A New Species of the Genus Agauopsis (Acari: Halacaridae) from Jeju Island, Korea

Abstract

A new marine halacarid species of the genus Agauopsis Viets, 1927 (Acari: Halacaridae) is recorded from Jeju Island, Korea. Agauopsis tetrasetosa n. sp. belongs to the microrhyncha group in sharing one ventral and three ventromedial spines on tibia of leg I, of which two ventromedial ones are adjacent to each other, with its 20 congeneric members. Agauopsis tetrasetosa n. sp. is most similar to A. miliaris Bartsch, 2005 and A. similis Bartsch, 1979 in sharing the similar chaetotaxy of legs I-IV, positions of the second and fourth dorsal setae, and non 'H'- or 'M'-shaped costae on anterior dorsal plate. However, the new species is distinguished from them by four pairs of perigenital setae in female, the relatively anterior location of gland pores on posterior dorsal plate, and three ventral spines on the tibia of leg II. We describe the new species herein, with detailed illustrations under a differential interference contrast microscope. We also make some brief comments on the affinities between the congeneric species of the microrhyncha group and the new species, based on a tabular key to species of the group.

INTRODUCTION

The genus Agauopsis Viets, 1927 is cosmopolitan, inhabiting the range from tidal to the abyss, and most records are from warm and temperate waters(Bartsch, 2006). Currently, 89 species or subspecies are recognized and account for the largest genus of all Halacarinae species described (WoRMS, 2019).

However, in the northwestern Pacific, the taxonomic study of the genus is rather scanty, and only nine species have been recognized: A. robusta Sokolov, 1952 from the Russian coast of the Sea of Japan (Sokolov, 1952); A. pseudoornata Bartsch, 1985 from Cebu, the Philippines (Bartsch, 1985); A. okinavensis Bartsch, 1986 from Okinawa Islands, Japan (Bartsch, 1986); A. humilis Bartsch, 1992, A. sordida Bartsch, 1992, A. ammodytes Bartsch, 1992, and A. arenaria Bartsch, 1992 from Hong Kong (Bartsch, 1992a, 1992b); and A. invanomorsellii Chatterjee and Chang, 2007 from Jeju Island and A. youngilensis Chatterjee and Chang, 2007 from Youngil Bay, Pohang, Korea (Chatterjee and Chang, 2007). So, this is the third record of the genus Agauopsis from Korea.

MATERIALS AND METHODS

Halacarids were collected by rinsing the coralline algae on the rocks around a tidal embankment at Sehwa port, which is situated at the northeast part of Jeju Island, South Korea, in April 2006. Algal samples gathered in several buckets or plastic bags were treated with same volume of freshwater for osmotic shock for about five minutes, and heavily swirled and rinsed, then filtered through a nylon net (64 μm in pore diameter) repeatedly. Specimens were fixed in 5% buffered formalin in the field, and substituted with 80% ethanol in the laboratory.

Halacarid specimens were soaked in lactic acid for 1-2 days on the H-S slide (Shirayama et al., 1993). Drawings were conducted for the type specimens on the H-S slide using a camera lucida under a differential interference contrast microscope (Olympus BX-50, Tokyo, Japan) with Nomarski optics. When needed, dissection was performed for the right appendages only in lactic acid on the H-S slide. Measurements were made using a digital camera for microscope (Cool SNAP 5.0M, Roper Scientific Co., USA) with a calibration software QCapture Pro (Media Cybernetics Inc., USA).

Type specimens are deposited at the Marine Interstitial fauna Resources Bank (MInRB) of Korea Institute of Ocean Science & Technology (KIOST), Busan, Korea. Some paratypes are also kept in the author’s(CYC) research collection at the specimen room of the Department of Biological Science, Daegu University (DB), Korea.

Abbreviations in the text and figure legends follow Bartsch (2006): AD, anterior dorsal plate; AE, anterior epimeral plate; ds-1 to ds-6, dorsal setae 1 to 6 on the idiosoma; ep, epimeral pore; GA, genitoanal plate; glp, gland pore; GO, genital opening; mc, membranous cuticle between plates; OC, ocular plate(s); P-1 to P-4, first to fourth palpal segments; PAS, parambulacral setae; PD, posterior dorsal plate; PE, posterior epimeral plate(s); PGS, perigenital setae; SGS, subgenital setae. The position of a seta is given in a decimal system, with reference to the length of a plate, from the anterior to posterior margin.

