Zinzulùsa is a karst cave that opens a few meters above the sea level of the Italian coastline of the Otranto Channel in the neighboring city of Castro (geographical coordinates, 40°00′43″ N, 18°25′50″ E) (Figure 1C). The cave is registered at the Regional Karst Archive with the code 107 Pu, and it has an aerial extension of about 150 m that is intensely visited by tourists. The cave has a karst origin, possibly Pliocene (Tyrrhenian, 5–2 million years). The erosive processes acted on an external, young Eocenic rock (55–34 million years), and an innermost, elder Cretaceous rock (141–65 Million years). The internal portion, prohibited to visitors, starts at 150 m from the entrance and after 20 m, submerges below the water level in an anchialine environment, named Cocìto, for additional 150 m of extension, until a maximum depth of 12 m (Figure 1D). The whole submerged system of Zinzulùsa is inhabited by 25 species of aquatic organisms, with two of them (one Harpacticoida, and one Porifera) unknown in any other site of the world (pointed endemics) (Ciccarese and Pesce, 1999).

In recent years, an intense research effort (from 2013 to 2020) has been carried out to describe underwater conditions and collect living organisms from the Cocìto (see Talà et al., 2021). The site, notwithstanding its underground collocation, has appeared variable either in a short time-span (e.g., in the sea level oscillation due to external tide excursions) or over long periods (with a multiannual, intense pH oscillation).

The site has been visited from 2013 to 2020 by speleo scuba divers at distant intervals to avoid excess disturbance to the system, and in the frame of a multidisciplinary study aimed to describe the anchialine part of Zinzulùsa cave (Castro, Otranto Channel, Mediterranean Sea). Each expedition was carried out to collocate a multi-parametric probe in situ, with a battery charge useful for a continuous multi-day monitoring of the environmental parameters. Together with the probe, a modified plankton net (with a mesh size of 200 μm) transformed into a pot was positioned upside down over a hole in the muddy floor from where a water flow comes up in the Cocìto with an intermittent daily cycle. The two instruments were collocated at 35 m from the immersion point at a depth of about 4 m and a distance of 2.5 m from the floor (Figure 1D). Each expedition was concluded with the second visit of the speleo scuba divers after 2–5 days to recover instruments with their log of data and organisms.

The pot–net was also used to collect plankton during the entry and the exit of the speleo scuba divers (along a submerged path of about 35 m) at each visit.

The material collected by the pot–net was filtered in situ at the exit of the Cocìto and rinsed directly with ethanol 90% in a falcon tube (final ethanol concentration, 80–85%).

The samples were analyzed in a laboratory under a compound microscope, and Pseudocyclopiidae specimens were isolated to be studied under a camera lucida acting between 25 and 400 magnifications. For the morphological description, the distinction between body segment and appendage articles has been adopted following Dussart (1967) and Belmonte (1998). The terminology used for body regions follows Dudley (1986). To be compared with other existing Stygocyclopia species, the present description scheme has been arranged following the available literature (Jaume and Boxshall, 1995; Jaume et al., 1999, 2001).

The holotype (an adult female) has been deposited at Naturalis, Leiden, Netherlands (code number RMNH.CRUS.F.4200), and two adult females (paratypes) have been deposited at Marine Biology Museum “Pietro Parenzan” of Porto Cesareo (Lecce, Italy). One additional specimen is a male, damaged. It lacks the terminal part of the URS, the P4, and the terminal parts of Antennules. It was not considered as a reference individual for the species description. However, the P5 is described just for the systematic importance of this morphological detail.

One paratype was dissected to expose the anatomical details of metameric appendages and another paratype has been conserved entirely in 85% ethanol.

Diagnosis of the genus (modified from Jaume et al., 1999). Rostrum with two apical filaments. Antennules symmetrical, short, and composed of 23 articles (female) or 22 articles (male). Antennule articles 1–4 fused. First antenna endopod not fused with the basis. Maxillary endopod two-articled. Endopod of P1 with five setae. First exopod article of P3 without accessory spine. Male P5 with two unbranched rami, asymmetrical, each ramus bi-pointed at the extremity. Left ramus 5 articled, longer than right. Right ramus 3–4 articled. Female P5 with two unbranched, symmetrical rami, each ramus tri-pointed at the extremity. Genital segment (double somite) of female, symmetrical.

