Amber Snails a Host for Liver Fluke?

The Amber Snails (Succineidae), are a family of snails with thin-walled, glossy translucent shells with large body-whorls and very short spires. They are typically found in wet habitats and some are amphibous. Five species are found in Ireland, such as Oxyloma pfeifferi, Pfeiffer's Amber Snail, pictured below. O. pfeifferi has in fact been identified as a major pest of hardy nursery stock by horticulturalists, with losses of €3.5 - 4 milion being reported (Schuder et al., 2004 Crop Protection 23 pp. 945–953).

Pfeiffer's Amber Snail, Oxyloma pfeifferi

Succineidae have also been identified as another potential risk to another agricultutal sector. The liver fluke, Fasciola heptica, is an internal parasite of livestock that causes €25 million worth of loss to Irish farmers yearly with deaths and lost production, due to lowered weight gains, milk production and fertility. In 2008, deaths due to acute and chronic fasciolosis accounted for 20.5% of diagnosed causes of death in adult sheep in Ireland (Irish Regional Veterinary Laboratories Surveillance Report 2008). F. hepatica requires an intermediate molluscan host to complete its life cycle and worldwide species from the genera Lymnaea, Galba, Pseudosuccinea and Stagnicola act as these hosts. In Ireland and the UK the water snail Galba truncatula is the recognised host of F. hepatica. However, a study by Relf et al. in 2009 (Veterinary Parasitology 163 pp. 152–155) discovered a Succineid as an alternative intermediate host of F. hepatica. They found that in a hill and mountain grazing system, where the acidic soil conditions would not support populations of G. trunculata due to sufficient calcium for shell developement, infection among the sheep herd was 63.6%. Using PCR analysis of cytochrome c oxidase subunit 1 gene of F. hepatica, 79% samples of the same Succineid species showed presence of the fluke.

Water Walking Animal

Anurida maritima

The intertidal area of the shoreline is subject to high intensity of wave action, with the result that many of the flora and fauna present have had to adapt to this often harsh environment. Molluscs and arthropods present have tough, durable shells (e.g. mussels, whelks, sea slaters) and/or cling tightly to the rocks (e.g. limpets, barnacles) while algae present is tightly bound to the rock by holdfasts. Even the seemingly soft bodied anemones have a strong attachment to the rock via their pedal discs.

It is therefore quite surprising to find an animal in quite abundance that has neither of these attributes. Anurida maritima is a small (c. 3 mm), blue coloured springtail (Collembola) that scavanges for dead or dying matter in the intertidal zone. Interestingly, it cannot hypo-regulate its ionic concentration in water with less than 50% salt water, meaning it cannot survive in fresh water conditions. Collembolans are of terrestrial origin, meaning A. maritima is an amazing example of an animal of terrestrial origin that has become physiologically tied to a saline environment (Witteveen et al. 1987 Journal of Insect Physiology 33 pp. 59-66).

What is even more startling about A. maritima is its ability to walk on water. Its body is covered in hydrophobic hairs that allow it to walk with some ease across intertidal pools in search of food.

Anurida maritima walking on water

Anurida maritima walking on water

Crinoid Stem Fossils

Fertile Stems of The Field Horsetail

Strobilus of Equisetum arvense

Horsetails are represented by only one extant genus (Equisetum) but many extinct species are represented in the fossils record. Taxonomically, they are placed in the class Equisetopsid (Sphenopsida) order Equisetales and family Equisetaceae. Equisetopsids first appeared in the Devonian period but, attained their maximum diversity during the Carboniferous. From the Carboniferous to the present day, the group has experienced a gradual decline to where today just 15 species are recognised (Taylor et al. (eds), 2009 Biology and Evolution of Fossil Plants pp. 329-382). They are characterised as having whorled, gapped stems and connate, whorled leaves. Features of their spermatazoids group them with ferns, with their closest phylogenetic relative being the Marattiopsids (Smith et al., 2006 Taxon 55 (3) pp. 705–731)

Vegetative stem of Equisetum arvense

In Ireland, the most abundant horsetail species is the Field or Common Horsetail (Equisetum arvense). It favours wet soil conditions and is most common on or near river banks, but can establish on arable land becoming a troublesome weed.

