The covering setae of ground spiders ( Araneae : Gnaphosidae )

Previous study of the setae covering the opisthosoma of ground spiders shows that the morphology of the covering setae is genus-specific. The present study pursues the description of covering setae across the whole Gnaphosidae family using SEM. A detailed morphology of the setae of ground spiders (Araneae, Gnaphosidae) is present ed. The six major types of covering setae recognized among gnaphosid spiders are squamose, plumose, lanceolate, pinnate, arborate and sicate setae. Squamose setae are characteristic for Micaria lenzi and Nauhea tapa. Plumose setae are more common in ground spiders and occur in the genera Drassodes, Haplodrassus, Anagraphis, Nodocion, Zelotes and the species Berlandina caspica, Nomisia aussereri, Minosiella intermedia, Sosticus loricatus, Leptodrassus memorialis, Intruda signata, Parasyrisca caucasica, Scopoides catharius, Echemoides tofo, Zimiromus medius, Encoptarthria echemophthalma, Apodrassodes trancas, Apopyllus silvestri, Hemicloea sundevalli, Zelanda erebus, Orodrassus assimilis, Callilepis nocturna and Synaphosus turanicus. The species Matua valida, Anzacia gemmea, Hypodrassodes maoricus, Homoeothele micans and Scotophaeus blackwalli have lanceolate setae. Spiders of the genus Gnaphosa have pinnate setae. Fedotovia uzbekistanica has arborate setae. The species Cesonia bilineata, Herpyllus propinquus, Litopyllus temporarius, Aphantaulax seminigra and Kishidaia conspicua have sicate setae. Some genera, such as Drassodes and Synaphosus, have a combination of different types of setae on their opisthosoma, whereas others, like Eilica sp., Laronius erawan, Urozelotes rusticus, have no covering setae on their opisthosoma at all. This study reveals the existence of different types of covering setae and provides a set of characteristics important for the classification and phylogenetic analysis of Gnaphosidae.

All ground spiders possess setae that cover their bodies.Ovtsharenko (1983Ovtsharenko ( , 1985Ovtsharenko ( , 1989) ) and after that Murphy (2007) recognized 10 different types of setae on the cuticle of ground spiders.Setae have different morphologies and diverse functions, depending on their location on the body (Ovtsharenko 1985(Ovtsharenko , 1989)).Aculeate setae are the most common type of setae on the cuticle.These setae are widely distributed over the spider's body.The majority of these setae are sensory organs or mechanoreceptors (Murphy 2007).Covering setae are located mostly on the abdomen, dorsally, ventrally and laterally, and may also cover the cephalothorax, legs, pedipalps and spinnerets.Covering setae have no connection with sensory receptor cells, they have no sensory function (Townsend & Felgenhauer 1998a, 1998b, 1999, 2001, Foelix 2011), and are identified by the following characteristics: (a) the covering setae rest in the shallow depression or small elevation of the cuticle, (b) the pedicel is bent at an obtuse angle where it emerges from the socket, (c) the main axis of the setae is pa-rallel to the surface of the spider's body, and (d) the trunk of the setae has appendages.
The covering setae are of special interest.Lehtinen was among the first who noted the importance of these cuticular structures for spider classification (Lehtinen 1967(Lehtinen , 1975a(Lehtinen , 1975b)).Thus, he called the covering setae 'feathery hairs' on the tibia of Micaria pulicaria (Lehtinen 1975b).Hill (1979) and Townsend & Felgenhauer (1998a, 1998b, 1999) made a significant contribution to our understanding of the diversity of the shapes of these cuticular structures, which they called 'scales'.Studies of ground spiders (Araneae: Gnaphosidae) demonstrate that they are greatly varied in shape and are genus-specific (Ovtsharenko 1983, 1985, 1989, Murphy 2007).The value of scales for classification and establishing evolutionary relationships were demonstrated for jumping spiders (Hill 1979) and lynx spiders (Townsend & Felgenhauer 2001).The wide diversity of scales and their value for phylogenetic analysis were used for the reconstruction of the phylogeny of araneomorph spiders (Griswold et al. 2005, Ramírez 2014).However, knowledge about the diversity of the covering setae among gnaphosid spiders is far from complete and still has to be addressed.As Murphy (2007: 31) said: "A serious study of spider setae may yet reveal much of interest".
