Rhombognathus levigatoides, Pepato & Da Rocha, 2007

Pepato, Almir R. & Da Rocha, Carlos E. F., 2007, Description of a new species of Rhombognathus (Halacaridae, Acari), its spermiogenesis and spermatozoa, Journal of Natural History 41 (37 - 40), pp. 2433-2445 : 2435-2440

Rhombognathus levigatoides sp. nov.

( Figures 1–8 )

Material examined

Holotype: female (MZUSP), on intertidal algae at Massaguaçu Island , Caraguatatuba, 16 March 2001, coll. BIOTA/FAPESP . Paratypes: three females ( Author’s collection), on intertidal algae at Massaguaçu Island, Caraguatatuba, 16 March 2001 , coll. BIOTA/ FAPESP; 12 females ( Author’s collection), on intertidal algae at Massaguaçu Island, Caraguatatuba, 16 March 2001 , coll. BIOTA/FAPESP; three males (MZUSP) on intertidal algae at Massaguaçu Island , Caraguatatuba, 16 March 2001 , coll. BIOTA/ FAPESP; 14 males ( Author’s collection), on intertidal algae at Massaguaçu Island, Caraguatatuba, 16 March 2001 , coll. BIOTA/FAPESP; three tritonymphs (MZUSP) on intertidal algae at Massaguaçu Island , Caraguatatuba, 16 March 2001 , coll. BIOTA/ FAPESP; six tritonymphs ( Author’s collection), on intertidal algae at Massaguaçu Island, Caraguatatuba, 16 March 2001 , coll. BIOTA/FAPESP; female ( Author’s collection), on intertidal rock shore at Martim de Sá Beach, Caraguatatuba, 19 September 2001 , coll. BIOTA/FAPESP; female ( Author’s collection), on intertidal rocky shore at Baleia Beach, São Sebastião, 16 October 2001 , coll. BIOTA/FAPESP; tritonymph ( Author’s collection), on Sargassum cymosum C. Agardh, 1820 at Lázaro Beach, Ubatuba, July 1991, coll. R. Curvelo ; female ( Author’s collection), on Sargassum cymosum C. Agardh, 1820 at Lázaro Beach, Ubatuba, July 1991, coll. R. Curvelo.

Description

Measurements as shown in Table I. Female. Dorsal plates almost smooth, lateral portions of PD, medial AD and OC pierced by canaliculi ( Figure 1A ). Medial PD slightly reticulated as shown in Figure 1B . Anterior dorsal plates with ds-1 at 0.45–0.56 of AD length, such setae 23–25 mm long. First pair of gland pores at same level as leg I insertion. Posterior line of muscle scars at 0.79–0.84 of AD overall length. Pairs of ds-2, ds-3, gp-2 and gp-3 on OC, which also bears a couple of corneae and a pore canaliculus. Length/height ratio of OC 1.80–2.34. Posterior dorsal plate with only pair of ds-4 at 0.11–0.18 of its length, and pair of gp-4 at its posterior margin. Anterior dorsal plate 1.00–1.18 as broad as PD. Adanal setae dorsal on anal papilla.

Gnathosoma short, length: width ratio equal to 1.00–1.23. Rostrum 26–30 mm long, 15– 18 mm wide, shorter than gnathosoma basis and as long as 0.36–0.41 times gnathosoma length.

Ventral plates AE, PE, and GA fused in a ventral shield, apart from anal plate by a band of membranous cuticle. Both AE and PE with single pair of adjunct setae. Genital area with five pairs of perigenital setae. Genital sclerites with two pairs of subgenital setae. Ovipositor 57–61 mm long, with three pairs of posterior and two pairs of anterior eugenital setae (only three individuals with everted ovipositor). Eugenital setae are strong dorsally pectinate spines ( Figure 1E ).

Leg chaetotaxy, bipectinate setae referred with roman numerals: leg I, 1,2,7,5,5(II),3; leg II, 1,2,7,5,5(I),3; leg III, 1,2,4,3,5(I),4; leg IV, 0,2,4,3,5(II),3. Telofemora I–IV with 5/2, 5/ 2, 3/1, and 3/1 dorsal/ventral setae; length: height ratio of telofemora I–IV: 1.94–2.17; 1.90– 2.36; 1.88–2.39; 1.77–2.29. Tarsus I with papiliform famulus, setiform solenidion and pair of doublet eupathidia ( Figure 2B ). Tarsus II with a setiform solenidion and a pair of doubled eupathidia ( Figure 2H ). Tarsus III with a single eupathid and a faintly pectinated spine. Tarsus IV with double slender setae and spine similar to that on tarsus III. Lateral claws welldeveloped, medial one lacking. Dorsal accessory process pectinate, with five to seven teeth.

Male. Similar to female in most features. Anterior: posterior dorsal plates width ratio 1.00– 1.21. Posterior line of muscle scars on AD at 0.74–0.79 of its length. Genital area with 18– 23 branched perigenital setae ( Figure 1C ). Genital sclerites with two pairs of subgenital setae. Spermatophorotype 40–49 mm long, 35–50 mm wide, surpassing anterior edge of GO by 16–22 mm. Tarsus IV with a plumose setae and a spine as parambulacral setae.

