Drassodes lapidosus (Walckenaer, 1802)

3.1. Chitin characterization from Drassodes lapidosus View in CoL

3.1.1. Chitin content of D. lapidosus

The chitin rate of crustaceans like crab and shrimp is about 20% by dry weight (Kucukgulmez et al., 2011;

Wang et al., 2013). In insects, this rate is between 15% and 20% (Gonil and Sajomsang, 2012; Zhang et al., 2000). In this study, we reached the following findings. D. lapidosus ’s dry weight chitin content was nearly 7%. This ratio is similar to that of other arachnids (Demir and Seyyar, 2020; Kaya et al., 2014; Seyyar and Demir, 2020). Since the abdomen is softer in spiders than in other arthropods, the amount of chitin is lower than that of crustaceans and insects. Although we might assume that this spider has soft opisthosoma, their chitin amount indicates that they are an important source of chitin.

3.1.2. FT-IR

In several studies, the structure of chitin analyzed by FT-IR spectroscopy, revealing characteristic peaks for α–chitin (Cho et al., 2000; Gonil and Sajomsang, 2012; Hu et al., 2007; Ifuku and Saimoto, 2012; Wang et al., 2013; Yen et al., 2009; Zhang et al., 2000). These bands are: 3259 (N-H stretching), 1650 (Amide I), 1621 (Amide I), and 1550 cm−1 (Amide II). In this research, chitin extracted from the D. lapidosus was analyzed by FTIR. Two peaks around 1650 and 1621 cm−1 were observed, consistent with former studies ( Figure 3 View Figure 3 ). Additional peaks are listed in Table 1. These findings indicate that the chitin extracted from D. lapidosus is in the α-form.

3.1.3. XRD

The XRD findings of chitin were scanned at 2θ angles between 5 and 45°, showing peaks ( Figure 4 View Figure 4 ). As depicted in the figure, isolated chitins exhibit two sharp peaks around 9° and 19°. Similar peak patterns were observed in XRD results from shrimp, crab, insects, and krill, consistent with those reported in this study (Liu et al., 2012; Sajomsang and Gonil, 2010; Wang et al., 2013; Yen et al., 2009). The crystalline index value (CrI) of D. lapidosus chitin is 69.16%. Liu et al. (2012) reported crystalline index (CrI) values for chitin extracted from an insect and a shrimp as 89.05% and 89.17%, respectively. In contrast, CrI values for silkworm pupa and larvae cuticles of B.

EMINI et al. / Turk J Zool mori ranged between 54% and 58% ( Zhang et al., 2000). Additionally, the crystalline index (CrI) values for chitin from spiders and opilionids were recorded as 70.1% and 69.6%, respectively ( Seyyar and Demir, 2020; Yürtmen and Seyyar, 2019). Comparatively, the CrI value of D. lapidosus was found to be similar to other arachnid groups.

3.1.4. TGA

In previous studies, the findings of TGA analysis of chitins isolated from living organisms such as crabs, shrimps, and insects revealed that mass losses take place in two different stages (Abdou et al., 2008; Al Sagheer et al., 2009; Juárez-de La Rosa et al., 2012). The first mass loss is from water evaporation in the chitin, and the second is from decomposition of the chitin structure ( Wang et al., 2013). In this study, the mass loss in the chitin in D. lapidosus occurred in two different steps, similar to former studies ( Figure 5 View Figure 5 ). For D. lapidosus , the first mass loss was 8% and the second mass loss was 72%. The mass loss occurred at 0–150 °C, as a result of the removal of H 2 O-molecules in the first stage, while the second mass loss occurred at 150– 400 °C due to the deterioration of chitin compounds. The highest deterioration temperature of chitin (DTGmax) observed for D. lapidosus was 356.9 °C. The TGA values of spider, crab, shrimp, krill, and insect chitin showed a twostage mass loss similar to that in our work.

3.1.5. SEM

The surface image is one of the most important properties that significantly influences the use of chitin and its derivatives (Aranaz et al., 2009). The optimal utilization field for chitin can be determined based on its surface image. The morphology of chitin obtained from arachnid and crustaceans such as shrimp, krill and crab reveals a nanofibre structure with pores ( Seyyar and Demir, 2020; Yürtmen and Seyyar, 2019). In the current study, the morphology of the chitin extracted from the D. lapidosus was investigated and a different type of surface morphology was observed. In this type of chitin, the surface is composed of long and wide nanofibers, but nanopores are not observed ( Figure 6 View Figure 6 ). When compared with the chitin morphology of the previously studied Hogna radiata and Geolycosa vultuosa spiders (Kaya et al., 2014), it was observed that D. lapidosus chitin has a different surface morphology than the other two species with its lack of pores. Further studies are needed to learn more about the biological or ecological reasons for these differences in chitin morphology of spider species.