Balaustium medicagoense Meyer & Ryke 1959
Creators: name: Xu, Si-Yuan
name: Zhang, Zhi-Qiang
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Trombidiformes
Erythraeidae
Balaustium
Balaustium medicagoense

description: Balaustium medicagoense Meyer & Ryke, 1959   
 Balaustium medicagoense Meyer & Ryke, 1959: 311 (Figs 10–14); Halliday 2001: 327.   
 Diagnosis. Larva. Palpfemur with one seta, palpgenu with four setae, fn BFe 4-4-3, fnTFe 5-5-5, fnTi 13-13-13; ASens and PSens both with fine setules all their length.   
Deutonymph and Adult. Scutum with only one pair of normal setae (AL), placed anterior to ASens. Palpgenu without semipectinalae. Coxae I and II, and trochanters I and II covered with rounded papillae (Adult).  
 Description. Egg (Fig. 1). The eggs are spherical or broadly elliptical (160 by 180 μm) and initially scarlet, becoming black after eight to twelve hours.   
 Larva (Figs. 2–15 & 37–38). The newly hatched larva is orange-red, gradually becoming scarlet after feeding on pollen (Fig. 2).   
Dorsum. Idiosoma almost oval, with 82 (fD=80–84) barbed setae, one pair of setae located between scutum and eyes at level with PSens bases (Figs. 3 –5 & 37–38). Scutum longitudinal, longer than wide, with indistinct lateral margin. Anterior margin almost straight or wavy, posterior margin V-shaped. Crista metopica distinctly vis- ible, between bases of ASens and PSens. Scutum with three pairs of normal setae (AL, ML and PL) (Figs. 4 & 37) or four pairs of normal setae (AL, ML, PL and PPL) (only two specimens) (Figs. 5 & 38) and two pairs of sensilla (ASens and PSens). All scutalae entirely barbed; AL subequal to ML <PL of scutum with three pairs scutalae; AL, ML and PL of similar length <PPL of scutum with four pairs scutalae (Table 1). AL located at the sclerotized area of scutum. ASens almost at level with AL bases, ASens and PSens both with fine setules all their lengths (Figs. 4–5 & 37–38).  
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a–e = scutum with three pairs scutalae, f–g = scutum with four pairs scutalae.  
 Venter. All ventral setae, including coxalae, barbed, and with pointed ends (Fig. 6). Three pairs of sternalae (intercoxal setae) (1a, 2a and 3a), 1a slightly longer than 2a and 3a; 1a located between and slightly posterior to coxae I, 2a between coxae II, and 3a almost at a line with anterior edges of coxae III. Three pairs of coxalae (1b, 2b and 3b), 1b and 3b subequal, slightly longer than 2b. 21–25 setae present between coxae II and III, 49–56 setae posterior to coxae III (fV=49–56). NDV= 132̅140.   
 Gnathosoma (Figs. 7–9). With one pair of barbed galealae (cs), one pair of spine-like setae (as), and one pair of barbed subcapitular (bs); bs longer than as, bs subequal to cs (Table 1). Palpfemur with one barbed dorsal seta; palpgenu with two barbed dorsal setae and two barbed ventral setae. Palptibia with one barbed ventral seta, one nude ventral seta, and one nude dorsal seta; palpal tibial claws simple with tooth-like protrusion located ventrally at c. half of the odontus length. Palptarsus with six setae, of which three nude, one barbed, one solenidion, and one eupathidium. fPp = B-B-BBBB-BNN-BNNNωζ. Palpal supracoxal setae (ep) peg-like.   
Legs (Figs. 6, 10̅15). With six free segments (femora subdivided). IP= 946̅1104. All leg tarsi terminated with two claws and claw-like empodium. Claw-like empodium with ciliations, longer and slender than lateral claws. Anterior claw falciform with ciliations. Posterior claw composed of two branches: one similar to anterior claw and another one pulvilliform. Normal setae on legs barbed and pointed. Leg setae formula: Leg I: Cx—1n; Tr—3n; Bfe—4n; Tfe—5n; Ge—1σ, 1κ, 8n; Ti—2φ, 1κ, 13n; Ta—1ω, 2ζ, 1Cp, 20n. Leg II: Cx—1n; Tr—3n; Bfe—4n; Tfe—5n; Ge—1κ, 8n; Ti—2φ, 13n; Ta—1ω, 2ζ, 20n. Leg III: Cx—1n; Tr—2n; Bfe—3n; Tfe—5n; Ge—8n; Ti— 1φ, 13n; Ta—1ζ, 21n.  
