Listriella longipalma, Othman, B. H. R. & Morino, H., 2006

Othman, B. H. R. & Morino, H., 2006, Listriella longipalma sp. nov., a new amphipod species (Crustacea: Liljeborgiidae) from the Straits of Melaka, Malaysia, Zootaxa 1305, pp. 21-32 : 22-30

Listriella longipalma sp. nov

( Figs. 1–2 )

Material examined

Holotype, male, body length 3.7 mm (from tip of rostrum to apex of telson) (Ref: UKMMZ­1130); allotype, female, body length 3.5 mm (UKMMZ­1131); paratypes, 1 male, 10 females (UKMMZ­1132) and 1 male 5 females (Ibaraki University).

Type locality: Sg. Udang, Melaka, Straits of Melaka, Malaysia; latitude 2°09’N, longitude 102°19’E; Station 3.1.3, sandy mud bottom; 18/5/1997.

Male

Body moderately stout, laterally compressed, greatest width 24% of body length. Head slightly longer than pereonite 1, 6.4% body length, subrectangular, anterodorsal margin produced into small acute rostrum, ventral margin produced anteriorly and rounded. Eyes prominent, reddish brown, almost oval in shape with irregular margin. Pereonites 1–4 subequal in length, following pereonites progressively increase in length, pereonite 5 ca. 1.2 times as long as 1, pereonite 7 ca. 1.8 times of 1. Pleonites with serrated posterior margins interspersed with minute setules, most prominent on pleonite 3 with 11 posterodorsal teeth with minute setules.

Epimeron 1 anteriorly with sinuous margin and weakly produced anteroventral angle, posteriorly with convex margin bearing a notch at middle and another one just above pointed posteroventral angle, both lodging a minute seta each; in epimeron 2 anterior margin concave, anteroventral angle bluntly produced, posterior margin crenulated and bearing 2 setae, one at middle and another just above truncated posteroventral angle; epimeron 3 anteroventrally roundly produced with entire margin posteroventrally produced, armed with a small tooth at lower corner and forming a convex serrated margin above, serrated spines on posterior margin lodging a minute seta each, and ventral margin wide and evenly convex.

Urosomites 1–2 each with a dorsomedial tooth, one on urosome 1 flanked with a seta.

Antenna 1 short, extending up to peduncle of A2. Pedunclar article 1 of of A1 broad and long, longer than the next 2 articles combined, dorsal margin with a row of 5 setules and 2 setules at the distal end, ventral margin with a row of 6 setules and 6 setules in group at the distal end. Article 2 ca. 0.6 times as wide as article 1, with many setules on lateral margin. Article 3 short, 0.2 times as long and 0.4 times as wide as article 2, ventral and dorsal margin naked, lateral and distal margin with setules. Flagellum 8­articulate, ca. 0.5 times as long as peduncle, all articles except penultimate one with asthetascs. Accessory flagellum 2­articulate ca. 0.1 times as long as peduncle.

Antenna 2 ca. 1.5 times as long as A1, length ratio of peduncular articles 3–5 is 19:33:25. Article 3 with row of robust setae on dorsal margin, ventral margin naked except near distal end. Article 4 with row of robust setae on dorsal margin ending with bundles of setules near distal end, ventral margin with row of setules and ending with bundles of setules near distal end. Article 5, dorsal margin with 7 groups of setule bundles and ventral margin with 4 groups of setule bundles. Flagellum 1.7 times as long as article 5, 8­ articulate.

Upper lip with labrum broader than long and smaller than epistome, apical margin sinuous. Lower lip with distinct inner lobe, outer lobe oblong and apex with dense setae, mandibular process roundly produced.

Mandible incisors well developed, 5­dentate, lacinia mobilis prominent, also 5­ dentate, rakers with 8 stout blunt spines, longest near incisor with decreasing length towards molar, intermitantly with rows of setules, molar reduced represented by 3 setae. Palp 3­articulate, length ratio of articles 1:2:3 is 31:38:25. Article 1 naked, article 2 of right mandible with 1 medial seta and a row of 7 setae distally, article 3 with row of minute hairs beyond 1/3 of proximal end of inner margin interspersed by 10 short pectinate setae, apex with 4 long pectinate setae.

Maxilla 1 inner plate small, conical with 2 apical setae, outer lobe with 7 well developed pectinate spines, palp biarticulate, article 1 ca. 0.5 times legth of 2, naked, article 2 oblong with 3 stout apical spines and two rows of 8 medial setae.

