Shin, Jong Hak ¹ ; Lee, Jimin ² and Chang, Cheon Young ³

¹Department of Biomedical Science, Daegu University, Gyeongsan 38453, Korea.
²Ocean Climate Response · Ecosystem Research Department, Korea Institute of Ocean Science and Technology, Busan 49111, Korea.
³✉ Department of Biomedical Science, Daegu University, Gyeongsan 38453, Korea.

2024 - Volume: 64 Issue: 1 pages: 244-255

ZooBank LSID: 81D43216-92C9-46BB-A72D-62922135F518

Original research

Keywords

Abstract

Introduction

The genus Agauopsis Viets, 1927 currently comprises 90 valid species, accounting for 7.6% of all species in the family Halacaridae. It is the third most diverse genus after Copidognathus Trouessart, 1888 with 380 species (32.2%) and Rhombognathus Trouessart, 1888 with 110 species (9.3%) (Bartsch 2015a; WoRMS 2023). In this genus, 79 species are allocated to seven different species groups: the brevipalpus, conjuncta, furcata, microrhyncha, okinavensis, ornata, and pugio (Bartsch 1986a, 1996a, 2005, 2015a; Bartsch and Iliffe 1985; Chatterjee et al. 2009; Macquitty 1983), and the remaining 11 species have not yet been clearly identified as part of any specific group. Among these groups, the brevipalpus group is the most species-rich group, comprising 25 species (Bartsch 2015a).

In the northwest Pacific region, 14 Agauopsis species have been documented to date: A. robusta Sokolov, 1952 from the Russian coast of Sea of Japan (Sokolov 1952); A. pseudoornata Bartsch, 1985 from Philippines (Bartsch 1985); A. okinavensis Bartsch, 1986 from Japan (Bartsch 1986a); A. ammodytes Bartsch, 1992, A. arenaria Bartsch, 1992, A. humilis Bartsch, 1992, and A. sordida Bartsch, 1992 from Hong Kong (Bartsch 1992a, 1992b); A. arborea Bartsch, 2003, A. dissimilis Bartsch 2015, A. longirostris Bartsch, 2015, A. moorea Bartsch, 1992, and A. sordida from Singapore (Bartsch 2015a, 2015b); A. ivanomorsellii Chatterjee & Chang, 2007, A. tetrasetosa Shin & Chang, 2019 and A. youngilensis Chatterjee & Chang, 2007 from South Korea (Chatterjee and Chang 2007; Shin and Chang 2019). Among them, only seven species belong to the brevipalpus group: A. arborea, A. dissimilis, A. ivanomorsellii, A. longirostris, A. moorea, A. sordida, and A. youngilensis.

This study deals with a new species of Agauopsis belonging to the brevipalpus group collected from mussels in the intertidal rocky shores on the southern coast of Korea, based on detailed illustrations and scanning electron microscope photographs of both females and males. Additionally, we provide a character comparison table of the A. brevipalpus group in the genus Agauopsis as well as a key to the 15 Agauopsis species known in the northwest Pacific.

Material and methods

Halacarid mites were collected from clumped mussels (Mytilus sp.) on rocks in the intertidal zone. Specimens were obtained by immersing the mussels in a bucket of tap water for approximately 10 minutes to induce osmotic shock, and rinsing through a nylon net (64 μm in pore diameter). Filtered specimens were immediately fixed with 80% ethanol or 5% formalin. Detailed methods for preparing slide specimens and creating illustrations are referenced from Lee et al. (2023), and scanning electron microscopy follows Lee and Chang (2017). Scale bars in the figures are in µm.

Type specimens are deposited at the Honam National Institute of Biological Resources (HNIBR), Mokpo, Korea.

Terminology and abbreviations in the text and figure captions follow Bartsch (2006): AD, anterior dorsal plate; AE, anterior epimeral plate; ds, dorsal setae on idiosoma (ds-1 to ds-6, first to sixth dorsal setae on idiosoma); GA, genitoanal plate; glp, gland pore(s), numbered glp-1 to glp-2 from anterior to posterior; GO, genital opening; OC, ocular plate(s); P, palp (P-1 to P-4, first to fourth palpal segments); pas, parambulacral setae; PD, posterior dorsal plate; PE, posterior epimeral plate; pgs, perigenital setae; sgs, subgenital setae.

