Eremobiotus alicatai (Binda, 1969)

Camarda, Daniele, Frigieri, Federica, Guidetti, Roberto, Cesari, Michele & Lisi, Oscar, 2025, Lights on tardigrade biodiversity: integrative redescription of Eremobiotus alicatai (Eutardigrada, Isohypsibiidae) with new insights on its morphology, phylogeny, and biogeography, Organisms Diversity & Evolution 25 (1), pp. 55-80 : 63-66

Redescription of Eremobiotus alicatai

Species: Eremobiotus alicatai ( Binda, 1969) ( Figs. 3 - 5 , 7 - 10 ). Material examined

Holotype and paratypes of E. alicatai : 10 specimens; slide nos. 956, 957, 959–963, 1339, 1875, 2017.

Topotypic population of E. alicatai : 20 specimens; slide nos. 6023–6027, 6029, 6036, 6038–6039, 6046–6049, 6057, 6060, 6061. Three specimens; stub nos. DFG2-19, DFG2-20.

Population of E. alicatai from Orbetello (Grosseto): 11 specimens; slide nos. C3089 S1a_6062– V6 _6072.

Type depositories: Holotype and paratypes of E. alicatai are preserved in the University of Catania, in the Pilato and Binda collection. Eighteen specimens of the topotypic population are preserved in the University of Catania, Pilato and Binda collection, while two are in the University of Modena and Reggio-Emilia, Bertolani collection. Specimens of the topotypic population which are mounted on SEM stub are preserved at the University of Catania (stub nos. DFG2-19, DFG2-20) in the Pilato and Binda collection. Samples of moss from which the additional specimens of E. alicatai were extracted are dry preserved in the University of Catania (sample UNICT-DFG 2) and University of Modena and Reggio Emilia (sample C3089).

Description

Body whitish, eyespots absent. Dorsal and ventral cuticle with wrinkles (with PCM visible in exuviae and very rarely in specimens; well visible with SEM) almost invisible; cuticular pores absent. Distal portion of the buccal ring with internal septa ( Fig. 3a ), which with PCM could give the impression of the presence of papular lamellae. Six peribuccal lobes visible with SEM (Fig. 4a, b); the oral cavity armature of Isohypsibius type, showing a single band with two to five rows of teeth visible only with SEM (Fig. 4a). Bucco-pharyngeal apparatus of Isohypsibius type; the AISM of the Isohypsibius - type; apophyses and two macroplacoids (length sequence 1> 2) in the pharynx, the first of which showing a central constriction (Fig. 4b, d); microplacoid and septulum absent. cuticular thickening at the base of the lunula; asterisks indicate some claws with angles between primary and secondary branch visibly narrower than 180°. Scale bars: 10 μm

Internal claws of legs I–III of modified Isohypsibius - type; the angle between the primary and secondary branches is very wide (ca. 160–180°) but the basal section of the claw and the insertion of the primary branch on the secondary branch still recognizable; secondary branch short, primary branch with very small and symmetrical accessory points ( Fig. 7b, d ); distance between the insertion point of the main branch and the claw base very short; lunules at the base of the claws present with very small teeth almost impossible to observe with PCM ( Fig. 7c ) but visible with SEM ( Fig. 7b, d ). External claws of legs I–III of Isohypsibius - type, having a lesser wide angle between primary and secondary branches (ca. 130°), secondary branch short, primary branch with very small and symmetrical accessory points ( Fig. 7b, c ). A long and irregular singular cuticular thickening (single indented bar) develops from the lunula of the internal claws of legs I–III ( Figs. 7a, c, d and 9c ), with thick and evidently indented external margins, which teeth are positioned on the external cuticle ( Fig. 7d ). Anterior and posterior claws IV of Eremobiotus - type, with primary and secondary branches fused forming a relatively long common triangular tract. The angle between primary and secondary branches very wide (ca. 170–180°); primary branches with thick and asymmetrical (with respect to the main axis of the primary branch) accessory points, giving the impression, with PCM, of a primary branch with a secondary point pointing upwards ( Figs. 9d and 10 ); claw bases with small indented lunules which often present supernumerary small teeth ( Fig. 10a–c, e, f ). A cuticular thickening present at the base of the lunulae of claw IV, bigger in anterior claws and smaller and slightly visible in posterior claws ( Figs. 5a–e and proposed here for the Eremobiotus - type claws (i.e., the fourth pair of claws in Eremobiotus species). c Posterior claws. d Anterior claws. sb, secondary branch; pb, primary branch; cb, claw base; bd, distance between branches

10a, c). A furbelow structure present on all legs (i.e., an area surrounding the claws with fine but very dense granulation, visible with SEM ( Figs. 7b, d , 8a , and 10e ) and, partially with PCM ( Fig. 10a, c ). Eggs smooth laid in the exuviae.