Maxilla 2 inner plate slightly shorter than outer plate, both plates equal in breadth and apically rounded and armed with plumose setae.

Maxilliped inner plate small, conical with a short apical spine, 3 apical setae and a plumose seta on lateral margin. Outer plate reaching ca. 1/3 of article 2 of palp, distal border rounded with 3 apical robust setae, 2 apical setae, 4 medial setae and a row of hairs on lateral margin. Palp normal, length ratio of articles 1–4 is 10:25:15:12, article 1 with a medial seta, article 2 ca. 1.2 times broader than 1, with dense medial setae and lateral distal seta, article 3 ca. 0.6 times width of 2, with 6 medial setae, 4 lateral and 4 apical setae, distal end rounded with dense minute hairs, article 4 with a short seta and a tuft of fine hairs 1/3 length of lateral margin, medial margin with row of very fine hairs, tapering and terminating in an articulate stiff seta and a short stiff spine.

Coxal plate 1 almost as broad as coxa 2 and 3 combined, anteroventrally roundly produced and overreaching anterior margin of head, ventrally with evenly convex margin, and posteriorly with vertically straight margin, and posteroventral angle with a notch lodging a minute seta; coxae 2 and 3 very similar in size and shape, both oblong, as deep as coxa 1 but much narrower, anteroventral angle rounded, posteroventral angle with a notch bearing a minute setae and just after it with a setae on ventral side; coxa 4 largest, subquadrate, with anterior margin vertically straight and entire, ventral margin gently convex and with a minute seta at middle, posterior margin distinctly serrate throughout, excavate near its base, and all serrated notches lodging a minute seta; coxae 5 to 7 much shorter than preceding ones, all with a notch bearing a seta at posteroventral corner, coxa 5 and 6 ventrally indistinctly bilobed but 7 ventrally entire.

Gnathopod 1 larger than gnathopod 2, and strongly subchelate; length ratio of articles from basis to dactylus ca. 9:2:1:2:10:10; basis slender, longer than coxa (6:5), anterior margin with some 10 long and short setae while posterior margin with 5 long and one short setae; ischium, slightly excavate on anterior margin, with a seta on sub­posterodistal corner; merus subtriangular, anterior margin longer; carpus posterodistally with a set of 3 setae; propod, elongate, palmar margin medially deeply concave about its half length and concavity bearing several paired plumose setae inside and defined by 2 robust setae from posterior margin and a pair of robust setae followed by a single robust seta on distal prominence, distal prominence abruptly slope down and running towards distal end of propod, anterior margin normal and lacking setae; dactylus stout, curved, falcate, posterior grasping margin with a hump at about 1/3 length from proximal end and a series of tiny robust setae along its length.

Gnathopod 2 strong and subchelate; length ratio of articles from basis to dactylus ca. 9:3:3:4:8:5; basis slightly longer than coxa 2 (90: 88); anterior margin straight and with 7 long setae placed almost equally from distal to proximal ends, posterior margin gently expanded towards distal end but at 8/9 of its length from proximal end abruptly slope down as a notch and proximally with 5 long setae, medially with 2 short setae and anteriorly with 2 long plus one short setae; ischium, anterior margin medially convex and lacking setae, posterior margin with a pair of setae at 2/3 length from proximal end; merus, subrectangular, posterior margin with a set of 4 long setae on distal end and a single long seta at 2/3 length from proximal end; distal free margin with 4 robust setae of equal length and a single seta; carpus, subtriangular, anterior margin longer and with a short robust setae and a long seta on distal end, posterior margin shorter and with 2 long and 2 short setae; propod well broader but shorter than basis, oval, palm setose and with a row of robust setae throughout and defined by 3 apparent robust setae, posterior margin with a row of tuft setae of 3–4 along its length; anterior margin with a row of setae on its distal ½ length; dactylus stout, strongly curved, lacking setae on grasping margin.

Pereopod 3 slender, slightly longer than peraeopod 4; length ratio basis to dactylus almost 11:2:5:4:6:5; basis linear, almost equal in length to that of peraeopod 4; anterior margin proximally with 2 setae and distally with 3 setae, posterior margin with one seta at distal end and 6 setae placed in equal distance along its length; ischium, anterodistal ½ roundly expanded, with a short seta on posterodistal end; merus longer and wider than carpus, both with a seta each on anterodistal and posterodistal ends; propod longer than carpus, posterior margin with 2 minute setae, one at 2/3 and other at 1/3 lengths from proximal end, anterior margin medially gently convex; dactylus, slightly curved, tapering to pointed tip, with a single anteroproximal seta.

