences, 43e Session, Le Havre, C. R.: 535-536) drew attention to this inconsistency and raised the question whether it was due to an editorial error or whether it a should be explained on the ground that Barrois was aware of the fact that the name Pedalion Hudson, 1871, was invalid and tried to get over this difficulty by substituting the variation form Pedalia in the title of his paper. It must be noted however that an abstract of this paper of Barrois' was published in the issue of the Revue scientifique of 29th September, 1877 and that in this paper only the spelling Pedalion occurs. In this abstract no title was given for this paper and it possible that it is for this reason that the spelling Pedalia did not appear on this occasion, for it was only in the title of Barrois' paper that the spelling Pedalia was used. It may be noted incidentally at this point that the species dealt with by Barrois in the foregoing paper is not only not (as he supposed) the species which in 1871 Hudson had named Pedalion mira; it is not even referable to the same genus; it is actually a marine species of the genus Synchaeta Ehrenberg, [1832] (Abh. Preuss, Akad. Wiss, 1831: 135).
3. Since 1913 the genus named Pedalion by Hudson has been called both by that name and by the reputed name Pedalia Barrois, 1878, the latter having even made its way into Neave's Nomenclator zoologicus (3: 632), where it is quoted as a substitute name for Pedalion Hudson, 1871, the reference being given as "Pedalia Barrois, 1878, C. R. Ass. Franc. 6 (1877 Le Havre), 661".
4. I am bound to say that, in my view, it is impossible to accept, as a valid substitute name, a name (such as Pedalia) which appears only in the title of a paper, the correct spelling (in this case, Pedalion) occurring at every point in the body of the paper itself, where, if Barrois had intended to emend Hudson's name Pedalion in this way, he would certainly have used the spelling "Pedalia". It is clear, however, that no progress can be made in the stabilisation of the name of this important genus until this preliminary question has been disposed of. I accordingly ask the International Commission on Zoological Nomenclature to give a ruling that the use of the word Pedalia in the title of Barrois' paper does not constitute the publication of a generic name consisting of this word, the spelling "Pedalia" being due, it must be concluded, to some inadvertence on the part of the editor of Barrois' paper or on that of printer.
5. It is necessary now to consider whether there is any nominal genus possessing a valid name, the type species of which can be regarded as belonging to the genus Pedalion (or Pedalia) as hitherto understood. An examination of the literature shows that there is such a nominal genus, which does, or may, satisfy this condition. This is the genus Hexarthra Schmarda, 1854 (Denskr. Acad. Wiss. Wien. (Math.-natur. K1.) 7 (no.2): 15). This genus in monotypical, its sole species being Hexarthra polyptera Schmarda 1854, a then newly described (: 15) nominal species. This species is therefore type species of the genus Hexarthra Schmarda by monotypy.
6. Our next step must be to consider the claims of the nominal species Hexarthra polypteraSchmarda to regarded as representing a species of Pedalion (or Pedalia). The specimen upon which Schmarda based his description and figures of this nominal species, which was hardly visible to the naked eye, was discovered by him in a pool at El Kab in Egypt. At first Schmarda mistook this animal for a crustacean larva, but the "Raderorgan" and jaws showed that it was a Rotifer. The jaws had seven teeth on each side. Schmarda's type specimen is missing, and the species which he described has not been reported by any subsequent worker.
7. The drawing up his description and preparing his figures of this species, Schmarda was severely handicapped by reason of the fact that he was working under field conditions and had no opportunity for studying the animal at leisure. This stand is taken also by Daday, 1903 (Mikroskopsche Susswassertiere aus Kleinasien. Wien. Sitzungsber. (Math.-Natur. Kl.) 112 (Abth. 1): 139-168) When after the publication of the name Pedalion, the view was advanced that the genus so named as indistinguishable taxonomically from the genus Hexarthra Schmarda, Hudson objected on the ground that Schmarda had described the six plumose appendages as originating from the ventral side, as in nauplius larva, while in his genus Pedalion these appendages were arranged around the animal. Hudson admitted, however, the difficulty of studying the arrangement of the hairs on the appendages of Pedalion species, a difficulty which may be illustrated by the mistakes which he himself made in some of his own figures and descriptions.
8. Daday (1886, Morph. Physiolog. Beitrage zur Kenntniss der Hexarthra polyptera Schmarda. Termeszetraize Fuzetek 10: 214-249, pls. VIII, IX) believed that, in representing the appendages of Hexarthra polyptera as arising from the ventral side of the animal, Schmarda had been influence by the apparent similarity between members of the genus Pedalion and the nauplius larva of Crustacea, a resemblance which, though apparent at first glance, is found on closer examination to be entirely superficial in character.
