Murrayidae Guidetti et al., 2000

Family: Murrayidae Guidetti et al., 2000 View in CoL Genus: Dactylobiotus Schuster, 1980 (in Schuster et al. (1980))

Dactylobiotus taiwanensis sp. nov. ( Figs. 2–9 View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig , Tables 3–4) urn:lsid:zoobank.org:act:

Material examined: 82 animals, 73 eggs mounted on microscope slides in Hoyer’s medium (some of the eggs were embryonated), six animals and two eggs examined in SEM and two specimens processed for DNA sequencing.

Type locality: 25.0506021, 121.4628704; 3 m asl: Xinzhuang Touqian Sports Park, New Taipei City, Taiwan; debris from the leaf of Limnophila sp. ; coll. Chih-Yu Pai; 1 December 2022.

Etymology: The species is named after the country in which it was discovered.

Type depositories: Holotype: slide TW.001.11 and 46 paratypes (slides: TW.001.*, where the asterisk can be substituted by any of the following numbers: 04, 05, 07–10, 12, 13) and 59 eggs (slides: TW.001.*: 01, 14–17) are deposited at the Institute of Systematics and Evolution of Animals , Polish Academy of Sciences , Sławkowska 17, 31-016, Kraków , Poland, whereas 35 paratypes (slides: TW.001.*: 03, 06) and 14 eggs (slide: TW.001.02) deposited in the Biodiversity Research Center of Academia Sinica. 6 animals and 3 eggs prepared for SEM (UNICT-Stub N.67) are deposited at the University of Catania, Italy.

DNA voucher : Two exoskeletons mounted on permanent slides, labelled Dac.tai._TW.001.01 and Dac.tai._TW.001.02, are deposited at the Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Sławkowska 17, 31-016 Kraków, Poland.

Description of the new species

Animals (measurements and statistics in Table 3):

Body transparent in juveniles and whitish in adults, but transparent after fixation in Hoyer’s medium ( Fig. 2A View Fig ). In live specimens, eyes are present but they dissolve in Hoyer’s medium (out of 21 measured animals). In the dorso-lateral head region an area with minute pores (probably chemosensory function) can be identified in both sides of the head, but only with SEM ( Fig. 3A– B View Fig ). Other than that cuticle is without typical pores but wrinkled with two flat, oval papillae present on the dorsum between legs III and IV in adults and juveniles ( Figs. 2B–C View Fig and 3C–D View Fig ). Granulation absent on all legs.

Claws of the Dactylobiotus type with short basal portion and primary branches with distinct accessory points ( Figs. 4 View Fig and 5 View Fig ). Lunules absent, but under PCM a robust semilunar cuticular connection is present between external/posterior and internal/anterior claws ( Fig. 4 View Fig ). Under SEM this connection is visible as discontinuous, being composed of extended lunulelike thickenings under the claws on the lateral sides whereas its median portion is located within or under cuticle ( Fig. 5 View Fig ). Claws on the first three pairs of legs similar in size but obviously larger on the hind legs. A cuticular thickening is present above claws I–III ( Fig. 4C View Fig and 5A View Fig ), which under PCM is visible a darkened continuous cuticular bar ( Fig. 4C View Fig ). Under PCM the area above claws IV is darkened (4D), being similar to the darkened area present in horseshoe structure connecting the anterior and the posterior claw in many species of the family Macrobiotidae . The cuticle of this area under SEM appears smooth when compared to the surrounding cuticle ( Fig. 5C View Fig ).

Mouth antero-ventral followed by ten short peribuccal lamellae, bucco-pharyngeal apparatus of the Macrobiotus type ( Fig. 3A View Fig , 6A View Fig and 7 View Fig ). Under PCM, only the second and third bands of teeth are visible in the oral cavity armature ( Fig. 6B–C View Fig ). However, in SEM three bands of teeth are clearly visible with the first band being situated at the base of peribuccal lamellae and composed of several rows of scattered small conical teeth arranged around the oral cavity ( Fig. 7 View Fig ). The second band of teeth is situated below the ring fold, and comprises 4–6 rows of small cone-shaped teeth which are larger than those of the first band and increase in size towards the third band of teeth ( Figs. 6B–C View Fig and 7 View Fig ). The teeth of the third band are located within the posterior portion of the oral cavity, between the second band of teeth and the buccal tube opening ( Figs. 6B–C View Fig and 7B– C View Fig ). The third band of teeth is discontinuous and divided into dorsal and the ventral portions. Under PCM, the dorsal teeth are seen as three distinct transversal ridges whereas the ventral teeth appear as two separate lateral transverse ridges, between which a roundish median tooth is visible ( Fig. 6B–C View Fig ). In SEM, both dorsal and ventral teeth are also clearly distinct ( Fig. 7B–C View Fig ). Under PCM, in the lateral view of the buccal apparatus, a strengthening bar (ventral lamina) with an incision determining a ventral hook is clearly visible ( Fig. 6D View Fig ). Pharyngeal bulb spherical, with triangular apophyses, two rod-shaped macroplacoids which sometimes have jagged edges ( Fig. 6E–G View Fig ). The macroplacoid length sequence 2 <1. The first macroplacoid has a central constriction, whereas the second macroplacoid is only gently constricted sub-terminally ( Fig. 6E–G View Fig ).

