Table 2 in Three new deep-sea species of Thyasiridae (Mollusca: Bivalvia) from the northwestern Pacific Ocean

Table 2 (continued on next page). Main differentiating characters of species of Parathyasira Iredale, 1930 lacking a shell micro- sculpture of calcareous spines.
SpeciesShellSculptureAnterodorsal marginPosterodorsal marginLunuleLigamentProdissoconch length (µm) and sculptureHeel of footReferencesP. coani sp. nov.Obliquely- rhomboidal; drown out anteriorly, solidThin, commarginal ribs and weak, irregular undulations; micro-sculpture of densely spaced wrinklesLong, slightly concave, gently sloping from beaksLong, convex, steeply sloping from beaksLong, weakly defined, wide, flatWell visible externally, thick, long235–250; sculptured with 5 lamellated foldsAbsentPresent studyP. pauli sp. nov.Rhomboidal; drown out anteriorly, solidThin, commarginal ribs and weak, irregular undulations; micro-sculpture of densely spaced pitsLong, straight, sloping rather steeply from beaksLong, slightly convex, sloping steeply from beaksLong, well defined, wide, strongly excavated, demarcated by ridgesWell visible externally, thick, long252–260; sculptured with 6 lamellated foldsAbsentPresent studyP. kaireiae Okutani, Fujikura & Kojima, 1999Pyriform, with well developed posterior sulcus; high, solidConspicuous, commarginal ribs and weak, irregular undulations; micro-sculpture of densely spaced wrinklesLong, straight or slightly concave, sloping steeply from beaksLong, convex, sloping steeply from beaksLong, weakly defined, flatLongNo dataNo dataOkutani et al. 1999P. fragilis Kamenev, 2020Rhomboidal; thin and fragile, transparentConspicuous, commarginal ribs and weak, irregular undulations; micro-sculpture of densely spaced pitsLong, straight, sloping very steeply from beaks, descending below mid-point of shellLong, slightly convex, sloping very steeply from beaksLong, weakly defined, wide, flatSlightly visible externally, short232; sculptured with 2 radial, wide, rounded folds and closely spaced shallow pits.Distinct, smallKamenev 2020P. magellanica (Dall, 1901)Subquadrate; translucentFine, low growth linesShort, slightly convex or straight, sloping gradually from beaksLong, slightly convex, sloping steeply from beaksSmall, weakly defined, narrowVisible externally, long120; initial part sculptured with 10–14 lamellated folds, sometimes bifurcated at baseAbsentDall 1901; Zelaya 2009P. dearborni (Nicol, 1965)Rhomboidal; thinCommarginal ribs composed by microscopic irregular corrugations and pustulesLong, straight or slightly concave, sloping steeplyLong, slightly convex, sloping steeply from beaksShort, weakly definedVisible externally, long115; sculptured with 28 lamellated folds, symmetrically distributed with respect to main central axisAbsentNicol 1965; Zelaya 2009P. dunbari (Lubinsky, 1976)Pyriform; high, strongly asymmetric, solidConspicuous, commarginal ribsLong, concave, sloping very steeply from beaks, descending below mid-point of shellLong, convex, sloping very steeply from beaksLarge, well defined, strongly excavated, cordateVisible externally, long160; smoothAbsentLubinsky 1976; Oliver & Killeen 2002P. equalis (Verrill & Bush, 1898)Ovate to pyriform and diamond shaped; solidWeak commarginal lines and growth stops, frequently with irregular dents, weak ridges and fine radial striaeShort, concave or straight, sloping steeply from beaksLong, convex, sloping steeply from beaksSmall, weakly defined, excavatedNot visible externally, long155–167; series folds or wrinkles radiating from the anterior end to apexAbsentVerrill & Bush 1898; Payne & Allen 1991; Oliver & Killeen 2002P. biscayensis (Payne & Allen, 1991)Obliquely-rhomboidal; drown out anteriorlyIrregular indented commarginal growth lines and weak, irregular undulationsLong, almost straight, sloping steeply from beaksLong, convex, sloping steeply from beaksNo dataLongNo dataAbsentPayne & Allen 1991; present studyP. marionensis (E. A. Smith, 1885)SubquadrateFine, commarginal ribsLong, concave, sloping gradually from beaksLong, convex, sloping steeply from beaksShort, narrowNo dataNo dataNo dataSmith 1885