Rissoa genus of minute sea snails , marine gastropod mollusks or micromollusks in the family Rissoidae.
The genus was first introduced by M. de Freminville for some small shells observed by M. Antoine Risso , a distinguished naturalist of Nice, France. They were described by M. Demarest in 1814 in the "New Bulletin of the Philomatic Society".
The soft body of the snail is elongated and spiral. The somewhat prolonged mouth has a proboscis . The tentacles are awl-shaped with the eyes on a small prominence near the base. The foot is oval or elliptical. The species is phytophagous.
The conical shell has an elongated spire with its apex nipple-shaped. The size of the shell varies between 1 mm and 8 mm. The whorls are generally convex-shaped with a distinct suture. The aperture is ovate, roundish or pear-shaped with its anterior end rounded, the posterior end acute and with the peristome complete. The thin and horny operculum is spirally marked and equally ovate, roundish or pear-shaped.
This species can be found on brown algae (genus Fucus
Species within the genus Rissoa include:
Species brought into synonymy Rissoa adarensis E.A. Smith, 1902: synonym of Onoba kergueleni Rissoa albella Lovén, 1846: synonym of Pusillina sarsii Rissoa albella Alder, 1844: synonym of Rissoella diaphana (Alder, 1848)Rissoa albolirata Carpenter, 1864: synonym of Lirobarleeia albolirata (Carpenter, 1864)Rissoa alifera Thiele, 1925: synonym of Hoplopteron alifera Rissoa alveata Melvill & Standen, 1901: synonym of Iravadia quadrasi (O. Boettger, 1893)Rissoa atomus E. A. Smith, 1890 : synonym of [[Eatonina fulgida ]] (Adams J., 1797)Rissoa australis Watson, 1886: synonym of Powellisetia australis (Watson, 1886)Rissoa basispiralis Grant-Mackie & Chapman-Smith, 1971 † a: synonym of Diala semistriata Rissoa boscii (Payraudeau, 1826): synonym of Melanella polita Rissoa calathus Forbes & Hanley, 1850: synonym of Alvania beanii Rissoa carnosa Webster, 1905: synonym of Fictonoba carnosa (Webster, 1905)Rissoa cazini Vélain, 1877: synonym of Pisinna cazini (Vélain, 1877)Rissoa cerithinum Philippi, 1849: synonym of Cerithidium cerithinum Rissoa columna Pelseneer, 1903: synonym of Onoba kergueleni Rissoa coronata Scacchi, 1844: synonym of Opalia hellenica (Forbes, 1844)Rissoa costata (J. Adams, 1796): synonym of Manzonia crassa Rissoa costulata Alder, 1844: synonym of Rissoa guerinii Récluz, 1843Rissoa crassicostata C. B. Adams, 1845: synonym of Opalia hotessieriana (d’Orbigny, 1842)Rissoa deserta E.A. Smith, 1907: synonym of Powellisetia deserta Rissoa diaphana Alder, 1848: synonym of Rissoella diaphana (Alder, 1848)Rissoa dolium Nyst, 1845: synonym of Pusillina philippi Rissoa dubiosa C. B. Adams, 1850: synonym of Schwartziella dubiosa (C. B. Adams, 1850)Rissoa edgariana Melvill & Standen, 1907: synonym of Rissoa parva (da Costa, 1778)Rissoa edwardiensis Watson, 1886: synonym of Skenella edwardiensis Rissoa emarginata Hutton, 1885: synonym of Nozeba emarginata (Hutton, 1885)Rissoa emblematica Hedley, 1906: synonym of Emblanda emblematica Rissoa eulimoides (C.B. Adams, 1850): synonym of Melanella eulimoides (C. B. Adams, 1850)Rissoa filostria Melvill & Standen, 1912: synonym of Onoba filostria Rissoa finckhi Hedley, 1899: synonym of Chrystella finckhi (Hedley, 1899)Rissoa garretti Tate, 1899: synonym of Iravadia quadrasi (O. Boettger, 1893)Rissoa georgiana Pfeffer, 1886: synonym of Onoba georgiana Rissoa gracilis Pease, 1860: synonym of Pyramidelloides