SUNDAY 8 DECEMBER 2013

PRAEGER CENTRE, NATIONAL BOTANIC GARDENS

LEADER: ROY ANDERSON

MOLLUSCS

This was the sequel to Roy’s workshop which was held on 1st September. He brought us up to date on developments in slug taxonomy, nomenclature and identification which has been driven/facilitated by the use of a combination of external features, internal features (dissection) and the current DNA technology. DNA work has helped to solve some of the mysteries of the origin and spread of a number of species. 
Terrestrial molluscs have been traditionally divided into Prosobranchs and Pulmonates. The former which contain marine, aquatic and some land snails breath through gill type structure and the latter have a respiratory pore and airway system for gas exchange. The workshop was wide ranging giving coverage in relation to land snails, freshwater snails and bivalves. This account is in no way comprehensive but rather a non-random sample.

There are now known to be 46 species of slugs in Britain and Ireland with 37 confirmed to date in Ireland. Arion vulgaris is a new arrival in Ireland and has the potential to become a serious pest as it spread. In the US it is referred to as the “Spanish Slug” because of its Western European origin and while it appears to be currently restricted to some of northerly mid-west states it appears to be spreading rapidly. The Kerry slug Geomalacus maculosus , once considered to be of very limited range is now known from Connemara and from conifer plantations in the south-west.

Not all invaders go to the New World from the old world. Acute or lateritic bladder snail Physella acuta and Tadpole bladder snail P. gyrina are both now known from Northern Ireland. The former is a cotton related freshwater mollusc which appears to have arrived in Lancastrian canals with imports of cotton from the US in the 19th Century.

Sandhill snail Theba pisana a Mediterranean species known from sand dunes on the east coast from the Liffey to the Boyne has been confirmed from Co Cork

The invasive Asian clam Corbicula fluminea first found as St Mullins, Co Carlow is now known from a few sites in Ireland.

Zebra Mussel Dreissena polymorpha first found in the Shannon Lakes has spread to many of the limestone lakes of Ireland by attachment to the under surface of boats.

Keeled Ramshorn Planorbis carinatus is widespread although originally an introduction. Its shell is a regular, flat coil with a conspicuous keel near the mid line. Aperture is a broad oval with the keel roughly in the middle. Last whorl about ⅓total shell width.

Brown-lipped Snail Cepaea nemoralis has a rare shared lineage between samples from Ireland and the Eastern Pyrenees, along the Spanish-French border, but nowhere in between and is not directly related to the British species.

Limacus maculatus Irish Yellow Slug A medium to large slug with pale greenish-grey body overlaid with large irregular dark green markings. Keel very short, sole whitish or yellowish. Mucus pale yellow to deep orange. Tentacles grey to bluish. A common variant has the dark mottling broken up into fine spots which create a spotted appearance rather similar to that of Limacus flavus which it appears to displace. A late introduction from south-east Europe, now widespread and common.

Large Black Slug Arion ater a large roundback slug varying in colour through browns to black, with a similarly coloured, dull foot fringe and exhibiting a strong rocking response when stimulated. Ubiquitous up to moderate altitudes. It is predominantly olive-, yellow-, reddish- to dark-brown or black with sole of more or less the same shade or lighter. A jet black form occurs on peatlands. The foot fringe is lined and coloured a similar shade to the back.

Strawberry Snail Trochellus striolatus a medium-sized globular shell with depressed, low, conical spire. Whorls convex, with moderately deep sutures and last whorl noticeably angled on the periphery. Umbilicus medium-sized. Whitish to yellow-brown or red-brown with rather coarse irregular growth lines and often a pale band on the angled periphery. Hairless when adult, with scattered coarse hairs when juvenile. Widespread in Ireland.

Oxychilus draparnaudi Draparnaud’s Glass Snail. Is more solid, less glossy shell than O. cellarius, and of a deeper, more opaque brown. The animal deep cobalt blue with a dark grey mantle edge which may suggest O. navarricus but that species is much smaller when mature. Widespread in Ireland but tends to become commoner southwards.

Round-mouthed Snail or Land Winkle Pomatias elegans is a medium-sized, pinkish to reddish-brown shell with darker apex. Very solid with a strong sculpture of spiral striae crossed by broad radial grooves. Aperture closed by a thick, horny operculum. A southern European species only known in Ireland from the Burren, Co Clare, on limestone pavement south of the wall along the coastal road north of Cnoc an Bhoirinn.  

Common Bithynia Bithynia tentaculata is a slightly globose, short-conical operculate shell with deep sutures and large body whorl found commonly in freshwater.

Slender Amber Snail Oxyloma sarsii The Irish form of this species is indistinguishable from some forms of Oxyloma elegans (Pfeiffer's Amber Snail). Often more laterally compressed and taller than that species. Can only be reliably identified by dissection. Very rare and localised. Not on Red List (“data deficient”).

Myxas glutinosa Glutinous Snail like a small, spireless Radix balthica but the voluminous mantle covers a good proportion of the shell in the living animal giving a spongy, wet feel when picked up. The mantle is never reflected over the shell in other pond snail species. Shell extremely thin, fragile, light brown. Very rare and declining. A canal species in Ireland. Red List status is endangered in Europe.

Common Pond Snail or Wandering Snail Radix balthica (Lymnaea peregra) A moderately large pond snail with a large, oval, body whorl, up to 4/5ths the shell height and with a small spire. Aperture semi-oval, lip not reflected. Rather variable in form, the more extreme soft-water forms possessing bubble shells and sunken spires reminiscent of Myxas glutinosa though without the expanded mantle. Widespread and abundant. is a species of air-breathing freshwater snail, an aquatic pulmonate gastropod mollusc in the family Lymnaeidae, the pond snails.

Point Snail Acicula fusca is a tiny species 2.2-2.8 mm with glossy cylindrical shell and an operculum living in deep, stable leaf litter, moss or soil in wooded habitats on base-rich soils. Oceanic Temperate distribution centred upon the British Isles but known also from Belgium, north-west Germany and France south to the Basses Pyrénées. Commonest in the west, including Ireland -  widespread, sometimes common, in old woods or scrub in limestone areas eg. central limestone plain. Local and rare elsewhere.  

Mollusc Ireland http://www.habitas.org.uk/molluscireland/is an excellent site but bear in mind that parts or it will soon be superseded when a new Field Studies Council key is published in 2014. Look at the species lists on this site for further information.

 

   

 

       

Myxas glutinosa  Pomatias elegans  Corbicula fluminea

  

Photographs © P Lenihan & bottom row  © Roy Anderson

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