Anterior Median Research Articles

Discovery of a new eye pattern in Araneoid spiders, with the description of two new species of Testudinaria from the Ecuadorian Amazon (Araneae: Araneidae)

Summary. Two new species from the genus Testudinaria Taczanowski, 1879 are described: T. charapa n. sp. (♀♂) and T. derocheae n. sp. (♀) from the Amazonian region of Ecuador. The female and male of T. charapa n. sp. present a peculiar and unique eye arrangement, never observed in araneoid spiders, where the anterior median eyes and the posterior median eyes are situated on the sides of the carapace. Members of the genus Testudinaria are unlike any other Araneidae and are distinguished by three morphological characters, the absence of radix in male palp, the absence of flagelliform gland spigot on posterior lateral spinnerets in both males and females, and the absence of a sustentaculum. In situ and in captivity observations shows that members of the genus do not construct an orbicular web. Detailed morphology of the group as well as SEM of male and female spinnerets gland spigots are presented for the first time. Finally, the limit of the group Testudinarieae sensu Simon, 1895 is discussed.

Topographic anatomy of the ascending and descending colons of children and adolescents according to intravital imaging

The aim of the study was to establish the age and sex patterns of the topography of the ascending and descending colons of children and adolescents according to intravital imaging data. Material and methods. Computed tomograms of the abdomen of 88 children and adolescents without visible abdominal organs pathology were analyzed. The surveyedwere divided into 4 age groups: periods of early, first and second childhood, adolescence. The study was performed on 16-slice computed tomographs with the determination of the distances from the ascending and descending colon to the surface of the body, neighboring organs and anatomical structures of the abdomen, skeletotopia. The data obtained were subjected to variation-statistical processing with the determination of the median, the values of the 25th and 75th percentiles and the significance of differences according to the Mann – Whitney U test. Results and discussion. The article presents the topographic and anatomical characteristics of the ascending and descending colons of children and adolescents and establishes the patterns of change, taking into account the sex and age of the examined. Conclusions. A significant increase in the distance from the ascending colon to the right ureter, jejunum and ileum, and quadratus lumborum was determined. The distance from the body surface to the ascending colon increased with age along all the studied lines. The proximal part of the ascending colon among all those examined was mostly defined from the intervertebral disc LIV–LV to the intervertebral disc LV–SI, and the hepatic flexure of the colon was defined at the level from LI to the intervertebral disc LII–LIII. A significant increase in the distance from the descending colon to the left ureter, pancreas and quadratus lumborum was found. The distance from the body surface to the descending colon increased with age along the anterior median, left middle axillary, and left scapular lines. The splenic flexure of the colon was located at the level from LI to the intervertebral disc LI–LII, and the distal part of the descending colon was located at the level from LIV to the intervertebral disc LIV–LV.

Surgical Strategy for Anterior Tibial Plateau Fractures in Hyperextension Knee Injuries.

ObjectiveThe aim of the present study was to summarize the clinical characteristics, treatment strategies, and clinical results for anterior tibial plateau fractures caused by hyperextension injuries.MethodsWe performed a retrospective analysis of 26 cases of anterior tibial plateau fractures that were treated with open reduction and internal fixation from January 2016 to December 2019, including 16 men and 10 women, aged 26–68 years old, with an average age of 47 ± 12.5 years. According to the three‐column theory classification, there were 16 cases of single‐column fractures (9 cases of anteromedial fractures and 7 cases of anterolateral fractures), 3 cases of two‐column fractures (anteromedial + anterolateral fractures), and 7 cases of three‐column fractures. Options for the surgical approach included anteromedial, anterolateral, modified anterior median, and anterolateral + posteromedial incision. The implants included a T‐shaped plate, an L‐shaped plate, a horizontal plate, and a TomoFix plate. The surgical approach and fixation method were selected based on the characteristics of the anterior tibial fracture. The Rasmussen radiological criteria were used to evaluate the effects of fracture reduction and fixation. The knee joint function was evaluated using the knee function evaluation criteria of the Hospital for Special Surgery. Medial and lateral stress tests, the Lachman test, and the pivot shift test were used to evaluate the stability of the knee joint. The range of knee motion was recorded.ResultsAll cases were followed up for 12–24 months, with an average follow up of 15.7 months. The operation time was (148 ± 42) min; the intraoperative blood loss was (150 ± 50) mL. A total of 22 cases were anatomically reduced and 4 cases were well‐reduced, and the compression reduction rate was 100%. According to the Rasmussen radiology scoring, 17 cases were excellent and 9 cases were good. The excellent and good rate was 100%. The fracture healing time was 3.3 months. There is no difference in fracture healing time for different fracture types. Both the Lachman and pivot shift test findings were normal in 24 patients and nearly normal in 2 patients. The posterior drawer test was normal in 25 patients and close to normal in 1 patient. The varus stress test was normal in 24 patients and nearly normal in 2 patients, while the valgus stress test was normal in 23 patients, nearly normal in 2 patients, and abnormal in 1 patient. The range of motion (ROM) was 100°–137°, with an average of 125° ± 11.7°. The Hospital for Special Surgery (HSS) knee score at the last follow up was 79–98 points, with an average of 87.54 ± 8.36 points; the results were excellent in 21 cases and good in 5 cases. Therefore, 100% of results were excellent or good. Two cases had superficial wound infections after the operation. The recovery of 2 patients with common peroneal nerve injury was poor.ConclusionThe appropriate surgical approach and fixation method were performed according to the different positions of the anterior tibial fracture and satisfactory results were obtained after surgery.

