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Comparative Study
. 2014 Dec 3;9(12):e112913.
doi: 10.1371/journal.pone.0112913. eCollection 2014.

Homology of the lateral eyes of scorpiones: a six-ocellus model

Stephanie F Loria  1 , Lorenzo Prendini  2
Affiliations
Free PMC article
Comparative Study

Homology of the lateral eyes of scorpiones: a six-ocellus model

Stephanie F Loria et al. PLoS One. .
Free PMC article

Abstract

Scorpions possess two types of visual organs, the median and lateral eyes. Both eyes consist of simple ocelli with biconvex lenses that differ in structure and function. There is little variation in the number of median ocelli across the order. Except for a few troglomorphic species in which the median ocelli are absent, all scorpions possess a single pair. In contrast, the number of pairs of lateral ocelli varies from zero to five across Scorpiones and may vary within species. No attempt has been made to homologize lateral ocelli across the order, and their utility in scorpion systematics has been questioned, due to the variation in number. A recent study examined the number of lateral ocelli among various Asian Buthidae C.L. Koch, 1837 and proposed a "five-eye model" for the family. This model has not been examined more broadly within Buthidae, however, nor compared with the patterns of variation observed among other scorpion families. An eyespot, referred to as an accessory lateral eye, situated ventral or posteroventral to the lateral ocelli, has also been reported in some scorpions. Analysis of its structure suggests it serves a nonvisual function. We present the first comparative study of variation in the lateral ocelli across the order Scorpiones, based on examination of a broad range of exemplar species, representing all families, 160 genera (78%), 196 species (9%), and up to 12 individuals per species. We propose a six-ocellus model for Recent scorpions with four accessory ocelli observed in various taxa, homologize the individual ocelli, and correct erroneous counts in the recent literature. We also investigate the presence of the eyespot across scorpions and discover that it is more widespread than previously recognized. Future work should investigate the genetic and developmental mechanisms underlying the formation of the lateral ocelli to test the hypotheses proposed here.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Six-ocellus model with four accessory ocelli, indicated in black (A), and nine general patterns with fewer than six ocelli (B–J), indicating most common positions and relative sizes (AALMa PLMa> PDMi>ADMi; PDMi> PLMi; PLMi> APLMi1; PLMi  =  APLMi2; PLMi> APLMi3) of lateral ocelli in Recent scorpions.
B. Type 5, shaded areas represent positional variation in ADMi and PDMi. C. Type 4A. D. Type 4B. E. Type 4C. F. Type 3A. G. Type 3B. H. Type 2A. I. Type 2B. J. Type 1. Abbreviations: accessory anterolateral major ocellus (AALMa); anterolateral major ocellus (ALMa); mediolateral major ocellus (MLMa); posterolateral major ocellus (PLMa); posterolateral minor ocellus (PLMi); posterodorsal minor ocellus (PDMi); anterodorsal minor ocellus (ADMi); three accessory posterolateral minor ocelli (APLMi1, APLMi2, APLMi3).
Figure 2
Figure 2. Lateral ocelli of Recent scorpions (family Buthidae C.L. Koch, 1837).
