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Gastropod

Flat Top Shell

Steromphala umbilicalis

Steromphala umbilicalis (da Costa, 1778) · Trochidae WoRMS 1039850

Reference photos

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A small top shell, broader than it is tall, dull greenish-grey to cream with broad reddish-purple bands radiating from the apex. Look for the large, round, deep 'navel' (umbilicus) in the underside; the bands are broader, and about half as many, as on the grey top shell Steromphala cineraria.

Depth

Between the tide marks on rocky shores, from the upper shore down to the low-water line; only sometimes found below the tide

Size

Shell up to 1.6 cm high and 2.2 cm across

Habitat

Sheltered rocky shores, on fucoid seaweeds, under stones and in rock pools; tolerates drying out and brackish water

Behaviour

Grazes brushings off seaweed and rock, and keeps feeding when shore crab scent is in the water, showing very little alarm response

Diet

I eat

  • Fine growth brushed off seaweed and rock, and algal debris; in rockpools this grazing keeps seaweed diversity low
  • Kelp detritus, taking more of the warm-water kelps Laminaria ochroleuca and Saccorhiza polyschides than of cold-water kelps
  • Microalgae and microbial films, since it is not an obligate kelp grazer and will select those over kelp detritus

Where you'd find it

Mostly seen in the English Channel, the Irish Sea and the waters west of Scotland, and only here and there elsewhere.

ChannelCeltic SeaNorth SeaIrish SeaW of IrelandW of Scotland
Often seenNow and thenWhere PEBL filmsBased on marine survey records (OBIS). Blank seas can mean nobody has looked there, not that the animal is absent.

Sources

Open-access references behind this page. Every statement on this page was read out of one of them; anything that could not be traced to a source was taken off the page rather than left standing. Each link was checked on the date shown, and confirmed then to be about this species.

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