What can we learn from confusing Olivella columellaris and O. semistriata (Olivellidae, Gastropoda), two key species in panamic sandy beach ecosystems?

Abstract

Olivella columellaris (Sowerby 1825) and O. semistriata (Gray 1839) are suspension-feeding, swash-surfing snails on tropical sandy beaches of the east Pacific. While they often are the numerically dominant macrofaunal element in their habitats, their biology is poorly understood; the two species actually have been confused in all of the few publications that address their ecology. Frequent misidentifications in publications and collections contributed also to an overestimation of the geographic overlap of the two species. To provide a sound taxonomic basis for further functional, ecological, and evolutionary investigations, we evaluated the validity of diagnostic traits in wild populations and museum collections, and defined workable identification criteria. Morphometric analysis demonstrated that shell growth is allometric in O. columellaris but isometric in O. semistriata, suggesting that the species follow distinct developmental programs. The taxonomic confusion is aggravated by the existence of populations of dwarfish O. semistriata, which originally had been described as a separate species, O. attenuata (Reeve 1851). At our Costa Rican study sites, the occurrence of such dwarfish populations correlates with low wave energies but not with predation pressure and anthropogenic disturbances, indicating significant ecological plasticity in the development of O. semistriata.

Complexity of the prey spectrum ofAgaronia propatula(Caenogastropoda: Olividae), a dominant predator in sandy beach ecosystems of Pacific Central America

“…The taxonomy within the Olividae is notoriously problematic ( Tursch & Greifeneder, 2001 ; Kantor et al, 2017 ). The widely distributed and very abundant O. semistriata (Gray 1839), for example, has consistently been confused in the recent literature with the equally common but more southerly distributed O. columellaris (Sowerby 1825), as reviewed by Troost et al (2012) .…”

Opportunistic suspension feeding in the intertidal gastropod Olivella columellaris and its implications for the regulation of tidal migrations

“…Evidently, O. columellaris cannot perform suspensionfeeding at high flow velocities (as reported for O. semistriata Olivella columellaris (Sowerby 1825) y O. semistriata (Gray 1839) (Olivellidae, Caenogastropoda) son gasterópodos comunes de playas arenosas de la costa occidental de América tropical (Olsson 1956) con hábitos alimenticios inusuales. Ambas especies usan 2 pares de apéndices laterales-que no se encuentran en otros Olivellidae-para suspender películas de moco (mucus sheets) en el agua fluyente para capturar partículas (Troost et al 2012). El moco, así como el plancton y detrito capturado, es consumido en intervalos cortos (Seilacher 1959).…”

“…Ya que esta zona se mueve con la marea, para una alimentación eficiente estos caracoles necesitan realizar migraciones mareales, lo cual ambas especies logran usando sus pies extendidos como velas bajo el agua. Parecía razonable interpretar esta navegación bajo el agua y la alimentación suspensívora como elementos funcionalmente vinculados de una adaptación específica a las condiciones en la zona intermareal de playas arenosas (Schuster 1952, Schuster-Dieterichs 1956, Seilacher 1959, Friedrich 1969, lo que llevó a afirmar (Vanagt et al 2008) que un reloj endógeno que marca los ritmos mareales es crucial para explicar los patrones de migración observados (todos estos autores confundieron O. semistriata y O. columellaris; ver Troost et al 2012).…”

“…Olivella columellaris (Sowerby 1825) and O. semistriata (Gray 1839) (Olivellidae, Caenogastropoda) are common sandy-beach gastropods of the tropical American west coast (Olsson 1956) with unusual feeding habits. Both species use 2 pairs of lateral appendages, which are not found in other Olivellidae, to expose semispherical mucus sheets to flowing water (Troost et al 2012). The mucus, together with captured plankton and detritus, is eaten in short intervals (Seilacher 1959).…”

“…Since this zone moves with the tide, efficient feeding requires tidal migrations, which both species achieve by using their expanded feet as underwater sails. It seemed plausible to interpret underwater sailing locomotion and suspension feeding as functionally linked elements of a specific adaptation to the conditions in the sandy beach intertidal zone (Schuster 1952, Schuster-Dieterichs 1956, Seilacher 1959, Friedrich 1969, leading to the claim (Vanagt et al 2008) that an endogenous circatidal clock is crucial for explaining the observed migration patterns (all these authors confused O. semistriata and O. columellaris; see Troost et al 2012).…”