Asymmetrione harmoniae, Williams & Boyko & Madad, 2019

Williams, Jason D., Boyko, Christopher B. & Madad, Asma Z., 2019, Branchial parasitic isopods (Crustacea: Isopoda: Bopyridae: Pseudioninae) of hermit crabs (Crustacea: Decapoda: Diogenidae) from the western Pacific, with descriptions of a new genus and three new species, Raffles Bulletin of Zoology 67, pp. 83-118 : 88-91

Asymmetrione harmoniae , new species

( Figs. 1C, D , 2, 3)

Asymmetrione nossibensis — Madad, 2008: 2, 5, 6, 16, 27, 28, 46, 47, 49, 51, 82, fig. 7F [ Philippines, infesting Dardanus lagopodes (Forskål, 1775) ] (not A. nossibensis Bourdon, 1976 ).

Material examined. Philippines: 1 dextral mature ♀ holotype (14.8 mm), 1 mature ♂ allotype (4.6 mm) ( ZRC 2018.0827 ), from right branchial chamber of ♂ Dardanus megistos (Herbst, 1804) (12.4 mm SL), Panglao, Momo Beach , Sta. M 7, reef platform with seagrass, 9°36.1′N, 123°45.2′E, 0–3 m, coll. Panglao Expedition 2004, 1 June 2004 ; 1 dextral ovigerous ♀ paratype (5.2 mm), 1 ♂ paratype (2.3 mm) ( USNM 1493915 ) from right branchial chamber of ♂ Dardanus lagopodes (Forskål, 1775) (3.8 mm SL), host also infested with Bopyrissa xiphidiostega , new species ( USNM 1493992 ), Mactan Island , Cebu, coll. P. Cassidy, 6 December 1996 ; 1 dextral ovigerous ♀ paratype (9.6 mm), 1 ♂ paratype (2.9 mm) ( USNM 1493916 ) from right branchial chamber of ♂ D. lagopodes (6.4 mm SL), Batangas, Sombrero Island , coll. JDW, 30 January 1999 ; 1 early juvenile non-type ♀ (2.3 mm), 1 non-type mature ♂ (2.0 mm) ( USNM 1493917 ) from right branchial chamber of ♀ D. lagopodes (2.3 mm SL), Batangas, Sombrero Island , coll. JDW, 30 January 1999 ; Indonesia: 1 dextral mature ♀ paratype (11.2 mm) ( ZRC 2018.0828 ), 1 mature ♂ paratype (3.0 mm), from right branchial chamber of ♂ D. lagopodes (6.9 mm SL), North Sulawesi, Tanjung Merah, coll. 31 March 2003 .

Description. Holotype female outline ovoid, body margins slightly distorted dextrally (~65°; paratypes up to 70°) (Fig.

2A); total length 14.8 mm, maximal width at third pereomere. Antennae and pereopods visible in dorsal view; head distinct from first pereomere, broader than long, surface smooth, front with broad recurved, medially notched lamina; anterolateral corners of head rounded; eyes and pigmentation absent. Maxilliped distally tapering, palp lacking, spur short and thin (Fig. 2H). Antennules of three articles each (Fig. 2C); basal article subquadrate with rounded lateral projection, lacking setae; second article subcylindrical, lacking setae; third article elongate with lateral indentations possibly indicating fusion of articles, tuft of apical setae. Antennae of six articles each (Fig. 2C); basal article ovate, lacking setae; article 2 ovate, lacking setae; articles 3–5 subcylindrical, distal articles progressively narrower, distalmost with ring of distal setae, terminal article minute, tuft of small setae at tip. Barbula with two pairs of acute, distally recurved, tapered, laterally smooth lobes, subequal in length; central region with narrow lateral area of irregular digitate projections (Fig. 2D, E). Pereomeres dorsally, ventrally and laterally distinct; narrow coxal plates on pereomeres 1–5 with large dorsolateral bosses; coxal plates and bosses absent on pereomeres 5–7 (Fig. 2A). Oostegites fully enclosing brood pouch (Fig. 2B); first oostegite (Fig. 2I, J) external surface smooth; anterior segment subtriangular, internal surface with posterior ridge entirely lined with numerous large digitate projections; posterior segment inner margin rounded, outer margin with posterolateral tapered projection; oostegites 2–5 large and ovate, increasing in size posteriorly, all with area of setae on anterior margins; fifth oostegite with posterior marginal fringe of setae (Fig. 2B). Pereopods subequal in shape but with proportionally longer ischia posteriorly (Fig. 2K, L), basis wide and subqudrate, ischium cylindrical with ventral edge bearing area of low tubercles, meri subquadrate, carpi conical, larger posteriorly, propodi swollen distoventrally with deep socket for insertion of dactyli; dactyli strongly recurved. Pleon approximately 35% as long as head plus pereon (Fig. 2A); five pleomeres plus pleotelson, all dorsally and laterally separated; pleomeres laterally rounded, 1–4 with large foliose lateral plates bearing tubercles on surfaces, pleomere 5 with pair of ovate, dorsally displaced lateral plates (Fig. 2F, G), surfaces smooth; five pairs of well developed biramous foliose pleopods, endopod and exopod (Fig. 2B) margins and surfaces covered in tubercles (Fig. 2B); uropods biramous, similar to pleopods, with tubercles on surfaces (Fig. 2A); pleotelson with medially placed anal cone flanked by pair of rounded, dorsally projecting, structures similar to lateral plates of fifth pleomere but smaller and more rounded (Fig. 2F, G).