At this time of the year, the green stems of E. arvense are nowhere to be seen, having died away during the winter. Instead, pinkish-brown stems are visable and will be until June. These are the fertile stems of the horsetail. The cone at the top of the stem (the strobili) is comprised of peltate sporangiophores that bear the sporanhia.

The Green Worm, Eulalia viridis

Eulalia viridis

The Green Worm, Eulalia viridis ia a marine polychaet worm of the family Phyllodocidae that inhabits intertidal pools. At one time thought to be a predator it is now know to scavenge mainly on damaged, dead and decomposing material, mainly barnacles and mussels (Emson, 1977 Journal of the Marine Biological Association of the UK 57 pp. 93-96).

Centipedes Are Quite Odd

Of the 3000 centipede species described world wide, each one has an odd number of segments, ranging from 15 to 191. Chipman et al. (Current Biology 14 pp. 1250–1255, 2004) report that variation in segment number is caused by variation in the number of cycles of a primary segmentation oscillator, each cycle of which generates two segments.

Interestingly, the genes responsibly for this double segmental periodicity in centipedes (odd-skipped and caudal) are homologues of Drosphilia genes (Nüsslein-Volhard and Wieschaus, 1980 Nature 287 pp. 795-801). These genetic similarities may be a result of evolutionary convergence or could be an indication of a common ancestor of both flies and centipedes (Damen, 2004 Current Biology 14 pp. R557–R559). This may help shed some light on the relatedness of the myriopods to the other arthropod groups.

Lithobius forficatus

Haplophilus subterraneus

Ireland has 26 species described, from the families Himantariidae, Schendylidae, Geophilidae, Cryptopsidae, Lithobiidae and Henicopidae (Ferriss et al. (eds.) Irish Biodiversity: a taxonomic inventory of fauna, Irish Wildlife Manuals, No. 38, 2009).

The Aggression of The Beadlet Anemone, Actinia equina

Actinia equina. Acrorhagi (blue) visable on left hand side

Actinia equina, the beadlet anemone, is the most common anemone to be found in Irish and European waters. In fact, its range extends all over the Mediterranean and even down the coast of Africa. Most conspicuous at low tides when the solitary, deep red polyps are visable clinging to rockfaces, A. equina can be an aggressive individual, with a full arsenal of toxins at its disposal.

Actinia equina exposed at low tide

It is named after the circle of blue, bead-like structures found at the base of the feeding tentacles. These are the acrorhagi, organs found only on certain species of the Actiniidae family. They are small sacs full of cilia-covered nematocysts that the beadlet anemone uses to subdue and kill prey. The acrorhagi are dilated by absorbing seawater and pressed against the victim. Outer pieces of the acrorhagi stick to the prey, into which the nematcysts are discharged (Shiomi 2009, Toxicon 54 pp. 1112–1118).
A. equina reproduces both sexually and asexually by parthogenesis, with reproductive modes varying at different sites. Non-clonal anemones can be quite aggressive to each other, and this has been shown to be linked to the colour of pedal disc colouration (Brace et al. 1979 Journal of Animal Behavour 27 pp. 553). Three morphs exist on Irish shores, U, M and L morphs (see table). This variation in reproductive modes, coluration and aggression suggest that A. equina may not be a single species at all but may be several cryptic species, subspecies or morphs (Chomsky et al. 2009 Journal of Experimental Marine Biology and Ecology 375 pp. 16–20).

Morph	Pedal Disc Colour	Location
U	Dark red	Upper shore
M	Light red	Mid-shore
U	Grey-green	Lowershore

As can be seen from the table, the U morphs are the most aggressive of the three. The reason for this lies in they fact that they populate the verticle sides of gullies, where wave action provides a large supply of food. Competition for this resource would therefore be fierce, promoting aggression. The weapons used by A. equina in this aggression are peptide toxins contained in the nematcysts which block sodium and potassium ion channels (e.g. acrorhagin I and II).