In this study, we use the term 'covering setae' based on the following reasoning: 1.A scale is thin, flat plate, which is the most common shape for these structures among jumping and lynx spiders.However, this type of shape is comparatively rare among gna-phosids.Ground spiders often have feather-shaped setae, far from being a flat plate.2. The term feathery hair was first used by Lehtinen for these structures (Lehtinen 1975b, Fig. 7, image 12). 3.In studies of ground spiders (Araneae: Gnaphosidae) the term 'se- tae' was traditionally used for these structures (Ovtsharenko 1983, 1985, 1989, Ovtsharenko et al. 1994, 1995, Ovtsharenko & Platnick 1995, Platnick et al. 2001, Murphy 2007).Thus, in the article on spiders of the genus Synaphosus the authors wrote that the abdomen of the spider is "covered by thick, plumose setae bearing 4-7 pairs of appendages originating from ventral surface of setae (Figs 5,6)" (Ovtsharenko et al. 1994, p. 3).

Materials and methods
Specimens were examined with a Hitachi S-4700 Field Emission SEM at the American Museum of Natural History (New York).The cut-off abdomen was dehydrated in acetone, critically point dried in carbon dioxide, mounted with double-sided sticky carbon tape, and sputter coated using the necessary materials.The resulting images were combined using Photoshop.

Results
Almost all ground spiders (Araneae: Gnaphosidae) have covering setae.Some species possess a combination of different types of setae on their body.Density of the setae varies on the spider's body.Some species have few setae loosely scattered over the dorsal side of the abdomen.In other species, setae entirely cover the opisthosoma, cephalothorax and legs, and create the shingle-like overlapping coverage that may be iridescent as in Nauhea tapa (Fig. 1D).The covering setae rest in a shallow depression of the cuticle that is slightly elevated above the integument surface or located on small tubercle of the cuticle.The pedicel of the seta is bent at an obtuse angle after it emerges from the socket on the cuticle.As a result of this bending, the main axis of the setae is parallel to the surface of the spider's body (Fig. 1A, B).
Setae have a comparatively short pedicel bent on one side, and an apex -on the other side.The apex may be sharp, flattened, or rounded (Fig. 1C,  D).In Gnaphosa the apex bifurcates (Fig. 6E).The trunk of the setae consists of fused shafts.Often there are three shafts that create ridges of the trunk (Fig. 1A, B).Following Hill (1979), short triangular outgrowths are defined as spines.There are superior spines (SSp) that are located on the upper surface of the trunk, lateral spines (LSp) on both sides, and inferior spines (ISp) on the side of the trunk that faces the body surface (Fig. 1A, B).The inferior spines often have a hook-like shape and, probably, provide a connection between the seta and the body surface (Murphy 2007).Setae may also have long outgrowths called appendages (A) (Fig. 1A, B).Depending on the shape of the setae shaft and types of accessory structures, there are six major types of covering setae among gnaphosid spiders: squamose, plumose, lanceolate, pinnate, arborate and sicate.
Squamose setae are flat and broad.They are comparatively short.They may bear some accessory structures and may have a spinous apex.Usually, this type of seta creates a dense, iridescent coverage of the spider's abdomen and cephalothorax (Fig. 1C, D).Squamose setae are characteristic of small ground spiders: Micaria and Nauhea.Thanks to the iridescent squamose setae these spiders have a metallic blue to green colour.Micaria demonstrates the diversity of squamose setae, which take many forms and may or may not have proximal appendages.The sides and tips of the setae are serrated.Murphy called this type "uncinate squamose setae".These setae show variation in size and shape.The side of some setae which face towards the body bears hook-like inferior spines (Murphy 2007).The tip of the setae may be serrated or have a sharp spike (Fig. 1C).Murphy thought that "uncinate squamose setae" are a characteristic feature of Micaria (Murphy 2007).In the New Zealand spider Nauhea tapa the pedicel of the seta proximally bears one or two pairs of appendages.The tip of the setae is wide, serrated, and with a sharp terminal spike (Fig. 1D).
