Mitromorpha (Mitrolumna) olivoidea ( Cantraine, 1835 )

Amati, Bruno, Smriglio, Carlo & Oliverio, Marco, 2015, Revision of the Recent Mediterranean species of Mitromorpha Carpenter, 1865 (Gastropoda, Conoidea, Mitromorphidae) with the description of seven new species, Zootaxa 3931 (2), pp. 151-195 : 163-165

Mitromorpha (Mitrolumna) olivoidea ( Cantraine, 1835)

( Figs 8 A–O; 9A–E; 10; 27G; 28B)

Mitra olivoidea Cantraine, 1835:391

? Mitra striarella Calcara, 1841: 66 , pl. 2, fig. 9

Mitrolumna melitensis, Mifsud, 1993: 14 –17, 2 figs Mitromorpha (Mitrolumna) melitensis Mifsud, 2001: 16 , fig. 30

Type material. M. olivoidea : lectotype (H. 8.3 mm) ( Fig. 8 A, B) and 1 paralectotype ( Cernohorsky 1970: Pl. 12, fig. 8) IRSN- IG 3354. M. striarella : probably lost, not present in the MZUP and MCZR. M. melitensis : holotype MUB- 011673 (H 9 mm) ( Fig. 8 C, D) and 4 paratypes, Malta 120–160 m (coll. Mifsud).

Type locality. M. olivoidea : ‘Mediterraneo’. M. striarella: Altavilla , Sicily, Pliocene. M. melitensis: Ras il- Wahx, Malta 120– 160 m.

Other material esamined. Italy: Caprera Is., Sardinia, 70 m, mud-rocks, 1992, 1 sh (CS); Cala Gonone, Dorgali, Sardinia, bioclastic sand, unspecified depth, fishing by-catch, viii.2010, 1 lv (BA); Marina di Camerota, 90 m, fishing by-catch, viii.1985, 4 sh (CS); S. Vito lo Capo, Sicily, 3 sh ( MCZR, coll. Monterosato, M- 21-17319); Ganzirri, Sicily, unspecified depth, fishing by-catch, 2 sh (DS); Palermo, Sicily, 2 sh ( MCZR, coll. Monterosato, M- 21-17319); Elba Is., 1 sh ( MCZR, coll. Monterosato ex coll. Caifassi, M- 21-17319); Capri Is., 4 sh ( MCZR, coll. Monterosato, M- 21-17319); unspecified locality, 1 sh ( MCZR, coll. Monterosato, M- 21-17319); off Lampedusa Is., 130 m, bioclastic coarse sand, 1 sh (MO).

Distribution and habitat. Central Mediterranean Sea. Pliocene ( M. striarella, Pliocene of Altavilla and Montepellegrino: Calcara 1841: 66–67) to Recent. Empty shells usually found in bioclastic sediments (fine mud to coarse sands) in 70– 160 m. Found sympatric, often at different depths, with M. columbellaria , M. karpathoensis , M. bogii n. sp., M. mariottinii n. sp., M. nofronii n. sp. and M. tricolorata n. sp.

Description: Shell large for the genus ( Figs 8 A–O; 9A–E; 27G), height 8.3–9.5 mm, width 4.1–4.55 mm, solid, fusiform, biconic, slender, H/W=2.021–2.306. Protoconch paucispiral ( Fig. 28B ) shiny, of 1.4 whorl, the first convex, the last part nearly flat, d 0.20–0.225 mm, Do 0.40–0.44 mm, DM 0.55–0.60 mm, h 0.45–0.50 mm, sculptured by rare microgranules and vertical riblets. Protoconch-teleoconch boundary scarcely marked, slightly flexuose, opisthocline. Teleoconch of da 5.2–5.5 barely convex whorls. Sculpture starting with 3–4 weak spiral cordlets crossed by 10–14 orthocline (or slightly opisthocline) axial ribs on the first whorls; axials occasionally lacking on the first whorls. Additional spiral cordlets between the adapical ones, and between the suprasutural one and the suture. Last whorl inflated, sculptured over the entire surface by 34–39 spiral fine cordlets, flat, equidistant, of equal size, as broad as (or a little broader than) the interspaces, of which 8–11 above the aperture. The three subsutural cordlets sometimes stronger and more spaced apart than the others. Axial sculpture not present; occasionally weak axial riblets (10–14) develop on the first three whorls, producing tubercles at the intersection with spirals. Two columellar folds, thick but not prominent, the posterior larger. Growth lines visible over the entire surface. Outer lip sharp, thickened internally, with 6–9 denticles, the three posterior larger. Anal sinus deep. Siphonal canal short, and wide. Coloration with a light chestnut-tawny background, rarely monochrome, usually with lighter and darker suprasutural blotches, and a lighter area in correspondence to the anal sinus. Soft parts milky white with black eyes (C. Mifsud at http://www.naturamediterraneo.com/forum/ topic.asp?TOPIC_ID=202901, as Mitromorpha melitensis , last accessed on 11/JAN/2015).