Systematics

Subclass Acari Leach, 1817

Order Trombidiformes Reuter, 1909

Suborder Prostigmata Kramer, 1877

Superfamily Halacaroidea Cunliffe, 1954

Family Halacaridae Murray, 1877

Genus Agauopsis Viets, 1927

Agauopsis bisetosa n. sp.

ZOOBANK: 9E2A5B99-D7E7-4AF0-8D93-B5FB2E1ADA42

(Figures 1–4)

Type locality — Korea: Jeollanam-do, Yeosu-si, Sindeok-dong, Sindeok beach (34°49′05ʺN, 127°46′01ʺE), mussels (Mytilus sp.) attached to rocks, 0−0.5 m depth, 19 Aug. 2018, Shin J.H.

Type material — Holotype: ♀ (HNIBRIV11667), mounted in glycerin on H-S slide, from the type locality. Paratypes: ♂ (allotype, HNIBRIV11668) and 5♀♀, 4♂♂ (HNIBRIV11669–11677) mounted in glycerin on H-S slide from the type locality.

Additional material examined — 5♀♀, 5♂♂ on a stub for SEM, same data as for holotype.

Etymology — The specific name, bisetosa, refers to'two' ventral'setae' on the posterior epimeral plate, the unique feature of the new species.

Description of female (holotype) — Idiosoma (Figures 1A and 3A) 453 µm long (449–521 µm, mean = 471 µm, n = 6), 320 µm wide (317–401 µm, mean = 346 µm, n = 6), length to width ratio about 1.42; with a small frontal process; all dorsal plates well-developed, separated from each other by membranous cuticle, and covered with small pores (canaliculi) on surfaces excluding areolae and costae.

AD (Figure 1A) 149 µm long (144–164 µm, mean = 155 µm, n = 6), about 0.33 times as long as idiosoma, 160 µm wide (152–175 µm, mean = 165 µm, n = 6), length to width ratio 0.93; triangular-shaped, rounded posterolaterally, and concave medially at posterior margin;'H'-shaped areola protuberant (Figure 3C), decorated with 2−3 polygonal porose panels wide; each porose panels with 6−12 canaliculi (Figure 3D); anterior part of transverse ridge of'H'-shaped areola much shorter than rear part; pair of glp-1 located at anteromedial end of anterior arms of'H'-shaped areola.

OC (Figure 1A) 61 µm long (59–68 µm, mean = 64 µm, n = 6), about 0.13 times as long as idiosoma, 116 µm wide (112–125 µm, mean = 120 µm, n = 6), length to width ratio 0.53; narrowing posteriorly and pointed distally; posterior end extending near insertion of leg III; each with 2 corneae on raised transverse areola laterally; areola covered with 9−11 polygonal porose panels; glp-2 and pore canaliculi located at posterolateral to posterior cornea.

PD (Figures 1A and 3E) 238 µm long (236–257 µm, mean = 247 µm, n = 6), about 0.53 times as long as idiosoma, 218 µm wide (211–227 µm, mean = 221 µm, n = 6), length to width ratio 1.09; anterior margin almost truncate; narrowest at anterior 18% of PD, approximately 0.52 times as wide as PD; with 2 pairs of longitudinal costae, medial costae more distinct than lateral ones; medial costae gradually close to each other towards posterior margin, and each costa with 2−3 polygonal porose panels wide; each lateral costa narrow, with 1−2 polygonal porose panels wide; porose panels on costae consisting of 7−14 canaliculi; remaining area of PD covered with canaliculi (Figure 3F).

Dorsal setae (Figure 1A): ds-1 situated at anterior 38% of AD; ds-2 on membranous cuticle anterior to OC; ds-3 on membranous cuticle among AD, OC, and PD; 3 pairs of dorsal setae (ds-4, ds-5, and ds-6) at anterior 22%, 55%, and 100% of PD, respectively, of which anterior two (ds-4 and ds-5) situated at lateral edge of raised medial costae, ds-6 at posterior margin of PD.

