Phoxocephalus tiomanensis, Shin & Azman & Kim, 2015

Shin, Myung-Hwa, Azman, B. A. R. & Kim, Won, 2015, A new species of the genus Phoxocephalus from Pulau Tioman, Malaysia (Crustacea: Amphipoda: Phoxocephalidae), Raffles Bulletin of Zoology 63, pp. 529-535 : 530-535

Phoxocephalus tiomanensis , new species

( Figs. 2–4 )

Type material. Holotype — male (body length 3.03 mm) ( UKMMZ – 1532), Abect’s House Reef, Kg. Tekek, Pulau Tioman, Pahang, 2°49’05.0”N 104°09’15.0”E, Light-trap, 8 m, coll. Y.K., Tan et al., 23 May 2014 . Paratypes — 5 males, 2.7–3.0 mm ( UKMMZ – 1534) ; 3 males, 2.7–2.9 mm ( MADBK201906 _001) ; 5 males, 2.8–3.0 mm ( ZMB 28477) , all with same data as holotype .

Type locality. Abect’s House Reef, Kg. Tekek, Pulau Tioman, Pahang, Malaysia .

Description of holotype ( Figs. 2–4 ). Head ( Fig. 4 HD) about 15 percent of total body length, rostrum curved downwards, unconstricted, broad, extending slightly beyond penduncular article 1 of antenna 1, hood-like. Eyes subcircular, large.

Antenna 1 ( Fig. 2A 1 ), peduncular article 1 stout, about 1.2 times as long as wide, about 2.3 times as wide as article 2, pubescent on distal half of ventral margin; article 2 about 0.4 times article 1 length, with 4 posterodistal setae; main flagellum 5-articulate, about 2 times as long as peduncular article 1, bearing aesthetascs; accessory flagellum 3-articulate.

Antenna 2 ( Fig. 2A2 ) about 0.6 times body length; peduncular article 3 with long setae on anterior margin; peduncular article 4 obliquely truncated, with long setae along anterior margin and 4 distal robust setae; posterior margin short, with long robust setae; peduncular article 5 slightly shorter than article 4, provided with facial robust setae; flagellum with 17 articles, about 4 times as long as articles 1–5 of peduncle combined.

Mandible ( Fig. 4 MDl) rather slender with medium palpar hump; incisor and lacinia mobilis broad, serrate; 3 accessory spines finely pectinate; molar process triturative, distinctly protruded; molar rasp tuberous; palp 3-articulate, almost uniform in width; palp article 1 small; palp article 2 slightly longer than article 3, with 2 inner distal setae; palp article 3 obliquely truncate, with 11 apical long setae.

Upper lip ( Fig. 4 UL) broad. Lower lip ( Fig. 4 LL) mandibular process reduced; shoulders triangular.

Maxilla 1 ( Fig. 4 MX 1) inner plate medium; outer plate provided with one trifid, 2 bifid, and 4 simple tooth-like spines (all simple spines serrate unilaterally); palp uniarticulate, slightly extending beyond outer plate, with 3 apical robust setae.

Maxilla 2 ( Fig. 4 MX 2) inner plate shorter than outer, with facial oblique row of 4 robust setae; outer plate with 4 apical robust setae.

Maxilliped ( Fig. 4 MP) rather slender; inner plate small, with 3 apical setae; outer plate not reaching middle of palp article 2, provided with 2 short and 2 mid-length robust setae on margin; palp articles 2–3 with short and long robust setae along inner margin, article 3 with one facial seta, no setae in outer margin; nail of article 4 long and falcate, with two accessory setules.