Plumose setae are bilateral and look like a feather.Lehtinen (1967) called this type of seta a "feathery hair".Later he came to the conclusion that all types of feathery setae are adaptations of a setal structure that has appeared many times independently and may be regarded as different modifications of the plumose seta type (Lehtinen 1975b, see Fig. 7.12).Thus, we adopt the term "plumose setae" as the basic name for all variations of this type of setae.These setae have a long narrow trunk, sharp at the apex.The comparatively long appendages are branched from both sides of the trunk.The appendages may be set along the whole length of the trunk, or only on a part of it, usually the proximal third of the trunk length.The position and length of appendages are also greatly varied and may provide significant features for the spiders' classification (Figs 2, 3, 4).The middle part of the trunk is enlarged, whereas its tip is sharpened.Appendages are set in two rows on the lateral sides of the trunk.The total number of appendages is genusspecific and varies from 2 to 44.The appendages may be long, slender, and sharp at the tip, or enlarged in their middle part, or clavate, i.e. enlarged at the tip.As a rule, appendages are more or less of the same length.However, there are exceptions.In these cases, the longest appendages are situated at the base of the trunk, and the shortest ones closer to its tip.The setae are immovably attached to the body surface on the cuticular elevation that has fine longitudinal stripes.The trunk of the setae bends proximally.This position and their immovable attachment are characteristic for covering setae only.All other setae are at a right angle or significantly far away from the integument.This suggests that plumose setae are mostly covering structures, have a protective function for the spiders' integumentary system, and do not have a sensory function (Foelix 2011).They are always present on the dorsal side of opisthosoma.They may create a continuous coverage or may be loosely distributed over the body surface (Ovtsharenko 1985).
The plumose setae of Berlandina, Nomisia, Minosiella and Pterotricha have lateral appendages along almost their entire length.The upper part of the setae that have no appendages may be only 1 / 4 -1 / 5 of its length as in Nomisia (Fig. 2B), Minosiella (Fig. 3F) and Pterotricha (Fig. 4D), or even less, as in Berlandina (Fig. 2A) (Ovtsharenko 1985).The number of appendages is also different.Minosiella intermedia has 11-18 appendages, Pterotricha strandi -23-38.In Nomisia, it is 10-20, whereas in Berlandina it is 30-44 appendages or 15-22 pairs.The structure of the setae may change, depending on the body part.The abdominal setae of Berlandina, for example, have 30-32 appendages; setae on the carapace may have up to 44 appendages.Nomisia has setae with 10-12 pairs of appendages on its abdomen, 10-16 pairs on its carapace, and 10-20 pairs on the legs.In all these genera, the plumose setae create a dense coverage that completely covers all of the spider's body (Ovtsharenko 1985).
Species of the genera Haplodrassus (Fig. 2C) and Drassodes (Fig. 1F) have at the tip a clear part of their plumose setae two times longer than its base, which bears lateral appendages.The number of appendages varies.Haplodrassus dalmatensis has 8-14 appendages (Fig. 2C), Haplodrassus soerenseni has 8 appendages.Haplodrassus signifier has from 7 to 10 appendages (Ovtsharenko 1985(Ovtsharenko , 1989)).The number of appendages in this species is different on both sides of the setae's trunk.Setae on one side may have one or even three fewer appendages than on the other side.Often, if on one side it is even, then on the other it is uneven (Ovtsharenko 1985).The plumose setae of Drassodes vary in number from 8 to 14, but the most common is 10 (Fig. 1F).
In Sosticus (Fig. 2D) and Leptodrassus (Fig. 2E) the tip part is equal or only a little longer than the base with its appendages attached.Sosticus has 8-14 appendages.These appendages are of different lengths.The longest appendages are in the middle part of the trunk.Leptodrassus memorialis has 8-11 appendages.The tip of the setae is laterally serrated.Intruda signata has plumose setae with 9 appendages at the base of the trunk; 4 appendages on one side and 5 appendages on the other side (Fig. 3A).