All ventral plates (Figures 1B and 3B) well-developed and separated by membranous cuticle, and just as dorsal plates covered with small pores.

AE (Figure 1B) 191 µm long (188–216 µm, mean = 204 µm, n = 6), 298 µm wide (291–341 µm, mean = 322 µm, n = 6), length to width ratio 0.64; posterior margin straight or weakly convex; with 3 pairs of ventral setae; a pair of epimeral pores present near trochanter II; 2 pairs of lyrifissures (= pore canaliculi) located consecutively posterior to epimeral pores.

PE (Figure 1A, B) with 3 pairs of setae, consisting of 1 dorsal and 2 ventral setae; both ventral setae located at the level of insertion of leg III, each ventrolaterally and ventromedially (the latter indicated by an arrowhead); ventral seta lacking in coxal field at the level of insertion of leg IV.

GA (Figure 1B) 171 µm long (164–185 µm, mean = 177 µm, n = 6), 0.86 times as long as AE, 207 µm wide (201–218 µm, mean = 212 µm, n = 6), length to width ratio 0.83; anterior margin almost straight or slightly convex; distance from anterior margin of GO to that of GA, 40 µm, about 0.45 times length of GO; with 3 pairs of pgs located at anterior 23%, 53% and 67% of GA, respectively, foremost seta at the level similar to anterior end of GO, second pgs at the level of half of GO, and last seta at posterolateral margin of GO, both second and last setae close to GO; sgs absent. GO 89 µm long, about 0.52 times as long as GA.

Gnathosoma (Figure 2A) 131 µm long (128–138 µm, mean = 135 µm, n = 6), about 0.29 times as long as idiosoma, 76 µm wide (74–80 µm, mean = 78 µm, n = 6), length to width ratio 1.72; dorsal and ventral surface covered with punctate pores; with 4 pairs of setae, consisting of 3 pairs of setae on rostrum and 1 pair of setae on gnathosomal base; protorostral and deutorostral setae situated at tip of rostrum, tritorostral setae at anterior 20% of rostrum ventrally, and basirostral setae at anterior 15% of gnathosomal base; gnathosomal base about 2.05 times length of rostrum. Rostrum 43 µm long, 0.33 times as long as gnathosoma, its tip slightly reaching beyond end of P-3. Palp (Figures 2A, B and 4C) consisting of 4 segments, their lengths 7, 28, 9, and 9 µm, respectively; P-1 without setae; P-2 longest, with 1 dorsodistal seta; P-3 with 1 dentate spine (9 µm long, equal to length of P-3) medially; P-4 with 1 long dorsal and 1 short ventral setae proximally, and 3 spinelets at its distal end. Tectum truncated at its anterior margin (Figure 2B). Chelicera (Figure 2B) 56 µm long, 11 µm wide, reaching to anterior margin of rostrum.

All legs (Figure 2C–F) shorter than idiosoma, legs I–IV 367, 307, 340, and 345 µm long, respectively, and basifemora to tarsi I–IV with pores on surfaces. Chaetotaxy of all legs as follows: trochanters 1-1-1-0; basifemora 2-2-2-2; telofemora 7-6-3-3; genua 5-5-3-3; tibiae 9-6-5-5; tarsi (excluding pas and solenidion) 6-3-3-3. Trochanters III and IV about 2.23 times longer than trochanters I and II. Telofemur I armed with 1 ventral and 2 ventromedial bidentate spines. Genu I with 1 ventral and 1 ventromedial bidentate spines. Tibia I with 1 ventral and 2 ventromedial bidentate spines; tibia II with 1 ventral and 1 ventromedial bidentate spines; tibiae III–IV, each with 1 ventromedial bidentate spine. Tarsi I–IV 48, 55, 69, and 71 µm long, respectively; tarsus I (Figure 2C, G) with 3 dorsal, 2 ventral setae, 1 ventromedial bidentate spine, 1 tiny solenidion (indicated by arrowhead in Figure 2G), and a pair of doublet eupathid pas; tarsus I with a pair of smooth lateral claws, and bidentate median claw; tarsus II (Figures 2D, H and 4D) armed with 3 dorsal setae, 1 tiny solenidion, 1 lateral doublet (consisting of 1 eupathid and 1 short spinelet) and 1 medial spinelet pas; tarsi III–IV (Figure 2E, F) with 3 dorsal setae and 1 lateral spinelet pas, respectively; tarsi II–IV, each with a dorsal accessory process and 6–7 teeth on either side of curved area on lateral claw (Figures 2H and 4D), and without median claw.

