Horatia stygorumina Grego & Rysiewska, sp. nov.

Falniowski 1, Andrzej, Grego 2, Jozef, Rysiewska 1, Aleksandra, Osikowski 3, Artur & Hofman 4, Sebastian, 2021, Two new stygobiotic species of Horatia Bourguignat, 1887 (Hydrobiidae) from Croatia, Subterranean Biology 37, pp. 89-104 : 89

Horatia stygorumina Grego & Rysiewska, sp. nov. Figure 4F-H , 5B

Type locality.

Mali Rumin cave, Rumin, Sinj District, Croatia, 43°46'50.88"N, 16°38'56.75"E.

Holotype.

Dry specimen, J. Grego, A. Falniowski, M. Olšavský and J. Olšavská leg., August 5-th 2020, OZRM 11602 (Fig. 4F ).

Paratypes.

From Type locality: J. Grego, A. Falniowski, M. Olšavský and J. Olšavská leg., August 5-th 2020, OZRM 11603/1 specimen; NHMW 113608/1 specimen, JG F1526/160 specimen; Type locality, J. Grego, G. Jakab and B. Šmída leg. March 17-th 2017, JG F0736/26 specimens.

Other material.

Morphologically similar stygobiotic Horatia shells were found in following spring localities (springs at left tributaries of Upper Cetina River: Vrelo Kosinac 1, Sinjski Obrovac, Sinj district, Croatia, 43°43'40.89"N, 16°42'2.29"E JG/8; Vrelo Kosinac 2, Sinjski Obrovac, Sinj District, Croatia, 43°43'43.11"N, 16°42'0.83"E JG/4; Grabske Mlinice, Grab, Sinj District, Croatia, 43°38'27.26"N, 16°46'13.57"E JG/3). For the time being we treat those as H. cf. stygorumina .

Diagnosis.

Shell minute, trochiform, distinguished from the other species of Horatia by its very wide umbilicus showing earlier whorls inside. From the H. ozimeci s. nov. distinguished by higher conical spire and suture reaching the aperture, as well by more swollen protoconch and by slight sinuation at labral columellar margin. From stygobiotic cf. Horatia knorri different by much wider umbilicus and by aperture shape less declined from the columella in its labral profile.

Description.

Shell (Fig. 4F ) 2.08 mm high and 1.57 mm broad, conical, fresh shells milky white and translucent, with 3 rounded inflated whorls and deep suture, the whorls regularly tapering towards the aperture. Spire conically elevated, body whorl prominent. Smooth shell surface covered with blunt regular axial growth lines more prominent at the body whorl. Aperture almost rounded, tear-shaped, shortly attached to the body whorl by weak grove. Labral lateral profile backward protruded almost straight, columellar margin slightly sinuated at its middle. Umbilicus open.

Measurements of holotype of H. stygorumina : Table 2 .

Soft parts morphology and anatomy. Not known.

Derivatio nominis.

The specific epithet Horatia stygorumina is derived from the stygobiont habitat and from the type locality: cave Mali Rumin also referring to the name of the nearby settlement Rumin.

Distribution and habitat.

Known only from the type locality, where empty shells can be found in the cave sediments, as well as in the sandy sediments of the intermittent spring. The shells are washed out from their stygobiont habitat. The cave is 50 m long, with two branches, acting as an intermittent overflow of the larger permanent spring Vrilo Rumin, situated 730 m east-southeast. Both springs are draining karstwater from middle part of Livansko Polje Basin (Bosnia and Herzegovina) Under Dinara Mts. towards upper Cetina River Valley. The following Hydrobiidae were detected in the locality: Horatia klecakiana , Orientalina curta germari , Kerkia jadertina sinjana ( Kuščer, 1933) and a Montesieriid species of Paladilhiopsis Pavlović, 1913 and/or Lanzaia Brusina, 1906.

Figures

Figure 4. Shell variability of two Horatia species A-E H. ozimeci A sequenced specimen (2 H 76) B holotype OZRM 11603 C-E paratypes E NHMW 113607, (Photo NHMW by Ivo Gallmetzer) F-H H. stygorumina F holotype OZRM 11600 G-H paratypes NHMW 113608, (Photo NHMW by Gallmetzer) I Cf. Horatia knorri Schuett, 1961, spring of Ombla in Komolac, holotype SMF 164247 (Photo SMF by Sigrid Hof) J-P sequenced specimens of H. klecakiana J Vrelo Kosinac 2 K H. klecakiana, Gala spring L H. klecakiana, Ruda Begusa M, N, P H. klecakiana, Vrelo Kosinac 1 O H. klecakiana, Grabske Mlinice. The shell measurements are also shown: a shell height, b body whorl breadth, c aperture height, d spire height, e aperture breadth, α apex angle, β angle between body whorl suture and horizontal surface. Scale bars: 1 mm.

Figure 5. SEM images of H. ozimeci (A) juvenile specimen from the type locality (SBMNH 635080) and H. stygorumina (B) juvenile shell from cave Mali Rumin (SBMNH 635079). SEM SBMNH by Vanessa Delnavaz.