MRI T2-Hyperintense Signal Structures in the Cervical Spinal Cord: Anterior Median Fissure versus Central Canal in Chiari and Control-An Exploratory Pilot Analysis.

Cervical spine axial MRI T2-hyperintense fluid signal of the anterior median fissure and round hyperintense foci resembling either the central canal or base of the anterior median fissure are associated with a craniocaudad sagittal line, also simulating the central canal. On the basis of empiric observation, we hypothesized that hyperintense foci, the anterior median fissure, and the sagittal line are seen more frequently in patients with Chiari malformation type I, and the sagittal line may be the base of the anterior median fissure in some patients. Saggital line incidence and the incidence/frequency of hyperintense foci and anterior median fissure in 25 patients with Chiari I malformation and 25 contemporaneous age-matched controls were recorded in this prospective exploratory study as either combined (hyperintense foci+anterior median fissure in the same patient), connected (anterior median fissure extending to and appearing to be connected with hyperintense foci), or alone as hyperintense foci or an anterior median fissure. Hyperintense foci and anterior median fissure/patient, hyperintense foci/anterior median fissure ratios, and anterior median fissure extending to and appearing to be connected with hyperintense foci were compared in all, in hyperintense foci+anterior median fissure in the same patient, and in anterior median fissure extending to and appearing to be connected with hyperintense foci in patients with Chiari I malformation and controls. Increased sagittal line incidence (56%), hyperintense foci (8.5/patient), and anterior median fissure (4.0/patient) frequency were identified in patients with Chiari I malformation versus controls (28%, 3.9/patient, and 2.7/patient, respectively). Increased anterior median fissure/patient, decreasing hyperintense foci/anterior median fissure ratio, and increasing anterior median fissure extending to and appearing to be connected with hyperintense foci/patient were identified in Chiari subgroups. A 21%-58% increase in observed anterior median fissure extending to and appearing connected to hyperintense foci in the entire cohort and multiple sagittal line subgroups compared with predicted occurred. In addition to the anticipated increased incidence/frequency of sagittal line and hyperintense foci in patients with Chiari I malformation, an increased incidence and frequency of anterior median fissure and anterior median fissure extending to and appearing to be connected with hyperintense foci/patient were identified. We believe an anterior median fissure may contribute to a saggital line appearance in some patients with Chiari I malformation. While thin saggital line channels are usually ascribed to the central canal, we believe some may be due to the base of the anterior median fissure, created by pulsatile CSF hydrodynamics.

Anterior Median Skull Base Reconstruction Using a Vascularized Free Flap: Rationale, Patient Selection and Outcome.