Peraeopod 4 very similar to peraeopod 3, length ratio of articles from basis to dactylus having ca. 11:2:5:4:6:5, but basis bearing 3 short robust setae and 4 long setae on posterior margin.

Peraeopod 5 length ratio of basis to dactylus ca. 10:2:7:6:6:3; basis broadly expanded, oval, produced posterodistally and forming distal margin bilobed, distal 2/3 length of posterior margin serrated and bearing 11 robust setae, one robust seta each on every denticle, a series of 9 robust setae of unequal length on distal ½ of anterior margin; ischium as long as wide, anterodistally with a set of 3 robust setae; merus, anterior margin straight with 2 robust setae carrying one at 1/3 and another at 2/3 lengths from proximal end and a pair of robust setae at distal end, posterior margin slightly expanding backward along its length except a proximal short distance, bearing a pair of robust seta at distal end; carpus slender, narrower than merus, anterior margin with 2 middle and one distal pair of robust setae, posterior margin with a single distal pair of robust setae, subapical margin with a pair of short robust setae; propod slender, anterior margin with a set of 2 very long plus 2 short robust setae on distal end and a pair of robust setae at 1/3 length from proximal end, posterior margin with 2 separate robust setae on distal end, a pair of robust setae and 2 separately placed single robust setae at ¾, ½, and ¼ lengths from proximal end; dactyusl hardly curved, gently tapering to pointed tip.

Peraeopod 6 longer than peraeopod 5, length ratio of basis to dactylus ca. 10:2:9:7:8:4; basis broadly expanded, elliptic, about ¼ as long as peraeopod 6, produced posterodistally and forming distal margin bilobed, posterior margin serrated throughout its length and bearing 16 robust setae, anterior margin with a pair of short robust setae at distal end, followed by another 6 short robust setae dispersed in line on distal ½ length; ischium, slightly longer than wide; merus, anterior margin straight but posterior margin slightly expanding backward medially, anterior margin distally with a set of 3 robust setae and medially with a pair of robust setae and a single robust seta, posterior margin with a pair of distal robust setae and 2 medial single robust setae; carpus slender, anterior margin distally with a set of 3 robust setae and medially with 2 pairs of robust setae placed at 1/3 and 2/3 lengths from proximal end, posterior margin with a pair of distal robust setae; propod narrow and long slender, distal margin with 2 very long and 3 short robust setae, anterior margin medially with 2 pairs of robust setae (each included one very long and one short robust setae), posterior margin with a single subdistal robust setae followed by 2 pairs of robust setae and a single robust setae placed in equal distance along its length; dactylus hardly curved, gradually tapering to pointed tip.

Peraeopod 7 length ratio of basis to dactylus ca. 7:2:6:8:7:3; basis broadly expanded, elliptic, about ¼ as long as peraeopod 6, distal margin medially concave, posterior margin distally 2/3 serrate and bearing 12 robust setae, anterodistally with a set of 3 robust setae, followed by a series 5 robust setae on distal ½ of anterior margin; ischium as long as wide, with a pair of anterodistal robust setae; merus wider than carpus, but slender, anterior margin with a set of 3 robust setae at distal end and 2 pairs of robust setae on medial part, posterior margin with a set of 3 robust setae at distal end and 3 single robust setae dispersed along its length; carpus slender, anterior margin distally with a set of 3 robust setae and medially with 3 pairs of robust setae equally far apart along its length, posterior margin distally with a set of 3 robust setae and medially with a single robust seta and a pair of robust setae placed at 2/3 and 1/3 lengths from proximal end; propod, anterior margin with a distal pair of robust setae and 3 medial pairs of robust setae, posterior margin with a set of 2 long plus 2 short robust setae at distal end, followed by a set of one short and 2 long robust setae, a pair of long robust setae and 2 single robust setae dispersed in equal distance along its length; dactylus straight, tapering to pointed tip, and spine like.

Pleopods well developed, similar, with stout peduncle and hairy rami; length ratio of peduncle to rami in pleopods 1, 2 and 3 ca. 8:9, 7:9 and 7:9, respectively.

