Olivella semistriata
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| Olivella semistriata | |
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| Olivella semistriata, scale bar: 1 cm. Arrowhead highlights lateral propodial appendage. From [1] | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| Subclass: | Caenogastropoda |
| Order: | Neogastropoda |
| Family: | Olividae |
| Genus: | Olivella |
| Species: | O. semistriata |
| Binomial name | |
| Olivella semistriata | |
Olivella semistriata is a species of small sea snail, a marine gastropod mollusk in the family Olividae, the olives. Species in the genus Olivella are commonly called dwarf olives[3] With the very similar Olivella columellaris it forms the subgenus Pachyoliva.[4] 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.[1] 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.[1]
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 Olivellinae; 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 distinctly 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.[1][4][5][6][7]
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 Olivellinae and its family, the 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.