Raphitoma petanii Prkić, Giannuzzi-Savelli & Pusateri, 2020

Prkić, Jakov, Giannuzzi-Savelli, Riccardo, Pusateri, Francesco, Russini, Valeria, Fassio, Giulia & Oliverio, Marco, 2020, Three new species of Raphitoma Bellardi, 1847 (Mollusca, Gastropoda, Raphitomidae) from Croatian waters (NE Adriatic Sea), Zoosystema 42 (16), pp. 215-237 : 219-225

Raphitoma petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp.

( Figs 3 A-G; 4 A-H; 6 A-C; 7 A, B)

urn:lsid:zoobank.org:act:779382FF-84AC-451D-932D-C27E6BAE6AD3

Raphitoma sp. B – Russini et al. 2020: 301.

TYPE MATERIAL. — Holotype. Croatia • lv; MNHN-IM-2000-34887 (height 10.65 mm, width 3.93 mm); Stari Trogir Bay ; 43°29’21”N, 16°02’37”E; 1-4 m depth.

Paratypes. Croatia • 1 lv; MNHN-IM-2000-34888; same locality data as holotype • 1 lv; MCZR-M-TYPE-00118; same locality data as holotype • 1 lv; HPM 11500; same locality data as holotype • 1 lv; MZB 60233; same locality data as holotype • 12 lv; coll. PRK; same locality data as holotype • 2 lv; coll. RGS- 120245, coll. RGS- 120246; same locality data as holotype • 1 lv; coll. PUS-2798; same locality data as holotype • 1 lv; coll. PET; same locality data as holotype • 6 lv; BAU-2269.1-3 , BAU-2273.1 , BAU-2273.3 , BAU-2273.4 ; Sukošan ; 44°01’30”N, 15°20’50”E; 2-6 m depth .

TYPE LOCALITY. — Croatia, Stari Trogir Bay (Sevid); 43°29’21”N, 16°02’37”E; 1-4 m depth.

OTHER MATERIAL EXAMINED. — Croatia • 1 lv; coll. PET; Vrsi , Jase- novo • 1 lv; coll. PET; Zaton , Bilotinjak • 6 lv; coll. PET; Sukošan , Mala Makarska • 1 lv; coll. PET; Sukošan , Tustica • 1 lv; coll. PET; Turanj • 9 lv; coll. PRK; Biograd , Bošana • 58 lv; coll. PET; Biograd , Bošana • 1 lv; coll. PET; Pakoštane • 3 lv, 3 sh; coll. PRK; Murter Island , Kosirina Bay • 1 lv; coll. PET; Murter Island , Kosirina Bay • 7 lv, 2 sh; coll. PRK; Sevid , Stari Trogir Bay • 24 lv; coll. PET; Se- vid, Stari Trogir Bay • 5 lv; coll. RGS; Sevid , Stari Trogir Bay • 5 lv; coll. STA; Brač Island , Milna • 9 lv; coll. STA; Brač Island , Maslinova Bay • 1 lv; coll. PRK; Duće Vavlje • 3 sh; coll. PRK; Mljet Island .

DISTRIBUTION. — This species is so far known only from Croatia, based on the material examined, with samples collected in 0-19 m depth, but we do not exclude the possibility that it occurs also in some other Mediterranean areas.

ETYMOLOGY. — After Alen Petani, for his great contribution to the study of the Croatian raphitomids and to the present paper.

HABITAT. — This species has been collected on rocky bottoms with plenty of small and medium-sized stones, on the underside of which the specimens are found at daytime. This is a shallow-water species, more than 150 live specimens having been found at 0.5-4 m depth, and only a few on slightly deeper bottoms (max 19 m, at Brač Island: R. Stanić, pers. comm.). R. petanii Prkić , Giannuzzi- Savelli & Pusateri n. sp. often lives in sympatry/syntopy with other raphitomids ( Cyrillia linearis , Leufroyia concinna (Scacchi, 1836) , L. leufroyi (Michaud, 1828) , Raphitoma contigua , R. cordieri , R. densa , R. echinata AA. - morphotype 2 [see below], R. laviae , R. stanici Prkić, Giannuzzi-Savelli & Pusateri n. sp., etc.), sometimes with specimens of 5-6 different species occurring under the same stone.

DESCRIPTION [in square brackets the data of the holotype] Shell

Solid, fusiform-acute, of medium size for the genus. Height: 8.2-12.4 mm [10.65]; width: 3.06-4.94 mm [3.93]; h/d: 2.38-2.84 [2.71].