Male ( Figs. 1D , 3) body unpigmented, elongated, all segments clearly separated dorsally, ventrally and laterally; head trapezoidal, indistinct from first pereomere, approximately 1.6 times as wide as long, anterolateral corners rounded and laterally produced; head approximately 85% as wide as first pereomere; eyes present posterolaterally; antennules of three articles each, antennae of six articles each, both distally setose (Fig. 3C). Maxilliped with elongate palp (Fig. 3D). Pereomeres not widely separated, maximal width at second and third pereomeres, gradually tapering anteriorly and posteriorly; midventral tubercles absent; generally isomorphic pereopods but with progressively smaller dactyli and propodi and larger ischia in posterior pairs (Fig. 3C, E). Pleon with five segments plus pleotelson. Pleomeres progressively narrower posteriorly, distinctly separated, posterolateral margins rounded and ventrally curved; globose uniramous medial pleopods on pleomeres 1–5 (Fig. 3B). Pleotelson with two elongate tapered posterolateral lobes (Fig. 3A, B); prominent medial anal cone present, small tuft of setae and region of scales on distolateral tips of projections (Fig. 3F); uropods absent.

Type locality. Panglao, Momo Beach, Sta. M 7, reef platform with seagrass, 9°36.1′N, 123°45.2′E, 0–3 m, Philippines .

Etymology. In Greek mythology, Harmonia was the daughter of Zeus and Electra and sister to Dardanus . The specific name is given because A. harmoniae , new species appears to be the sister species to A. dardani Bourdon, 1968 .

Distribution. Batangas, Cebu and Panglao, Philippines; Sulawesi, Indonesia.

Hosts. Diogenidae : Dardanus lagopodes (Forskål, 1775) , D. megistos (Herbst, 1804) .

Size range (length). Mean length of mature female specimens was 10.2 ± 4.0 mm (n=4). Mean length of male specimens was 3.2 ± 1.0 mm (n=4).

