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Olivella semistriata
''Olivella semistriata'' is a species of small sea snail, a marine gastropod mollusk in the family Olivellidae, the dwarf olives. With the very similar ''Olivella columellaris'' it forms the subgenus ''Pachyoliva''.〔(Olsson A. A. (1956) Studies on the genus ''Olivella''. ''Proceedings of the Academy of Natural Sciences of Philadelphia'' 108: 155-225 )〕 Both species are suspension feeders. They use unique appendages of the propodium (front part of the foot) to deploy mucus nets which capture suspended particles from the backwash on sandy beaches of the tropical eastern Pacific.〔(Troost A. I., Rupert S. D., Cyrus A. Z., Paladino F. V., Dattilo B. F., Peters W.S. (2012) What can we learn from confusing ''Olivella columellaris'' and ''O. semistriata'' (Olivellidae, Gastropoda), two key species in panamic sandy beach ecosystems? ''Biota Neotropica'' 12(2): 101-113 ) doi: 10.1590/S1676-06032012000200011〕 ''Olivella semistriata'' is a swash-surfer; the snails use their expanded foot as an underwater sail to follow the tidal movement of the backwash zone in which they feed.〔
==Description==
(''this section compiled from'' 〔〔〔〔〔(Burch J. Q., Burch R. L. (1963) Genus ''Olivella'' in eastern Pacific. ''Nautilus'' 77: 1-8. (plus 3 plates) )〕)
Shell of elongate oval shape, with relatively high and pointed spire and a large body whorl. The shell is smooth and shiny except for the upper (= posterior) half of the body whorl which carries dense longitudinal grooves, or striae (hence the name ''semistriata''). These striae are a distinctive character that separates ''O. semistriata'' from all other Olivellidae; however, the striae do not begin to form before the animal exceeds 10 mm shell length. The suture is open. The aperture is elongate, and the inner lip (= the inner border of the aperture) is covered by thick parietal callus that may extend to the suture. Lirae (= ridges or plications) on the inner lip are lacking, but there is a conspicuous notch in the anterior third of the lip. The ground color is a dark brown or olive with a varying number (0 to 4) of lighter or darker, often fading bands. A rare color morph lacks the darkest pigments and shows golden-orange tones all over. The fasciolar band (= a distincly structured portion of the shell around the siphonal notch) is brownish gray to white, and so is the apex in most individuals. A chitinous (= horny) operculum is present.
The living animal is brownish gray with characteristic dark marks on the propodium, the front part of the foot. It lacks cephalic tentacles and eyes. As in all Olivellidae and the closely related Olividae, the propodium is separated by a pronounced groove from the main foot, the metapodium. In ''O. semistriata'' (as well as in ''O. columellaris''), the lateral tips of the propodium are greatly extended and function in suspension feeding. The propodium is further divided into a left and a right half. The mouth opening which can be everted on a proboscis, is located on the dorsal face of the foot between the left and right lobes of the propodium.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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