Remarks. M. olivoidea differs from M. columbellaria and M. wilhelminae in the different chromatic pattern: M. columbellaria is almost monochrome, with rare specimens bearing a differently colored subsutural band; M. wilhelminae has very fine darker spiral lines.

From M. columbellaria it differs also in the number of spirals on the last whorls (34–39 of which 8–11 above the aperture, v. 16–28 of which 4–6, rarely up to 8, above the aperture in M. columbellaria ), and in the deeper habitat (70–160 m for empty shells v. 1–60 m).

See under M. bogii n. sp. and M. cossyrae n. sp. for comparisons with those species.

The original description of Mitra striarella ( Calcara, 1841: 66) and the subsequent one ( Calcara 1845: 42) reported features typical of Mitromorpha olivoidea , such as the tawny coloration, the weak spirals, the obsolete axials on the first whorls, and the large size. Therefore, M. striarella is placed doubtfully in the synonymy of M. olivoidea pending the finding of topotypic specimens currently under search.

Mitromorpha scarponii Tabanelli, 2014 has been recently described from the Pliocene of Romagna (Central Italy) and it is very similar to M. olivoidea . Several features fall within the known range of M. olivoidea (large size, spirals on the last whorls and above the aperture, H/W ratio, protoconch sculpture), but a decision on a possible synonymy is postponed pending the examination of more material.

M. melitensis has been diagnosed from M. olivoidea basing on larger apical size and an allegedly different coloration ( Mifsud 2001). Actually, the lectotype of M. olivoidea ( Fig. 8 A, B) has a tawny-brown background color, with lighter and darker medial blotches, and a marked decoloration in correspondence with the anal sinus, definitely not distinguishable from M. melitensis ( Fig. 8 C, D). The apical measures reported by Mifsud (1993:16, fig. 1: ‘a’ 0.43 mm, ‘b’ 0.53 mm) were incorrectly derived, and were subsequently ( Mifsud 2001: pl 4, n. 58) corrected after using a more standard method ( Verduin 1982: 129): mean Do = 0.44 mm, mean DM = 0.57 mm. These mean values fall within the known range of M. olivoidea (Do 0.40–0.44 mm, DM 0.55–0.60 mm). The holotype of M. melitensis is a little more slender than the lectotype of M. olivoidea (H/ W 2.227 v. 2.085) and shows a less evident sculpture on the periphery, a variation observed within most species of Mitromorpha .

Figures

FIGURE 8. Mitromorpha olivoidea (Cantraine, 1835). A – B. lectotype of Mitra olivoidea Cantraine, ‘ Mediterraneo’, H = 8.3 mm (IRSN, IG 3354); C – D. Holotype of Mitromorpha melitensis (Mifsud, 1993), Malta, H = 9 mm (MZB- 011673); E – H. Cala Gonone, Sardegna, Italy, H = 9.2 mm (BA); I. Marina di Camerota 90 m, Italy, H = 9 mm (CS); J – K. Elba Is., Italy, H = 7.2 mm (MCZR, M- 21 - 17319); L-M. Palermo, Italy, H = 7.3 mm (MCZR, M- 21 - 17319); N – O: S. Vito lo Capo, Italy, H = 7.75 mm (MCZR, M- 21 - 17319).

FIGURE 28. A – L. Mitromorpha spp. Fist whorls (SEM). A. Mitromorpha columbellaria, Marina di Camerota, Italy (CS); B. Mitromorpha olivoidea, Lampedusa Is., Italy (MO); C. Mitromorpha karpathoensis, Salina Is., Italy (BA); D. Mitromorpha wilhelminae morph A, Alboran Is., Spain (CS); E. Mitromorpha wilhelminae morph B, Alboran Is., Spain (MO); F. Mitromorpha alyssae, holotype (MNHN); G. Mitromorpha bogii, paratype, Secca delle Vedove, Italy, 200 – 300 m, (MCZR, 00080); H. Mitromorpha cossyrae, holotype (MNHN); I. Mitromorpha mariottinii, holotype (MNHN); J. Mitromorpha mifsudi, olotipo (MNHN); K. Mitromorpha nofronii, holotype (MNHN); L. Mitromorpha tricolorata, holotype (MNHN). Scale bars: 100 µm.