**3. Acharan sulfate, the new glycosaminoglycan from** *A. fulica*

The giant African snail, *Achatina fulica*, is one of the large and most widely distributed land snails, considered as an agrihorticultural pest [4].Since *Achatina* develops rapidly and produces large numbers of offspring, it is now listed as one of the top 100 invasive species in the world [5]. Moreover, *Achatina* is a unique species and maintains three different life cycle stages in the same individual, surviving in the environment for millions of years. Apart from maintaining the critical life cycle stages, *A. fulica* has survived successfully, consequently, gaining the disre‐ pute as an agricultural pest in India. In addition, these snails are considered as bio‐indicators of ecosystem health. Although they do not possess immunoglobulins, they have evolved unique modalities to detect and respond to microbial surface antigens such as lipopolysaccharides

Terrestrial snails are well known for accumulating heavy metals in their tissues and serve as a pertinent species for monitoring trace metals, agrochemicals, urban pollution and elec‐ tromagnetic exposures [7]. The effect of accumulated heavy metals in different molluscan tissues and possible use of such alterations as biomarkers of exposure to xenobiotics has been investigated in some detail [8, 9]. Although snails are considered as alleged pest they are used by humans for various purposes including vigorous consumption of mollusc meat in several countries around the globe, including tribal and urban populations of India and Bangladesh [10]. Another important aspect is the ethno‐medicinal use of several mollusc species high‐ lighted by several authors [11, 12]. Pharmacological application of different body parts of mollusc are used to treat several diseases which suggests its potential to act as a source of drug [12]. In the present chapter, various characters of *Achatina* will be described including their unique immune system that contributes toward the evolutionary success of *A. fulica* in

Invertebrates are not able to synthesize immunoglobulins, rather they have developed a potential defense system against microbial surface antigens such as lipopolysaccharides (LPS)/endotoxins and glucans [13]. Among various kinds of innate immune mechanisms in invertebrates, two types of coagulation mechanisms are on record: (i) in crustaceans such as lobster, crayfish [14] and insects [15] clotting occurs through Ca‐dependent transglutamin‐ ase, (ii) serine protease zymogens dependent coagulation system is reported which is similar to mammalian system [13]. In *Limulus polyphemus*, commonly known as the horseshoe crab, endotoxins are sensed by amoebocytes. In invertebrates, amoebocytes are known to be associ‐ ated in both hemostasis and innate or nonadaptive immune responses against microbial infec‐ tions [16]. Amoebocytes behave like macrophages in mammals and can either bind pathogens directly or recognize and engulf pathogens that have been opsonized by serum proteins. This direct recognition plays a major role in host defense [17]. It has been proposed that activation of the innate immune system is initiated when pathogens bind to nonclonally distributed pat‐ tern recognition receptors on immune cells [18]. In *Limulus*, the ancient horse shoe crab, the

(LPS), lipoteichoic acids, lipoproteins, peptidoglycans and (1→3) β‐d‐glucans [6].

**2. Molecules in the Innate Immune System of** *A. fulica*

the terrestrial ecosystem.

220 Organismal and Molecular Malacology

**2.1. Coagulation system in** *A. fulica*

Acharan sulfate, a glycosaminoglycan isolated from *A. fulica*, has a major disaccharide repeat‐ ing unit of 2‐acetyl,2‐deoxy‐a‐d‐glucopyranose‐2‐sulfo‐a‐l‐idopyranosyluronic acid, which is structurally related to both heparin and heparin sulfate. Acharan sulfate is known to be a polydisperse, with an average molecular mass of 29 kDa that contain un‐sulfated iduronic acid. This glycosaminoglycan was found to be located in the body of this species and consid‐ ered to be the major constituent of the mucus and the structure and compartmental distribu‐ tion of acharan sulfate in the snail body [25]. Different populations of acharan sulfate having charge and/or molecular mass heterogeneities were isolated from *Achatina* whole body, mucus and the organic shell matrix. A minor glycosaminoglycan fraction was also purified which appeared to be susceptible to degradation by nitrous acid confirming the presence of N‐sulfated glycosaminoglycan molecules. Furthermore, application of histochemical tech‐ niques of metachromatic staining and histoautoradiography (following metabolic radiolabel‐ ing with [35S] sulfate) was evident that acharan sulfate is of wide distribution in the snail body.