Uropod 1 not extended beyond uropod 3, peduncle almost as long as rami, with 6 outer and 7 inner marginal robust setae, distolateral robust setae strong, rami equal in length, each with one apical robust setae and a pair of subterminal robust setae, outer ramus with 3 outer and 2 inner marginal robust setae, inner ramus with 4 outer and 2 inner marginal robust setae; uropod 2 shorter than uropod 1, peduncle subequal to rami in length and bearing one inner distal robust setae and 3 outer marginal robust setae, rami subequal in length, slightly shorter outer ramus with one apical robust seta, a subterminal robust seta, 3 outer marginal robust setae, inner ramus with one apical robust seta, a pair of subterminal robust setae, 3 outer submarginal robust setae and 2 inner marginal robust setae; uropod 3 extending far beyond others, peduncle shorter than rami, with one dorsodistal robust setae and 2 inner marginal robust setae, outer ramus fairly narrower and shorter than inner one, 2­articulated, distal article short, ending in a short distal spine­like nail, about 1/3 length of its ramus, proximal article with outer margin bearing a pair of strong robust setae at distal end and 3 other pairs of robust setae equally placed along its length, inner margin carrying single distal robust setae and 3 other robust setae placed in equal distance along its distal ½ length, inner ramus lanceolate, distally pointed and ending in a short nail, with outer margin distally bearing 2 single robust setae and inner margin distally carrying 2 single robust setae and one proximal robust setae.

Telson about ½ as long as uropod 3, deeply cleft to ¼ point from base, each lobe with a pair of apical robust setae, inner one of which longer than outer one, and with a short distolateral setae each.

Female

This species exhibits a strong sexual dimorphism, especially in coxa 1, dactylus and propod of gnathopod 1, antennular flagella, and pleon 3. In females, unlike the male, coxa 1 with anteroventral expansion not reaching anteroventral margin of head; gnathopod 1 with dactylus lacking protuberance on grasping margin and with palm smoothly convex, spinose and setose, defined by 2 stout distinct robust setae, and without excavation; gnathopod 2 in female almost similar to male, basis slightly slender and propod slightly broader than male and pleon 3 posterodorsally not being serrated.

Remarks

Barnard and Karaman (1991) compiled species belonging to the genus Listriella worldwide to consist of 35 species which have so far been described, and provided a key dividing the 5 genera of Liljeborgiidae as Idunella, Isipingus , Liljeborgia , Sextonia and Listriella . Of these, the two genera, Idunella and Listriella were noticably similar with some transition characters through the previous works of Barnard (1959), Rabindranath (1971), Karaman (1980), and Barnard and Karaman (1991).

Sars (1895) established the genus Idunella for the single species Liljeborgia aequicornis Sars 1876 , in 1979, Karaman added bowenae to the list, followed by chilkensis by Chilton (1921), curvidactyla by Nagata (1965), dahli by Schellenberg (1938), janisae , pauli and, serra by Imbach (1967), nagatai by Karaman (1979) pirata by Krapp­Schickel (1975) were described under this genus.

Barnard (1959) revised the diagnosis of the family Liljeborgiidae , in which the presence of an elongated article 1 in the mandibular palp, the geniculation of the mandibular palp between articles 1 and 2, and the telson splitting right down to its base were proposed to be characteristics of the family. He also created a new genus, Listriella composed of his 5 new species, goleta , diffusa , melanica , eriopisa and albina based on the gnathopods’ sizes being gnathopod 2 as large as or larger than gnathopod 1, and the two Idunella species, I. dahli and I. picta , were combined with his genus.

When studying many species of the genera Idunella and Listriella, Karaman (1980) merged the genus Listriella Barnard 1959 into genus Idunella Sars 1895 as synonym since any distinct taxonomic character dividing the species of both genera to each other was not observed. However, most of his Idunella species were found under the genus Listriella in Barnard & Karaman’s (1991) work.

Since the present specimens at hand hold such characters of 2 articulated accessory flagellum, feeble mandible molar process, powerful gnathopods, and incised telson with lobes bearing apical robust setae like in J.L. Barnard’s (1991) family diagnosis of Liljebergiidae, they fall under that family, and are further confirmed as the species belonging to Listriella by their elongated article 1 of mandibular palp.