SYSTEMATIC ACCOUNTS

Subclass Acari Leach, 1817

Order Trombidiformes Reuter, 1909

Suborder Prostigmata Kramer, 1877

Superfamily Halacaroidea Murray, 1877

Family Halacaridae Murray, 1877

Subfamily Halacarinae Viets, 1927

Genus Agauopsis Viets, 1927

Agauopsis tetrasetosa n. sp.(Figs. 1-3)

Fig. 1. Agauopsis tetrasetosa n. sp. A-E, Female (holotype): A, Idiosoma, dorsal; B, Idiosoma, ventral; C, Costae on PD between ds-5 pair; D, Right side of PE, lateral view; E, Gnathosoma, ventral. F, Male (paratype, DB50029): chelicera. Scale bars: A, B=100 μm, C, D=50 μm, E, F=20 μm.

Fig. 2. Agauopsis tetrasetosa n. sp., female (holotype): A, Leg I, ventral; B, Leg II, lateral; C, Leg III, lateral; D, Leg IV, ventral; E, Tarsus I; F, Tarsus II. Scale bars: A-D=50 μm, E, F=20 μm.​​​​​​​

Fig. 3. Agauopsis tetrasetosa n. sp. A-D, Male (allotype): A, Idiosoma, dorsal; B, Idiosoma, ventral; C, GO and PGS; D, Gnathosoma, ventral. E, Male (paratype, DB50028): GO with abnormal SGS arrangement. Scale bars: A, B=100 μm, C-E=20 μm.​​​​​​​

Type locality. Korea: Jeju Island, Jeju-si, Gujwa-eub, Sehwa-ri (33°31ʹ48ʺN, 126°51ʹ22ʺE; among coralline algae upon the rocky shore, along the eastern tidal embankment at Sehwa port).

Type material. Holotype: ♀(MInRB-Hl02-L001), undissected and preserved in 80% ethanol. Paratypes: ♂(allotype, MInRB-Hl02-L002), undissected and preserved in 80% ethanol; 1♀, 2♂♂(MInRB-Hl02-L003), undissected and preserved in 80% ethanol; 1♀, 3♂♂(DB50027-50030), dissected, mounted in glycerine on H-S slide; 2♀♀, 1♂(DB 50031-50033), undissected, mounted in glycerine on H-S slide; 2♀♀, 7♂♂(DB50034), undissected and preserved in 80% ethanol. All type specimens collected on 23 Apr 2006 from the type locality.

Description. Female (holotype): Idiosoma (Fig. 1A) 487 μm long, 331 μm wide (length to width ratio 1.47), protruding anteriorly, forming triangular-shaped ‘frontal spine’, with simple, blunt tip. AD slightly longer than wide, 166 μm long, 158 μm wide (length to width ratio 1.05); longitudinal costae each with 2 porose-panels wide, not showing apparent ‘H’-shaped areola, lacking transverse ridge, slightly narrowing anteriorly; AD densely sculptured with numerous polygons; posterior margin forming thickened rim, gently concave anteriorly. Paired glp (gland pore) present near anterolateral corner.

OC (Fig. 1A) 126 μm long, 100 μm wide (length to width ratio 1.26); with 2 corneae, anterior one nearly circular (11 μm in diameter), posterior one ovoid (11×17 μm), slightly larger than anterior one; transverse porose areola present in the middle of OC; glands and pore canaliculi behind posterior cornea. Paired glp located at posterolateral to posterior cornea.

PD (Fig. 1A, C) 276 μm long, 197 μm wide (length to width ratio 1.40); anterior margin strongly convex or arched; paired middle costae 2 porose-panels wide, narrowing posteriorly to each other; rest of PD covered with numerous polygons and canaliculi; 6-9 canaliculi arranged around each polygon, as shown in Fig. 1C. Paired glp opened just ahead of level of ds-4.

Dorsal setae (Fig. 1A): ds-1 situated at 0.42 level of AD on anteromedial corner of costae; ds-2 locating near anterior corner of OC; ds-3 on mc among AD, OC and PD; ds-4 placed at 0.27 level of PD on anterolateral margin; ds-5 situated lateral to middle costae of PD at 0.56 level; ds-6 near posterior margin of PD.

All ventral plates separate and porose (Fig. 1B). AE about 2 times wider than long, 168 μm long, 308 μm wide (length to width ratio 0.55), with 3 pairs of ventral setae; 1 ep present near trochanter of leg II, on level of ds-2; paired lyrifissures (=pore canaliculi) situated posterior to epimeral pore, 5 μm wide at opening; posterior margin of AE nearly straight or slightly concave anteriorly. PE (Fig. 1B, D) with 1 dorsal seta and 3 ventral setae; anterior wing of PE forming costa along lateral margin, with porose-panels, anterior to level of leg III, as shown in Fig. 1D; numerous pits on lateral surface of posterior wing of PE, anterior to level of leg IV.

GA (Fig. 1B) 206 μm long, 178 μm wide (about 42% of whole idiosoma length), anteriorly truncate. GO (Fig. 1B) 78 μm long, 51 μm wide. Distance from anterior margin of GA to anterior tip of GO 100 μm, about 1.28 times as long as GO, pyriform. Four pairs of PGS arranging symmetrically; foremost seta slightly ahead of GO; succeeding seta positioned slightly posterolateral to midway of GO; next two adjacent to each other, situated nearly at level of posterior end of GO, respectively. SGS absent.

