Euspira catena  (da Costa, 1778)

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Synonyms: Cochlea catena da Costa, 1778; Natica catena (da Costa, 1778); Polinices catena (da Costa, 1778); Lunatia catena (da Costa , 1778); Natica monilifera Lamarck, 1822.

Current taxonomy: World Register of Marine Species (WoRMS) 

https://www.marinespecies.org/aphia.php?p=taxdetails&id=140528

Vernacular: Large necklace shell (English); Chwalcen rwyllog (Welsh); Gewone tepelhoren (Dutch); Gefleckte Halsbandnabelschnecke (German); Grande natice (French); Καδενοφέγγαρο (Greek).

GLOSSARY below.

Shell description.

The globose shell of E. catena grows up to 30 mm high and 30 mm wide. When full grown it has five tumid whorls. The large body whorl occupies about 90% of the shell height 01Ec. The distinct sutures give the spire whorls a stepped profile. The apex is flattened. The smooth surface lacks any sculpture other than some faint wrinkles running into the large round umbilicus. Ploughing through sand usually removes the periostracum; sometimes dark remnants survive in the suture and near the base 02Ec.

The large ‘D’ shape aperture is about 75% of the shell height. The smoothly curved palatal (outer) lip meets the parietal (upper, inner) lip at about 90º, and curves smoothly into the nearly straight, white columellar lip and parietal lip. The parietal lip often has a broad transverse band coloured as the exterior of the shell 01Ec. The aperture interior is a similar colour to the exterior and lacks any teeth or other sculpture. The external ground colour of the shell varies from pale buff through pinkish to brown. The umbilical groove and area around the umbilicus are whitish 03Ec. The only exterior decoration is a single, subsutural, spiral line of brown or purplish curved and zigzag marks 07Ec, which is sometimes hidden by periostracum remnants 08Ec. Colours are strongest on live specimens in water.  

 The large, transparent, horn-coloured operculum with flexible edges fits the ‘D’ shape aperture precisely. It consists of a rapidly expanding oligogyrous spiral of about three turns originating at a small, depressed nucleus near the columellar edge 04Ec.

Body description

The white flesh 05Ec may be tinted, with varying intensity, grey 06Ec or brown 07Ec on surfaces which are exposed when active. Euspira catena is in the Naticidae, the only mollusc family which can inflate the foot not only by internal blood pressure but also by intake of water into a series of aquiferous canals. When fully inflated, the animal weighs up to three times its deflated weight, and it is impossible for it to withdraw completely into its shell (Yonge & Thompson, 1976). The inflated foot has three distinct parts 05Ec. The large frontal propodium forms a ploughshare for penetrating through sand, with its posterior edge raised like a mouldboard to protect the entrance of the respiratory mantle cavity against entry of sand. A fold in the left of the raised posterior edge of the propodium acts as an inhalant respiratory siphon 07Ec & 08Ec. The mesopodium forms the majority of the sole. The metapodium covers the posterior of the shell against ingress of sand and carries the operculum hidden by the opercular lobes.

On an active inflated specimen usually the only visible parts of the head are the flattened cephalic tentacles sliding out from between the shell and closely adpressed posterior edge of the propodium 06Ec. The edges of the tentacles curl up to form a shallow canal on the upper surface 07Ec.

More features may be seen on deflated contracted specimens. The cephalic tentacles are connected basally by a rib similar in colour and creased texture to the tentacles 08Ec . The acrembolic feeding proboscis is everted from the mouth of its sac below the tentacle rib and above the propodium. 09Ec.The pink buccal mass visible by translucency and the active end of the radula are within its distal tip, which is the most deeply invaginated part when the proboscis is introverted into the body like a sock turned inside out. A pad shaped accessory boring organ (ABO) is attached to the ventral lip of the proboscis mouth 10Ec. The eyes are embedded within the flesh and usually not visible.

Key identification features

 E. catena

1) Maximum shell height width 30 mm. Operculum 01Ec made of transparent conchiolin.

2) Distinct sutures give the spire whorls a stepped profile 01Ec .

3) Body whorl has a single subsutural, spiral line of brown, purplish or reddish brown curved and/or zigzag marks 07Ec.

4) Large round umbilicus 03Ec.

5) Adapically, the palatal (outer) lip meets the parietal lip at a right angle 01Ec .

6) White flesh often tinted grey 06Ec or brown 07Ec on surfaces exposed when active, but no distinct red-brown marks on pale flesh.

7) Egg collar about 75 mm diameter.

