Spirolaxis Monterosato, 1913

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 : 42

Genus Spirolaxis Monterosato, 1913

Type species. Pseudomalaxis centrifuga Monterosato, 1890 ; by monotypy. Present-day, Atlantic Ocean.

Original diagnosis. “ Shell discoidal; whorls quadrangular, detached, solute ” (Monterosato 1913: 363).

Revised description. “ Teleoconch: very small to small (usually 1.5-2.5); whorls detached (“open coiling”) throughout or after about 1.5 whorls; small specimens coin-shaped and largely planispiral, larger forms helicoidal; two peripheral keels formed by two usually equally strong ribs (LPR and rib of the basal area), resulting in quadratic (rarely hexagonal) cross-section of whorl; axial sculpture lacking or distinctly developed, with upper and lower surfaces similar; subsutural rib and rib surrounding extremely wide umbilicus often weak, without distinct crenae; peripheral region between keels with few thin spiral threads; coloration indistinctly off-white to tan, occasionally with weak irregular flames or blotches. Protoconch: very small to small (ca. 0.48-0.72), almost planispiral to distinctly heterostrophic, without anal keel” ( Bieler 1993: 321) ( Fig. 2 ).

Synonyms. Paurodiscus Rehder, 1935 [type species Pseudomalaxis (Paurodisms) lamellifera Rehder, 1935 ; present-day, Atlantic Ocean]. Aguayodiscus Jaume & Borro, 1946 [type species Spirolaxis (Aguayodisms) clenchi Jaume & Borro, 1946 ; present-day, Atlantic Ocean.

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.