Rough keyhole limpet • Diodora aspera
{Diodora = 'with a passage through;' aspera = rough}
Identification
The common name of this species makes it easy to identify - its shell has a rough texture and a circular opening at its apex, which is off-centre to one end (anterior). The shell's raised lattice sculpture creates the rough texture and matches a pattern of purplish-brown radial stripes. The shell is often overgrown with other sea life like bryozoans, masking the shell texture and colouring - however in such cases the circular "keyhole" is still visible. Keyhole limpet shells grow to 7 cm long. Click here and here for more photos of live rough keyhole limpets.
Habitat & Range
This common species can be found attached to rocks in the intertidal and shallow subtidal (to a depth of 40 m). It lives in rocky areas along coastlines from northern Alaska to Nicaragua.
Similar Species
The shell of the two-spot keyhole limpet (Fissurellidea bimaculata) also has a central opening, but the hole is much larger and elongated. This difference is not as evident when the shell is occupied by the animal - in this case the shell is usually mostly covered by the large mantle and the animal can be mistaken for a nudibranch. In contrast, the rough keyhole limpet's mantle may cover the very edge of the shell or not be visible at all.
Intriguing Info
The rough keyhole limpet often hosts the symbiotic scale worm (Arctonoe vittata). The worm lives in the limpet's mantle groove and occasionally sticks its head out to bite at the tube feet of sea stars that prey on the limpet. The limpet also defends itself against sea stars by extending its mantle over the shell edge.
The rough keyhole limpet is not actually a true limpet - it is more closely related to abalone species such as Haliotis kamtschatkana.
iNaturalist
https://www.inaturalist.org/taxa/64148-Diodora-aspera
The common name of this species makes it easy to identify - its shell has a rough texture and a circular opening at its apex, which is off-centre to one end (anterior). The shell's raised lattice sculpture creates the rough texture and matches a pattern of purplish-brown radial stripes. The shell is often overgrown with other sea life like bryozoans, masking the shell texture and colouring - however in such cases the circular "keyhole" is still visible. Keyhole limpet shells grow to 7 cm long. Click here and here for more photos of live rough keyhole limpets.
Habitat & Range
This common species can be found attached to rocks in the intertidal and shallow subtidal (to a depth of 40 m). It lives in rocky areas along coastlines from northern Alaska to Nicaragua.
Similar Species
The shell of the two-spot keyhole limpet (Fissurellidea bimaculata) also has a central opening, but the hole is much larger and elongated. This difference is not as evident when the shell is occupied by the animal - in this case the shell is usually mostly covered by the large mantle and the animal can be mistaken for a nudibranch. In contrast, the rough keyhole limpet's mantle may cover the very edge of the shell or not be visible at all.
Intriguing Info
The rough keyhole limpet often hosts the symbiotic scale worm (Arctonoe vittata). The worm lives in the limpet's mantle groove and occasionally sticks its head out to bite at the tube feet of sea stars that prey on the limpet. The limpet also defends itself against sea stars by extending its mantle over the shell edge.
The rough keyhole limpet is not actually a true limpet - it is more closely related to abalone species such as Haliotis kamtschatkana.
iNaturalist
https://www.inaturalist.org/taxa/64148-Diodora-aspera
References
Adams, M.J. (2005). Diodora aspera (Rough Keyhole Limpet). Beach Watchers. Washington State University. Accessed 07/11/2014.
Cowles, D. (2004). Diodora aspera. Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed 07/22/2014.
Harbo, R. M. (1999). Whelks to whales: Coastal marine life of the Pacific Northwest. Madeira Park, BC: Harbour Publishing. P. 136.
Lamb, A., and Hanby, B. (2005). Marine Life of the Pacific Northwest [electronic version]. Madeira Park, BC: Harbour Publishing.
Authors and editors of page
Kelly Fretwell and Brian Starzomski (2014).
Adams, M.J. (2005). Diodora aspera (Rough Keyhole Limpet). Beach Watchers. Washington State University. Accessed 07/11/2014.
Cowles, D. (2004). Diodora aspera. Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed 07/22/2014.
Harbo, R. M. (1999). Whelks to whales: Coastal marine life of the Pacific Northwest. Madeira Park, BC: Harbour Publishing. P. 136.
Lamb, A., and Hanby, B. (2005). Marine Life of the Pacific Northwest [electronic version]. Madeira Park, BC: Harbour Publishing.
Authors and editors of page
Kelly Fretwell and Brian Starzomski (2014).