Eggs (measurements and statistics in Table 4): Laid freely, whitish, spherical ( Fig. 9A View Fig ). Processes in the shape of short and wide cones with apexes usually divided into multiple (typically three to six) short, nodular, finger-like apices ( Figs. 8 View Fig and 9 View Fig ). Under SEM, apices usually covered with microgranulation ( Fig. 9C View Fig ). The egg surface between the processes appears wrinkled; however, this is barely visible under PCM ( Fig. 8C, D View Fig ), where most often the surface appears to be smooth ( Fig. 8A, B View Fig ), whereas wrinkles are clearly distinguishable under SEM imaging ( Fig. 9 View Fig ). Under PCM, the margins of the process bases appear serrated and are surrounded by a crown of faint, small thickenings/projections, usually with faintly visible pores ( Fig. 8A–D View Fig ). Under SEM these dark projections are clearly visible as vertical thickenings present on basal portions of processes walls and each process base is surrounded by a line of around 25 small, but evident pores ( Fig. 9 View Fig ). Eggs are sticky because they are covered by mucus which most likely enhances their adhesion to the substrate and maybe has also a protective function. This mucus is sometimes visible under SEM as a web of flexible filaments that cover the egg surface ( Fig. 9C View Fig ).

Differential diagnosis and PCA results

Currently, there are four other species of Dactylobiotus that possess dorsal papillae: D. selenicus , D. dispar ( Murray, 1907) , D. parthenogeneticus , and D. grandipes . However, the new species differs specifically from these taxa as follows:

Dactylobiotus dispar : The new species has two flat dorso-caudal papillae, whereas D. dispar exhibits two large conical papillae in the caudal region of the body. The new species also shows less pronounced constriction in the first macroplacoid. While D. dispar was described as having three macroplacoids, it is more likely to have only two, with the first one being profoundly constricted. Additionally, the eggs of the new species have interprocess distances smaller than the widths of the process bases, whereas in D. dispar , the interprocess distances are equal to the widths of the process bases.

Dactylobiotus grandipes : The new species differs by having two flat dorso-caudal papillae compared to the two large conical papillae in D. grandipes . The posterior primary claws on leg IV have lower pt values in the new species ( pt 50.4–66.5) than in D. grandipes ( pt 70.7–89.2). The eggs of the new species have fewer processes around the circumference (38–42 compared to 50–57 in D. grandipes ) and possess process bases surrounded by a crown of faint, small thickenings or projections, usually with faintly visible pores. These projections and pores are absent or not visible in D. grandipes .

Dactylobiotus parthenogeneticus : The new species has egg process bases surrounded by numerous pores (approximately 25) that are faintly visible under light microscopy, but well-visible with SEM. In contrast, D. parthenogeneticus exhibits scarce, small, singular pores visible only with SEM. The egg processes of the new species have generally wider bases (5.0–7.2 µm compared to 3.1–5.2 µm in D. parthenogeneticus ) and a smaller interprocess distance (1.2–2.7 µm compared to 2.0–4.8 µm in D. parthenogeneticus ). Although the ranges of egg measurements slightly overlap, these measurements differentiate the species most effectively (see the PCA results section below).

Dactylobiotus selenicus : The new species has conical egg processes, whereas D. selenicus has truncoconical or crater-shaped processes. The eggs of the new species also have fewer processes around the circumference (38–42 compared to approximately 60 in D. selenicus ). Additionally, the claws of the new species exhibit evident accessory points, which are absent or not visible under PCM in D. selenicus .

Among the four species, D. parthenogeneticus is the most similar to the new species. Given that an abundant population of D. parthenogeneticus was recently studied by Pogwizd and Stec (2020), we utilized their data to perform more detailed comparisons using PCA analysis.

The PCA analysis revealed partial overlap in absolute and relative ( pt) morphometric data for animals of D. taiwanensis sp. nov. and D. parthenogeneticus . However, it showed a clear separation (no overlap) in egg morphometric data between the two species ( Fig. 10 View Fig ). For the absolute measurement dataset, PC1 explained 87.89% of the variance, while PC2 explained 3.63%. Almost all morphometric traits contributed similarly to PC1, except for body length and ventral lamina length, which contributed more to PC2. For relative measurements ( pt values), the loadings of the traits were more dispersed compared to absolute measurements. Body length and ventral lamina length again contributed more to PC2 than PC1, with PC1 explaining 52.88% of the variance and PC2 explaining 9.78%. In the PCA analysis of egg morphometric data, the two species were clearly separated. The PC1 explained 70.79% of the variance, while PC2 explained 13.12%. The egg morphometric traits contributing most to this separation were the number of processes around the egg circumference (positive), the ratio of process base width to height (positive), and the interprocess distance (negative). Other traits contributed similarly to PC1 and PC2, except for process height, which contributed more to PC2 than PC1.