Protoconch

Multispiral, of 2.6-3.25 [2.9] convex whorls. Height: 546 µm, maximum diameter: 447 µm (in specimen with PW = 3.1, Fig. 6 A-C). Protoconch I of 1 whorl, 196 µm in diameter, covered by dense cancellate sculpture; protoconch II with axial threads below the suture and less dense and diagonally cancellate sculpture on the rest of whorl. A strong keel at the end of last whorl covered with microgranules, denser above the keel. Protoconch-teleoconch boundary of flexuose, opisthocline growth lines. Colour brownish with white nucleus.

Teleoconch

Of 6.1-7.25 [7] slightly convex, not stepped whorls, suture incised, sculpture prominent, whole surface covered with dense microgranules. Axial sculpture of 18-27 [24] equidistant, narrow, orthocline or slightly opisthocline ribs, narrower than interspaces, broader than spiral cords. Spiral sculpture of 20-26 [23] spiral cords on the last whorl, of which 6-8 [7] primary cords above the aperture, and two [2] secondary cordlets on the subsutural ramp. Siphonal fasciole with 9-12 [10] strong nodulose cords. Cancellation usually subquadrate, sometimes slightly rectangular, with not very elongate tubercles at intersections; tubercles on first 3 adapical primary cords more or less spinulose, often also on secondary cordlets. Subsutural ramp narrow, inclined. Columella simple, straight and inclined to the right anteriorly, gently angled posteriorly.Siphonal canal of medium length, widely open at the end; posterior canal broad. Outer lip thick, with 9-14 [11] strong inner plicate denticles.

Colour

Brownish or chestnut brown background, often very dark, sometimes with brown-yellowish or brown-greyish hue, interspaces always darker. White, whitish or ash grey blotches and spots of variable size, occasionally absent or very small, or covering most of surface.

Soft parts

Foot long and broad, deeply bilobed anteriorly and with recurved anterolateral corners, narrowly tapering posteriorly. Head small with a pair of long cylindrical tentacles, black eyes on bulges about halfway along their length, the distal part slightly longer and much narrower than the basal. Proboscis rather long and much narrower at the base than at the tip. Colour translucent white or yellowish-white on background, with minute white speckles covering the whole body, including entire length of tentacles, scattered or absent on the sole. Black to dark-grey pigments on head around the base of tentacles and extending on right side down to about halfway to edge of foot. Siphon tip with dense white speckles and a translucent white or yellowish ring, rest of siphon dark grey or grey-brownish with few and scattered white specks. Proboscis pure white and without specks.

Diagnostic nucleotides

37, 70, 112, 250, 533, 539 (COI), and 297 (ITS2).

REMARKS

The number of teleoconch whorls significantly varies in specimens of the same size, while specimens very different in size may have the same number of TW: for example, two specimens 10.28 mm and 8.35 mm long, respectively, both have the same number of whorls (6.25).

Sometimes only one cordlet (adapical) may be present in the frontal view, but also in such cases the other one always gradually appears on the dorsal side of the last whorl, so at dorsal side both secondary cordlets are always present. These two secondary cordlets are often quite strong and with spinulose nodules, so they often look almost as primary cords.

This species can be confused only with Raphitoma densa ( Monterosato, 1884) with which is often found living in sympatry. In Croatia, where R. petanii Prkić , Giannuzzi- Savelli & Pusateri n. sp. is c. 5 times more frequent than R. densa , the two species live in the same bathymetrical range and habitat, and no living or dead specimen has ever been found deeper than 19 m. They share the presence of microgranules over the whole teleoconch, a similar protoconch, same maximum size of the shells, and same colour pattern of the soft parts. In our molecular phylogenetic analyses, R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. and R. densa were sister species, reciprocally monophyletic and their genetic divergence (K2p) was 5-7%, indisputably above the species level threshold.

R. densa is rather variable across its range in the Mediterranean (Giannuzzi-Savelli et al. 2018). However, Croatian specimens of R. densa have quite constant morphological characters which, in most cases (and with very few exceptions), allow to distinguish them relatively easily from shells of R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. Therefore, we provide here diagnostic features between the two species as observed in the Croatian material.

Protoconch

The number of whorls varies similarly in both species, with R. densa showing only slightly fewer whorls (2.5-3.0, mean 2.79) than R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp., (2.6-3.25, mean 2.98). Also the exposed height of the protoconch seems to be slightly different, in a specimen of R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. ( Fig. 6 A- C) with 3.1 protoconch whorls the height is 546 µm, while in a specimen of R. densa ( Fig. 6D, E ) with 3.0 whorls the height is 508 µm.

