Setae morphology and the phylogeny of ground spiders

(Araneae, Gnaphosidae)

By Amanda Tsang

LaGuardia Community College

March 10, 2014

Introduction Gnaphosids (commonly known as ground

spiders) are one of the biggest families of spiders. The group includes 122 genera and 2,162 species (Platnik, 2013).

This study aims to provide an updated description of the morphology of ground spider setae, integumentary accessory organs located on the cuticle. Previous studies have demonstrated that these structures differ among gnaphosids and may give researchers cues for the ground spiders classification on the generic and subfamily level (Ovtsharenko, 1983, 1985, 1989; Murphy, 2007).

Research Goals To demonstrate morphological differences of

setae in each genera.

To provide necessary key characteristics for more precise genera description and subfamilies delineation.

To gather data for a future cladistic analysis that will allow us to draw a phylogenic tree of the gnaphosid group for the first time.

Methods

Descriptions are based on specimens preserved in 75% ethanol. To prepare the specimens for examination, the abdomen of each specimen was desiccated using the critical point drying technique, and then coated with gold and palladium.

Specimens were then imaged using a Hitachi S-4700 Field Emission Scanning Electron Microscope (SEM) at a 5 kv beam voltage, and 15 mA probe current.

The Hitachi Scanning Electron Microscope

Findings

Anzacia gemmeaSquamous setae with brachia close to the root. Serrated with one spine on the top, and three to four brachia at the root.

Apopyllus silvestri

Plumose setae with roughly seven brachia on the first half of the stem.

Berlandina caspicaApproximately eleven flattened brachia covering almost the entire stem.

Drassodes lapidosus

Plumose setae with brachia covering the lower half of the stem. Brachia consists of five to seven branches of different lengths.

Notiodrassus distinctus

Plumose setae with two paired brachia at the base.

Gnaphosa muscorumFlattened setae with a longitudinal groove in the stem. Very short, spine-like apophysis of uniform size running from the bottom to top of the stem on each side.

Gnaphosa tauricaFlattened setae with a longitudinal groove in the stem. Very short, spine-like apophysis of uniform size running from the bottom to top of the stem on each side.

Herpyllus propinqus (2 types of setae)

1. Saber-shaped setae, serrated on the concave side and flat on the convex side.

2. Plumose setae with two to three brachia at the base.

Hypodrassodes maoricus Squamous setae

with two pairs of brachia at the base, and a single spine at the top. Two rows of scaly outgrowths on the top half.

Litopyllus temporarius Elongated saber-

shaped setae, serrated on one side and flat on the other. Three to five pairs of brachia close to the base.

Leptodrassus sp.Plumose setae with four long brachia almost the same length as the stem, located on the first half of the stem.

Micaria lenziSquamous with a serrated top and no brachia.

Nomisia ausseriPlumose setae with six to seven brachia of the same length on the first half of the stem.

Parasyrisca caucasicaPlumose setae with first one third of stem brachiated with four to five unpaired brachia.

Pterotricha sp.Plumose with three to five short unpaired brachia.

Sosticus loricatusPlumose setae with on average seven brachia, mostly located on first two thirds of the stem.

Results The plumose setae of Apopyllus, Drassodes,

Leptodrassus, and Nomisia all have lateral appendages covering the first half of the stem. The number of brachia varies per genus. In Leptodrassus and Nomisia, the brachia are almost the same length as the stem, while in Apopyllus and Drassodes, the brachia are shorter and vary in length along the stem.  

Parasyrisca, Pterotricha and Sosticus also have plumose setae with unpaired brachia. Parasyrisca typically has 4 to 5 brachia, while Pterotricha has 3 to 5 short brachia and Sosticus has approximately 7 brachia. The plumose setae of Berlandina has approximately 11 pairs of flattened brachia covering almost the entire stalk, while Notiodrassus only has two paired brachia at the base. 

Results Anzacia has squamous setae with 3-4 brachia close

to the root. The top is serrated with one spine. Hypodrassodes also has squamous setae, with two pairs of brachia at the base, and a single spine at the top. Two rows of scaly outgrowths characterize the top half. Micaria is characterized by squamous setae with a serrated top and no brachia.

The Gnaphosa genus is characterized by a very special type of setae which were not found among other spiders of the family. Such a peculiar characteristic needs explanation which may be found in the specifics of the family evolution.

Litopyllus and Herpyllus exhibited a peculiar type of saber-shaped setae that points to their close evolutionary relation.

Conclusions Our study shows that all ground spiders, with

only a few exclusions, possess setae that cover their abdomen. There are different types of covering setae characteristics for different gnaphosid genera and groups of genera, which makes setae a valuable characteristic for the ground spiders’ classification on subfamily level and establishing of their evolutionary relationship. Our study supports previous studies (Ovtsharenko, 1983, 1985, 1989; Murphy, 2007) that setae of gnaphosid spiders greatly vary in shape and demonstrate genus specific characteristics.

References Hill, D.E. 1979. The scales of salticid spiders. Zoological Journal of the Linnean Society

65: 193-218.

Lehtinen, P.T. 1967. Classification of the Cribellate spiders and some allied families, with notes on the evolution of the suborder Araneomorpha. Ann. Zool. Fenn. 4: 199-468.

Lehtinen, P.T. 1975. The significance of hair ultrastructure in phylogenetic classification of spiders. Journal of Ultrastructure Research 50: 362-395.

Murphy, J. 2007. Gnaphosid genera of the World. British Arachnological Society, St. Neots, Cambs. 2 volumes, The Dorset Press, Dorchester, UK.

Ovtsharenko, V.I. 1983. Spiders of the family Gnaphosidae of the European part of the USSR and Caucasus. Zoological Institute of the Academy of Science of the USSR, Leningrad.

Ovtsharenko V.I. 1985. Cuticular microstructure of the spider family Gnaphosidae (Aranei) and its use in the systematics. Proceedings of the Zoological Institute of the USSR Academy of Science 139: 27-35.

Ovtsharenko, V. I. 1989. Microstructures on the cuticle of the spiders of the family Gnaphosidae (Arachnida, Aranei). Fauna and ecology of spiders and scorpions, Nauka Publishers, Moscow: 5-13.

Platnick, N.I. 2013. The world spider catalog, version 13.5, American Museum of Natural History, NY, online at: http://research.amnh.org/entomology/spiders/catalog/index.html.

Acknowledgements

Thank you to Dr. Boris Zakharov who has mentored and guided me through the entire research process.

Many thanks to Dr. Vladmir Ovtsharenko for his suggestions and support.

Thank you to Henry Towbin and Morgan Hill at the American Museum of Natural History Microscopy and Imaging Facility for their technical support with the SEM.