9. Levander (1894, Beitrage zur Kenntniss der Pedalion Arten mit einer Tafel. Soc. Faun, Flor. fenn. 11: 1-34, figs. 1, 2, 3) considered that, if one were to identify Pedalion with Hexarthra, it would be necessary to attribute to Schmarda a lack of observation which, in his view, there was no ground for assuming. Levander quoted the opinion of Plate-that, if Schmarda could show (as he did) the arrangement of the hairs on the appendages (which in Pedalion are found only on the ventral appendage) and the number of teeth in the jaws, he could not possibly have made the mistake of representing appendages as arising from the ventral side of the animal instead of being arranged in a circle around it. Plate concluded that, in view of these facts, the presence of hooks on appendages other than the ventral appendage, and the origin of the appendages from the ventral side of the animal, it was impossible to synonymise Hexarthra with Pedalion. As regards Plate's comment on these lateral hooks on the appendages, it is, however, worth nothing that Daday recorded the presence of similar hooks on the dorsal appendage in his figure of his Pedalion mucronatum Daday, 1909 (Trav. Soc. Nat. Petersb. 39: 9-38, pl. 1, figs. 2-6), a nominal species which has been identified with Pedalion oxyure Sternov, 1903 (Turkestanskago Otd, imp. russ. georgr. Obsch. 4 (Pt. 3): 9, pl. 1, figs. 2,3), in the figures of which no lateral hooks are shown on the dorsal appendage. This difference between the illustrations given by Sernov and Daday, to which attention has not so far been drawn, has not prevented authors from accepting Pedalion mucronatum Daday and Pedalion oxyure Sernov as being no more than different names for a single species. I have never noted lateral hooks on any but the ventral appendage. Daday's (1909) representation of hooks on the dorsal appendage may be due to incorrect interpretation.
10. Thus against the view that Hexarthra polyptera Schmarda is a species of the genus that Hudson named Pedalion is the observation by Schmarda that the appendages arise from the ventral surface and that there are lateral hooks on appendages other than the ventral appendage. As already noted however Daday himself showed incorrectly the presence of a such hooks in his P. mucronatum (= P. oxyura Sernov). It must be noted also that at times the fold of the integument on the appendages can give somewhat laddered appearance which under low magnification may be mistaken for hooks. The presence of jaws in H. polyptera speaks for its being a rotifer. In view of the absence of posterior digitiform appendages posteriorly (such as are found in Pedalion mira Hudson), Schmarda's species might well belong to the fennicum-group of the genus Pedalion. The arrangement of the hairs on the appendages is very similar to that found in a species of Pedalion which occurs in the Saskatchewan lakes on Canada. The principal objection to the acceptance of Schmarda's species as belonging to the genus Pedalion is therefore his statement that the appendages come from the ventral side of the animal. As regards this, it must be noted, however, that a similar appearance can be obtained by placing a specimen of an undoubted species of Pedalion under a cover slip, the weight of which has flattened the animal (Schmarda's figure seems to have been drawn from a flattened specimen); unless one constantly alters the focus while drawing the animal as a whole or one of its appendages in order to obtain the correct relation, it is very easy to arrive at the same conclusion as that reached by Schmarda. An inaccuracy of this kind on the part of Schmarda would not be surprising if we recall the difficulties with which he was faced, by reason of having to examine his material in the field instead of in a laboratory.
11. The next point which it is important to note is that Schmarda found his species Hexarthra polyptera in abundance in the waters which he examined. This fact suggests that that species, whatever it was, would have been found again by subsequent workers. The species Pedalia fennicum Levander, 1892. (Zool. Anz. 15: 403) has, in fact, been reported from North Africa, where it appears to be rather widely distributed. Recent observations show that this species shows considerable variation in the arrangement of the hairs and some variation in the tooth formula - a fact which may account, in part, for some of the special features shown in Schmarda's figures. Further, Bryce in his paper on the Rotifera of Devil and Stump Lakes (1924, J. Quekett microscop. Club 15: 81-108) mentioned having examined a slide of Pedalia from El Kab (the type locality of Schmarda's species) that had been prepared by Rousselet. I have myself examined a slide of a specimen from this locality that was bought from Rousselet by the United States National Museum. The specimen mounted on this slide is a Pedalion.
12. The conclusion which I draw from an examination of Schmarda's (admittedly poor) description and figure is that the species which he described as Hexarthra polyptera belongs to Hudson's genus Pedalion. This conclusion becomes a virtual certainty, now that we have an actual specimen of a Pedalion from the very pond in which Schmarda took his polyptera but in spite of the abundance of that species noted by Schmarda no specimen of a species belonging to a separate genus recognisable from Schmarda's description as Hexarthra is known from that very restricted locality. Schmarda's description of the arrangement of the hairs on the ventral appendages, the number of hooks on the ventral appendage that he noted, as also the number of teeth (seven) in each uncus, all place the animal described by Schmarda in the fennicum-group of the genus Pedalion.
