Dorceus C. L. Koch

Miller, Jeremy A., Griswold, Charles E., Scharff, Nikolaj, Řezac, Milan, Szűts, Tamas & Marhabaie, Mohammad, 2012, The velvet spiders: an atlas of the Eresidae (Arachnida, Araneae), ZooKeys 195, pp. 1-144 : 25-30

Dorceus C. L. Koch

Dorceus C. L. Koch, 1846: 15. C. L. Koch 1850: 70. Simon 1864: 300; 1892: 254; 1910: 290. Lehtinen 1967: 231. El-Hennawy 2002: 58. Type species Dorceus fastuosus C. L. Koch, 1846.

Note.

Dorceus contains five recognized species previously recorded only from North Africa. The genus was revised by El-Hennawy (2002). We examined specimens of Dorceus fastuosus C. L. Koch, 1846 from Israel and Senegal and the Tunisian holotype of Dorceus viberti Simon, 1910, which is a junior synonym of this species. The holotype of Dorceus fastuosus is a dry pinned specimen and was not examined. But we examined material that El-Hennawy examined for his 2002 revision (9126, AR5404, NMHN and 1237, AR 5405, NMNH) and compared to the holotype.

Diagnosis.

Distinguished from other eresid genera except Seothyra by the small median eyes subequal in size (Fig. 26C, G; AME/PME> 0.7), and the long, extensible ALS contrasting with reduced PLS (Fig. 32A; although ALS may be retracted and therefore not look so long); distinguished from other eresid genera except Loureedia gen. n., some Dresserus , and Paradonea splendens by the cephalic region, which is wider than long. Male distinguished from Seothyra by the subequal legs I and II (Fig. 26A; leg I enlarged in Seothyra , Figs 72A, 74A) and by the form of the conductor, which is a simple spiral or L-shaped hook shorter than the tegulum (Fig. 27 A–C, El-Hennawy 2002; highly variable and elaborate in Seothyra , usually longer than the tegulum; see Dippenaar-Schoeman 1990); distinguished from Loureedia gen. n. by the unbranched conductor (Fig. 27 A–C; bifid in Loureedia gen. n., Fig. 63D, E); distinguished from Dresserus by the lack of prominent tubercles bearing the ALE and the palpal conformation, which has a proximal-ventral axis with the helical embolus encircling the distal part (Figs 26I, J, 27 A–E; obliquely ventral-do rsal in Dresserus with the embolus encircling the ventral part, Figs 33 I–K, 34 A–D); from Paradonea splendens by the subrectangular shape of the cephalic region, which does not overhang the thoracic region posteriorly and the mesally contiguous chelicerae (Figs 8F, 26A, C; subtrapezoidal, slightly overhanging the thoracic region, chelicerae mesally excavated in Paradonea splendens , Fig. 68D, F). Female distinguished from Seothyra by the median lobe of the epigynum, which is as wide as long or wider with more or less straight, converging lateral margins (Figs 16B, 29C; clearly longer than wide with a central constriction in Seothyra ; see Dippenaar-Schoeman 1990); from Loureedia gen. n. by the small eyes subequal in size (Fig. 26C, G) and details of the female genitalia.

Distinguishing species.

Dorceus was revised by El-Hennawy in 2002. However, the quantity and quality of specimens available to him for several species was limited.

Phylogenetic affinities.

Past morphological studies have placed Dorceus and Seothyra as close relatives (Fig. 8A; Lehtinen 1967). A recent molecular study contradicted this hypothesis (Fig. 7B; Miller et al. 2010a). Although some of us were involved in that molecular study, we do not consider the question resolved. Morphological similarities, including features of the eyes and spinnerets, remain compelling. On the other hand, Peters (1992a) pointed out morphological characteristics shared (through parallel evolution) by Seothyra and the distantly related sparasid Leucorchestris arenicola exclusive of the eresid Stegodyphus , particularly the large ALS, which are extensible and retractable. This morphology is apparently linked to burrowing in loose sand, which Dorceus does as well. Whether these attributes ultimately prove to be the result of shared ancestry or convergence in Eresidae remains fertile ground for future study.

Natural history.

Known from sand dunes in deserts with very sparse shrub, grass, and annual herb patches. Juveniles feed on their mother’s corpse before dispersing ( El-Hennawy 1998; cf. Fig. 3D). Males take approximately 3 years to mature, females one year longer (Martin Forman, personal observation).