8) In clean sand 06Ec at ELWS to 125 m depth all round Britain and Ireland and southwards to Mediterranean.

Similar species

Euspira nitida (Donovan, 1803) 11Ec & 12Ec

1) Maximum shell height 15 mm. Operculum made of translucent conchiolin.

2) Sutures weak. Short, blunt spire has nearly flat profile.

3) Body whorl has five spiral lines of chestnut brown curved.

4) Oval umbilicus is narrow adapically

5) Adapically, the palatal (outer) lip meets the parietal lip at an acute angle.

6) Flesh is cream or yellow with red-brown marks.

7) Egg collar about 25 to 30 mm diameter.

8) In sand and on firmer substrates such as gravel at ELWS and sublittorally, usually to 50 m but recorded to 2000 m depth. All round Britain and Ireland and from Norway to Mediterranean.

 Euspira montagui (Forbes, 1838) 13Ec

1) Maximum shell height 8 mm. Operculum made of translucent conchiolin.2) Spire has deep sutures creating stepped profile.

3) No colour marks on shell.

4) Groove in umbilicus extends as a nick onto the columella.

5) Adapically, the palatal (outer) lip meets the parietal lip at nearly 90°.

6) White or cream flesh with brown posterior edge on propodium.

7) Egg collar about 25 to 30 mm diameter.

8) On sublittoral fine sediment and on firmer substrates at depths accessible to scuba divers. Mainly from northern Norway to Scotland, Northern Ireland and northern half of North Sea with scattered records in deep cold water to Iberia.

Euspira  fusca (Blainville, 1825). 14Ec & 15Ec

1) Maximum shell height 25 mm. Operculum made of translucent conchiolin.

2) Sutures weak. Spire has nearly flat sided profile, but taller than on E. nitida.

3) Dark brown or chestnut shell with no colour pattern or unobtrusive spiral line of ‘v’s.

4) Columella is always brown and is narrower, but not notched, near umbilicus,

5) Adapically, the palatal (outer) lip meets the parietal lip at an acute angle.

6) Tentacles and flesh are reddish; may have blotches of more intense red.

7) No information found about spawn

8) On sublittoral muddy sand from Mediterranean northwards to western Ireland and west Scotland.

Euspira pallida (Broderip & G. B. Sowerby I, 1829) 16Ec & 17Ec

1) Maximum shell height 20 mm. Operculum made of translucent conchiolin.

2) Distinct sutures give the spire whorls a stepped profile.

3) Shell is white or cream or, depending on periostracum, brownish.

4) Small narrow umbilicus partially closed with calcareous pad. Broad white columellar lip.

5) Adapically, the palatal (outer) lip meets the parietal lip at a right angle.

6) Flesh cream.

7) Egg collar about 30 to 45 mm diameter.

8) On sublittoral clay from 10 m depth in the north to 2000 m in the south of its range. Circumpolar reaching south at depth with scattered records on GBIF to English Channel, Japan, California and Florida.

Cryptonatica affinis (Gmelin, 1791) 18Ec, 19Ec & 20Ec

1) Maximum shell height 12 mm. Operculum opaque white and glossy with external calcareous layer.

2) Distinct sutures give the short spire a stepped profile; often eroded.

3) Shell usually retains periostracum so not glossy except when wet; whitish where eroded.

4) Umbilicus completely closed with calcareous pad. Broad white columellar lip.

5) Adapically, the palatal (outer) lip meets the parietal lip at a right angle.

6) Flesh is cream.

7) Egg collar has only 3 or 4 rows of egg capsules, each containing a single ovum.

8) On sublittoral soft substrate from 4 m depth in the north to 2000 m in the south of its range. Circumpolar reaching south at depth with scattered records on GBIF to Mediterranean, Japan, California and North Carolina.

Habits and ecology

E. catena, unlike the great majority of European Caenogastropoda, lives on 21Ec and in clean sand 22Ec & 23Ec at ELWS and sublittorally to about 125 m. It feeds on bivalves such as Cerastoderma edule, Chamelea striatula and Donax vittatus 24Ec and sometimes on gastropods 25Ec. If while travelling on the surface of the sand the sensitive propodium senses a buried bivalve, E. catena digs into the sand to grip it, covers it with slime and examines it for any gap which will admit its radula to feed. If access cannot be obtained, the bivalve is manoeuvred to be pulled behind the snail into the sand where the grip is adjusted to bring the beak of the bivalve to the anterior of the propodium which is folded so the right and left halves can hold the bivalve firmly against the anterior boring organ (ABO) of the everted proboscis 10Ec. A hole is then bored through the bivalve shell by the combined action of the radula and application of acid by the ABO. Then the proboscis, accurately fitted to the circular hole, ingests with its radula the contents of the bivalve. The hole tapers inwards 24Ec  & 25Ec, and incomplete borings have a central boss on the base. Muricid borings are distinguished from them in being cylindrical and with no boss when incomplete.  