Remarks

Binda (1969) reported the presence of cuticular pores (“cuticola cosparsa di perle,” meaning “cuticle sprinkled with pores”); however, our analysis of types through LM, and analysis of the two investigated populations of E. alicatai through LM and SEM, revealed the absence of cuticular pores .

Differential diagnosis

Given that the main characters to differentiate E. alicatai from E. ginevrae are not constant and well visible in all specimens of the former species (indentation of the lunulae of the legs I–III), the two species differs only in the dimension and indentation of the lunulae of the IV pair of legs and in morphometric characters.

Eremobiotus alicatai differs from E. ginevrae in having bigger lunulae of the fourth pair of legs; those have a well-developed indentation in E. alicatai while they are only slightly indented in E. ginevrae .

The species are also differentiated based on certain morphometric traits ( Tables 2, 3, 4, and 5; see also remarks paragraph of E. ginevrae ).

Eremobiotus alicatai differs from E. ovezovae by different dimension and shape of claws on all legs (i.e., bigger and more slender in E. alicatai ); the external claws of legs I–III more closely resemble Isohypsibius - type claws, whereas in E. ovezovae , all claws more closely resemble Eremobiotus - type claws. The species differ also in morphometric characters ( pt of all claws).

arrowheads indicate a well-developed single, indented cuticular bar. White indented arrowheads indicate short accessory points; white arrowheads indicate the furbelow-like structure; black arrowheads indicate the poorly indented lunula of the internal ( c, d) and external ( b) claws. ( a, c, PCM; b, d, SEM). Scale bars: 10 μm

Figures

Fig. 3 Buccal opening of Eremobiotus alicatai (a PCM, topotypic population, slide no. 6046; b SEM, topotypic population, stub DFG2-19). a Buccal opening showing the subdivision of the distal buccal ring (black indented arrowhead). b Mouth opening with the

Fig. 5 Eremobiotus claws IV (PCM). a–c E. alicatai, specimens from the topotypic population; d, e E. alicatai, specimens from Orbetello, Tuscany population; f paratype of E. ovezovae; g, h paratype (g) and holotype (h) of E. ginevrae. White indented arrowheads indicate the

Fig. 7 a, b Claws of Eremobiotus alicatai (topotypic population). External view of leg III showing the external claw of Isohypsibius type (claw on the left) and internal claw of the modified Isohypsibius claw (claw on the right). c, d Internal view of leg III showing the external claw of Isohypsibius type (claw on the right) and internal claw of the modified Isohypsibius claw (claw on the left); empty

Fig. 8 Habitus and cuticle details of Eremobiotus alicatai (a, c, specimen from topotypic population, Stub DFG2-20; b, d, specimens from topotypic population). a Habitus (SEM); white arrowheads indicate well- visible furbelow-like structures on legs. b Habitus (PCM, Slide No. 6046). c Wrinkled cuticle (SEM, stub no. 16). d Wrinkled cuticle (PCM, Slide No. 6025). Scale bar a, b 25 μm; c, d: 10 μm

Fig. 9 Holotype of E. ali- catai (PCM, slide no. 960). a Habitus. b Bucco-pharyngeal apparatus of Isohypsibius-type (flat arrowheads =constric- tions of the macroplacoids). c Claws of the third pair of legs with a well-visible cuticular bar (empty arrowhead). d Claws of the fourth pair of legs with well-developed indented lunules (black indented arrowhead) and accessory points (white indented arrowhead). Scale bar: a 50 μm; b–d 10 μm

Fig.10 Eremobiotus alicatai IV pair of claws. a, b Specimen from Orbetello, Fonteblanda (PCM, slide 6065); c–f speci- men from topotypic popula- tion (PCM, slide 6046; SEM, Stub DFG2-19). b Detail of an indented lunula. d Detail of accessory points (SEM). f Detail of an indented lunula (SEM). White indented arrow- heads indicate accessory points; black indented arrowheads indicate supernumerary teeth of the lunula; asterisk indi- cates granulation around the claws; empty arrowheads indi- cate the cuticular thickening at at the base of the lunula. Scale bars a, c, e 10 μm; b, d, f 2 μm