Objectives To present our method of median anterior skull base (ASB) reconstruction using a subcranial approach with a free flap in cases of naso-fronto-orbital (NFO) bony segment failure and in patients at high risk for future failure of the bony frontal segment. Design This study presents as a retrospective case series. Setting Tertiary university-affiliated medical center. Participants Adult and pediatric patients who underwent median ASB resection via the subcranial approach with a free flap reconstruction were participated in this study. Main Outcome Measures Pathologic outcome and postoperative quality of life (QoL) as assessed by a validated Hebrew version of the "Anterior Skull Base Quality-of-Life Questionnaire." Results The departmental database yielded 13 suitable patients aged between 15 and 70 years. The main indication ( n = 7) for ASB surgery was osteoradionecrosis (ORN) of the NFO bony segment which was first detected at an average of 3.6 years (range: 2-32 years) postradiation therapy. High-risk patients for future ORN of the NFO segment ( n = 3) were primarily reconstructed using a vascularized free flap. Nine patients had malignant disease, and four of them were alive without evidence of disease during the follow-up period (average, 48 months). Their QoL was comparable to that of patients who had undergone subcranial ASB resection without free flap reconstruction. Conclusions The ASB median free flap method of reconstruction is a safe and reliable in cases of large complex median ASB defects without orbital resection or maxillectomy. This approach is suitable for patients who had undergone previous surgery, radiotherapy and/or those who present with osteoradionecrosis, as well as for patients with high risk of NFO segment ORN.

Morphological Patterns of the Anterior Median Fissure in the Cervical Spinal Cord Evaluated by Computed Tomography After Myelography.

ObjectiveComputed tomography following myelography (CTM) revealed an unusual flow of contrast dye into the anterior median fissure (AMF) in a patient with cervical spondylotic myelopathy. Since then, several AMF configurations have been observed on CTM. Therefore, we evaluated morphological patterns of the AMF on CTM and investigated the significance and mechanisms of contrast dye flow into the AMF. MethodsMorphological patterns of the AMF on CTM were examined in 79 patients. Group A (24 patients) underwent surgery because of symptomatic cervical myelopathy. Group B (43 patients) had no clinical symptoms but showed spinal cord compression on CTM. Group C (12 patients), who showed neither clinical symptoms nor cord changes, underwent CTM for lumbar lesion evaluation. AMF patterns were classified into 4 types according to their configurations on CTM (reversed T, Y, V, and O types). ResultsIn group B, the reversed T type and Y type appeared significantly more often near the compressed portion (p<0.001). A similar tendency was seen in group A. The V and O types were most frequently observed in group C (p<0.001). ConclusionOn CTM, contrast dye tends to flow into the AMF of the cervical cord when the spinal cord is compressed. We speculate that there may be 3 possible mechanisms for this phenomenon: deformation of the epipial layer of the AMF due to cervical cord compression, AMF dilatation due to atrophy of the anterior funiculus or anterior horn, and temporary AMF dilatation when it becomes an alternative route for cerebrospinal fluid circulation.

Psychophysical investigation of vigilance decrement in jumping spiders: overstimulation or understimulation?

The inability to maintain signal detection performance with time on task, or vigilance decrement, is widely studied in people because of its profound implications on attention-demanding tasks over sustained periods of time (e.g., air-traffic control). According to the resource depletion (overload) theory, a faster decrement is expected in tasks that are cognitively demanding or overstimulating, while the underload theory predicts steeper decrements in tasks that provide too little cognitive load, or understimulation. Using Trite planiceps, a jumping spider which is an active visual hunter, we investigated vigilance decrement to repetitive visual stimuli. Spiders were tethered in front of two stimulus presentation monitors and were given a polystyrene ball to hold. Movement of this ball indicates an attempt to turn towards a visual stimulus presented to a pair of laterally facing (anterior lateral) eyes for closer investigation with high acuity forward-facing (anterior median) eyes. Vigilance decrement is easily measured, as moving visual stimuli trigger clear optokinetic responses. We manipulated task difficulty by varying the contrast of the stimulus and the degree of 'noise' displayed on the screen over which the stimulus moved, thus affecting the signal:noise ratio. Additionally, we manipulated motivation by paired testing of hungry and sated spiders. All factors affected the vigilance decrement, but the key variable affecting decrement was stimulus contrast. Spiders exhibited a steeper decrement in the harder tasks, aligning with the resource depletion theory.

Giving invertebrates an eye exam: an ophthalmoscope that utilizes the autofluorescence of photoreceptors.