Gnathosoma (Fig. 1E) 138 μm long, 78 μm wide (length to width ratio about 1.77). Rostrum 4/5 times as long as gnathosomal base. Palp consisting of 4 segments; tip of rostrum extending to middle of P-4; lengths of P-1 to P-4 9, 38, 7, 19 μm long, respectively; P-1 devoid of any seta; P-2 elongate, 2 times longer than P-4, with 1 dorsal seta subdistally; P-3 armed with 1 naked spine inner subdistally, 9 μm long, subequal to length of P-3; P-4 tri-furcated apically, with 1 slender seta ventrally and 1 long, naked seta dorsally. Proto- and deutorostral setae situated at tip of rostrum; tritorostral seta located ventrally at distal 1/3 of rostrum; paired basirostral setae long, naked, situated at anterior 1/5 of gnathosomal base. Ventral surface of gnathosomal base porose. Chelicera slender, 105 μm long, 27 μm wide; slightly curved dorsally; armed with movable digit terminally, 22% as long as whole chelicera, its dorsal margin with row of minute teeth.

All legs (Fig. 2) porose on nearly whole surface. Leg I stout and longer than following legs. Chaetotaxy of legs: trochanter 1-1-1-0; basifemur 2-2-2-2; telofemur 8-5-3-3; genu 5-4-3-3; tibia 10-6-5-5; tarsus(PAS excluded) 7-4-3-3. Telofemur I with 1 ventral and 2 ventromedial spines; genu I with 2 spines, ventral spine shorter than ventromedial one; tibia I with 1 ventral and 3 ventromedial spines, of which 2 ventromedial spines adjacent to each other; tarsus I with 1 ventromedial spine. Tibia II with 2 ventral spines and 1 bipectinate ventromedial spine. Tibiae III and IV furnished with 2 ventral spines. Tarsus I (Fig. 2E) with 3 dorsal setae, 1 solenidion, 1 thick ventromedial spine, 2 ventral setae, and 2 doublets eupathid PAS. Tarsus II (Fig. 2F) with 3 dorsal setae, 1 solenidion, 1 spur-like and 1 eupathid PAS. Tarsi III and IV each with 3 dorsal setae and 1 spur-like PAS.

Claws on tarsus I(Fig. 2E) shorter than those on succeeding tarsi, smooth ventrally, devoid of accessory process; bidentate median claw present. Claws on tarsi II-IV with accessory process; pectine consisting of about 20-25 tines running along ventral margin of each claw, extending from proximal quarter to subdistal end, as shown in Fig. 2F; median claw lacking. Carpite on tarsus I small, but well developed on tarsi II-IV.

Male (allotype): Idiosoma (Fig. 3A) 479 μm long, 333 μm wide (length to width ratio 1.44), slightly broader than in female. AD slightly wider than long, 146 μm long, 152 μm wide (length to width ratio 0.96); ‘frontal spine’ triangular, with simple, blunt tip. OC (Fig. 3A) 119 μm long, 90 μm wide (length to width ratio 1.32). PD (Fig. 3A) 288 μm long, 214 μm wide (length to width ratio 1.35). Position of dorsal setae similar to that of female, except for ds-3, which adjacent to each other and nearer to anterior margin of PD than in female. AE (Fig. 3B) about 2 times wider than long, 151 μm long, 295 μm wide (length to width ratio 0.51).

GA (Fig. 3B, C) 209 μm long (about 43% of whole idiosoma length), 194 μm wide (length to width ratio 1.07). GO(Fig. 3C) 78 μm long, 35 μm wide, anterior portion protruding anteriorly, bottle-neck shaped. Distance from anterior margin of GA to anterior tip of GO 89 μm, about 1.14 times as long as GO. PGS comprising 42 setae around GO, excluding 1 pair of outlying setae slightly ahead of anterior tip of GO. Four pairs of short, spine-like SGS present, grouped as 2 pairs at nearly midway of GO and other 2 pairs at nearly posterior quarter of GO. Gnathosoma (Fig. 3D) 129 μm long, 73 μm wide (length to width ratio about 1.76). Palpal segments of P-1 to P-4 8, 34, 7, 17 μm long, respectively. Other characteristics nearly same as in holotype.

Measurements and variability. A total of 15 type specimens (five females and ten males) were examined and measured. In the five females examined, lengths of idiosoma ranged 466-508 μm (mean 487 μm, standard deviation 21.00), maximum widths 331-342 μm (mean 337 μm, standard deviation 5.51), mean ratio of length to width 1.45; number of PGS was consistent as four in each side, symmetrically. In the ten males examined, idiosoma lengths ranged 448-516 μm (mean 477 μm, standard deviation 20.04); maximum widths ranged 309-363 μm (mean 334 μm, standard deviation 14.12), mean ratio of length to width 1.43.