angustus Rissoa griegi Friele, 1879: synonym of Cingula griegi (Friele, 1879)Rissoa grisea Martens, 1885: synonym of Onoba grisea Rissoa inconspicua Alder, 1844: synonym of Pusillina inconspicua Rissoa inconspicua C. B. Adams, 1852: synonym of Alvania monserratensis Baker, Hanna & Strong, 1930Rissoa inflatella Thiele, 1912: synonym of Onoba inflatella Rissoa infrequens C. B. Adams, 1852: synonym of Opalia infrequens (C. B. Adams, 1852)Rissoa integella Hedley, 1904: synonym of Attenuata integella (Hedley, 1904)Rissoa interrupta (J. Adams, 1800): synonym of Rissoa parva (da Costa, 1778)Rissoa janmayeni Friele, 1878: synonym of Frigidoalvania janmayeni Rissoa kelseyi Dall & Bartsch, 1902: synonym of Lirobarleeia kelseyi (Dall & Bartsch, 1902)Rissoa kergueleni E. A. Smith, 1875: synonym of Onoba kergueleni (E. A. Smith, 1875)Rissoa labiosa (Montagu , 1803): synonym of Rissoa membranacea (J. Adams, 1800)Rissoa laevigata C. B. Adams, 1850: synonym of Zebina browniana Rissoa lantzi Vélain, 1877: synonym of Onoba lantzi (Vélain, 1877)Rissoa lineolata Michaud, 1830: synonym of Pusillina lineolata Rissoa lirata Carpenter, 1857: synonym of Lirobarleeia lirata (Carpenter, 1857)Rissoa marionensis Watson, 1886: synonym of Eatoniella subrufescens (E.A. Smith, 1875)Rissoa miliaris Thiele, 1912: synonym of Skenella sinapi (Watson, 1886)Rissoa observationis Thiele, 1912: synonym of Onoba kergueleni (E. A. Smith, 1875)Rissoa paucilirata Melvill & Standen, 1912: synonym of Onoba paucilirata Rissoa pelseneeri Thiele, 1912: synonym of Powellisetia pelseneeri Rissoa principis Watson, 1886: synonym of Powellisetia principis (Watson, 1886)Rissoa proxima Forbes & Hanley, 1850: synonym of Ceratia proxima (Forbes & Hanley, 1850)Rissoa punctatostriata Tenison Woods, 1879: synonym of Leucotina casta (A. Adams, 1853)Rissoa punctulum Philippi, 1836: synonym of Pisinna glabrata (Von Mühlfeldt, 1824)Rissoa rufilabris Alder, 1844: synonym of Rissoa lilacina Récluz, 1843Rissoa scalarella C. B. Adams, 1845: synonym of Schwartziella scalarella (C. B. Adams, 1845)Rissoa scotiana Melvill & Standen, 1907: synonym of Onoba semicostata Montagu , 1803)Rissoa semistriata Philippi, 1849: synonym of Diala semistriata Rissoa sinapi Watson, 1886: synonym of Skenella sinapi (Watson, 1886)Rissoa sinuosa Scacchi, 1836: synonym of Melanella sinuosa (Scacchi, 1836)Rissoa striata (J. Adams, 1797): synonym of Onoba semicostata Rissoa striatula Jeffreys, 1847: synonym of Ceratia proxima (Forbes & Hanley, 1850)Rissoa studeriana Thiele, 1912: synonym of Onoba steineni Rissoa suavis Thiele, 1925: synonym of Onoba suavis (Thiele, 1925)Rissoa subangulata C.B. Adams, 1850: synonym of Schwartziella bryerea Rissoa subantarctica Thiele, 1912: synonym of Onoba subantarctica Rissoa subcostulata Schwartz, 1864: synonym of Rissoa guerinii Récluz, 1843Rissoa subtruncata Pelseneer, 1903: synonym of Powellisetia pelseneeri Rissoa subtruncata Vélain, 1877: synonym of Scrobs subtruncata (Vélain, 1877)Rissoa syngenes (A. E. Verril, 1884): synonym of Alvania syngenes Rissoa transenna Watson, 1886: synonym of Onoba transenna (Watson, 1886)Rissoa valdiviae Thiele, 1925: synonym of Onoba steineni Rissoa venusta Garrett, 1873: synonym of Iravadia quadrasi (O. Boettger, 1893)Rissoa vitrea C. B. Adams, 1850: synonym of Zebina vitrea (C. B. Adams, 1850)Rissoa xanthias Watson, 1886: synonym of Benthonellania xanthias Rissoa xanthias var. acuticostata Dall, 1889: synonym of Benthonellania acuticostata 