One of the most important functional features of eyes is focusing light, as both nearsightedness and farsightedness have major functional implications. Accordingly, refractive errors are frequently assessed in vertebrates, but not in the very small invertebrate eyes. We describe a micro-ophthalmoscope that takes advantage of autofluorescent properties of invertebrate photoreceptors and test the device on the relatively well-understood eyes of jumping spiders and flies. In each case, our measurements confirmed previous findings with a greater degree of accuracy. For example, we could precisely resolve the layering of the anterior median eyes and could map out the extensive retina of the anterior lateral eyes of the spider. Measurements also confirmed that fly ommatidia are focused into infinity, but showed that their focal plane is situated slightly below the receptor surface. In contrast to other approaches, this device does not rely on reflective tapeta and allows for precise optical assessment of diverse invertebrate eyes.

Fluid-Signal Structures in the Cervical Spinal Cord on MRI: Anterior Median Fissure versus Central Canal.

Hyperintense fluid-signal anterior median fissure and hyperintense foci resembling the central canal are seen on cervical spine axial T2 MR imaging. They may also be associated with a channel-like T2-hyperintense craniocaudad line on sagittal images. We hypothesized that the hyperintense foci and the sagittal line may represent the base of the anterior median fissure. In this exploratory study, 358 cervical MR images were analyzed for recording and comparing the incidence/numbers of hyperintense foci, anterior median fissure, and sagittal line as hyperintense foci, anterior median fissure, and sagittal line per patient when present alone or together, both with and without the sagittal line. Hyperintense foci were identified on 238/358 (66.5%) studies; an anterior median fissure, on 218/358 (60.9%). The hyperintense foci/anterior median fissure ratio was 3.7/2.3 (P = .00001). Anterior median fissures were seen alone less commonly than hyperintense foci were seen alone (P = .045). We identified increased anterior median fissure/patient in a hyperintense foci +anterior median fissure group compared with an anterior median fissure-only group (4.0 versus 3.2, P = .05), with similar hyperintense foci/patient in the hyperintense foci+anterior median fissure and hyperintense foci-only groups (5.5 versus 5.8, P = .35), and proportional distribution of both across the hyperintense foci+anterior median fissure subgroups (hyperintense foci/anterior median fissure ratio, 1.3). The sagittal line in 89 (24.9%) patients was associated with increased hyperintense foci and anterior median fissure/patient. Greater correlation of anterior median fissure/patient to sagittal line presence was seen in sagittal line subgroup analysis. This exploratory analysis found an increased anterior median fissure per patient in conjunction with hyperintense foci presence, a proportional increase of both across the hyperintense foci+anterior median fissure group, and greater correlation of anterior median fissure per patient with the sagittal line. These findings suggest that anterior median fissure and hyperintense foci are structurally related, that hyperintense foci may commonly be the base of the anterior median fissure, and that the sagittal line is a manifestation primarily of an anterior median fissure, occasionally appearing as channels that may simulate the central canal.

Descriptions of the two-eyed African spider genera Chedimanops gen. n. and Hybosidella gen. n. (Araneae, Palpimanidae, Chediminae)

Two new genera of chedimine palpimanids are described. Chedimanopsgen. n. includes the type species, Chedimanopseskovisp. n. (♂♀), and Chedimanopsrwenzorensissp. n. (♂♀), both from the far eastern part of the Democratic Republic of Congo (Rwenzori Mts.). The monotypic Hybosidellagen. n. is based on Hybosidellaetindesp. n. (♂) from Cameroon. The new genera differ from all other Palpimanidae by possessing only the anterior median eyes (all other eyes are lost). These new genera can be distinguished from one another by the shape of the thoracic fovea (a narrow bracket-shaped pit vs. a longitudinal groove, respectively), as well as by the structure of the abdominal scuta and the male copulatory organ, peculiarities of coloration, amongst other characters. The taxonomic position and relationships of the newly described taxa are briefly discussed. The distinctive characters and a key to both species of Chedimanopsgen. n. are also provided.

Fine structure of the anterior median eyes of the funnel-web spider Agelena labyrinthica (Araneae: Agelenidae)

Only few electron microscopic studies exist on the structure of the main eyes (anterior median eyes, AME) of web spiders. The present paper provides details on the anatomy of the AME in the funnel-web spider Agelena labyrinthica. The retina consists of two separate regions with differently arranged photoreceptor cells. Its central part has sensory cells with rhabdomeres on 2, 3, or 4 sides, whereas those of the ventral retina have only two rhabdomeres on opposite sides. In addition, the rhabdomeres of the ventral retina are arranged in a specific way: Whereas in the most ventral part they form long tangential rows, those towards the center are detached and are arranged radially. All sensory cells are wrapped by unpigmented pigment cell processes. In agelenid spiders the axons of the sensory cells exit from the middle of the cell body; their fine structure and course through the eye cup is described in detail. In the central part of the retina efferent nerve fibres were found forming synapses along the distal region of the receptor cells. A muscle is attached laterally to each eye cup that allows mainly rotational movements of the eyes. The optical performance (image resolution) of these main eyes with relatively few visual cells is discussed.

