Gibbula delgadensis

Gibbula delgadensis is a species of marine gastropod in the family Trochidae (top snails)^[1] The species was first described by F. Nordsieck in 1982.^[1] Recent DNA barcode data indicate G. delgadensis (and the co‐endemic Jujubinus pseudogravinae) form a distinct clade in the Azores, unexpectedly grouping closer to Jujubinus species than to other Gibbula.^[2] This suggests further taxonomic review may be warranted.

The shell is very small and conical in shape.^[3] It reaches only about 3 mm in height. The exterior is often smooth or faintly sculptured, and the interior of the aperture is nacreous as is typical for trochids.^[3] Shell coloration can be variable; many specimens are pale brown or olive, but some show pink or red hues, as noted in living specimens from the Azores.^[4] The operculum is corneous and multispiral, fitting the aperture snugly.^[3] Due to its tiny size and coloration, G. delgadensis can be overlooked in the field.

Gibbula delgadensis is endemic to the Azores archipelago in the North Atlantic.^[1] All known records come from Azorean waters; it has not been reported elsewhere. Recent DNA barcoding studies confirm the species’ presence on all major Azorean islands.^[5] Within this range, it inhabits shallow coastal waters. Like other top shells, it favors hard, rocky substrates in the littoral zone.^[3] It has been collected from low intertidal down to shallow subtidal depths (generally <50 m), consistent with habitat of related trochids. It often lives on or under rocks and among algae or encrusting organisms on the seafloor. Because the snail is so small, specific depth records are limited, but it is not considered a deep-water species.

Although G. delgadensis itself has not been studied in detail, members of the family Trochidae are predominantly herbivorous grazers. They use a radula to feed on microalgae and detritus on rock surfaces^[3]. Based on this, the species is presumed to feed on surface films of diatoms and turf algae, similar to other top snails. Trochids may also ingest some organic detritus along with their algal diet.^[3] Filter feeding is not known in Gibbula, so grazing is the likely mode of feeding. In the ecosystem, G. delgadensis probably functions as a small grazer, contributing to the biofilm and algal community structure on Azorean rocks. Its exact diet has not been measured, but the family-level pattern suggests it consumes microscopic plants and animal detritus on the sea bottom.^[3]

Little specific information is available for G. delgadensis. However, trochid gastropods generally have separate sexes and reproduce by external fertilization.^[3] They release eggs and sperm into the water column. The eggs may be laid singly or embedded in gelatinous masses; in either case the larvae are planktonic. According to family-level data, trochid embryos develop into free-swimming trochophore larvae and then veligers before settling as juveniles.^[3] Thus G. delgadensis likely has a planktonic larval stage that aids dispersal around the Azores. No information is available on lifespan, but given its small size, individuals likely live only a few years. Other behaviors (e.g. activity rhythms, predator avoidance) have not been documented; G. delgadensis is presumed to be sluggish, moving slowly over rocks like other trochids.

Gibbula delgadensis has not been evaluated by the IUCN Red List or any regional conservation assessment.^[6][7] It is known only from the Azores, but within that range it is locally uncommon due to its tiny size. No specific threats have been documented. However, as an endemic littoral snail, potential risks include habitat disturbance (e.g. coastal development, pollution) and climate-related changes (e.g. sea temperature or acidity shifts). Because data are scarce, its conservation status would be Data Deficient by most criteria. Continued monitoring of Azorean coastal ecosystems would help determine if G. delgadensis faces any future declines.