Gnathopod 1 ( Fig. 2G 1 ) similar to gnathopod 2 in shape. Coxae 1–2 subrectangular, with 5 and 4 subdistal simple setae on posterior half of ventral margin. Gnathopod 1, basis longest, slightly expanded posteriorly, posterior margin with 2 long setae, one medium seta and one distal short seta, anterior margin with one distal short seta. Ischium short with one short posterodistal seta. Merus about 0.6 times carpus length, meeting middle expansion of carpus with one posterodistal short seta; carpus growing at proximal part of merus, furnished with 2 medium length setae, concave in distal half of its posterior margin, concavity of which receiving propodus. Propodus subrectangular, provided with one robust seta and one tooth posterodistally; palm slightly transverse with stout and small robust setae. Dactylus falcate, reaching inner side of posterodistal tooth, with one short plumose seta at 1/3 length along anterior margin.

Gnathopod 2 ( Fig. 2G2 ) slightly larger than gnathopod 1. Basis posterior margin with one long marginal seta and one medium length distal seta. Ischium short with one short posterodistal seta. Merus slightly longer than ischium with one short posterodistal seta. Carpus about same length as merus, with 2 posteroproximal setae. Propodus longer than broad, with nearly parallel lateral margin, and with transverse palm defined by strong corner tooth bearing one robust seta at outer margin. Dactylus with one short plumose seta at outer margin.

Pereopods 3–4 ( Fig. 3P3–P 4 ) similar to each other. Coxa 3 subrectangular, ventral margin with 4 posterior submarginal medium length setae. Coxa 4 posterior margin deeply excavated. Pereopod 4 ischium with one short posterodistal seta; merus 2.2 times carpus length; carpus short, slightly longer than broad, bearing 3 long setae middle part on margin, provided with 2 long robust setae and 1 long seta apically; propodus narrow, posterior margin with one medial seta and with 4 distal unequal slender robust setae; dactylus slender, recurved, slightly shorter than propodus, with one short plumose seta at outer margin.

Pereopod 5 ( Fig. 3P 5) relatively short, coxa bilobed, posterior lobe expanded; basis subtriangular, anterior margin slightly concave with several distal long setae, bearing developed posterodistal lobe with only 2 setules along posterior margin; ischium-merus-carpus-propodus progressively longer, bearing long marginal setae; dactylus slender, exceeding half of propodus.

Pereopod 6 ( Fig. 3P 6) nearly twice as long as pereopod 5. Coxa bilobed, anterior lobe shallow; basis subovoid, anterior margin strongly convex, with numerous bunches of long simple and plumose setae, posterior margin with 1 setules, posterodistal lobe well developed, reaching distal tip of ischium; merus and carpus subequal in length, with several short robust setae along both margins; propodus slender, anterior margin with 2 medial short robust setae; dactylus slender, about half of propodus length.

Pereopod 7 ( Fig. 3P 7) shorter than pereopod 6. Coxa entire; basis prominently expanded backward, extending beyond middle of merus, slightly truncated ventrally, anterior margin with one distal short robust seta, posterior margin weakly serrate with setules; carpus shorter than merus bearing 3 blunt robust setae on margin; propodus subequal to merus in length; dactylus 0.75 times propodus length, with one short plumose seta at outer margin.

Epimeral plates 1–3 slightly produced posterolaterally; epimeral plates 1–2 bearing slightly concave ventral margin, no facial setae; epimeral plate 3 provided with two short setae on notched posteroventral corner.

Uropod 1 ( Fig. 4U 1r ) extending beyond uropod 2; peduncle slightly longer than rami, with 2 lateral facial setae, 2 dorsomedial and 2 dorsodistal robust setae; rami subequal in length, acuminate; outer ramus provided with one medial robust seta, with one short marginal seta, inner ramus smooth.

Uropod 2 ( Fig. 4U 2l ) peduncle with one dorsomedial and 2 dorsodistal robust setae; outer ramus slightly longer than inner one, bearing one mediodorsal robust seta, inner ramus smooth.

