Mathilda O. Semper, 1865

Harzhauser, Mathias & Landau, Bernard, 2023, The Architectonicidae and Mathildidae (Gastropoda, Heterobranchia) of the Miocene Paratethys Sea-victims of the Miocene Climatic Transition, Zootaxa 5370 (1), pp. 1-74 : 45-46

Genus Mathilda O. Semper, 1865

Type species. Turbo quadricarinatus Brocchi, 1814 , subsequent designation by De Boury (1883: 112). Pliocene, Italy.

Original diagnosis. “ Testa turriculata; apice revoluto, abrupte dextroverso; anfract. in speciebus typicis cingulis transversis et striis longitudinalibus reticulosis; apertura integra, subrotunda, basi nonnunquam subeffusa; labro acuto; labio adnato; columella laevi, non plicata ” [Shell turriculate, apex reversed to the right; whorls typically with spiral cords and longitudinal striae, reticulate; aperture complete, subrounded, basis sometimes slightly effused; lip thin, attached; columella smooth, not plicate] (Semper 1865: 330).

Revised description. “ Protoconch: diameter 440-640 μm; hyperstrophic, diverging about 100-145° from teleoconch axis; with 1.5 to 2.5 whorls; smooth, glassy, without distinct sculptural elements […]. Teleoconch: length usually 3-20 mm at 4 ¼ to 14 whorls, but large-shelled forms occasionally up to 40 mm at 19 whorls; slender to broadly cone-shaped, spire angle 17-38°; upper side with concave, straight or slightly bulging whorls; periphery with single or double keel or rounded; aperture round to quadrangular, apertural lip often slightly channeled at columella and under major spiral ribs of body whorl; first teleoconch whorl already with at least a subset of the adult axial and spiral sculpture; exposed primary sculpture on upper side consisting of 3 to 4 spiral ribs (often with interspaced additional ones), 1 or 2 of the main spiral ribs markedly more prominent than the others; spiral ribs crossed (at right angles or following more-or-less sinuous shape of apertural lip) by weaker axial ribs, threads or enhanced growth lines; at rib intersections usually with sculpture of rounded more-or-less coarse nodules; interspaces between spiral ribs cancellate due to axial ribbing; upper point of attachment of the following whorl at a spiral rib less prominent than at least one of the exposed ribs above; this attachment rib and an additional rib next to it forming a distinct double edge at outer shell base; flat, concave or slightly inflated basal area with several more-or-less well-defined spiral threads or ribs, surrounding solid columella, or narrow umbilical chink, or funnel-shaped umbilicus ” ( Bieler 1995: 599).

Synonyms. Granulicharilda Kuroda & Habe in Kuroda, Habe & Oyama, 1971, type species Granulicharilda sagamiensis Kuroda & Habe in Kuroda, Habe & Oyama, 1971. Present-day, Japan. Mathildona Iredale, 1929 , type species Mathildona euglypta Iredale, 1929 . Present-day, Indo-West Pacific. Opimilda Iredale, 1929 , type species Mathilda decorata Hedley, 1903 . Present-day, Indo-West Pacific. Eucharilda Iredale, 1929 , type species Mathilda elegantula Angas, 1871 . Present-day, New South Wales, Australia. Mathildia Bosquet, 1869 : ( Bosquet 1869: 261), unjustified emendation of Mathilda Semper, 1865 .

Discussion. Gŗndel (1976) and Gŗndel & Ņtzel (2013) discussed the number of primary spiral cords on the first teleoconch whorl as taxonomically important feature within Mathildidae . For the type species Mathilda quadricarinata, Gr ̧ndel (1976) counted four primary spiral cords. The most adapical of these cords, however, is only a weak cord over the sutural ramp. Therefore, we interpret the pattern as consisting of three prominent primary spiral cords and a weaker cord at the adapical suture (see Tabanelli et al. 2021: figs 2a–b).

Many of the species described herein, display the same number of primary cords, termed S1 (most adapical), S2, S3 herein ( Figs 2 , 22 ). Mathilda species with this S1-S2-S3-mode of spiral sculpture appear already during the mid-Jurassic, as documented by Mathilda makowskii Kaim (2004) from Poland ( Kaim 2004: fig. 95). This makes Mathilda an enormously long-lived genus existing since 165 Mio years and experienced its maximum diversity during Mesozoic times (Gŗndel & Ņtzel, 2013). Four of the species revised or described herein display such a S1- S2-S3-mode of formation of spiral cords ( Mathilda clarae Boettger, 1902 , M. margaritula Semper, 1865 , M. monilis Semper, 1865 , Figs 22A –D ). In Mathilda brusinai de Boury, 1883 , M. gloriosa Boettger, 1907 and M. praeclara , 1902 one or two secondary spiral cords are intercalated but S1, S2, and S3 remain the predominant cords ( Figs 22E–G ). The periphery of these species typically coincides with S2. ‘ Cerithium’ fimbriatum Michelotti, 1847 and Fimbriatella subfilogranata Montanaro Gallitelli & Tacoli 1951 strongly deviate from that basic pattern. In these species, S2 is weakest and lies in a deep concavity between S1 and S3. The periphery is formed by S3. Therefore, species included in the genus Mathilda have three strong primary cords, with the periphery coinciding with S2. A fourth weaker cord may be present from the first teleoconch whorl or appear later just above the suture. Secondary spirals are intercalated in some species on the subsutural ramp or between the primary cords below, but these secondaries are not present at the teleoconch/protoconch junction. Therefore, we exclude these species from Mathilda and propose to resurrect Fimbriatella Sacco, 1895 , which was introduced by Sacco (1895) for Cerithium fimbriatum Michelotti, 1847 (see below under Fimbriatella ).

Figures

FIGURE 2. Whorl cross-sections of Architectonicidae genera. All modified after Bieler (1993) except for Simplexollata, Basisulcata and Ammotectonica. Solatisonax? refers to Solatisonax? kostejana (Boettger, 1907), Bold genera are represented in the Paratethys Sea. SSC: subsutural cord, MC: mid cord(s), UPC: upper peripheral cord, LPC: lower peripheral cord, IPC: infraperipheral cord; UC: umbilical crenae; PUC: proxumbilical cord.

FIGURE 22. Whorl profiles of Mathilda (A–E), Fimbriatella (F–H) and Pseudotuba (I).