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Leptodoras marki is distinguished from its congeners by having a large dark submarginal blotch on distal half of dorsal-fin spine and anteriormost dorsal-fin branched rays (vs. dorsal fin hyaline in L. acipenserinus, L. cataniai, L. linnelli, L. myersi, L. nelsoni, L. rogersae, or dorsal fin with basal third to half of dorsal-fin spine and dorsal-fin branched rays blackened, forming a triangular blotch tapered posteriorly in L. copei, L. oyakawai, L. praelongus, or dorsal fin with base of branched rays darkened in L. juruensis); lower labial extension of modified oral hood extending more posteriorly than upper labial extension (vs. upper labial extending posteriorly to lower labial extension in L. acipenserinus, L. cataniai, L. juruensis, L. myersi, L. nelsoni, L. rogersae, or upper and lower labial extensions finishing more or less even in L. hasemani, L. linnelli); relatively few midlateral scutes (34–37 vs. 37–46 per side in all congeners except in L. copei, L. oyakawai, L. praelongus); gas bladder moderately sized, not reduced (vs. reduced in all congeners, except in L. oyakawai); paired bony capsules on anteriormost vertebrae reduced to paired cup-like laminar ossifications separated by a triangular septum (vs. paired bony capsules longitudinally expanded, rounded, and more bulbous, not compressed anteriorly in all congeners, except in L. oyakawai); pair of small, swelling-like diverticula on each side of the anterior chamber of gas bladder (vs. gas bladder with smooth walls, without diverticula in L. oyakawai); a well-developed anterior nuchal plate and parieto-supraoccipital not contacting middle nuchal plate (vs. anterior nuchal plate reduced, permitting contact between parieto-supraoccipital and middle nuchal plate in most specimens of L. praelongus); and nuchal foramina present (vs. absent in medium to large specimens of L. copei, L. hasemani, L. praelongus) (Ref. 84244). |