Uropod 3 ( Fig. 4U 3r ) exceeding tip of uropods 1–2; peduncle short, almost 0.5 times outer ramus length, with 2 laterodistal robust setae and one medial subdistal robust seta. Outer ramus biarticulate, proximal article nearly 3 times distal one length, bearing 2 and one short robust setae at both lateral and medial corner, and with one laterodistal and 4 medial pinnate setae; distal article truncate, with 2 apical setae; inner ramus 0.8 times proximal article of outer ramus in length, with 5 lateral and 2 apical pinnate setae, no setae on lateral margin.

Telson ( Fig. 4T ) completely cleft; each lobe rather slender, truncate, provided with 2 apical robust setae and one apical plumose seta, and a dorsal pair of plumose setae at third proximal part.

Female. Unknown.

Other specimens. Based on 13 paratype males, body length 2.7–3.0 mm, smaller than holotype. Other specimens exhibit slight variations on antennae. In specimens with 2.7–2.9 mm long bodies, peduncular articles of antennae bear less aesthetascs compared to the holotype. In case of 2.7 mm male, the number of flagellum is 14 articles, while that of the holotype with 17 articles.

Etymology. Named after the type locality, Pulau Tioman.

Remarks. The present Phoxocephalus tiomanensis , new species, is the first species of genus Phoxocephalus known from South East Asian waters. Although P. tiomanensis , new species, is described from male specimens, it bears many distinct features by which it is easy to distinguish from other males of known species of Phoxocephalus . The general appearance of the new species is closely related to P. prolixus Hirayama, 1987 from West Kyushu, Japan, by presenting antenna 2 not ensiform; uropod 3 distal article of outer ramus elongate; telson both lobes slender, truncate, with two apical robust setae and a small seta, and a dorsal pair of penicilate setae at the third proximal part.

However, P. tiomanensis is differentiated from P. prolixus by the morphological features of the male gnathopod 2, epimeron 2, and urosomite 3. In P. tiomanensis , the merus of male gnathopod 2 is not extended, whereas that of P. prolixus protrudes postero-distally far beyond the backward expansion of carpus and forms a prominent slender extension. The epimeron 2 lacks ventral setae in P. tiomanensis , whereas there is a long plumose ventrolateral seta on epimeron 2 in P. prolixus . The urosomite 3 of P. tiomanensis , moreover, has the smooth margin dorsally, while that of P. prolixus is produced a distinct upheaval.

In New Zealand and Australian waters, where the genus Phoxocephalus has been well studied, seven species of Phoxocephalus ( P. burleus , P. geniculatus , P. keppeli , P. kukatus , P. obtusus , P. rupullus , and P. tunggeus ) have been reported ( Barnard & Drummond, 1978). Comparing these taxa with P. tiomanensis , only one species P. kukatus shows considerable resemblance by having elongated second article of outer ramus in male uropod 3. Phoxocephalus kukatus , however, appears to have posteroventral long setae of epimeron 1, while these are absent in P. tiomanensis .

Although some characters have not been recorded in all of Phoxocephalus species and it is impossible to complete a worthy comparison with male specimens of all species, several differences with respect to P. tiomanensis , new species, are noted. Combinations of characters such as: (1) pereopod 5 with subtriangular basis; (2) lack of posteroventral and facial setae of epimera 1–3; and (3) the particular setae at carpus of the pereopod 7, can be easily distinguished from all other known species of the genus. These characters do not exhibit sexual dimorphism.

Figures

Fig. 2. Phoxocephalus tiomanensis, new species, holotype, male, (UKMMZ – 1532) 3.03 mm. Scale bars: A1 = 0.05 mm; A2, G1, G2 = 0.2 mm.

Fig. 3. Phoxocephalus tiomanensis, new species, holotype, male, (UKMMZ – 1532) 3.03 mm. Scale bars = 0.2 mm.

Fig. 4. Phoxocephalus tiomanensis, new species, holotype, male, (UKMMZ – 1532) 3.03 mm. Scale bars: HD, MDl, U1r, U3r = 0.1 mm; UL, LL, MP, U2l, T = 0.05 mm; MX1, MX2 = 0.025 mm.

Fig. 1. Map showing the sampling area.