 Protonymph (Figs. 16 –17). Protonymph orange-red, oval, legless, and quiescent. The larval cuticle of beyond coxae II remains attached to the back of the body. Dorsal knobbed setae cover the body and eyes visible through the cuticle.   
 Deutonymph (Figs. 18 –23 & 39–40). Body broadly oval. Its color red to bright red (Fig. 18).   
Dorsum. Dorsal scutum elongate, length distinctly longer than width, with indistinct lateral margin (Figs. 20 & 39). Anterior margin almost straight, posterior margin deep V-shaped. Crista metopica inserted in scutum, between bases of ASens and PSens. Scutum with one pair of normal setae (AL) and two pairs of sensilla (ASens and PSens). AL located on scutum, anterior to bases of ASens. AL subequal to or slightly longer than ASens, but shorter than PSens. ASens and PSens both with fine setules all their lengths. One eye and one urnula on each side of scutum.  
Venter. Ventral setae thinner than dorsal setae, and setules of dorsal setae denser than ventral setae. Coxae I and II, and trochanters I and II without papillae (Fig. 40). Genital opening rudimentary, still closed, valves covered with two barbed setae; anus oval, with six nude setae (Fig. 21).  
 Gnathosoma (Figs. 22 & 23). Palpal supracoxal setae (ep) tiny and peg-like. Palp femur and palp genu longer than wide, PaFe L/W ratio = 1.51–1.88, PaGe L/W ratio = 1.32–1.46 (Table 2). Palp tibia triangular in outline with seven setae; palp tibial claws simple with tooth-like protrusion located ventrally at c. half of the odontus length. Palp tarsus cylindrical, rounded terminally, with one normal nude seta and c. ten solenidia.   
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 Legs. With six free segments (femora subdivided). IP= 2274̅2402 (Table 2). Leg IV slightly longer than Leg I; leg III the shortest, leg III is almost the same length as leg II. Supracoxalae of legs I (eI) and II (eII) tiny and peg-like; the ventral side of tarsi covered with brush-like setae, tarsi I had the largest number of brush-like setae. All leg tarsi terminated with two sickle-like claws, covered with fimbriae. Normal setae on legs barbed. Leg special setae formula: Leg I: Ge—2σ, 1κ; Ti—4φ, 1κ; Ta—~11ω, 4ζ. Leg II: Ge—1σ, 1κ; Ti—2φ, 1κ; Ta—2ω, 2ζ. Leg III: Ge—1σ; Ti—1φ; Ta—1ω, 2ζ. Leg IV: Ge—2σ; Ti—1φ; Ta—2ζ.   
 Tritonymph (Figs. 24 –27). Tritonymph orange-red or scarlet. In the initial phase of the tritonymph, it is morphologically to the deutonymph (Figs. 24 & 25). Subsequently, its morphological characteristics are similar to protonymph (Figs. 26 & 27).   
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 Adult (Figs. 28–36, 41 & 42). Idiosoma covered with thick setae, strong red to dark red in color (Fig. 28).   
Dorsum. Scutum longitudinal, length distinct longer than width, with middle part of the lateral margin indistinct (Figs. 30 & 41). Anterior margin slightly convex, posterior margin deep V-shaped narrower than in deutonymphs. Sclerotized part of crista metopica inserted between anterior and posterior sensillary areas linear in scutum. AL placed slightly anterior to bases of ASens; AL slightly longer than ASens, but shorter than PSens. ASens and PSens both with fine setules all their lengths. One eye and one urnula on each side of scutum (Fig. 29).  
Venter. Ventral setae slender than dorsal setae, and setules of ventral setae sparser than dorsal setae. The ventral view of coxae I and II and trochanters I and II covered with large numbers of conspicuous rounded papillae (Fig. 42).  