13. In the light of the foregoing consideration, I reach the conclusion that the nominal genera Hexarthra Schmarda, 1854, and Pedalion Hudson, 1871, must on taxonomic grounds, be regarded as subjectively identical with one another. Accordingly, the name which under the Code should be applied to this genus is Hexarthra Schmarda and, as it is the older of the two names, would still be the correct name for this genus, even if Pedalion Hudson, 1871, were not an invalid homonym. In view of the considerable discussion that has taken place in regard to this question and also of the importance and interest of this genus, I thick that it is important that this subject should now be closed by the name Hexarthra Schmarda being placed on the Official List of Generic Names in Zoology and the invalid name Pedalion Hudson, 1871, on the Official Index of Rejected and Invalid Generic Names in Zoology, together with the reputed, but non-existent, name Pedalia Barrois, 1878. It would be useful also if all other invalid uses of the name Pedalion subsequent to the name Pedalion Dillwyn, 1817 (Class Pisces) were at the same time to be relegated to the Official Index.
14. At this point we encounter a difficulty of quite a different order. The nominal species Hexarthra polyptera Schmarda, though incorrectly and inadequately described, must be regarded as belonging to the highly variable group represented by Pedalion fennicum Levander, 1892. Accordingly, under the Code the trivial name polyptera Schmarda, 1854, being much older than fennicum Levander, would replace the latter name. The trivial name fennicum Levander is however so deeply entrenched in the literature that its replacement by the hitherto contentious name polyptera Schmarda would certainly give rise to confusion and would be open to strong objection. In order to prevent this confusion, I accordingly ask the International Commission on Zoological Nomenclature to use its plenary powers to suppress the trivial name polyptera Schmarda, thereby validating the later name fennicum Levander for the same species. As part of this proposal, I ask the International Commission to use the same powers to designate Pedalion fennicum Levander, 1892, to be the type species Hexarthra Schmarda, in place of the older nominal species Hexarthra polyptera Schmarda, the name of which it is now proposed should be suppressed. The trivial name fennicum Levander, 1892 as published in the binomial combination Pedalion fennicum should then be placed upon the Official List of Specific Trivial Names in Zoology. Incidentally, it would be helpful if at the same time the International Commission were to place on this Official List the trivial names, each an available name and the oldest name for the species concerned, of two other well-known species of this genus. These trivial names are: (1) the trivial name mira Hudson, 1871 (Mon. microscop. J. 6: 121) (as published in the binominal combination Pedalion mira); (2) the trivial name intermedia Wiszniewski, 1929 (Bull. Acad. pol. Sci. Lettr. (Cl Sci. math. Nat.) (B) 1929 (2): 137) (as published in the binominal combination Pedalia intermedia).
15. The specific proposals which I now therefore lay before the International Commission on Zoological Nomenclature are that it should:-
(1) use its plenary powers:-
(a) to suppress, for the purposes of the Law of Priority but not for those of the Law of Homonymy the trivial name polyptera Schmarda, 1854 (as published in the binominal combination Hexarthra polyptera);
(b) to set aside the indication, by monotypy, of Hexarthra polyptera Schmarda, 1854, as the type species of the genus Hexarthra Schmarda, 1854, and having done so, to designated Pedalion fennicum Levander, 1892, to be the type species of that genus;
(2) place the generic name Hexarthra Schmarda, 1854 (type species, by designation, as proposed in (1)(b) above, under the plenary powers: Pedalion fennicum Levander, 1892) (gender of generic name: feminine) on the Official List of Generic Names in Zoology;