Male (allotype) — Idiosoma (Figure 1C) 508 µm long (492–521 µm, mean = 508 µm, n = 5), 370 µm wide (362–401 µm, mean = 382 µm, n = 5). Similar to female, except for genital region. GA (Figures 1D and 4A, B) 197 µm long (188–206 µm, mean = 198 µm, n = 5), 0.98 times as long as AE, 221 µm wide (217–230 µm, mean = 224 µm, n = 5), length to width ratio 0.89; anterior margin concave; armed with 41 pgs, a pair of outlying pgs located at anterior 17% of GA, and 39 pgs arranged in two rows around GO (with a range of 36–42 pgs); with 5 pairs of sgs on genital sclerite, 2 pairs at anterior part and 3 pairs at posterior part, of which fourth sgs (14 µm long) larger than others (8 µm long) (Figures 1E and 4B). GO 84 µm long, about 0.43 times as long as GA; distance from anterior margin of GO to that of GA, 55 µm long, about 0.65 times length of GO. Spermatopositor large, its anterior end reaching to the level of insertion of leg III.

Remarks — Considering the classification by Bartsch (2015a), A. bisetosa n. sp. evidently belongs to the A. brevipalpus group with 25 congeners, and is characterized by the following combination of characters: AD with an'H'-shaped areola; PE with two ventral setae; P-4 with two basal setae and three apical spinelets; telofemur I with one ventral and two ventromedial dentate spines; and tibia II with one ventral and one ventromedial dentate spines.

In the brevipalpus group, the number of dentate spines serves as a highly valuable feature for easy identification (Bartsch 2015a). Notably, eight species including the new species, exhibit three dentate spines on telofemur I: A. newelli Krantz, 1973 and A. filirostris Macquitty, 1983 from U.S.A.; A. reticulatus Newell, 1984 from Chile; A. luxtoni Bartsch, 1986 and A. novaezelandiae Bartsch, 1986 from New Zealand; A. ivanomorsellii from Korea; and A. glabra Bartsch, 2009 from Australia (Bartsch 1986b, 2009; Chatterjee and Chang 2007; Krantz 1973; Macquitty 1983; Newell 1984). Among them, A. bisetosa n. sp. is closely allied with A. ivanomorsellii and A. luxtoni in sharing a short frontal process, the presence of an'H'-shaped areola on the AD, and two pairs of costae on the PD. However, the new species is distinguishable from them by the following characteristics (Table 1): (1) ds-4 is located on the PD in the new species and A. ivanomorsellii, whereas it is positioned on the membranous cuticle at the front of the PD in A. luxtoni; (2) PE has two ventral setae in the new species, while three ventral setae are present in A. ivanomorsellii and A. luxtoni; (3) the length ratio of rostrum/gnathosoma is 33% in the new species, whereas it is 45% and 40% in A. ivanomorsellii and A. luxtoni, respectively; (4) P-4 possesses three apical spinelets in the new species, while two spinelets are present in A. ivanomorsellii and A. luxtoni; and (5) the number of spines on tibiae II–IV is 2-1-1 spines in the new species and A. luxtoni, whereas A. ivanomorsellii has 3-2-2 spines.

In general, halacarid mites have one dorsal (or lateral) and three ventral setae on the PE (Abé 1998; Green and Macquitty 1987; Newell 1984). Despite the same is true within the genus Agauopsis, it is reduced to one or two setae in rare cases. In the genus Agauopsis, two species, A. bacescui Konnerth-Ionescu, 1977 and A. crassipes (Gimbel, 1920), belonging to the ornata and microrhyncha groups, respectively, have been recorded as bearing two ventral setae on the PE (Gimbel 1920; Konnerth-Ionescu 1977). In the brevipalpus group, A. bisetosa n. sp. is the sole species with two ventral setae on the PE. As for another member of the brevipalpus group, A. glabra, Bartsch (2009) described two ventral setae on PE for the female holotype, whereas three for one female and one male paratypes. Furthermore, in the holotype of A. glabra, the position of the two ventral setae on PE are different from that of A. bisetosa n. sp.: the rear seta locates near the coxal insertion of leg IV in A. glabra, while ventromedial corner of PE at the level of insertion of leg III in the new species (indicated by an arrowhead in Figure 1B).