The number of PGS in female was consistent as four in each side, symmetrically. The number of PGS in male ranged 36-46 (mean 40), excluding one pair of outlying setae; one male paratype specimen showed an abnormal array in SGS, as 1+1 pairs(Fig. 3E). Among 10 males examined, a specimen showed an asymmetrical setal armature on tibia I, that is, bearing an additional ventral seta near proximal spine on tibia of left leg I.

Etymology. The proposed specific name, tetrasetosa, refers to the decisive characteristic of this new species, bearing four PGS on each side of GA in female.

Remarks. Considering the seta/spine ornamentation of the tibia I, which bears one ventral and three ventromedial spines including the two basal ones immediately adjacent to each other, A. tetraseta n. sp. should be allocated as a new member of the microrhyncha group (= “Key group 7000” in Newell, 1984) (see Bartsch, 1986, 1996, 2005, 2007; Otto, 1994). As yet 20 species have been known in this species group (Table 1).

Table 1. A tabular key to species of the microrhyncha group​​​​​​​

As shown in the Table 1, almost all of the members of this group have three pairs of PGS in the female except for A. insularis Newell, 1984 which bears six pairs, while the present new species is exceptional in having four pairs, as indicated in the specific name, tetrasetosa.

The ‘frontal spine’ on AD is somewhat variable in shape according to the species, and its style has been dealt as an important character (see Newell, 1984; Bartsch, 1996). Agauopsis tetrasetosa n. sp. has a triangular frontal spine, and shares it with eight congeners, A. bilophus Pepato and Tiago, 2003, A. crassipes (Gimbel, 1920), A. microrhyncha Trouessort, 1889, A. miliaris Bartsch, 2005, A. mokari Otto, 1994, A. pusilla Viets, 1950, A. similis Bartsch, 1979, and A. vinae Newell, 1984.

Among them, A. tetrasetosa n. sp. is most similar to A. miliaris from western Australia and A. similis from New Zealand in sharing the similar chaetotaxy of legs I-IV, positions of the ds-2 and ds-4, and non ‘H’- or ‘M’-shaped costae on AD (see Bartsch, 1979, 2005). However, besides the number of PGS in the female as already mentioned above, A. tetrasetosa n. sp. differs from the former in the location of gland pores on PD in both sexes, that is, situated ahead of ds-4 in A. tetrasetosa n. sp., while behind ds-4 in A. miliaris; from the latter, in the location of gland pores on PD (on the same level of ds-4) and less PGS in male (31 setae versus 36-46 in A. tetrasetosa n. sp.). Moreover, both the two congeners differ from A. tetrasetosa n. sp. in bearing two spines and one naked seta on ventral surface of tibia II (versus three spines in A. tetrasetosa n. sp.).

Agauopsis bilophus, described from Brazil by Pepato and Tiago (2003), is clearly discernible from A. tetrasetosa n. sp. in showing distinctly ‘M’-shaped costae on AD and in bearing two spines and a naked seta on ventral surface of tibia II. Agauopsis crassipes from West Africa shows a different style of long and narrow ‘frontal spine’(while much shorter with a blunt tip in A. tetrasetosa n. sp.), and the different armature on tibia I (three spines, versus four in the new species). Agauopsis microrhyncha from France is discriminated from A. tetrasetosa n. sp. by a little less PGS in male (34+2 setae versus 36-46+2 in A. tetrasetosa n. sp.) and by bearing two spines and one naked seta on ventral surface of tibia II. Agauopsis mokari, described from Australia by Otto (1994), is clearly distinguished from A. tetrasetosa n. sp. by a distinct ‘H’-shaped costae on AD, four spines on telofemur I and the gland pores on PD situated behind ds4. Agauopsis pusilla from the Antarctic Sea differs from the new species in the position of ds-2 on mc between AD and OC (versus on OC in A. tetrasetosa n. sp.) (see Viets, 1950). Agauopsis vinae described by Newell (1984) from the Antarctic Sea is discernible from this new species by nine setae or spines on tibia I(versus ten setae in A. tetrasetosa n. sp.).

In this species group, two species were recorded from the northwestern Pacific, A. robusta Sokolov, 1952 from the Russian coast of the Sea of Japan (Sokolov, 1952) and A. humilis Bartsch, 1992 from Hong Kong (Bartsch, 1992a). Both of them are clearly distinguished from the present new species by a truncated tip of the frontal spine. Furthermore, A. humilis is discriminated from the new species by the position of ds-4 and the number of setae on genu II (three in A. humilis versus four in A. tetrasetosa n. sp.); A. robusta differs from the present new species by two spines and one naked seta on ventral surface of tibia II.