Plumose setae of Anagraphis have 12-15 appendages.The appendages are not organized into pairs.Their number on opposite sides of the trunk is different.Usually, if on one side there are six appendages, the other side has eight.Beside that the setae of Anagraphis spiders have two rows of superior spines (SSp) and lateral spines (LSp) along the total length of the trunk (Fig. 1B).Plumose setae on the abdomen of Nodocion meteonus possess 12 long appendages, occupying almost half of the trunk, and 5-6 long spines distributed on the distal part of the setae; all trunk and appendage setae have fine, longitudinal ridges (Fig. 4A).In Parasyrisca caucasica on the abdomen there are plumose setae with 13 appendages; all appendages have different lengths (Fig. 4C).Plumose setae on the abdomen of Scopoides catharius have 5-15 appendages, they occupy less than half of the proximal part of the trunk; the distal part of the trunk is coved by short spines and look like scales (Fig. 4F).Plumose setae of Echemoides tofo have 9-11 appendages.Their number on both sides may be different and vary from 4 to 6.All of these appendages are located at the proximal 1 / 3 of the trunk.The SSp are distributed along the total length of the trunk from the pedicel to the apex (Fig. 1E).Zimiromus medius has plumose setae with 10 appendages.Appendages are long and are flattened in a dorso-ventral direction.The apex of the trunk is sharp.Superior and lateral spines are also present (Fig. 3B).Encoptarthria echemophthalma has plumose setae with 7-8 pairs of proximal appendages, the distal part of the trunk is short, less than 1 / 3 of the trunk (Fig. 3C).Apodrassodes trancas has plumose setae with 4 pairs (total amount of appendages 8) of appendages symmetrically set on the proximal 1 / 3 of the trunk (Fig. 3D).Apopyllus silvestri has plumose setae with 6-8 appendages on the proximal 1 / 3 of the trunk.The distal 2 / 3 of the trunk is flattened (Fig. 3E).Hemicloea sundevalli has plumose setae with 4-5 proximal appendages on the base of the trunk.In Zelanda there are 4 pairs of proximally situated appendages (Fig. 4E).In Orodrassus assimilis the plumose setae possess 4 pairs of appendages, the trunk of the setae is smooth, serrated apically (Fig. 4B).Some genera have a reduced number of covering setae.These spiders may have covering setae only on the abdomen and the legs, most commonly on their femur.As a rule, the number of appendages on these setae varies from 0 to 6.In the case that appendages are absent the trunk remains present on the cuticle.Thus, the plumose setae of the Palaearctic species Callilepis nocturna have 4-6 appendages of different lengths on their base (Ovtsharenko 1985).Its North American relative Callilepis pluto has 5-8 appendages (Platnick 1975).Species of two genera close to Callilepis, Eilica sp. and Laronius erawan, completely lost the covering setae.Synaphosus (Fig. 2F) has plumose setae with 6-7 pairs of appendages.The tip of the setae is slightly enlarged.It is two times longer than it is wide at its base.For species of the genus Zelotes the number of appendages is characteristically decreased.Thus, Zelotes subterraneus has 2-4 appendages on its setae, Z. longipes has 2-3.The plumose setae in these spiders are only on the dorsal side of the opisthosoma (Ovtsharenko 1985).The setae of Drassyllus praeficus do not have appendages at all.The opisthosoma of Urozelotes rusticus has no covering setae, only sensillae.
Spiders of the genera Matua, Anzacia, Homoeothele, Hypodrassodes and Scotophaeus have lanceolate setae (Fig. 5).The lanceolate setae are, as a rule, flat.An oval ridge ornaments them on both lateral sides.The trunk is slightly bent.The tips of the setae are serrated.This type of setae was found on the dorsal side of the opisthosoma, cephalothorax and legs; setae can be modified depending on their location on the body.The trunk of the setae of Anzacia gemmea is comparatively narrow and short, and also bears 4 long appendages in its proximal part, close to the base of the setae.The remainder of the trunk is broad and serrated with a sharp spike on the tip (Fig. 5C) (Ovtsharenko & Platnick 1995).Lanceolate setae on the opisthosoma of Hypodrassodes maoricus have one pair of proximal appendages and strongly serrated distal parts of the setae (Fig. 5D).Lanceolate setae on the cephalothorax of Homoeothele micans have 4 pairs of appendages in the proximal part that reach the middle of the seta; the distal part of the seta is flat and laterally serrated (Fig. 5E).The lanceolate setae on the abdomen of Scotophaeus blackwalli are narrow, smooth, with 3 pairs of long proximal appendages and with 4-5 slender spines at the apical part of the trunk (Fig. 6D).Modification of lanceolate setae occurs in Matua valida, thus setae on the abdomen are flat, wide, proximally with 3 pairs of appendages and distally on the tip with 3-4 spines on each side of the seta (Fig. 5A).The lanceolate setae on the legs of Matua valida are narrow, flat, with 7-8 long appendages in the proximal part of the seta and slightly serrated distal part of seta (Fig. 5B).Lanceolate setae occur sometimes together with plumose setae, mostly on the abdomen, for example in species of Drassodes and Synaphosus.