The simple structure of molar process in mandible distinguishes the present specimens from the genus Sextonia . The anteriorly setose or naked condition of gnathopod 2 propod was found not to be a sound character used in separating Listriella from Sextonia in Barnard & Karaman’s (1911) key. There are many Listriella species with gnathopod 2 propod bearing setae anteriorly as in present specimens.

Since Barnard and Karaman (1991), only two species of Listriella have been described, namely L. kensleyi Ortiz & Lalana (1996) and L. andresi Martin et al. (2000) . When comparing the present specimens with 37 known Listriella species, they were found to be different in many respects from all of them, except for L. janisae . The following features that can distinguish congeneric 36 species from the present species: eyes absent ( L. albina J.L. Barnard 1959 , L. mollis Myers and McGarth 1983 ); accessory flagellum 3­ articulate ( L. saldanha Griffiths 1975 ); accessory flagellum 4­articulate ( L. lindae Griffiths 1974 a, L. sinuosa Griffiths 1974 b, L. bowenae Karaman 1979 , L.spinifera Dauvin and Gentil 1983 ); accessory flagellum 5­articulate ( L. smithi (Lazo­Wasem 1985)) ; dactylus of gnathopods strongly toothed ( L. picta (Norman 1889)) ; dactylus of pereopod 7 short and stout ( L. bahia McKinney 1979 ); palm transverse ( L. dahli ( Schellenberg 1938) , L. tintinga Wakabara , et al. 1988), ( L. andresi Martin et al. 2000 ); gnathopod 2 larger than gnathopod 1 ( L. melanica J.L.Barnard 1959 , L. m. lazaris J.L. Barnard 1959, L. kensleyi Ortiz & Lalana 1996 ), ( L. andresi Martin et al. 2000 ); mandible palp slightly geniculated ( L. curvidactyla ( Nagata 1965) , L. pauli ( Imbach 1967) , L. serra ( Imbach 1967) , L. brevicornis ( Ledoyer 1973) , L. quintana McKinney 1979 , L. dentipalma Dauvin and Gentil 1983 , L. orientalis Hirayama 1985 ); outer ramus of 3rd uropod 1­articulate ( L. chilkensis (Chilton 1921)) , L. diffusa J.L.Barnard 1959 , L. eriopisa J.L.Barnard 1959 , L. clymenellae Mills 1962 , L. demersalis ( Sivaprakasam1972) , L. excavata Krapp­Schickel 1975 , L. nagatai Karaman 1979 , L. sketi ( Karaman 1980) , ( L. andresi Martin et al. 2000 ); peduncle of uropod 1 with a row of close­set robust setae ( L. janisae (Imbach 1967)) ; L. similis Rabindranath 1971 ); telson cleft ½ ( L.barnardi Wigley 1966 ); telson lobes with 3 distal robust setae each ( L. goleta J.L.Barnard 1959 ); telson lobe with one distal robust setae ( L. nana Krapp­Schickel 1975 ); pleonites and urosomites with carina ( L. carinata McKinney 1979 ).

The present species is similar to L. janisae described from the South China Sea by Imbach (1967) in having dorso marginal dentation on pleonite 2, the similar shape and structure of the outer ramus of uropod 3, posteriorly serrated epimeron 3, etc., but do not agree with the latter, on the lack of a row of close­set robust setae on uropod 1 peduncle which is distinct in L. janisae , for extending of anterior expansion of coxa 1 beyond the head, and for possession of a wide and deep excavation on posterior margin of gnathopod 1 propod in the male. The last two features are characters found only in the present species and not found in all other known Listriella species.

Etymology

The specific name longipalma , refers to the elongate propod of the male gnathopod 1.

Figures

FIGURE 1. Listriella longipalma n. sp., holotype, male, (UKMMZ­ 1130 a­c), 3.7 mm, allotype, female, UKMMZ­ 1131, 3.5 mm. Sg. Udang, Melaka. Scales for A 1, A 2, G 1 ♂, G 2 ♂, HD represent 0.5 mm; G 1 Ψ, urosome represent 0.25 mm.

FIGURE 2. Listriella longipalma n. sp., holotype, male, (UKMMZ­ 1130 a­c), 3.7 mm, allotype, female, UKMMZ­ 1131, 3.5 mm. Sg. Udang, Melaka. Scales for P 3 ­ P 7 represent 0.5 mm; MP represents 0.2 mm; U 1 ­ U 3 represent 0.25 mm; MD, UL, MX 1, MX 2 and T represent 0.1 mm.