Thoracophoracarus (Thoracophorurus), K. Viets, 1942

Gerecke, Reinhard, 2009, Revisional studies on Thoracophoracarus K. Viets, 1914 (Arachnida, Acari, Hydrachnidia, Arrenuridae), Zoosystema 31 (1), pp. 127-145 : 136

Subgenus Thoracophorurus K. Viets, 1942

TYPE SPECIES. — Thoracophoracarus (Thoracophorurus) petioluriger K. Viets, 1925 .

Thoracophoracarus (Thoracophorurus) petioluriger K. Viets, 1925 ( Fig. 6 )

Thoracophoracarus petioluriger K. Viets, 1925: 234 , figs 1, 55.

Thoracophoracarus mammosus K. Viets, 1925: 235 , figs 2, 56, 57, n. syn.

TYPE MATERIAL. — Lectotype of T. petioluriger (here designated): Cameroon, Mbúle stream near village Mbúle (4 m large, 0.4 m deep, running into river Njong in front of village Mangélle) at railway km 215, 5.I.1916, Damköhler leg., 3146, leg-bearing ♂ specimen on slide SMF 47464.

Paralectotypes: 2 ♂♂ without legs, slide-mounted together with lectotype.

MATERIAL EXAMINED. — Lectotype of T. mammosus (here designated), same site and date as type specimens of T. petioluriger , the ♀ with undissected idiosoma on slide SMF 47467; paralectotype ♀ with dissected idiosoma, slide-mounted together with lectotype.

DESCRIPTION

Body colour probably deep blue (traces of the colour still visible in the slide-mounted specimens). Most glandular openings associated with distinct humps that rise above the idiosoma surface, in particular in the dorsocaudal area ( Fig. 6A, B, D, E ). Extensions associated with anterior antenniformia strongly projecting. Legs as described for T. arrhenuroides . Genital field and caudal idiosoma with strong sexual dimorphism, acetabular fields narrow, their tips reaching the lateral parts of the dorsum, with about 40-50 acetabula on each side. Excretory pore terminal. Palp in shape and setation ( Fig. 6C ) as described for T. arrhenuroides .

Male ( Fig. 6A, B ): in lateral view, idiosoma in the posterior third gradually flattened, in dorsal view posterior margin truncated, but with an irregular surface due to symmetrically-arranged humps. Humps at anterior margin strongly developed and pointed. On posterior surface of dorsum a strong triangular projection directed caudally. Caudal tip of idiosoma bearing a slender petiole located dorsally to the excretory pore, with two slightly developed lateral wings bent dorsally, in shape like a tongue rolled-up along the longitudinal axis; its distal margin indented. Gonopore away from the posterior margin of Cx-4, immediately anterior to excretory pore, directed ventrocaudally; acetabular fields forming a large obtuse angle directed caudally. Measurements: idiosoma L/W 560/355, Cx-4 W 410; acetabular field L/W 50/250; palp L/H P-1 -/- (lacking), P-2 46/33, P-3 29/30, P-4 51/25, P-5 20/9.

Female ( Fig. 6 C-E): idiosoma humps nearly as strongly developed as in males, particularly in the dorsocaudal area. Anterior humps more rounded than in males. Posterior margin between posteriormost humps concave. Gonopore directed ventrocaudally. Shape of acetabular fields not clearly discernible (destroyed and given only sketchy in the specimen depicted by K. Viets; hardly visible in the other, undissected specimen), extending as slender transverse strips laterally from the anterior gonopore edge. Measurements: idiosoma L/W 480-560/400, Cx-4 W 420; acetabular field L/W 145/350; palp L/H P-1 20/18, P-2 46/33, P-3 33/33, P-4 55/25, P-5 20/8.

REMARKS

Due to generally strong sexual dimorphism, attribution of males and females is a problem in arrenurid species and the number of erroneous interpretations, or open questions, is considerable. As a general rule, character states not (or little) subject to sexual differentiation regard colour, formation of integument, shape of coxae, dimensions and shape and setation of palps. In species collected together, a similar development of these characters suggests conspecifity. This hypothesis can be verified (or falsified) by: 1) repeated collecting of both genders in the same locality and habitat; 2) increased knowledge of intraspecific variability; and 3) rearing experiments. Without giving reasons, K. Viets (1925) did not follow this tradition in the case of T. mammosus , collected at the same site and date as T. petioluriger . Development of the symmetrically-arranged integumental humps, similarity in colour (not mentioned in the description of T. petioluriger ) and agreement in palp setation suggest that female T. mammosus and male T. petioluriger represent the same species. Minor differences between genders in the shape of the extensions flanking the anterior antenniform setae (in males more pointed and bent medially) and of P-4 (in males more stout and with the ventrodistal edge less projecting) are found in a similar manner in T. arrhenuroides . On this background I consider T.mammosus a junior synonym of T.petioluriger . This species differs from all other species of the genus in more distinctly projecting humps on the idiosoma surface (in particular the posterior ones). Both sexes are furthermore characterized (but similar to some other species) in P-1 being without a seta, P-2 with two mediodistal setae only and the gonopore directed ventrocaudally. The male of T. petioluriger is unique within the genus in the presence of the caudal petiole.However,a closer relationship between T. petioluriger and T. arrhenuroides (that would suggest the synonymy of the subgenus Thoracophorurus with Thoracophoracarus s.s.) cannot be excluded. A common character is the presence of a dorsocaudal extension in males.

Figures

FIG. 6. — Thoracophoracarus petioluriger K. Viets, 1925: A, B, lectotype ♂ (SMF 47464); A, ventral idiosoma; B, dorsal idiosoma; C-E, ♀ (SMF 47467) (“T. mammosus”, type specimens);C, palp,paralectotype; D, ventral idiosoma, paralectotype;E, dorsal idiosoma (drawn combining observations from lecto- and paralectotype on the same slide SMF 47467). Scale bars: 100 μm.