Boring takes 4 hours for each 0.1 mm thickness of shell, and subsequent feeding can last up to 60 hours during which the snail may ingest its own weight of bivalve flesh (Ziegelmeier, 1954). While feeding, it defecates initially up to twelve white pellets of shell fragments followed by a chain of soft, slimy, dark green pellets.

E. catena is eaten by birds, other E. catena and starfish. It makes an immediate reaction, even when withdrawn into its shell, to the touch of Asterias rubens by covering the whole shell with expanded mucus-coated tissue which provides no hold for the tube feet of the starfish (Yonge & Thompson, 1976).

Most marine gastropods use muscular waves on the sole for locomotion, but this is ineffective on the soft mobile substrates frequented by E. catena as they do not give enough purchase for the waves. Instead, it and other Naticidae use cilia on the sole to glide seemingly effortlessly over the surface 21Ec. This is facilitated by the extremely large area of the cilia-covered sole 07Ec and the concomitant evolution of the large aperture to allow its passage in and out of the shell (Fretter & Graham, 1994).

The large globose shell might seem an obstacle to ease of burrowing despite its smoothness, but when the foot is fully distended by sea water much of the shell is covered and the animal becomes wedge shaped and fit for penetration through sand. The propodium is shaped like a ploughshare 05Ec and protects the entrance to the mantle cavity from ingress by sand. Burrowing movements of the foot are controlled by haemolymph pressure governed by muscular contraction (Yonge & Thompson, 1976). Entry into the sand is at a low angle to the surface 23Ec by elongation of the propodium followed by expansion of the tip into a securely fixed ‘terminal anchor’. The columellar pedal muscles then contract so the shell and body are pulled to the anchor which collapses on completion of the move. The shell then acts as a ‘penetration anchor’ while the foot elongates again for further penetration into the sand. The cycle of movements is repeated for further penetration (Fretter & Graham, 1994).

E. catena breeds in spring and early spring in Britain. The spawn mass is a circular gelatinous collar, diameter c. 75 mm, containing egg capsules, which is hardened and reinforced with sand grains 26Ec . Each capsule contains 80–90 ova but only one or two hatch as crawlers which consume the rest.

Distribution and status

E. catena lives in clean sand at ELWS to 125 m depth all round Britain and Ireland https://species.nbnatlas.org/species/NBNSYS0000175298 and on Atlantic coasts of Europe from Denmark southwards to the Mediterranean. It is not recorded from Norway (Høisæter, 2009) the Kattegat or Baltic. Caution is needed with the GBIF map https://www.gbif.org/species/5192503 as it includes fossils where it no longer lives.

Acknowledgements

I am indebted to Paul Brazier for specimens to photograph and to Jim Anderson, David Ballesteros, Sarah Bowen, Iain Dixon, Hans Hillewaert, Tim Johnson, Libby Keatley, Lonn Londis, Claude Nozères, Aleksandr Novikov, Keith Raven, Siôn Roberts, Guido Schmitz, Michiel Vos and Dawn Watson for use of their much valued images.

Links and references

Forbes, E. & Hanley S. 1849-53. A history of the British mollusca and their shells. vol. 3 (1853). London, van Voorst. (As Natica monilifera)

https://archive.org/details/historyofbritish03forbe/page/326/mode/1up?view=theater&q=catena

Fretter, V. and Graham, A. 1962. British prosobranch molluscs: their functional anatomy and ecology. London, Ray Society. (Has index of species.) As Natica catena

Fretter, V. and Graham, A. 1978. The prosobranch molluscs of Britain and Denmark. Part 6.  Cerithiacea, Strombacea, Hipponicacea, Calyptraeacea, Lamellariacea, Cypraeacea, Naticacea, Tonnacea, Heteropoda. J. Moll. Stud. Suppl. 9. As Lunatia catena.

Fretter, V. and Graham, A. 1994. British prosobranch molluscs: their functional anatomy and ecology. Revised edition. London, Ray Society. As Lunatia catena. (Much new material but lacks index of species.)

Graham, A. 1988. Molluscs: prosobranch and pyramidellid gastropods. Synopses of the British Fauna (New Series) no.2 (Second edition). Leiden, E.J.Brill/Dr. W. Backhuys. 662 pages.