Tritonymph. Dorsal plates reduced, ventral plates AE, PE, and GP separated from each other by bands of striated cuticle. Chaetotaxy of epimeral plates similar to adults, although adjunct seta is lacking asymmetrically in some individuals. On genital plate, three pairs of setae, the medial one tiny and close to the primordial genital opening.

Leg chaetotaxy, bipectinate setae as Roman numerals: leg I, 1,2,6,5,5(II),3; leg II, 1,2,6,5,5(I),3; leg III, 1,2,4,3,5(I),4; leg IV, 0,2,2,3,5(II),3. Telofemora I–IV with 4/2, 4/2, 3/1, and 2/0 dorsal/ventral setae.

Remarks

Rhombognathus levigatoides sp. nov. shares with R. levigatus Bartsch, 2000 all diagnostic traits presented in the original description of the latter species: dorsal plates faintly ornamented; PD with a single pair of dorsal setae; AE, PE, and GP fused in a ventral shield; only an adjunct setae on AE and PE; female with five pairs of perigenital setae; male with 10–12 pairs of branched perigenital setae; gnathosoma short; telofemora I–IV with 5/2, 5/2, 3/1, 3/1 dorsal/ventral setae; accessory process with five to six teeth in R. levigatus and five to seven in the species described herewith. Rhombognathus levigatus was described from the Great Barrier Reef, Queensland, and the Dampier Archipelago, Western Australia ( Bartsch 2000, 2003b).

However, the Brazilian specimens differ from the Australian species in some measurements, allowing us to consider it to be a new species. Whereas ds-1 is 12 mm in the holotype of R. levigatus , it is 19–25 mm long in males and 23–25 mm long in females of Rhombognathus levigatoides sp. nov.; AD: PD width ratio is 0.85 in R. levigatus and 1.00– 1.21 in the new species described here; and, finally, in the Brazilian species the spermatophorotype is 40–49 mm long whereas in R. levigatus it measures 60 mm.

Figures

Figure 1. Rhombognathus levigatoides sp. nov. (A) Idiosoma, dorsal; (B) ornamentation at medial portion of PD; (C) genital opening; (D) idiosoma, ventral; (E) ovipositor; (F) gnathosoma, medial; (G) gnathosoma, ventral. (A, B, D–G) Female; (C) male. Scale bars: 50 mm (A, D); 25 mm (B, C, E–G).

Figure 2. Rhombognathus levigatoides sp. nov. (A) Leg I; (B) tarsus I; (C) tarsus IV; (D) leg IV; (E) tarsus IV; (F) leg II; (G) tarsus III; (H) tarsus II; (I) leg III. (A–D, F–I) Female; (E) male. Scale bars: 50 mm (A, D, F, I); 25 mm (B, C, E, G, H).

Figure 3. Rhombognathus levigatoides sp. nov., tritonymph. (A) Idiosoma, dorsal; (B) idiosoma, ventral; (C) leg I; (D) leg IV; (E) leg III; (F) leg II. Scale bars: 50 mm (A, B); 25 mm (C–F).

Figure 4. Two early stages of spermiogenesis. (A) First stage with batches of heterochromatin, and dense cytoplasm; (B) second stage without heterochromatin, picture shows single crest mitochondria (arrow) and Golgi body [G]; (C) second spermatid stage. Scale bars: 1 mm (A, C); 0.5 mm (B).

Figure 5. (A) Intermediate spermatids: note the plasmalemmal infoldings; (B) spermatids with heterochromatin almost fully condensed: note mitochondria [M] of the somatic tissue between spermatids, acrosomal vesicles [AV] and thick and linear acrosomal filament [AF]; (C) mature sperm cells within cytoplasm of the somatic cells of germinative portion of testis. Scale bars: 1 mm.

Figure 6. (A) Lumen of testis. Mature sperm cells are surrounded by somatic tissue and are delivered in testis lumen [Lu]. Then spermatozoa are coated with secreted material produced in the glandular portion: note microvilli and dense apico-lateral cell borders indicative of zonulae adhaerens among cells; (B) detail of a cell from the secretory portion of testis. N, nucleus. Scale bars: 1 mm.

Figure 7. (A) Mature spermatozoa; (B) striated body within sperm cell. AF, acrosomal filament; AV, acrosomal vesicle. Scale bars: 0.5 mm.

Figure 8. (A) Vas deferens; (B) ductus ejaculatorius, the wall is composed by a thin epithelium associated with muscle fibers (arrows): note amorphous secretion on the left side of the picture and spermatozoa surrounded by globular bodies of secretion; (C) light micrograph of a cross-section through a male Rhombognathus: note general aspect of prospective spermatophore, with a secreted center upon which the sperm is laid. MG, excretory portion of midgut; N, nucleus of epithelial cell. Scale bars: 2 mm (A); 1 mm (B); 25 mm (C).