In females, genital opening (Fig. 31) at level of coxae IV; epivalves and centrovalves covered with needle-like nude setae; anterior part of centrovalves more sclerotized than epivalves. Anus oval, surrounded by sclerites with five pairs of nude setae.  
In males, genital opening (Fig. 32) oval; genital aperture slit-like. Genital valves covered with barbed setae and spine-like nude setae. External genital valves sclerotized, internal genital valves membranous and semitransparent. Internal genital organ strongly sclerotized (Fig. 33). Anus oval, with two pairs of valves; external anal valves with five nude setae on each side.  
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 Gnathosoma (Figs. 34–36). Setation on palps denser than in deutonymphs; palpal supracoxal setae (ep) tiny and peg-like. Palp femur and palp genu longer than wide; PaFe L/W ratio = 1.84–2.59, PaGe ratio = 1.55–2.17 in females (Table 3); PaFe L/W ratio = 1.76–2.12, PaGe ratio = 1.77–1.94 in males (Table 4). Palp tibia subtriangular in outline with seven setae; palp tibial claws simple with tooth-like protrusion located ventrally at c. half of the odontus length. Palp tarsus cylindrical, rounded terminally, with one normal nude seta and c. 14 solenidia.   
 Legs. With six free segments (femora subdivided). IP= 3129–3798 in females (Table 3); IP= 3669–3988 in males (Table 4). Leg I slightly longer than leg IV; leg II the shortest, leg III slightly longer than leg II. Supracoxalae of legs I (eI) and II (eII) tiny and peg-like; the ventral side of tarsi covered with brush-like setae, tarsi I with the largest number of brush-like setae. All leg tarsi terminated with two sickle-like claws, covered with fimbriae. Normal setae on legs barbed. The formula of special setae on a leg of females and males are different, particularly, the males with a large number of solenidia on TFe I and the females without solenidion on TFe I. In males with ~31 solenidia on Ge I and with ~34 solenidia on Ti I, in females with four solenidia on Ge I and with six solenidia on Ti I. Leg special setae formula by following: In females: Leg I: Ge—4σ, 1κ; Ti—6φ, 1κ; Ta—~18ω, 4ζ. Leg II: Ge—2σ, 1κ; Ti—3φ; Ta—4ω, 4ζ. Leg III: Ge —2σ; Ti—2φ; Ta—1ω, 2ζ. Leg IV: Ge—3σ; Ti—3φ; Ta—2ω, 2ζ. In males: Leg I: TFe—~23θ; Ge—~31σ, 1κ; Ti—~34φ, 1κ; Ta—~32ω, 2ζ. Leg II: Ge—2σ, 1κ; Ti—4φ; Ta—4ω, 4ζ. Leg III: Ge—2σ; Ti—2φ; Ta—1ω, 2ζ. Leg IV: Ge—3σ; Ti—3φ; Ta—2ω, 2ζ.   
 Examined material: Adult, 2 ♀, University of Auckland Tamaki campus, ex. gorse, 8 Jan. 2020, coll. S.-Y. Xu; 1 ♀, same location and host as the specimens collected on January 8, except 9 Jan. 2020, coll. S.-Y. Xu; 1 ♀, same location and host as the specimens collected on January 8, except 13 Jan. 2020, coll. S.-Y. Xu; 1 ♀, same location and host as the specimens collected on January 8, except 3 Feb. 2020, coll. S.-Y. Xu; 1 ♀, same location and host as the specimens collected on January 8, except 17 Mar. 2020, coll. S.-Y. Xu; 2 ♀, laboratory culture, 31 Mar. 2020, coll. S.-Y. Xu; 4 ♀, laboratory culture, 2 Apr. 2020, coll. S.-Y. Xu; 4 ♀, laboratory culture, 3 Apr. 2020, coll. S.-Y. Xu; 1 ♁, same location and host as the specimens collected on January 8, except 11 Jan. 2020, coll. S.-Y. Xu; 1 ♁, same location and host as the specimens collected on January 8, except 16 Jan. 2020, coll. S.-Y. Xu; 1 ♁, same location and host as the specimens collected on January 8, except 19 Feb. 2020, coll. S.