Itaquascon, Gąsiorek & Blagden & Morek & Michalczyk, 2024

Gąsiorek, Piotr, Blagden, Brian, Morek, Witold & Michalczyk, Łukasz, 2024, What is a ‘ strong’ synapomorphy? Redescriptions of Murray’s type species and descriptions of new taxa challenge the systematics of Hypsibiidae (Eutardigrada: Parachela), Zoological Journal of the Linnean Society 202 (1), pp. 1-63 : 24-26

Composition of Itaquascon and its consensus amended diagnosis

Taxonomy of Itaquascon appears very challenging, mainly owing to the fact that, like Parascon and Raribius , the genus is rarely found and, if encountered, usually only in small numbers (i.e. fewer than five specimens). This rarity means that opportunities for extensive morphometric analysis and the drawing of robust conclusions based on intra- and interspecific variability of phenotypic traits are also limited and infrequent. Luckily, we obtained an enormously high number of individuals of I. serratulum (50 in total), which represents the largest number of specimens recorded in the literature so far (Węglarska isolated tens of individuals of R. pawlowskii from a single moss sample collected in the Polish Tatras, but unfortunately did not publish that interesting finding; B. Węglarska, pers. comm.).

According to its original description, I. placophorum exhibits a dorsal papilla ( Maucci 1973), a character never recorded in any other eutardigrade, making it a suspicious taxon. Thus, we examined the holotype of this species and found that the ‘papilla’ is simply a conspicuous ventral cloacal fold. In a flattened individual, this ventral fold is visible through the translucent dorsal cuticle even when focusing on the dorsum (hence Maucci’s misinterpretation). It is not the first time that ventral structures have been interpreted as dorsal characters (see the case of the no longer valid ‘ Milnesium trispinosum ’ as discussed by Suzuki 2016). Internal bars on legs II–III of the I. placophorum holotype are thin but clearly visible ( Fig. 17B ), like those in I. biserovi . Furthermore, we independently confirm the findings of Guidetti et al. (1999), who validated the presence of stylet supports in I. placophorum ( Massa et al. 2021) .

There also seems to be a misunderstanding about the pattern of the pharyngeal tube annulation in the genus Itaquascon . Gąsiorek and Michalczyk (2020), based on high-quality SEM images, described the annulation in I. serratulum sp. nov. ( Itaquascon sp. then) as ‘complex, with annuli forking and merging irregularly’ (figs 4i–j therein). In contrast, Massa et al. (2021), when interpreting the somewhat blurred SEM images of the buccal apparatuses of Itaquascon magnussoni Massa et al., 2021 and I. placophorum (figs 5e–f and SM6 therein), described the annulation in these species as an ‘alternating hexagonal wire mesh’ and concluded that it is a different morphotype from that shown by Gąsiorek and Michalczyk (2020), thus suggesting that there is intrageneric variability. However, a careful comparison of the 2020 and 2021 microphotographs shows that the pattern in all analysed species is similar. In other words, the differences seem to be semantic, rather than morphological. Nevertheless, better-quality images of additional Itaquascon species are needed to allow more sound conclusions to be drawn.

The other difference in our interpretations pertains to the pharyngeal structures. Unlike Massa et al. (2021), we do not regard the extremely thin cuticular ridges present in the pharynx of most Itaquascon species as typical macroplacoids. Consequently, we merge the amended diagnoses of the genus ( Gąsiorek and Michalczyk 2020, Massa et al. 2021) into a single, unified diagnosis that addresses these disparate points of view: ‘Dorsoposterior apodeme (drop-like thickening) between the buccal tube and the pharyngeal tube absent. S-shaped (sinusoidal) stylet supports. Pharynx elongated, oval or pyriform in shape, with placoids reduced to thin cuticular ridges or absent. Claws of the Hypsibius type; external claws with primary branches markedly longer than the secondary branches’.

Taxonomic key to the genus Itaquascon Remark: Itaquascon enckelli (Mihelčič, 1971/72) and Itaquascon simplex (Mihelčič, 1971) have outdated descriptions that do not permit comparison with, or exclusion of other species. Thus, both are designated as nomen dubium and, consequently, not included in the key.

1. The buccal tube longer than half of the total length of the buccopharyngeal tube (pbf> 50%) .................................................. 2

– The buccal tube shorter than half of the total length of the buccopharyngeal tube (pbf <50%) ................................................ 3

2. Claws with distinct pseudolunulae and indented bases, cuticular bars on legs I–III absent .................... Itaquascon mongolicus

– Claws with indistinct pseudolunulae and smooth bases, cuticular bars on legs I–III present ...................... Itaquascon pisoniae

3. Cuticular internal bars on legs I–III present ............................................................................................................................................ 4

– Cuticular internal bars on legs I–III absent ............................................................................................................................................. 5

4. Claws IV with indented bases ................................................................................................................ Itaquascon serratulum sp. nov.

– Claws IV with smooth bases ........................................................................................................................................ Itaquascon biserovi

5. Pharynx with reduced macroplacoids (cuticular ridges) ...................................................................................................................... 6

– Pharynx without any cuticular structures ................................................................................................................................................ 7

6. The ratio between the length of the buccal tube and the total length of the buccopharyngeal tube pbf <20% .......................... .................................................................................................................................................................................. Itaquascon placophorum

– The ratio between the length of the buccal tube and the total length of the buccopharyngeal tube pbf> 45% .......................... ..................................................................................................................................................................................... Itaquascon magnussoni

7. The percentage ratio between anterior and posterior claw ap <58% ................................................................................................ 8

– The percentage ratio between anterior and posterior claw ap> 58% ................................................................................................ 9

8. The percentage ratio between anterior and posterior claw ap = 54–56% .................................................... Itaquascon umbellinae

– The percentage ratio between anterior and posterior claw ap <51% .................................................... Itaquascon cambewarrense

9. The ratio between the length of the buccal tube and the total length of the buccopharyngeal tube pbf <45%, the external buccal tube width pt> 15% .................................................................................................................................. Itaquascon unguiculum

– The ratio between the length of the buccal tube and the total length of the buccopharyngeal tube pbf> 45%, the external buccal tube width pt <15% ........................................................................................................................................... Itaquascon pilatoi

Figures

Figure 17. Claws of Itaquascon spp. (PCM, paratypes): A, claws IV of Itaquascon mongolicus Kaczmarek et al., 2002 (note serrated margin of the anterior claw basis); B, claws II of Itaquascon placophorum Maucci, 1973 (black arrowhead indicates internal bar). Scale bars: 10 μm.