A. Androctonus finitimus (Pocock, 1897), subad. ♂ (AMNH), Type 5. B. Tityopsis inexpectata (Moreno, 1940), ♀ (AMNH), abnormal six-ocellus condition with AALMa on sinistral side. C. Buthacus macrocentrus (Ehrenberg, 1828), subad. ♀ (AMNH), Type 5. D. Centruroides vittatus (Say, 1821), ♀ (AMNH), Type 5. E. Orthochirus scrobiculosus (Grube, 1873), ♀ (AMNH), Type 5. F. Razianus zarudnyi (Birula, 1903), ♀ (AMNH), Type 4C. G. Tityus bahiensis eickstedtae Lourenço, 1982, juv. (AMNH [LP 1596]), Type 5. H. Alayotityus nanus Armas, 1973, ♂ (AMNH [LP 1768]), Type 4A. I. Microtityus consuelo Armas & Marcano Fondeur, 1987, ♀ (AMNH [LP 3281]), Type 4A. J. Isometrus maculatus (DeGeer, 1778), ♂ (AMNH [LP 1798]), Type 5. K. Zabius fuscus Thorell, 1876, subad. ♀ (AMNH), Type 4C. L. Akentrobuthus atakora Vignoli & Prendini, 2008, holotype ♀ (AMNH [LP 8334]), Type 2A. M. Uroplectes carinatus (Pocock, 1890), ♂ (AMNH), Type 5. N. Afroisometrus minshullae (FitzPatrick, 1994), ♀ (AMNH [LP 7875]), Type 3A. O. Pseudolychas ochraceus (Hirst, 1911), ♀ (AMNH), Type 5. P. Lissothus bernardi Vachon, 1948, ♀ (MNHN RS 3420), Type 4C. Q. Karasbergia methueni Hewitt, 1913, ♂ (AMNH [LP 8225]), Type 3A. R. Pseudolychas ochraceus (Hirst, 1911), ♀ (AMNH), Type 4C. Abbreviations: AALMa (accessory anterolateral major ocellus); ADMi (anterodorsal minor ocellus); ALMa (anterolateral major ocellus); e (eyespot); MLMa (mediolateral major ocellus); PDMi (posterodorsal minor ocellus); PLMa (posterolateral major ocellus). Scale bars  = 0.1 mm.
Figure 3
Figure 3. Lateral ocelli of Recent scorpions (families Chactidae Pocock, 1893; Chaerilidae, Pocock, 1893; Euscorpiidae, Laurie, 1896; Iuridae Thorell, 1876; Pseudochactidae Gromov, 1998; Scorpiopidae Kraepelin, 1905).
A. Chaerilus variegatus Simon, 1877, ♀ (AMNH), abnormal three-ocellus condition with PLMi. B. C. variegatus, ♂ (AMNH [LP 6390]), abnormal three-ocellus condition with ALMa. C. C. variegatus, ♂ (AMNH [LP 6389]), Type 2A. D, E. Chaerilus chapmani Vachon & Lourenço, 1985, ♀ (AMNH), Type 2A on sinistral side (D), abnormal one-ocellus condition without MLMa (Type 1) on dextral side (E). F. Pseudochactas ovchinnikovi Gromov, 1998, subad. ♂ (AMNH), Type 1. G. Troglocormus ciego Francke, 1981, holotype ♂ (AMNH), Type 4C. H. Protoiurus kraepelini (von Ubisch, 1922), ♀ (AMNH), Type 4C. I. Calchas birulai Fet et al., 2009, ♀ (AMNH), Type 4C. J. Megacormus gertschi Díaz Najera, 1966, juv. ♂ (AMNH [LP 6474]), Type 4C. K. Euscorpius italicus (Herbst, 1800), ♂ (AMNH [LP 10297]), Type 3B. L. Troglocormus willis Francke, 1981, ♀ (AMNH), Type 3B. M. Chactopsis insignis Kraepelin, 1912, ♀ (AMNH [LP 8420]), Type 4C. N. Parascorpiops montana Banks, 1928, lectotype ♂ (MCZ), Type 3A. O. P. montana, paralectotype ♀ (MCZ), Type 2A. P. Alloscorpiops sp., ♀ (AMNH [LP 11279]), Type 4B. Q. Scorpiops feti Kovařík, 2000, ♀ (MCZ), Type 4B. R. Euscorpiops kaftani (Kovařík, 1993), juv. ♀ (AMNH [LP 11371]), Type 4B. Abbreviations: ADMi (anterodorsal minor ocellus); ALMa (anterolateral major ocellus); e (eyespot); MLMa (mediolateral major ocellus); PDMi (posterodorsal minor ocellus); PLMa (posterolateral major ocellus); PLMi (posterolateral minor ocellus). Scale bars  = 0.1 mm.