-Y. Xu; 2 ♁, same location and host as the specimens collected on January 8, except 17 Mar. 2020, coll. S.-Y. Xu; 1 ♁, laboratory culture, 1 Apr. 2020, coll. S.-Y. Xu; 1 ♁, laboratory culture, 2 Apr. 2020, coll. S.-Y. Xu; 2 ♁, laboratory culture, 3 Apr. 2020, coll. S.-Y. Xu; 2 ♁, laboratory culture, 5 Apr. 2020, coll. S.-Y. Xu; 2 deutonymphs, laboratory culture, 15 Feb. 2020, coll. S.-Y. Xu; 1 deutonymph, laboratory culture, 17 Feb. 2020, coll. S.-Y. Xu; 1 deutonymph, laboratory culture, 24 Feb. 2020, coll. S.-Y. Xu; 1 deutonymph, laboratory culture, 7 Mar. 2020, coll. S.-Y. Xu; 2 deutonymphs, laboratory culture, 8 Mar. 2020, coll. S.-Y. Xu; 1 deutonymph, laboratory culture, 11 Mar. 2020, coll. S.-Y. Xu; 2 larvae, same location and host as the specimens collected on January 8, except 5 Feb. 2020, coll. S.-Y. Xu; 5 larvae, same location and host as the specimens collected on January 8, except 6 Feb. 2020, coll. S.-Y. Xu; 1 larva, same location and host as the specimens collected on January 8, except 2 Mar. 2020, coll. S.-Y. Xu; 1 larva, same location and host as the specimens collected on January 8, except 3 Mar. 2020, coll. S.-Y. Xu; 3 larvae, same location and host as the specimens collected on January 8, except 4 Mar. 2020, coll. S.-Y. Xu; 1 larva, same location and host as the specimens collected on January 8, except 6 Mar. 2020, coll. S.-Y. Xu; 1 larva, laboratory culture, 29 Jan. 2020, coll. S.-Y. Xu; 1 larva, laboratory culture, 4 Feb. 2020, coll. S.-Y. Xu; 1 larva, laboratory culture, 9 Feb. 2020, coll. S.-Y. Xu; 1 larva, laboratory culture, 13 Feb. 2020, coll. S.-Y. Xu; 1 larva, laboratory culture, 18 Feb. 2020, coll. S.-Y. Xu; 1 larva, laboratory culture, 23 Feb. 2020, coll. S.-Y. Xu; 2 larvae, laboratory culture, 6 Mar. 2020, coll. S.-Y. Xu; 2 larvae, laboratory culture, 7 Mar. 2020, coll. S.-Y. Xu.   
 Distribution. New Zealand (Auckland); South Africa (Meyer & Ryke 1959); Australia (Halliday 2001).   
 Remark. Our adult specimens agree well with previous descriptions of this species (Please see Table 5 for comparisons) (Meyer & Ryke 1959; Halliday 2001); the New Zealand specimens are slightly smaller in size than South African ones as reflected in body size and a few other associated measurements. We interpret this as intraspecific geographic variation. Halliday (2001) examined adult specimens of B. medicagoense from Australia and South Africa, where he found a new consistent character: papillae on coxae I and II, and trochanters I and II. We also found these papillae on coxae I and II, and trochanters I and II in specimens collected in Auckland, New Zealand.   
 According to the key to species of Balaustium in Noei et al. (2019a), the larvae of B. medicagoense and B. brunoni Haitlinger, 2005 are very similar. The larvae of B. medicagoense can be separated from B. brunoni (Haitlinger 2005) by the following features: they differ in Ti setae formula (13-13-13 vs. 13-11-11), and in the shaped of scutum (the lateral margin is indistinct or absent, posterior margin V-shaped in B. medicagoense vs. the lateral margin is distinct, posterior margin approximately arched (according to the original illustration of B. brunoni).
description: Published as part of Xu, Si-Yuan & Zhang, Zhi-Qiang, 2020, Balaustium medicagoense Meyer & Ryke, 1959 newly discovered in New Zealand (Acari: Erythraeiddae): descriptions of all life stages, pp. 125-153 in Zootaxa 4900 (1) on pages 126-150, DOI: 10.11646/zootaxa.4900.1.9, http://zenodo.org/record/4409078