Stygocyclopia badinoi SP. NOV. (Figures 2–4).

Collection site: Zinzulùsa cave (Regional Karst code, 107 Pu), the Cocìto (submerged internal part, anchialine habitat) on the Italian coast of the Otranto Channel, Mediterranean Sea, geographic coordinates 40°00′43″ N, 18°25′50″ E (Figures 1C,D).

Holotype: adult female, total length 0.85 mm in 80% ethanol (Naturalis, Leiden, RMNH.CRUS.F.4564). Paratypes: one adult female dissected and mounted in glycerol on three slides (Museum of Marine Biology “Pietro Parenzan,” University of Salento, MBM.CR.SLa-c.0014); another paratype has been conserved entirely in 85% ethanol (Museum of Marine Biology “Pietro Parenzan,” University of Salento, MBM.CR.0014a). Other material: one male, lacking the terminal part of urosome, extremity of Antennulae, and with the absence of right P4 in 85% ethanol (Museum of Marine Biology “Pietro Parenzan,” University of Salento, MBM.CR.0014b). This damaged specimen was not proposed for the species description.

The material has been collected by Raffaele Onorato, Marco Poto, and Michele Onorato (“Apogon” Speleodiver Association) on different dates: March 28, 2017 (male damaged) July 31, 2017 (holotype), and October 24, 2018 (paratypes).

Body compact, with Prosome compressed. Eye absent. Rostrum not articulated, triangular with two filaments at the pointed extremity.

First pedigerous somite fused with the Cephalosome. Second pedigerous somite with rounded postero-lateral margins. A small sensillum is evident in the central position of the lateral margin of the third pedigerous somite (Figure 2 A). Fourth and fifth pedigerous somites fused, with postero-lateral margins rounded without setae. Cephalothorax cuticular surface smooth.

Urosome (length 1/3 of the whole body) 4-segmented, with cuticle without armature. Genital double somite symmetrical with a tiny hyaline frill on the dorsal posterior margin. Seminal receptacle visible on the left side (Figure 2 U). Genital operculum wave-shaped, without armatures. Second and third urosomites with tiny hyaline frill on dorsal posterior margin. Anal somite shorter than the preceding one, without anal operculum.

Furcal rami symmetrical, about as long as wide, without evident cuticular armature. Setae of the furcal rami symmetrically disposed, seta I very reduced, lateral; setae II and VII smooth (not plumose), dorso-laterally and ventro-medially positioned respectively. Seta VII longer than seta II (Figure 2 U). Setae III–VI longer than the URS and flexed (they give the sensation to be internal empty) (Figure 2 A).

Antennules (A1) symmetrical, 23-articulated, short (not longer than the Cephalothorax) stemming from a pedestal (Figure 2 A1). First article longest (fusion of ancestral antennomeres I–IV, according to the interpretation of Jaume et al., 1999), and bearing a total of 5 smooth setae, 1 spiny seta, and 1 aestetask. Each A1 article, but 7th–11th and 13th, provided with at least 1 smooth (not plumose) seta; aestetask present on 1st, 4th, 7th, 12th, 17th, and 23rd articles; a strong and spiny seta is present on 1st, 8th, and 22nd articles (see Figure 2 A1); 9th–11th, and 13th articles (XIII–XV and XVII antennomeres) are naked.

Antenna (A2) (Figure 2 A2) biramous, with a bilobate endopodal extremity and approximately as long as exopod. Coxa with one seta at the distal corner. Basis with two setae at the distal extremity. Exopod distinctly 6-articulated with the following armature formula: 1st art., short with one distal seta; 2nd art., long with three equidistant setae; 3rd art. short, with one seta; 4th art. short, with two setae; 5th art. short, with one seta; 6th art. long, with one medial seta and three distal setae. Endopod with two articles. The 1st art. (proximal) is the longest, with two medio-proximal and two medio-distal setae. 2nd art. (distal) evidently bilobate, medial lobe with eight distal setae (two short, six long), and external lobe with 6 setae (one short, five long).

Mandible (Mb) (Figure 2 Mb) with coxal gnathobasis equipped with five unequal robust teeth; palp with expanded basis with three proximal setae of growing length (from the proximal to the distal one). Mandible palp longer than endopod, indistinctly 4-articulated, with setal formula 1, 1, 1, 2. Endopod 2-articulated, proximal article with one disto-medial seta, and the distal article with a total of 10 setae (9 of the same length plus 1 shorter).