Figure 4
Figure 4. Lateral ocelli of Recent scorpions (families Chactidae Pocock, 1893; Iuridae Thorell, 1876; Troglotayosicidae Lourenço, 1998).
A. Megachactops kuemoi Ochoa et al., 2013, juv. paratype (AMNH [LP 9244]), Type 4C. B. Chactopsoides anduzei (González-Sponga, 1982), ♀ (AMNH), Type 4C. C. Taurepania porosus (Pocock, 1900), ♀ (AMNH [LP 5513]), Type 4C. D. Hadrurochactas machadoi González-Sponga, 1993, subad. ♀ (AMNH), Type 4C. E. Broteochactas nitidus Pocock, 1893, ♀ (AMNH [LP 1511]), Type 4C. F. Teuthraustes glaber Kraepelin, 1912, ♀ (AMNH), Type 3A. G. Vachoniochactas lasallei (González-Sponga, 1978), subad. ♂ (AMNH [LP 10000]), Type 4C. H. Chactas raymondhansi Francke & Boos, 1986, subad. ♀ (AMNH [LP 1586]), Type 2A. I. Troglotayosicus humiculum Botero-Trujillo & Francke, 2009, ♀ (AMNH), Type 2B. J. Brotheas granulatus Simon, 1877, ♂ (AMNH [LP 3656]), Type 4C. K, L. Neochactas delicatus (Karsch, 1879), ♀ (AMNH [LP 3441]), Type 4C (K), Type 3A (L). M, N. Anuroctonus phaiodactylus (Wood, 1863), ♂ (AMNH), Type 4C, sinistral side (M), dextral side (N). O. Hoffmannihadrurus gertschi (Soleglad, 1976), paratype ♀ (AMNH), Type 4C. P. Caraboctonus keyserlingii Pocock, 1893, ♂ (AMNH), Type 4C. Q. Hadruroides charcasus (Karsch, 1879), ♂ (AMNH), Type 4C. R. Hadrurus arizonensis Ewing, 1928, ♂ (IBUNAM), Type 3A. Abbreviations: ADMi (anterodorsal minor ocellus); e (eyespot); MLMa (mediolateral major ocellus); PDMi (posterodorsal minor ocellus); PLMa (posterolateral major ocellus). Scale bars  = 0.1 mm.
Figure 5
Figure 5. Lateral ocelli of Recent scorpions (families Bothriuridae Simon, 1880; Chactidae Pocock, 1893; Superstitioniidae Stahnke, 1940; Vaejovidae Thorell, 1876).
A. Superstitionia donensis Stahnke, 1940, ♀ (AMNH), Type 4C. B. Nullibrotheas allenii (Wood, 1863), ♀ (AMNH) Type 3A. C. Uroctonus mordax Thorell, 1876, ♂ (AMNH), Type 3A. D. Uroctonus mordax pluridens Hjelle, 1972, ♀ (AMNH [LP 2686]), Type 3A. E, F. U. m. pluridens, ♂ (AMNH [LP 2686]), Type 4C, dextral side (E), sinistral side (F). G. Uroctonites giulianii Williams & Savary, 1991, ♂ (AMNH), Type 3A. H. Paruroctonus surensis Williams & Haradon, 1980, ♂ (AMNH [LP 3139]), Type 3A. I. Smeringurus grandis (Williams, 1970), juv. ♀ (AMNH [LP 4462]), Type 3A. J. Vaejovis carolinianus (Beauvois, 1805), ♀ (AMNH [LP 8500]), Type 3A. K. Thorellius intrepidus (Thorell, 1876), ♀ (AMNH [LP 2022]), Type 3A. L. Stahnkeus subtilimanus (Soleglad, 1972), ♀ (AMNH), Type 3A. M. Bothriurus bonariensis (C.L. Koch, 1842), ♀ (AMNH), Type 3A. N. Timogenes mapuche Maury, 1975, ♂ (AMNH [LP 4312]), Type 3A. O. Vachonia martinezi Abalos, 1954, juv. ♀ (AMNH [LP 2441]), Type 2B. P. Centromachetes sp., ♂ (AMNH), abnormal four-ocellus condition with ADMi (Type 4C) on dextral side. Q. Lisposoma elegans Lawrence, 1928, ♂ (AMNH), abnormal four-ocellus condition with ALMa on dextral side. R. Lisposoma josehermana Lamoral, 1979, ♂ (AMNH), Type 3A. Abbreviations: ADMi (anterodorsal minor ocellus); ALMa (anterolateral major ocellus); e (eyespot); MLMa (mediolateral major ocellus); PDMi (posterodorsal minor ocellus); PLMa (posterolateral major ocellus). Scale bars  = 0.1 mm.
