20th International Congress of Arachnology

DENVER MUSEUM OF NATURE & SCIENCE

REPORTS

No. 3, July 2, 2016

International Congress of Arachnology

Spiders use various sensory modes to interact with other

individuals on an inter- and intraspecific level, and with

their environment or to get kinesthetic information.

Accordingly, the sensilla that perceive these signals can be

mechano-, hygro-, thermo- or chemosensilla. Some sensilla

types, i.e., trichobothria, tarsal organs or slit sense organs,

are well known in spiders regarding to their morphology

and fine structure, physiology and function. Their quantity

and distribution is assumed to be species specific and can be

used as taxonomic character. We investigated the structure,

quantity and distribution of tip-pore sensilla, trichobothria,

slit sense organs and tarsal organs on all walking legs and

pedipalps of

Argiope bruennichi

females by means of Scan-

ning Electron Microscopy. We chose

A. bruennichi

since this

species has been intensively studied as to its mating strate-

gies including the pheromone involved in mate attraction.

We show that

A. bruennichi

females possess all mentioned

sensilla types on all legs and pedipalps. Tip-pore sensilla

that are suspected to be chemosensory organs never occur

on the coxae and trochanter of the walking legs, but they

are common on the metatarsi and tarsi. The mechanosensi-

tive trichobothria are distributed on the distal part of the

tibiae and on the metatarsi. Lyriform organs are always

located next to the joints on the basal part of a segment,

mainly on ventral and lateral sides, whereas single slit sen-

silla are distributed on all segments mainly in rows. All tarsi

possess a tarsal organ on the dorsal side. Apart from provid-

ing a survey of sensory structures, our data pave the ground

for electrophysiological studies and ultrastructural analysis

of sensory organs and may lead to a better understand-

ing of the sensory ecology of spiders.

Keywords: sensory structures, tip-pore sensillum, tricho-

bothrium, slit sense organ, tarsal organ, Araneidae, SEM

Student - oral presentation

Widespread putative hygro-thermorecep-

tors in harvestmen (Arachnida, Opiliones):

an everted tarsal organ?

*Guilherme Gainett

1,2

, Nathália Fernandes

, Ricardo Pinto-

da-Rocha

, Prashant Sharma

, Peter Michalik

, Carsten H.

G. Müller

, Gonzalo Giribet

, Rodrigo H. Willemart

1,2,6

Laboratório de Ecologia Sensorial e Comportamento de

Artrópodes, Escola de Artes, Ciências e Humanidades,

Universidade de Sao Paulo, Rua Arlindo Bettio, 1000,

Ermelino Matarazzo, Sao Paulo, SP 03828-000, Brazil;

Programa de Pos-Graduaço em Zoologia, Instituto de

Biociências, Universidade de Sao Paulo, Rua do Matao,

321, Travessa 14, Sao Paulo, SP 05508-090, Brazil;

Department of Zoology, University of Wisconsin-Madison,

430 Lincoln Drive, Madison, WI, USA;

Zoological Institute

and Museum, Department of General and Systematic

Zoology, Ernst-Moritz-Arndt Universität Greifswald,

Loitzer Str. 26, D-17489 Greifswald, Germany.

Museum

of Comparative Zoology and Department of Organismic

and Evolutionary Biology, Harvard University, Cam-

bridge, MA 02138, USA;

Programa de Pos-Graduaço em

Ecologia e Evoluço, Universidade Federal de Sao Paulo,

Campus Diadema, Rua Professor Artur Riedel, 275,

Jardim Eldorado, Diadema, SP 09972-270, Brazil

ggainett@gmail.com

Most harvestman species are dependent on high humidity

levels and amenable temperatures for homeostasis. While

they are known to actively choose environments with these

conditions, no hygro/thermoreceptor has yet been identi-

fied in the group. Using scanning electron microscopy

(SEM) and transmission electron microscopy, we investi-

gated the fine morphology of two hair sensillar types of the

armored harvestman

Heteromitobates discolor

(Lania-

tores, Gonyleptidae): sensillum basiconicum (Sb) and

apical-hood sensillum (Ahs). With SEM, we investigated

their phylogenetic distribution in all four suborders: sam-

pling 43 Laniatores (in 30 families), three Dyspnoi, two

Eupnoi and five Cyphophthalmi. Both structures occur in

small numbers on the body (Sb: 36 units; Ahs: four units)

and are distributed on the distal parts of the legs. The Sb

is innervated by 3-4 dendrites and has a sagittal slit that

results in a shaft with two flaps, which probably allows

evaporation of receptor lymph. The Ahs is innervated by

two bundles of three dendrites and has two pore-like struc-

tures on its tip. Ahs and a pair of Sb form a triad on the

distal-most parts of tarsomeres I and II, being highly con-

served in Laniatores, present in Dyspnoi and Eupnoi and

absent in Cyphophthalmi. Cuticular structure, putative

evaporation of receptor lymph and innervation support a