Role of the different eyes in the visual odometry in the wolf spider Lycosa tarantula (Araneae, Lycosidae)

The wolf spider Lycosa tarantula returns home by means of path integration. Previous studies demonstrated: (i) that the angular component of the outbound run is measured using a polarized-light compass associated with the anterior median eyes; (ii) changes in direction of the substratum are detected by the anterior lateral eyes (ALEs); and (iii) in relation to the linear component of the outbound run, an increase of optic flow, in either the lateral or ventral fields of view, caused spiders to search for the burrow at a point nearer to the goal. However, the role of the secondary eyes [ALEs, posterior lateral eyes (PLEs) and posterior median eyes (PMEs)] in the perception of this optic flow and the importance of them for gauging the distance walked is still unknown. In this study, lateral or ventral gratings of wavelength λ=1 cm were used, with two groups of spiders in each setup: (1) PLEs+PMEs covered and (2) ALEs covered. The largest reduction in the distance walked to return to the burrow was observed with the ventral grating/ALEs covered. These results show the importance of the previously neglected ALEs for the visual behavior of these spiders. The possibility of gathering information for locomotion from the three pairs of secondary eyes in the mushroom bodies is discussed.

New Data on the Spider Genus Levymanus (Araneae: Palpimanidae)

New data on the composition and distribution of the previously monotypic genus Levymanus Zonstein & Marusik, 2013 are provided. The type species L. gershomi Zonstein & Marusik, 2013 is recorded for the first time from the UAE, and L. ras sp. n., a second member of this genus, is described from a female collected in Ethiopia. The new species differs from L. gershomi by the coarser corrugation of the carapace(vs. less sharply corrugated carapace in the latter species), the shape of the thoracic fovea with the sulci set more closely to each other, and relatively larger anterior median eyes, as well as by structure of the vulva.http://zoobank.org/urn:lsid:zoobank.org:pub:A1DC9389-A312-4DA5-AF1E-85337E09372A

The synganglion of the jumping spider Marpissa muscosa (Arachnida: Salticidae): Insights from histology, immunohistochemistry and microCT analysis

Jumping spiders are known for their extraordinary cognitive abilities. The underlying nervous system structures, however, are largely unknown. Here, we explore and describe the anatomy of the brain in the jumping spider Marpissa muscosa (Clerck, 1757) by means of paraffin histology, X-ray microCT analysis and immunohistochemistry as well as three-dimensional reconstruction. In the prosoma, the CNS is a clearly demarcated mass that surrounds the esophagus. The anteriormost neuromere, the protocerebrum, comprises nine bilaterally paired neuropils, including the mushroom bodies and one unpaired midline neuropil, the arcuate body. Further ventrally, the synganglion comprises the cheliceral (deutocerebrum) and pedipalpal neuropils (tritocerebrum). Synapsin-immunoreactivity in all neuropils is generally strong, while allatostatin-immunoreactivity is mostly present in association with the arcuate body and the stomodeal bridge. The most prominent neuropils in the spider brain, the mushroom bodies and the arcuate body, were suggested to be higher integrating centers of the arthropod brain. The mushroom body in M. muscosa is connected to first and second order visual neuropils of the lateral eyes, and the arcuate body to the second order neuropils of the anterior median eyes (primary eyes) through a visual tract. The connection of both, visual neuropils and eyes and arcuate body, as well as their large size corroborates the hypothesis that these neuropils play an important role in cognition and locomotion control of jumping spiders. In addition, we show that the architecture of the brain of M. muscosa and some previously investigated salticids differs significantly from that of the wandering spider Cupiennius salei, especially with regard to structure and arrangement of visual neuropils and mushroom body. Thus, we need to explore the anatomical conformities and specificities of the brains of different spider taxa in order to understand evolutionary transformations of the arthropod brain.

