Thulyphoribius melitense, Camarda & Lisi & Stec & Vecchi, 2025

Thulyphoribius melitense sp. nov.

Figures 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7 , 8 View Figure 8 ; Tables 2 View Table 2 , 3; Files S 1, S 2 View Table 3

Etymology.

The specific epithet refers to the location where the new species has been found ( melitense meaning from Malta).

Type locality.

Malta • Qrendi, sediment collected in a dried freshwater rock pool; approximately 35°49'54"N; 14°26'29"E, elev. ~ 50 m, 23 March 2023; M. V. leg GoogleMaps .

Material examined.

58 animals, and 11 cysts mounted on microscope slides in Hoyer’s medium; 12 animals mounted on microscope slides in Polyvinyl Lactophenol mounting medium ( PVLF); 12 hatchlings mounted on microscope slides in PVLF, 4 exuviae on microscope slides in PVL. 7 animals prepared for SEM. 2 individuals used for DNA sequencing, 1 individual used for WGA and mitogenome sequencing.

Type depositories.

Holotype with 5 paratypes (slide CT. 6087 in Hoyer’s); 31 paratypes (slides: CT. 6088–6095 in Hoyer’s); 20 paratypes (slides CT. 6093–6099 in PVL); 7 animals mounted for SEM analysis (Stub No. UNICT- 39) deposited at the University of Catania, Via Santa Sofia 102, Catania, Italy. 7 paratypes (slides: MT.008.01 – 02 in PVL), 32 paratypes ( MT.008.03 –08 in Hoyer’s) deposited at the Institute of Systematics and Evolution of Animals (Polish Academy of Sciences), Sławkowska 17, Kraków, Poland

Animals.

Body size up to approximately 500 µm (Table 2 View Table 2 ), with hatchlings ranging from about 120 to 180 µm (Table 3 View Table 3 ). Hatchlings exhibit the same morphological characters as adults (Fig. 6 View Figure 6 ), although morphometric values differ slightly, the pt values being higher in adults for some measurement of placoids and claws (Tables 2 View Table 2 , 3 View Table 3 ). Before mounting, the animals appeared whitish / transparent and became transparent after mounting in PVLF or Hoyer’s medium. Eyes are present (Fig. 4 A View Figure 4 ), and the entire cuticle appears finely dotted under SEM (Fig. 3 E View Figure 3 ). The buccal ring appears divided under PCM (Fig. 4 B View Figure 4 ), giving the impression of the presence of papular lamellae, but under SEM it appears smooth (Fig. 3 A – D View Figure 3 ). Five – six papular peribuccal lobes are present (in correspondence to peribuccal lobes), visible only under SEM and only when the buccal cone is fully extended (Fig. 3 A, C View Figure 3 ).

The oral cavity armature ( OCA) is visible only in SEM and consists of two bands: the first band (probably homologous to the second band of teeth of the Macrobiotoidea) comprises small, rounded teeth (gradually decreasing in density toward the second band of teeth) (Fig. 3 B View Figure 3 ), second band composed by a single line of small round teeth, slightly bigger than those of the first band (Fig. 3 C, D View Figure 3 ). Buccal tube with two bends: the first, more pronounced, at the beginning of the anterior portion of the buccal tube, in correspondence with the area bearing the ventral lamina; the second, less pronounced, approximately halfway along the tube (Fig. 4 A View Figure 4 ). Ventral lamina present (Fig. 4 A, D View Figure 4 ), with characters described for the genus.

Typically-shaped stylet furcae (according to Pilato and Binda (2010 b )), each possessing a pair of condyles (symmetrical with respect to the medial axis of the furca) located between the stylet base and the two swellings at the base of the furca (Fig. 4 C View Figure 4 ).

Three macroplacoids (length sequence: 2 <3 <1) are present: the first is very long and rod-shaped (more than twice the length of the second), with a slight median constriction; the second, located almost adherent to the first macroplacoid, is granular; and the third is rod-shaped and nearly twice the length of the second (Fig. 4 E View Figure 4 ).

Claws are large and slender, similar to those of Thulinius , with humps on the primary branches of the internal claws (Fig. 4 E View Figure 4 ) and with Br ratio higher in internal claws (mean external / posterior claws = 68.2 %; mean internal / anterior claws = 73.2 %; mean general = 70.1 %. For detailed information see File S 1). Accessory points appear absent under PCM analysis; however, SEM reveals their presence adjacent to either side of the primary branch in all claws (Fig. 5 B, E, G View Figure 5 ). This overlap with the main branch prevents their observation under light microscopy. Only occasionally, they appear elevated above the primary branch on claws IV under PCM.

The claw bases on all claws appear internally septate (Fig. 5 C View Figure 5 ); such septa are internal structures and thus invisible under SEM (Fig. 5 B, G, E View Figure 5 ).

Lunulae and pseudolunulae are absent; a long, thin and smooth cuticular bar is present under the claw bases of claws I – III (visible under both SEM and PCM, as observed in Fig. 5 A – E View Figure 5 ), well-spaced from the claws and not originating from the internal claw (e. g., similar to the cuticular bar observed in the genus Thulinius ).

Moreover, a wrinkled button-like cuticular fold is present above the claws of the I – III pair of legs (Fig. 7 B – D View Figure 7 ) this structure is well visible under SEM and only sometimes slightly visible with PCM.

Cysts.

The animals form cysts that are dark in colour, ranging from dark green to nearly black (Fig. 8 View Figure 8 ). The legs are barely visible under PCM within the external cuticle. The surface of the cyst is covered with numerous folds and wrinkles, which trap a significant amount of sediment (Fig. 8 View Figure 8 ).

Eggs.

Laid in the exuvia, with smooth chorion. Whitish / transparent in colour, round in shape and in number of 4–8 per exuvia.

Additional observations.

Both sexes (see File S 6 for males stained with orcein) are reported for this species, with no evident secondary sexual dimorphism. Multiple instances of a behaviour in which a single female is surrounded by 2– 5 males that anchor themselves to her body using their mouth have been observed.

DNA.

The following DNA sequences are associated with the type population of the new species: 18 S: PV 016871 –2. — 28 S: PV 016873 –4. — COI: PV 017087 –8. — ITS 2: PV 019027 –8. — Mitogenome: PV 030524. — Genomic reads: Bioproject PRJNA 1215272.