Laphystius sturionis Sars, 1893 – synonym of Lafystius sturionis
Leander serratus – synonym of Palaemon serratus
Lebbeus orthorhynchus White, 1847 – synonym of Lebbeus polaris
Lekanesphaera levii Argano & Ponticelli – synonym of Sphaeroma monodi
Lembos versiculatus Bate, 1856 – synonym of Microdeutopus versiculatus
Lepidactylus dytiscus Say, 1818 – synonym of Haustorius arenarius
Leptocaris slabberi (Van Beneden, 1861) – synonym of Mesopodopsis slabberi
Leptocheirus cornaurei Sowinski, 1898 – synonym of Leptocheirus pilosus
Leptocheirus dellavalli Stebbing, 1899 – synonym of Leptocheirus pectinatus
Leptocheirus pilosus Boeck, 1871 – synonym of Leptocheirus hirsutimanus
Leptocheirus subsalus Norman, 1908 – synonym of Leptocheirus pilosus
Leptochelia dubia Sars, 1882 – synonym of Leptochelia savignyi
Leptochelia Edwardsii Bate and Westwood, 1868 – synonym of Leptochelia savignyi
Leptochelia Savignyi Sars, 1882 – synonym of Leptochelia savignyi
Leptognathia graciloides Norman and Stebbing, 1886 – synonym of Tanaopsis graciloides
Leptognathia laticaudata Sars, 1882 – synonym of Tanaopsis graciloides
Leptomera pedata (Gammarus) M. Sars, 1858 (1859) – synonym of Phtisica marina
Leptomera pedata Lamarck, 1818 – synonym of Phtisica marina
Leptomera rubra Lamarck, 1818 – synonym of Phtisica marina
Leptomera ventricosa H. Edwards, 1840 – synonym of Phtisica marina
Leptomysis linguura Zimmer, 1933 – synonym of Leptomysis lingvura
Leptomysis marioni Gourret, 1888 – synonym of Leptomysis lingvura
Leptomysis pontica Czerniavsky, 1882 – synonym of Leptomysis lingvura
Leptomysis sardica G.O. Sars, 1877 – synonym of Leptomysis lingvura
Leptopodia tenuirostris Leach, 1814 – synonym of Macropodia tenuirostris
Leucon cercaria Van Beneden, 1861 – synonym of Pseudocuma longicornis
Leucon emarginatus Krøyer, 1846 – synonym of Eudorella emarginata
Leucothoe aruiculosa Leach, 1814 – synonym of Leucothoe spinicarpa
Leucothoe phyllonyx Sars, 1858 – synonym of Arrhis phyllonyx
Leucothoe spinicarpa: Sars, 1892 – synonym of Leucothoe spinicarpa
Ligia belgia Bosc. – synonym of Ligia oceanica
Ligia scorpulorum Leach – synonym of Ligia oceanica
Liljeborgia shetlandica Bate and Westwood, 1862 – synonym of Cheirocratus sundevallii
Lilljeborgia kinahani Sars, 1894 – synonym of Liljeborgia kinahani
Limnoria terebrans Leach, 1815 – synonym of Limnoria lignorum
Limnoria uncinata Heller, 1866 – synonym of Limnoria lignorum
Liocarcinus puber Ingle, 1980 – synonym of Necora puber
Lissa fissirostra Say, 1817 – synonym of Hyas coarctatus
Lophogaster serratus Björck, 1916 – synonym of Lophogaster typicus
Lupa hastata Say, 1817 (not Cancer hastata Linnaeus, 1767) – synonym of Callinectes sapidus
Lysianassa audouiniana Bate, 1857 – synonym of Perrierella audouiniana
Lysianassa costae Bate and Westwood, 1861 – synonym of Lysianassa plumosa
Lysianassa humilis Costa, 1853 – synonym of Orchomene humilis
Lysianassa spinifera Stimpson, 1853 – synonym of Tiron spiniferus
Lysianax audouinianus Walker, 1889 – synonym of Perrierella audouiniana
Lysianax ceratinus Walker, 1889 – synonym of Lysianassa ceratina
Lysianax septentrionalis Della Valle, 1893 – synonym of Lysianassa plumosa