Maxillule (Mx1) (Figure 2 Mx1) prae-coxal arthrite bearing 6 strong spines and 4 setae. Coxal epipodite with 6 plumose setae; coxal endite with two setae; basal endite with four setae; distal endite not well distinguishable from the successive endopodite, which is not articulated with the basis. Both structures with a total of 16 setae. Exopod articulated with the basis, with 8 setae.

Maxilla (Mx2) (Figure 2 Mx2) proximal syncoxal endite with five long spines. Successive (three) syncoxal endites, each with 3 seate. Basal endite with four setae. Endopod short, 2-articulated, with setal formula of 3, 3.

Maxilliped (Mxp) (Figure 3 Mxp) long and evident also in lateral view of the whole specimen (Figure 2 A). Syncoxa long, with 9 unequal setae arranged in 4 different groups according to the formula of 1, 2, 3, 3. Distal extremity of syncoxa with an evident lobe. Basis long, approximately as the syncoxa, with three setae along the medial margin. Endopod 5-articulated, with a total of 21 setae arranged according to the formula of 6, 4, 3, 3 + 1, 4.

First swimming leg (P1) (Figure 3 P1): endopod 1-articulated, with two medio-basal short setae, and three medio-terminal long setae, with a triangular spine at the tip of the endopod article. Two small setae on the lateral margin. Exopod 3-articulated, with one long external smooth spine on each article, and an arrangement of 0, 1, 4 medial setae, respectively. First article of exopod, with a moon-shaped ornament on the postero-medial side. Short spiny setules grouped on the posterior side of the first and second articles of the exopod.

Second swimming leg (P2) (Figure 3 P2): right coxa with a medial plumose seta long until the end of the first exopod article. Left coxa without such a seta. Basis without setae, but with external short spinulae. Endopod 2-articulated in anterior view, and three-articulated in posterior view. Seta formula of 1, 1, 3 + 1. A small triangular tooth on the external corner of the first article. Posterior view of the endopod showing an evident, setulated, and lobed articulation between the second and third articles.

Exopod 3-articulated, with 1, 1, and 3 long lateral spines (the spine on the second exopod article is the longer). The exopod terminates with a long-toothed spine (long as that on the second article, but more robust) which is two-pointed. The spine-seta armature of the exopod is arranged according to the formula: I-1; I-1; III, I, 4. Setae of the third exopod article are plumose, articulated, and flexible. The posterior view of the bfirst and second articles are lightly setulated.

Third swimming leg (P3) (Figure 3 P3): coxae each with a medial plumose long spine reaching the half of the third endopod article. Basis with medio-distal tiny spines and lateral tiny spinules. Endopod 3-articulated with medial long plumose setae arranged according to the formula: 0-1; 0-1; 1,2,2. Small triangular spine on the distal-lateral side of first and second endopod articles. Exopod 3-articulated with strong spines on the lateral side and long setae on the medial side, according to the formula: I-1; I-1; III-I-4. Lateral and terminal spines are secondarily spiny. Setae are plumose and articulated (flexible).

Fourth swimming leg (P4) (Figure 3 P4): basis without spines or setae. Endopod 3-articulated with setae arranged according the formula: 0-1; 0-1; 1, 2, 2. Exopod 3-articulated with lateral spines and medial setae, arranged to according the formula: I-1; I-1; III-I-4.

Fifth leg (P5) (Figure 4 P5): reduced, with unbranched rami, symmetrical, 3-articulated, with tiny and short spines on the distal article. Two terminal spines and one lateral on the extreme article of each ramus, in females (Figure 4). In the male, the P5 right ramus longer, uniramous, 4-articulated. Left ramus shorter, 1-articulated. The right P5 ramus of the male ends with a double slender process, resembling a couple of long and conical spines, not ornamented. The short, left P5 ramus ends with two spines, one very short, and the other long and ornamented with lateral setae.

The species derives its name from Giovanni Badino, a professor of Geophysics at the University of Turin (Italy), and one of the greatest Italian speleologists (Silver medal 1981 for an emergency intervention; President of the Association La Venta; President of Italian Society of Speleology 1994–99; member of directorate of the International Union of Speleology), who passed away on August 8, 2017.