Sicate setae have a broad curved trunk and the appendages are all on one pro-curved side of the trunk, which differentiates them from the lanceolate setae (Fig. 6A-D).These setae were found mostly on the dorsal side of the abdomen and carapace (Ovtsharenko 1985).The species of the genus Herpyllus have sicate setae with 10 appendages of equal length set in the middle part of the setae.On its tip there are 1-2 short spines.In Herpyllus propinquus sicate setae bear only two rows of short (almost spine-like) 6-8 appendages on the dorsal surface of the distal part of the trunk (Fig. 6B).Beside sicate setae, spiders of this species have plumose setae on the dorsal side of their abdomen.In Aphantaulax seminigra and Kishidaia conspicua the sicate setae have up to 25-30 appendages, distributed over the whole length of the trunk (Ovtsharenko 1989).In Cesonia bilineata sicate setae have 4-36 appendages located on the rim of the trunk along the whole of its length.The tip of these setae bears 8-9 spines dorsally (Fig. 1A, 6A).In Litopyllus temporarius 15 short appendages are distributed along the total length of the trunk in two closely spaced rows, and 4 pairs of long appendages are located on the proximal part of the trunk (Fig. 6C).
Pinnate setae are characteristic of the spider genus Gnaphosa.They are bilateral and folded along the grooved longitudinal midline.The most peculiar characteristic of this type of setae is a marginal serration, created by short appendages, broad at the base, along the whole length of the trunk.The apex of the setae of Gnaphosa taurica bifurcates and has the shape of a snake's tongue (Fig. 6E).The setae of Gnaphosa lugubris like G. taurica have a longitudinal groove along the whole length of the trunk with lateral boarders bent toward the outside.These boarders have two rows of spines, broad at the base and sharp apically.The pedicel of the setae is narrow and is merged into the depression on the cuticle.Thus, the major characteristics of the setae of these spiders are the four rows of appendages, the grooved shape of the trunk, and the way it merges into the cuticle pedicel.Spiders of this genus have setae only on the dorsal side of the abdomen, where they create a dense coverage.Comparison of the nymphs of Gnaphosa lugubris with adult spiders shows that their setae are almost identical (Ovtsharenko 1985).
Arborate setae occur in the species Fedotovia uzbekistanica and this type of setae is the most unusual covering seta among the ground spiders.They look like branches on the trunk of a tree.The trunk of these setae has a shaft with four longitudinal ridges.The appendages are branched from these ridges in four directions almost along the whole length of the trunk (Fig. 6F).

Discussion and conclusions
More than a third of the total known genera of gnaphosid spiders have been studied.The obtained data allow us to make some generalizations.Almost all gnaphosid spiders have covering setae on the dorsal side of their opisthosoma and additionally on the cephalothorax, legs and spinnerets.Some groups of ground spiders have very little (subfamily Zelotinae) or have no covering setae on their abdomen at all (subfamily Laroniinae).Setae demonstrate diverse appearance depending on their location on the body.Our data show the existence of stable characteristics relating to setal morphology.Depending on the shape of the setae and their accessory structures, they may be classified into six groups: squamose, plumose, lanceolate, sicate, pinnate and arborate.Lehtinen (1967Lehtinen ( , 1975aLehtinen ( , 1975b) ) was the first who pointed out the value of setal morphology for taxonomy and reconstruction of phylogenetic relationships among spiders.Galiano (1975) and Hill (1979) considered the diagnostic value of salticid scales.Ovtsharenko (1983Ovtsharenko ( , 1985Ovtsharenko ( , 1989) ) came to the conclusion that morphology of gnaphosids' covering setae varies among the genera and provides additional characteristics for taxonomic analysis and reconstruction of phylogenetic relationships among ground spiders.Townsend & Felgenhauer (1998a, 1998b, 1999) studied these cuticular structures and showed their usefulness for the taxonomy of oxyopid spiders.Townsend & Felgenhauer (2001), Griswold et al. (2005) and Ramírez (2014) show the importance of these characters in the phylogenetic analysis of Oxyopidae, entelegyne, and dionychan spiders.Our study supports previous observations made by Ovtsharenko (1983Ovtsharenko ( , 1985Ovtsharenko ( , 1989) that setae in the family Gnaphosidae demonstrate specific subfamilial and generic characteristics and provide valuable information for taxonomy and phylogeny of these spiders.
The role of covering setae still remains unknown.However, the type of seta attachment, the shape of the setae, and the absence of a proven association of the setae with sensory neurons (Townsend & Felgenhauer 1998a, 1998b, 1999, 2001, Foelix 2011) allow us to suggest a protective function.Hill (1979) noted that there are no verified experimental data that may suggest a specific function of the spiders' scales.At the same time, the scales' shape and design create a reflective surface that refracts light and is responsible for the colourful body pattern of jumping spiders that may be displayed during courtship (Hill 1979).Some gnaphosid spiders, such as Micaria and Nauhea, also have a metallic coloured body created by dense coverage of squamose setae.