Agauopsis ivanomorsellii and A. youngilensis, both of which are recorded in Korea and belong to the brevipalpus group as A. bisetosa n. sp. is, exhibit distinct morphological differences from the new species. The morphological differences between A. ivanomorsellii and A. bisetosa n. sp. have been already stated above. Besides the unique characteristic of two ventral setae on the PE, A. bisetosa n. sp. is discernible from A. youngilensis as follows: (1) presence of an'H'-shaped areola on the AD (versus an'M'-shaped areola in A. youngilensis); (2) telofemur I with three spines (versus four spines in A. youngilensis); (3) tibiae II–III with two and one spines, respectively (versus three and two spines, respectively, in A. youngilensis); and (4) male with 5 pairs of sgs (versus seven sgs in A. youngilensis).

Key to the species of Agauopsis recorded from the northwest Pacific

Below is a dichotomous key for known Agauopsis species from the northeast Pacific, including the new species from this study.

1. Palp with longest fourth segment (P-4); P-3 with a long medial seta
...... A. okinavensis (okinavensis group)

— Palp with longest second segment (P-2); P-3 with a medial spine
...... 2

2. Idiosoma with five pairs of dorsal setae
...... 3

— Idiosoma with six pairs of dorsal setae
...... 5

3. OC with two corneae; AE with garland-like areolae
...... A. pseudoornata (ornata group)

— OC without cornea; AE without areola
...... 4 (furcata group)

4. AD as long as OC length; telofemur I with one spine
...... A. ammodytes

— AD longer than OC; telofemur I with three spines
...... A. arenaria

5. P-3 with a pointed spine; tibia I with one ventral and three ventromedial spines, of which two ventromedial spines adjacent to each other
...... 6 (microrhyncha group)

— P-3 with a blunted spine; tibia I with one ventral and two ventromedial spines
...... 8 (brevipalpus group)

6. Ds-4 located on membranous cuticle between OC and PD; palp shorter than rostrum
...... A. humilis

— Ds-4 located on PD; palp longer than rostrum
...... 7

7. Tibia IV with two setae; females with three pairs of pgs
...... A. robusta

— Tibia IV with two spines; females with four pairs of pgs
...... A. tetrasetosa

8. Telofemur I with three spines
...... 9

— Telofemur I with four spines
...... 10

9. Tibia II with three spines; tibiae III−IV each with one ventral spine
...... A. bisetosa n. sp.

— Tibia II with four spines; tibiae III−IV with two ventral spines
...... A. ivanomorsellii

10. AD with'M'-shaped areola; ds-4 located on PD
...... A. youngilensis

— AD with'H'-shaped areola; ds-4 located on membranous cuticle between OC and PD
...... 11

11. Tibia II with two ventral spines; tibia III without spines
...... 12

— Tibia II with three ventral spines; tibia III with two ventral spines
...... 13

12. Rostrum as long as gnathosomal base; P-4 with one basal seta
...... A. dissimilis

— Rostrum shorter than gnathosomal base long; P-4 with two basal setae
...... A. arborea

13. Gnathosoma 2.1−2.3 times longer than wide; basifemur IV with one seta
...... A. longirostris

— Gnathosoma 1.8−1.9 times longer than wide; basifemur IV with two setae
...... 14

14. Tectum with scaliform lamella; male with 30 pgs; AE with polygonal porose panels consisting of 6−8 canaliculi
...... A. moorea

— Tectum with slightly arched lamella; male with 35–47 pgs; AE with polygonal porose panels consisting of 10−15 canaliculi
...... A. sordida

Conflict of interest

No potential conflict of interest relevant to this article was reported.

Acknowledgements

This research was supported by a Daegu University Research Grant, 2019.

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