Axial ribs

Axial ribs are much stronger and broader in R. densa than in R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp., and as a consequence also the tubercles are much more elongated in R. densa . Their number is also frequently (though not always) higher in R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. (18-27, mean 22.55), than in R. densa (16- 19, mean 17.46).

Spiral cords

The spiral sculpture above the aperture consists in both species of primary cords and two secondary cordlets on the shoulder between a narrow subsutural ramp and the first primary cord. In R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. these two secondary cordlets are often quite strong and with spinulose nodules, so they often look al- most as primary cords, while in R. densa they are much weaker. In R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. the spiral cords are only slightly weaker than the ribs, while in R. densa the ribs are much stronger than the cords. The spiral cords on the last whorl are often less numerous in R. densa (19-22, mean 20.64) than in R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. (20-26, mean 23.5); above the aperture there are 5-6 (mean 5.85) primary cords in R. densa and 6-8 (mean 6.96) in R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp.

Apertural denticles

There are often slightly fewer denticles in R. densa (8-10, mean 9.5) than in R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. (9-14, mean 11.32).

Subsutural ramp

In both species the subsutural ramp is narrow, but in R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. the first secondary cordlet is very close to the suture and the ramp is quite inclined. In R. densa the first secondary cordlet is not so close to the suture and the ramp is much less inclined, resulting in more stepped whorls. White comma-shaped marks, which are very often present on the ramp of R. densa , are rarely observed in R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp.

Tubercles

They are more elongated and bluntly elevated in R. densa (only on the first 3 primary cords they can be moderately spinulose). In R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. the tubercles on the first 3 primary cords and two secondary cordlets are more or less spinulose, often very spinulose.

Colour

The variation in colour of the teleoconch mostly overlaps in the two species, but only R. densa always have many large white blotches, while in R. petanii Prkić , Giannuzzi- Savelli & Pusateri n. sp. these blotches can be present, but also completely absent (in the latter cases R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. is very easily diagnosed).

Slenderness (h/d)

The shells of R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. are generally more slender (h/d = 2.38-2.84, mean 2.6) than those of R. densa (h/d = 2.24-2.46, mean 2.37).

Other differences

Young and subadult shells are broader in R. densa , while at these growth stages R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. already has a quite slender shell. General aspect of the outline of the shells is different, being more fusiform in R. petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. because the whorls are not stepped. R. densa has a somewhat more robust aspect of the shell and more robust and less dense teleoconch sculpture.

Figures

FIG. 3. — Raphitoma petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp., Stari Trogir. A, holotype, MNHN-IM-2000-34887, h = 10.65 mm; B, paratype, coll. RGS 120245,h = 9.6 mm;C, paratype,MCZR-M-TYPE-00118,h = 9.25 mm;D, paratype,MNHN-IM-2000-34888, h = 9.3 mm;E, paratype,coll. PUS 2798,h = 9.7 mm; F, paratype, HPM 11500, h = 8.7 mm; G, paratype, MZB 60233, h = 8.2 mm.

FIG. 4. — Raphitoma petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp.: A, Stari Trogir, paratype, coll. PRK, h = 11.05 mm; B, Stari Trogir, paratype, coll. RGS 120246, h = 11.8 mm; C, Stari Trogir, paratype coll. PET, h = 11.55 mm; D, Sukošan, coll. PET, h = 12.4 mm; E, Stari Trogir, paratype, coll. PRK, h = 12.05 mm; F, Biograd coll. PRK, h = 10.3 mm; G, Murter Is., coll. PRK, h = 10.3 mm; H, Stari Trogir, coll. RGS, h = 9.1 mm.

FIG. 6. — A-C, Raphitoma petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp., Stari Trogir,h = 8.05 mm, frontal view of shell (A), apical (B) and frontal (C) view of protoconch;D, E, Raphitoma densa (Monterosato, 1884), protoconch (D) and detail of microgranules at first teleoconch whorl (E). Scale bars: A, 1 mm; B-E, 200 µm.

FIG. 7. — Photographs of living animals of Raphitoma petanii Prkić, Giannuzzi-Savelli & Pusateri n. sp. (A, B) and Raphitoma densa (Monterosato, 1884) (C). A, Zaton, depth 1-2 m, h = 7.85 mm; B, Sukošan, depth 0.5-1 m, h = 12.45 mm; C, Vir Is., depth 1 m, h = 11.1 mm. Photos courtesy: A. Petani.