Visual odometry in the wolf spider Lycosa tarantula (Araneae: Lycosidae)

The wolf spider Lycosa tarantula homes using path integration. The angular component of the displacement is measured using a polarized-light compass associated with the functioning of the anterior median eyes. However, how L. tarantula estimates the linear component of the displacement was not known prior to this investigation. The ability of L. tarantula to gauge the distance walked after being displaced from its burrow was investigated using experimental channels placed in an indoor setup. Firstly, we manipulated the perception of visual stimuli by covering all the spider's eyes. Secondly, we changed the optic flow supplied by a black-and-white grating (λ=2 cm) perceived either in the lateral or in the ventral field of view. Finally, the period of the lateral or ventral grating was changed from λ=2 cm to λ=1 cm. Our results indicate that visual information contributes to distance estimation because when the spider's eyes were covered, the spiders tended to search for the burrow at very variable distances. This visual information is created by the motion of the image as the spider walks, the motion in the lateral field of view being the most important. The preference of a lateral optic flow over the ventral flow can be explained by the difference in the resolution capacity of the posterior lateral eyes and the anterior lateral eyes.

Locking plate fixation for calcaneal fractures of Sanders type IV: a finite element analysis

Objective To evaluate the biomechanical performance of a calcaneal locking plate in fixation of calcaneal fractures of Sanders type IV through finite element（FE） analysis. Methods A healthy male volunteer was enrolled for this study who were 26 years old and 70 kg in weight. A 3D FE model of calcaneal fracture of Sanders type IV fixated with a ealcaneal locking plate （Synthes） was reconstructed using software Mimics 13.0 and Geomagic 10. 0 based on the 3D CT images of the volunteer＇s both feet. An axial load of 700 N was applied through the talus. The stress distribution and peak stress of fracture fragments and internal fixator, and the maximum stress point and maximum displacement area of the calcaneus and internal fixator as well, were analyzed. Results The lateral stresses on the calcaneus were concentrated on the 4 areas： the medial side of the subtalar joint （15. 224 MPa）, the bone-screw interface below the subtalar joint （13. 083 MPa）, the bone-screw interface beside the heel （9. 786 MPa） and the bone-screw interface beside the calcaneocuboid joint （7. 632 MPa）. The peek stress on the plate was about 260. 1 MPa, distributed on the fracture line between the posterior fragment and the median-anterior fragment. The maximal displacements occurred on the sustentaculum tali （0. 403 mm）, the interface between the posterior fragment and median fragment （0. 320 mm） and the interface between the anterior fragment and median fragment （0. 319 ram）. The maximal displacement of the plate-screw occurred on the distal side of the proximal screws, especially the one used to fixate the sustentaculum tali, about 0. 390 mm. Conclusions Since fixation with a locking plate for calcaneal fractures of Sanders type IV may lead to a high risk of traumatic arthritis, it is suggested that primary external fixation followed by subtalar fusion be a better choice or appropriate modifications be made of the current locking plate to achieve better mechanical performance. Key words: Calcaneal fracture; Finite element analysis; Computer simulation; Fracturefixation, internal

Characterisation and localisation of the opsin protein repertoire in the brain and retinas of a spider and an onychophoran

BackgroundOpsins have been found in the majority of animals and their most apparent functions are related to vision and light-guided behaviour. As an increasing number of sequences have become available it has become clear that many opsin-like transcripts are expressed in tissues other than the eyes. Opsins can be divided into three main groups: rhabdomeric opsins (r-opsins), ciliary opsins (c-opsins) and group 4 opsins. In arthropods, the main focus has been on the r-opsins involved in vision. However, with increased sequencing it is becoming clear that arthropods also possess opsins of the c-type, group 4 opsins and the newly discovered arthropsins but the functions of these opsins are unknown in arthropods and data on their localisation is limited or absent.ResultsWe identified opsins from the spider Cupiennius salei and the onychophoran Euperipatoides kanangrensis and characterised the phylogeny and localisation of these transcripts. We recovered all known visual opsins in C. salei, and in addition found a peropsin, a c-opsin and an opsin resembling Daphnia pulex arthropsin. The peropsin was expressed in all eye types except the anterior median eyes. The arthropsin and the c-opsin were expressed in the central nervous system but not the eyes. In E. kanangrensis we found: a c-opsin; an opsin resembling D. pulex arthropsins; and an r-opsin with high sequence similarity to previously published onychophoran onychopsins. The E. kanangrensis c-opsin and onychopsin were expressed in both the eyes and the brain but the arthropsin only in the brain.ConclusionOur novel finding that opsins of both the ciliary and rhabdomeric type are present in the onychophoran and a spider suggests that these two types of opsins were present in the last common ancestor of the Onychophora and Euarthropoda. The expression of the c-opsin in the eye of an onychophoran indicates that c-opsins may originally have been involved in vision in the arthropod clade. The lack of c-opsin expression in the spider retina suggests that the role for c-opsin in vision was lost in the euarthropods. Our discovery of arthropsin in onychophorans and spiders dates the emergence of arthropsin to the common ancestor of Onychophora and Euarthropoda and their expression in the brain suggests a non-visual function.