Figure 6
Figure 6. Lateral ocelli of Recent scorpions (families Diplocentridae Karsch, 1880; Hemiscorpiidae Pocock, 1893; Heteroscorpionidae Kraepelin, 1905; Hormuridae Laurie, 1896; Scorpionidae Latreille, 1802; Urodacidae Pocock, 1893).
Hemiscorpius lepturus Peters, 1861, ♂ (AMNH [LP 11080]), Type 3A. B. Heteroscorpion magnus Lourenço & Goodman, 2002, paratype ♂ (FMNH), Type 2B. C. Urodacus manicatus (Thorell, 1876), ♀ (AMNH), Type 2B. D. Cheloctonus jonesii Pocock, 1892, ♀ (AMNH), abnormal four-ocellus condition with PLMi (Type 4B) on dextral side. E. Cheloctonus jonesii Pocock, 1892, ♀ (AMNH), Type 3A. F. Hormiops davidovi Fage, 1933, ♀ (AMNH), Type 2B. G. Diplocentrus rectimanus Karsch, 1880, ♀ (AMNH [LP 2032]), abnormal four-ocellus condition with APLMi2 on dextral side. H. Nebo hierichonticus (Simon, 1872), ♂ (AMNH), Type 3A. I. Liocheles australasiae (Fabricius, 1775), ♀ (AMNH), Type 3A. J. Tarsoporosus macuira Teruel & Roncallo, 2010, ♂ (AMNH), Type 4B. K. Oiclus purvesii (Becker, 1880), ♀ (AMNH [LP 9037]), Type 2B. L. Pandinus gregoryi (Pocock, 1896), juv. ♂ (AMNH), Type 3A. M. Opistophthalmus jenseni (Lamoral, 1972), ♂ (AMNH), abnormal seven-ocellus condition with MLMa, PLMa, PLMi, PDMi, APLMi1, APLMi2 and APLMi3. N, O. O. jenseni, ♂ (AMNH [AH 4039]), abnormal five-ocellus condition with MLMa, PLMa, PDMi, PLMi and APLMi2 on sinistral side (N) and MLMa, PLMa, PDMi, PLMi and ADMi on dextral side (O). P. Opistophthalmus sp., ♂ (AMNH), Type 4B. Q. Scorpio maurus palmatus (Ehrenberg, 1828), ♂ (AMNH), Type 4B. R. Scorpio maurus palmatus (Ehrenberg, 1828), ♂ (AMNH), Type 3A. Abbreviations: anterodorsal minor ocellus (ADMi); APLMi1, APLMi2, APLMi3 (accessory posterolateral minor ocelli); MLMa (mediolateral major ocellus); PDMi (posterodorsal minor ocellus); PLMa (posterolateral major ocellus); PLMi (posterolateral minor ocellus). Scale bars  = 0.1 mm.
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SFL was supported by a fellowship from the Richard Gilder Graduate School of the American Museum of Natural History and a National Science Foundation Graduate Research Fellowship. Funding for this research was provided by a National Science Foundation Doctoral Dissertation Improvement Grant DEB 1310855 to LP and SFL. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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