Itaquascon serratulum Gąsiorek & 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 : 22-26

Itaquascon serratulum Gąsiorek & Michalczyk sp. nov.

Itaquascon sp. nov.; Uganda; Gąsiorek and Michalczyk (2020). ZooBank registration: urn:lsid:zoobank.org:act:AD578316-D601-4F5A-B00D-F37B94809FE9

Material examined: 50 individuals in total (for details, see Supporting Information, Table S1).

Type material: Holotype and 26 paratypes (slides UG.004.01– 11) from Uganda, Kibaale District (0°54 ʹ 55″N, 31°4 ʹ 44″E; 1188 m a.s.l.), moss from tree trunk, 21 October 2014, Przybyłowicz coll., are deposited in the Institute of Zoology and Biomedical Research, Jagiellonian University, Kraków.

Description: Body medium-sized to large ( Table 5), elongate and white, distinctly tapering in its anterior part ( Fig. 15A ). Cuticle smooth,without pores, wrinkling or granulation.Cribriform areas not visible under PCM. Legs very short and plump, legs IV barely distinguishable from the posterior body end ( Fig. 15A ). Eyes absent in live animals. Buccopharyngeal apparatus of the Itaquascon type, short (i.e. the pharynx reaches the level of the first pair of legs, Fig. 15 ). The OCA not visible under PCM ( Fig.15B ). Furcae of the Itaquascon type, with large and divergent apices. Stylet supports S-shaped, large and robust. Buccal-to-buccopharyngeal tube length ratio, pbf = 43–48% (46% on average). Pharyngeal apophyses absent ( Fig. 15B ). Pharynx oval and narrow, devoid of cuticular ridges (i.e. reduced macroplacoids).

Claws of the Hypsibius type, large and robust, with slightly protruding accessory points ( Fig. 16 ). External and posterior claw bases long and rectangular in shape. External claw bases visibly concave. Anterior and posterior claw bases with weak/slight indentation ( Fig. 16B, D ). Secondary claw branches short and bluntly terminated ( Fig. 16 ). Pseudolunulae absent. Internal cuticular bars I–III present, long and thick, with those on the first pair of legs occasionally less evident ( Figs 15A , 16A ).

Remarks: Claw bases with aberrant spines were found in only one specimen ( Fig. 16C, D ). Some itaquasconin taxa were described on the basis of single specimens (e.g. Platicrista itaquasconoide Durante Pasa & Maucci, 1975 ), and the spines on their claw bases were used in delineating them. Therefore, we would like to note that this trait seems vague and might not be an appropriate criterion for species delineation.

Etymology: From the Latin serratum = indented, which highlights the peculiar character of the new species, i.e. claw IV bases with small teeth. An adjective in nominative singular.

Differential diagnosis: The only other species of Itaquascon having indented claw bases is I. mongolicus . However, I. serratulum differs from it in having the indentation only on claw IV bases (all claw bases indented in I. mongolicus ). The general claw morphology is also different (more slender claws in I. serratulum vs. stout, massive claws in I. mongolicus ; compare Fig. 16A, B with Fig. 17A ), and the buccal tube constitutes less than half of the buccopharyngeal apparatus (pbf <50% in I. serratulum vs. pbf> 50% in I. mongolicus ). Following Pilato and Lisi (2009), we use pbf = 50% as the main discriminative criterion in the newly proposed key (see below). Therefore, it is only necessary to compare I. serratulum with the other member of the genus having pbf <50% and cuticular bars on legs I–III, namely Itaquascon biserovi Pilato et al., 1999 . The latter taxon, described from Central Africa, has all claws with smooth bases and S-shaped stylet supports inserted directly at the boundary between the buccal and pharyngeal tubes (pt = 100%), whereas in I. serratulum stylet supports are positioned in a more anterior position, and never on the border between these structures (pt = 89.9–98.0%).

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 15. Itaquascon serratulum sp. nov. (PCM): A, holotype habitus in ventral view; B, buccopharyngeal apparatus in toto (paratype). Scale bars are in micrometres.

Figure 16. Claws of Itaquascon serratulum sp. nov. (paratypes): A, claws II (PCM; black arrowhead indicates an internal bar); B, claws IV (PCM); C, claws II (SEM); D, claws IV (SEM). Note aberrant spurs on the basal portions of external and posterior claws.Scale bars: 10 μm.

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.