Left: about 17 spiral ribs above periphery of body whorl.
Right: littoral specimen; some of circa 25 spiral ribs below periphery have been eroded smooth.
1: current growth beyond most recent growth line mainly white and free from epiphytic growths.
2: previous year’s growth behind growth line is stained yellow, green etc by epiphytic growths.
With one exception, this specimen had the strongest red marks of about 100 living littoral specimens examined on a beach in Cardigan Bay. Most had no red marks.
marinvert.senckenberg.science/image-browse/
Key identification features
Gibbula magus
* Opaque white shell 04 Gibbula magus. Height 17.5 mm, breadth 19.5 mm Cardigan Bay, Wales. 2015. , sometimes with reddish marks 08 Gibbula magus. Height 19mm, breadth 25mm. Cardigan Bay, Wales. 2015. .
* Markedly stepped shell-profile 09 Gibbula magus. Height 19 mm, breadth 25 mm. Cardigan Bay, Wales. 2015. .
* Large conical umbilicus with wide comma-shaped groove leading into it 06 Gibbula magus. Height 19 mm, breadth 25 mm. Cardigan Bay, Wales. 2015. .
* Snout has transverse brown to purple-black lines 13 Gibbula magus. Cardigan Bay, Wales. 2015. , and distal half has dense beard of long bright blue papillae 12 Gibbula magus. Cardigan Bay, Wales. 2015. .
* Black eye-pupil in blue area on stout peduncle 12 Gibbula magus. Cardigan Bay, Wales. 2015. .
* Mainly sublittoral, but locally common at ELWS in favoured sheltered sites in Scilly Isles, Cardigan Bay, Connemara and Orkney. On stable sand, muddy-sand, maerl and gravel; sometimes on rock.
Similar species
Phorcus lineatus
* Shell, ground colour shades of buff 7Pl 07 Phorcus lineatus , yellow 8Pl 08 Phorcus lineatus , brown 1Pl 01 Phorcus lineatus and/or green 9Pl 09 Phorcus lineatus . Darker, more or less zig-zag, transverse streaks of dark-brown, -green, -grey or –reddish purple run across the whorls, parallel to growth lines.
* Shell-profile not stepped.
* Umbilicus completely sealed over by time 5mm wide, often leaving a dip in columella 4Pl 04 Phorcus lineatus (Occasionally narrow, open crack 5Pl 05 Phorcus lineatus . Iberian specimens often have open umbilicus).
* Snout black or grey, lacks dense beard of long bright blue papillae 14Pl 14 Phorcus lineatus
* Black eye-pupil on red or yellow peduncle 14Pl 14 Phorcus lineatus
* Upper rocky shores between Isle of Wight and Llandudno, and most of Ireland.
Gibbula umbilicalis
* Shell always has broad red to reddish-purple bands radiating from apex across the whorls 05 Gibbula umbilicalis. .
* Shell always has a large round umbilicus, but no wide comma-shaped groove leading into it 04 Steromphala umbilicalis .
* Shell-profile not stepped 02 Steromphala umbilicalis .
* Snout short, yellowish or greenish with dense transverse dark purple lines, lacks dense beard of long bight blue papillae 10 Steromphala umbilicalis. Radula action 3.
* Middle levels of rocky shores from Kent along south and west coasts round onto north coast Scotland, with a few records on west coast of Orkney.
Gibbula cineraria
* Shell has grey or bluish grey bands radiating from apex across the whorls 03 Steromphala cineraria .
* Umbilicus progressively narrows with age. Adult shell may have very restricted 26 Steromphala cineraria. April 2011. Menai Strait. or completely closed umbilicus 27 Steromphala cineraria. Adult with tall pyramidal profile. March 2011. Menai Strait. , but juveniles 27 Comparison small G. umbilicalis and G. cineraria. may have large round umbilicus.
* Shell profile of fully grown 15mm high G. cineraria may be like traditional bee-hive 06 Steromphala cineraria , but not stepped.
* Snout short, yellowish or brownish with transverse brown lines, lacks dense beard of long bright blue papillae 10 Steromphala cineraria. Shell height 14mm. Menai Strait, Wales. February 2014.
Gibbula albida
* Opaque white shell, sometimes with reddish marks www.conchology.be/?t=66&species=Gibbula+albida .
* Stepped shell-profile.
* Some shells have umbilicus with comma-shaped groove leading into it, www.animalbase.uni-goettingen.de/zooweb/servlet/AnimalBas… but smaller than G. magus, and often closed by callus. nature22.com/estran22/mollusques/gasteropodes/gasteropode…
* Soft parts resemble G. magus; eye-pupil in blue area on peduncle, and snout has transverse brown lines but lacks dense beard of long bright blue papillae. nature22.com/estran22/mollusques/gasteropodes/gasteropode…
* Brittany southwards; not Britain.