Hayward, P.J. & Ryland, J.S. (eds.) 1995. Handbook of the marine fauna of North-West Europe. Oxford University Press.

Høisæter, T. 2009. Distribution of marine, benthic, shell bearing gastropods along the Norwegian coast. Fauna Norvegica, 28: 5-106. https://doi.org/10.5324/fn.v28i0.563

Jeffreys, J.G. 1862-69. British conchology. vol. 4 (1867). London, van Voorst. (As Natica catena) https://archive.org/details/britishconcholog04jeffr/page/220/mode/2up?view=theater&q=catena

McMillan, N.F. 1968. British shells. London, F. Warn.

Yonge, C.M. and Thompson, T.E. 1976. Living marine molluscs. Collins, London.

Ziegelmeier, E. 1954 Beobachtungen über den Nahrungserwerb bei der Naticide Lunatia alderi (Donovan). Helgoland. Wiss. Meeresunters., 5: 1-33.

Glossary

ABO = accessory boring organ for boring holes with radula and acid through bivalve shells.

acrembolic = (of proboscis) introversible/eversible like finger of glove.

adapical = towards the apex of the shell.

aperture = mouth of gastropod shell; outlet for head and foot.

aquiferous = conveying, containing or yielding water.

buccal mass = anterior of digestive system including a radula, odontophore and muscles.

Caenogastropoda = mostly gonochoric sea snails with a ctenidium and operculum; includes majority of European sea snails. Approximately equivalent to the now unaccepted ‘Prosobranchia’ of the 20th Century.

cephalic = (adj.) of or on the head.

cilia = (pl.) vibrating linear extensions of membrane used in locomotion..

ciliated = (adj.) coated with cilia.

columella = axis of gastropod shell spiral, exposed on final whorl by aperture.

columellar = (adj.) of or near central axis of spiral gastropod.

columellar lip = lower (abapical) part of inner lip of aperture.

conchiolin = horny flexible protein that forms the operculum of most marine gastropods, the periostracum and a matrix for the deposition of calcium carbonate to create a mollusc’s shell. Chemical structure C₃₀H₄₈O₁₁N₃; ‘chitinous’ as it resembles, though not identical to, chitin (C₈H₁₃O₅N)n.

ctenidium = (pl. ctenidia) comb-like molluscan gill; usually an axis with a row of filaments either side.

distal = away from centre of body or from point of attachment.

ELWS = extreme low water spring tide (usually near March and September equinoxes).

everted = turned out of the body by reversing introversion.

gonochor(ist)ic = (syn. dioecious) having separate male and female individuals, not hermaphrodite.

height = (of gastropod shells) distance from apex of spire to base of aperture.

haemolymph = circulating fluid in molluscs which carries nutrients, waste and hormones. Analogous to vertebrate blood, but most molluscs have copper-based haemocyanin in it, instead of red haemoglobin, to carry oxygen.

introverted = (or inverted) brought into body by being turned outside in like a sock.

leg.  = (abbreviation of legit) collected/ found by.

LWS = low water spring tide, two periods of a few days each month when tide falls lowest.

mantle = sheet of tissue that secretes shell and forms a cavity for the gill in most marine molluscs.

mesopodial = (adj.) of the middle section of the foot.

mesopodium = middle section of the foot.

metapodial = (adj.) of the hind part of the foot.

metapodium = hind portion of the foot.

odontophore = tongue-like structure of cartilage supporting radula.

oligogyrous spiral = a spiral of few turns.

opercular = (adj.) of the operculum.

operculum = plate of horny conchiolin, rarely calcareous, used to close shell aperture.

palatal lip =  outer lip of gastropod aperture.

parietal lip = upper part of inner side of gastropod aperture adapically of columellar lip, often lacking clear lip structure with just a glaze on side of whorl.

periostracum = thin horny layer of chitinous material often coating shells.

propodial = (adj.) at the front of the foot.

propodium = anterior portion of gastropod foot.

protoconch = apical whorls produced during embryonic and larval stages; different in form from other whorls forming teleoconch.

radula = chitinous ribbon of teeth; extended on odontophore to rasp food.

sac = pouch or hollow space open at only one end in an animal or plant.

subsutural = close below the suture when shell positioned with apex uppermost.

sutural = (adj.) of or close to a suture.

suture = groove or line where whorls of gastropod shell adjoin.

teleoconch = entire gastropod shell, apart from apical protoconch.

umbilicus = cavity up axis of some gastropods, open as a hole or chink on base of shell, often sealed over.