Saccadic tracking of targets mediated by the anterior-lateral eyes of jumping spiders

The modular visual system of jumping spiders (Salticidae) divides characteristics such as high spatial acuity and wide-field motion detection between different pairs of eyes. A large pair of telescope-like anterior-median (AM) eyes is supported by 2-3 pairs of 'secondary' eyes, which provide almost 360 degrees of visual coverage at lower resolution. The AM retinae are moveable and can be pointed at stimuli within their range of motion, but salticids have to turn to bring targets into this frontal zone in the first place. We describe how the front-facing pair of secondary eyes (anterior lateral, AL) mediates this through a series of whole-body 'tracking saccades' in response to computer-generated stimuli. We investigated the 'response area' of the AL eyes and show a clear correspondence between the physical margins of the retina and stimulus position at the onset of the first saccade. Saccade frequency is maximal at the margin of AL and AM fields of view. Furthermore, spiders markedly increase the velocity with which higher magnitude tracking saccades are carried out. This has the effect that the time during which vision is impaired due to motion blur is kept at an almost constant low level, even during saccades of large magnitude.

The orientation-dependent visual spatial cut-off frequency in a spider

Cupiennius salei (Araneae, Ctenidae) has, like most spiders, eight camera-type eyes. The anterior median eyes are called principal eyes and have a movable retina; all of the other eyes are referred to as secondary eyes and are equipped with a reflecting tapetum. The photoreceptors in the secondary eyes are arranged in rows on the tapetum and the inter-receptor angle along such a row is smaller than normal to it. In this study, the vertical and horizontal spatial cut-off frequencies of moving gratings were measured for the posterior median (PM) eyes, and the data were then compared with the anatomical data reported in the literature. Detection of moving objects in the secondary eyes enhances the eye muscle potential frequency in the principal eyes. We thus recorded the eye muscle activity with a telemetric unit as a monitor for motion detection while moving stimuli - sinusoidally modulated bright and dark stripes - were presented to the PM eyes on a computer screen. A significant increase in the eye muscle activity was measured for gratings at an angular wavelength of 2.0 deg in the vertical orientation and of 2.7 deg in the horizontal direction. In the vertical orientation the critical wavelength is twice the inter-receptor angle; in the horizontal orientation the spiders responded to wavelengths that are smaller than twice the corresponding inter-receptor angle. The cut-off frequency seems thus to be limited by the visual field of the photoreceptors rather than the inter-receptor angle. The relative intensity modulations modelled for the two different grating orientations in single photoreceptor cells were in line with our data.

Description of a new species of armored spider from Myanmar (Araneae: Tetrablemmidae)

The Tetrablemmidae is a family of small to very small haplogyne, ecribellate, three-clawed spiders characterized mainly by the complex pattern of abdominal scuta (with dorsal, lateral and ventral plates) which justifies their common name “armoured spiders” (Shear 1978, Lehtinen 1981, Jocqué &amp; Dippenaar-Schoeman 2006). They have a dorsal shield of prosoma heavily sclerotized, usually with rugous, pitted or reticulated surface, distinctly modified in the males of many genera. They lack direct eyes (anterior median), and several genera may lack some or all of the indirect eyes as well. One of the recognized tribes, Tetrablemmini (subfamily Tetrablemminae), contains the type genus of the family: Tetrablemma O. Pickard-Cambridge typically known by having four eyes displaced posteriorly in males, which have a convex clypeus, sometimes with tubercles, and chelicerae with anterior horns (Figs 6, 8─9; Lehtinen 1981: 56; Tong &amp; Li 2008; Burger 2008).