(3) place the under-mentioned generic names or reputed generic name, on the Official Index of Rejected and Invalid Generic Names in Zoology:-
(a) Pedalia Barrois, 1878 (a reputed but non-existent name);
(b) Pedalion Swainson, 1838 (a junior homonym of Pedalion Dillwyn, 1817);
(c) Pedalion Hudson, 1871 (a junior homonym of Pedalion Dillwyn, 1817);
(d) Pedalion Buckton, 1903 (Monogr. Membr. 6: 251) (a junior homonym of Pedalion Dillwyn 1817);
(4) place the under-mentioned trivial names on the Official List of Specific Trivial Names in Zoology:-
(a) fennicum Levander, 1892 (as published in the binominal combination Pedalion fennicum) (trivial name of species proposed, under (1)(b) above, to be designated as the type species of Hexarthra Schmarda, 1854);
(b) intermedia Wisniewski, 1929 (as published in the binominal combination Pedalia intermedia);
(c) mira Hudson, 1871 (as published in the binominal combination Pedalion mira);
(5) place the trivial name polyptera Schmarda, 1854 (as published in the binominal combination Hexarthra polyptera) (a name proposed, under (1)(a) above, to be suppressed under the plenary powers) on the Official Index of Rejected and Invalid Specific Trivial Names in Zoology. (ref. ID; 3087)

[ref. ID; 4596]
With six, stout, setose appendages. Body conical. Corona with a double ciliary wreath, and a ciliated groove between. (ref. ID; 4596)

• Hexarthra barracootica Berzins, 1982 (ref. ID; 4606 original paper)
• Hexarthra brandorffi Koste, 1977 (ref. ID; 2716 original paper)
• Hexarthra bulgarica (Wiszniewski, 1933) (ref. ID; 2825) reported year? (ref. ID; 2619, 3688) reported author and year? (ref. ID; 1449)
• Hexarthra bulgarica canadensis Dumont, Coussement & Anderson, 1978 (ref. ID; 5932 original paper)
• Hexarthra bulgarica nepalensis Dumont, Coussement & Anderson, 1978 (ref. ID; 5932 original paper)
• Hexarthra fennica (Levander, 1892) (ref. ID; 830, 1488, 3505, 3516, 3688, 5932) reported year? (ref. ID; 5022), fennica fennica (Levander, 1892) (ref. ID; 4596)
  Syn; Hexarthra polyptera Schmarda, 1854 (ref. ID; 3688); Pedalia fennica Harring, 1913 (ref. ID; 3688); Pedalion fennicum Levander, 1892 (ref. ID; 3688)
• Hexarthra fennica oxyuris (Sernov, 1903) (ref. ID; 4596), var. oxyuris Zernov, 1903 (ref. ID; 3688)
  Syn; Pedalia oxyura Zernov, 1913 (ref. ID; 3688); Pedalion mucronatum Daday, 1908 (ref. ID; 3688); Pedalion oxyura Zernov, 1903 (ref. ID; 3688)
• Hexarthra insulana Hauer, 1938 (ref. ID; 3083)
  See; Hexarthra intermedia (ref. ID; 3508)
• Hexarthra intermedia Wiszniewski, 1929 (ref. ID; 830, 2284, 2715, 2812, 2825, 3180, 3508, 3514, 3688) reported year? (ref. ID; 2619, 3040, 5022)
  Syn; Hexarthra insulana Hauer, 1938 (ref. ID; 3508) or 1937-1938 (ref. ID; 3688); Pedalia insulana Hauer, 1937-1938 (ref. ID; 3514); Pedalia intermedia Wiszniewski, 1929 (ref. ID; 3508, 3514) reported author and year? (ref. ID; 3040)
• Hexarthra intermedia brasiliensis Hauer, 1953 (ref. ID; 2887, 2995)
• Hexarthra intermedia braziliensis Hauer, 1953 (ref. ID; 2265, 2545, 2810)
• Hexarthra jenkinae (de Beauchamp, 1932) (ref. ID; 830, 2194)
• Hexarthra jenkinae f. nakuru Koste, 1977 (ref. ID; 2716 original paper)
• Hexarthra libica (Manfredi) (ref. ID; 1448)
• Hexarthra mira (Hudson, 1871) (ref. ID; 830, 1804, 2261 , 2619, 2715, 2757, 2810, 2825, 3114 , 3514, 3688, 5932) reported year? (ref. ID; 3066, 3426, 5022, 5029)
  See; Hexarthra intermedia (ref. ID; 2825)
  Syn; Pedalia mira Harring, 1913 (ref. ID; 3688) or Hudson, 1871 (ref. ID; 2757, 3514); Pedalion mira Hudson, 1871 (ref. ID; 3514, 3688); Pedalion mirum Hudson & Gosse, 1886 (ref. ID; 3688)
• Hexarthra oxyuris (Sernov) (ref. ID; 1831) or Zernov (ref. ID; 3505), oxyura (ref. ID; 2261 )
• Hexarthra polydonta (Hauer, 1957) (ref. ID; 830, 1948)
• Hexarthra polydonta soaplakeiensis Koste, 1977 (ref. ID; 2716 original paper) reported author and year? (ref. ID; 830)
• Hexarthra polyodonta jasperina Dumont, Coussement & Anderson, 1978 (ref. ID; 5932 original paper)
• Hexarthra propinqua Bartos, 1948 (ref. ID; 2284)