A Spiny Cockle Shell Close-up

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Spiny Cockle (1) - View of posterior surface of an empty Spiny Cockle shell (Acanthocardia aculeata Linnaeus) on the sand at Rhossili Beach, Gower, South Wales.

One of the frequent shell finds on Rhossili Beach is the large Spiny Cockle Acanthocardia aculeata (Linnaeus) – at least that is what I think it is! (If you know better, please do let me know).  There are several similar large species of cockle found on UK coasts. I have identified the specimens I found on the shore this week as A. aculeata, rather than A. echinata (Prickly Cockle) or A. tuberculata , first because of the size, second because of the characteristic outline shape of the valves, and third because of the sculpturing and spines on the ribs.

It seems to me that the species exhibits quite a bit of variability possibly as the result of age and wear.  The greater the age of the living specimen, or the longer the shells have been rolling around on the sea bed, then the more likely it is that the spines are broken or worn down. However, the outline shape of all the specimens I looked at has a typical straight(-ish) posterior margin compared with the curved anterior edge. The spines, even when worn, are all joined by a continuous ridge down the centre of each rib.

 My hesitation over the identification relates to the hinge area of the shell and the relative size of the two cardinal teeth in the left valve.  There is always a possibility that different specimens I have been looking at are in fact different species – accounting for the fact that the teeth in the hinge don’t seem to conform to the descriptions and illustrations for A. aculeata in the reference works. Or it could be that the shape of the teeth is variable within the species. Mostly, it is just the empty shells, often still attached in pairs by the ligament, that end up on the strand-line. Occasionally, after very stormy weather for example, live specimens are washed ashore too.

I include in this post photographs (taken from various angles to show the typical diagnostic features) of the paired valves of a Spiny Cockle left on the sand after high tide this week. I have included two shots taken of live specimens stranded on the same beach on an earlier occasion. Finally, I have added some further views of a pair of empty valves to show details, in particular of the outline shape, the details of the inner hinge area, and the grooved margins on the edge of the shell.

Interested in seeing more posts about shells  in Jessica’s Nature Blog? Go to the drop-down Categories menu in the right-hand side bar of the home page and select SEASHELLS.

Spiny Cockle (2) - View of the dorsal surface showing the hinge line between the two valves, the rounded umbos and protoconch, and the brown external ligament to the right in the posterior half of the shell. Photographed on the sandy strand-line at Rhossili Bay, Gower, South Wales. Spiny cockle (3) - View of the right valve outer surface Acanthocardia aculeata L. showing outline shape, radiating ribs, and spines joined by a continuous ridge along each of the ribs. Rhossili Bay, Gower, South Wales.

Spiny Cockle (4) - View of the anterior (front end) of Acanthocardia aculeata L. shell, showing spines on the ribs of the anterior ventral margin where they become broader and bent backwards. Strand-line of the sandy beach at Rhossili Bay, Gower, South Wales.

Spiny Cockle (5) - Antero-dorsal view of the empty paired valves of Acanthocardia aculeata L., front side uppermost on right of image, back side nearer to sand with brown ligament between the valves. Rhossili Bay strand-line, Gower, South Wales.

Spiny Cockle 6 - Holding a living Spiny Cockle in which the two valves of the shell are gaping to reveal the translucent white fleshy mantle and the red muscular foot within. The shell of Acanthocardia aculeata L. is much larger than the Common Edible Cockle and is often tinted reddish brown. Rhossili Bay, Gower, South Wales.

Spiny Cockle (7) - A living Spiny Cockle in which the two valves of the shell are gaping making visible the translucent white mantle that lines the shell, the red muscular locomotory foot, and one of the relaxed adductor muscles connecting the two halves of the shell.

Spiny Cockle (8) - Outer surface of two Acanthocardia aculeata shells still joined by the ligament, showing wear to the spines which remain mostly at the lower edges of the valves,

Spiny Cockle 9 - View of the inside of a pair of Acanthocardia aculeata valves - opened out but still joined by the ligament - showing the relatively straight posterior margin compared with the curved anterior margin. Margins have deep crenulations continuous with prominent grooves extending throughout the inside of the shell.

Spiny Cockle (10) - Close-up of the internal hinge area of Acanthocardia aculeata, near the beaks and the external ligament, showing details of the cardinal teeth.

COPYRIGHT JESSICA WINDER 2012

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2 Replies to “A Spiny Cockle Shell Close-up”

  1. Hi thanks for this info helped me i.d the huge cockle shell I recently found as a spiny cockle. Now I can give my daughter a more definite answer than “it’s a big shell”!

    Like

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