Remarks. Asymmetrione harmoniae , new species was originally identified as A. nossibensis by Madad (2008). However, Asymmetrione harmoniae , new species is distinct from all previously described species in the genus and most similar to A. dardani Bourdon, 1968 (see Figs. 180–182 in Bourdon, 1968) and A. globifera An, Markham & Yu, 2010 (see Fig. 1 in An et al., 2010). All three of these species have the fifth pleomere with ovate and dorsally displaced lateral plates as well as a pair of more spherical swellings on the dorsal surface of the pleotelson. The new species differs from both of those previously described in the following characters (those of A. dardani and A. globifera in parentheses): 1) female body right side second and third pereomere lateral margins moderately projected laterally (those of A. dardani and A. globifera much more strongly projected with A. globifera also having oostegites on those segments extending outward beyond the outline of the body); 2) barbula lateral projections smooth (also smooth in A. globifera but highly digitate in A. dardani ); 3) barbula central region with small area of numerous digitate projections laterally but smooth medially (similar condition in A. dardani but A. globifera with only three discrete projections laterally); 4) inner ridge of first oostegite with fringe of digitate projections along entire length (similar condition in A. dardani but A. globifera with only four stout digitate projections medially; 5) tubercles on margins of pereopods weakly developed (strongly developed in A. dardani ; not shown or described in A. globifera so unclear if they are lacking or merely overlooked); 6) dorsal lobes on pleotelson spherical in shape, lateral plates of fifth pleomere ovate (similar condition in A. globifera but both sets of structures in A. dardani are spherical); Male: 1) head trapezoidal (similar in A. globifera but ovate in A. dardani ); 2) eyes present (also present in A. globifera but lacking in A. dardani ); 3) antenna of six articles (also in A. dardani but with five articles in A. globifera ; 4) maxilliped palp elongate and distally tapered (stout in A. dardani ; condition unknown for A. globifera ); 5) lateral margins of pleomeres strongly curved ventrally (similar condition in A. globifera ; weakly directed ventrally in A. dardani ); 6) pleotelson with elongate distolateral lobes (similar shape in A. globifera ; short lobes in A. dardani ).

The peculiar ovate to spherical fifth pleomere lateral plates found on A. dardani , A. globifera and A. harmoniae , new species, are very similar to those seen in species of Pseudostegias Shiino, 1933 ( Bopyridae : Athelginae). However, although some species of Pseudostegias have dorsal structures on the pleotelson (see Williams & Boyko, 2016 ), none have paired spherical lobes similar to those found on these three species of Asymmetrione .

Yu & An (2008: 691) listed Asymmetrione dardani from the Chinese fauna but without mentioning the identity of the host; this record is questionable because A. dardani is otherwise known only from Morocco ( Bourdon, 1968). Although not included in a synonymy list for A. globifera in An et al. (2010), the specimens from the Yu & An (2008) record are most likely conspecific with A. globifera based on their locality (the material may even be the same as that upon which A. globifera was described). An et al. (2010) compared A. globifera to A. nossibensis Bourdon, 1976 but, as noted above, A. globifera is much more similar to A. dardani . Asymmetrione nossibensis lacks the globose fifth pleomere lateral plates and dorsal spheres on the pleotelson. An et al. (2010) reported A. globifera from both Dardanus hessii (Miers, 1884) and a Spiropagurus sp. but did not describe or illustrate the sole female found on the latter host; that specimen should probably be reexamined as its host identity shows doubt about its conspecificity with those found on D. hessii .

A juvenile female ( Fig. 1C ) already shows the development of the lateral plates on the fifth pleomere but does not yet show the dorsal swellings on the pleotelson. This specimen also shows how the birfucated frontal lamina develops by a weak subdivision in the medial region that becomes progressively larger as the individual matures.

Ecology. Prevalence was 0.99% (2 of 203 hermit crabs examined) in the one collection for which host data was available. In total, three mature specimens and one immature specimen of A. harmoniae , new species were extracted from the hermit crabs Dardanus lagopodes and D. megistos in the Philippines. This is the first record of Dardanus megistos as a host for this species; the other Philippine material from D. lagopodes was previously cited by Madad (2008) but misidentified as A. nossibensis . In addition, A. harmoniae , new species was found in D. lagopodes collected in Indonesia. One of the Philippine Dardanus lagopodes was doubly infested with A. harmoniae , new species in the right brachial chamber and Bopyrissa xiphidiostega , new species in the left brachial chamber.

Figures

Fig. 1. Asymmetrione asymmetrica (Shiino, 1933), USNM 1493912 (A, B), JDW pers. coll. (E), and Asymmetrione harmoniae new species, USNM 1493917 (C, D). A, mature female, dorsal view; B, male paired with female shown in A, dorsal view; C, immature female, dorsal view; D, male paired with female shown in C, dorsal view; E, lateral view of Calcinus minutus doubly infested with Asymmetrione asymmetrica and Dipterosaccus sp. (two externae indicated by *). Scale bars = 1 mm (A, B, E); 500 µm (C, D).