A new species of Pereionotus (Amphipoda, Senticaudata, Phliantidae) from Pulau Tinggi, Sultan Iskandar Marine Park, Malaysia

A new species of Pereionotus Spence Bate & Westwood, 1861 from Pulau Tinggi, Sultan Iskandar Marine Park (SIMP) is described and the first record of the genus from Malaysia. It was collected from Kg. Tg. Balang, Pulau Tinggi, Johor, Malaysia (2°16'59.5"N, 104°07'21.9"E) and can be distinguished by having wide and dorsally truncate carinae of pereonites 2–7, maxillipedal palp as long as the outer plate, lacking additional robust seta in the middle of propodi of pereopods 1–4, and the absence of short robust setae on the anterodistal corner of merus and carpus of pereopods 6–7. An updated identification key for the 11 known species in the genus is also presented.

Sultan Iskandar Marine Park (SIMP), or formerly known as the East Johor Island Archipelago (EJIA), is situated off the east coast of Johor, Malaysia, in the South China Sea. The park comprises 13 small islands off Mersing, Johor, namely Pulau Harimau, Pulau Mensirip, Pulau Goal, Pulau Tengah, Pulau Hujung, Pulau Rawa, Pulau Sibu, Pulau Tinggi, Pulau Mentinggi, Pulau Sibu Hujong, Pulau Pemanggil, Pulau Besar, and Pulau Aur. Pulau Tinggi is about 30 km southeast of Mersing and has an area of about 16 km 2 . Ongoing faunistic investigations of the SIMP, especially at Pulau Tinggi, have yielded over 10 new crustacean taxa, belonging to Mysida, Amphipoda, and Isopoda (e.g., Azman and Melvin 2011;Azman and Othman 2013;Chew et al. 2014Chew et al. , 2016Gan et al. 2010;Lim et al. 2010Lim et al. , 2019Lim et al. , 2012Lim et al. , 2015Lim et al. , 2017Othman and Azman 2007;Azman 2017, 2018;Tan et al. 2014Tan et al. , 2015. The present study is the first to report the occurrence of phliantid amphipods in the Malaysian waters. In this paper, one new species from Pulau Tinggi is described.

Methods
The materials collected contain only female specimens (three individuals), collected in the rocky intertidal zone of Kg. Tg. Balang, Pulau Tinggi, Johor, (Fig. 1) on the east coast of Peninsular Malaysia. At the laboratory, the materials were preserved in 4% formalin in seawater in vials and later selected for dissection. Whole bodies and dissected appendages were mounted in glycerol on glass slides for illustration. Pencil drawings were made under a compound microscope Olympus BX43 fitted with a camera lucida. Then, line drawings were made following the guidelines described by Coleman (2003Coleman ( , 2009a Coleman and Lowry 2012). Pereon depressed, coxal plates 1-4 somewhat splayed. Urosome flexed under pleon. Head flat with short rostrum. Maxilla 1 with scale-like inconspicuous palp. Maxilla 2 with basally fused plates. Maxillipedal palp 3-articulate. Pereopods simple. Basis of pereopods 5 and 6 wide, rounded, and ventrally expanded; basis of pereopod 7 without ventral lobe and narrower. Inner ramus of pleopod 3 slightly shortened. Uropod 2 uniramous in female, biramous in male. Uropod 3 without rami.
Antenna 1 (Fig. 3, A1) peduncular article 1 robust with subterminal lateral lobe, almost twice as wide as article 2; peduncular article 2 longer than wide; peduncular article 3 half the width of article 2; flagellum of only one article with long aesthetascs apically. Antenna 2 (Fig. 3, A2) slender, almost reaching distal margin of article 2 of antenna 1; peduncular article 2 is as long as wide; peduncular article 3 is slightly longer than article 4; peduncular article 4 twice as long as article 5; peduncular article 5 with long flagellum apically.
Coxae 1-4 with sparse setae on the distal margin. Pereopod 1 (Fig. 3, P1) coxa subrectangular; basis slightly expanded posterodistally, one medial seta on the anterior margin, one apical seta each on the posterior and anterior margin; ischium longer than merus, setae as for basis; merus distally oblique, about the length of carpus, three setae on the posterior margin; carpus expanded anterodistally, one medial seta on the posterior margin, one apical seta each on the posterior and anterior margin; propodus longer than wide, almost as long as merus and carpus combined, medial face with row of stout apically setulose setae, one medial seta on the posterior margin, two apical setae each on the posterior and anterior margin, one apical robust seta on the posterior margin; dactylus falcate, with long unguis. Pereopod 2 (Fig. 3, P2) coxa wider than that of pereopod 1; basis slightly expanded posterodistally, one medial seta on the anterior margin, one apical seta each on the posterior and anterior margin; mid diameter of ischium is more than half the width of distal basis, one medial seta on the anterior margin, one apical seta each on the posterior and anterior margin; merus distally oblique, three setae on the posterior margin; carpus expanded anterodistally, posterior margin straight with two setae, one apical seta each on the posterior and anterior margin; propodus similar in shape as pereopod 1, without row of robust setae on medial face, one medial seta on the posterior margin, two apical setae each on the posterior and anterior margin, one apical robust seta on the posterior margin; dactylus falcate, with long unguis. Pereopod 3 (Fig. 4, P3) coxa similar in shape as pereopod 2; basis slightly expanded posterodistally; ischium expanded postero-and anterodistally with one seta on the posterior margin; merus with straight posterior margin and convex anterior margin, distal margin oblique, two medial and one apical seta on the posterior margin, one apical seta on the anterior margin; carpus expanded anterodistally with straight posterior margin, one apical seta on the anterior margin, posterior margin with three medial setae; propodus longer than wide, one medial seta on the posterior and anterior margin, one apical robust seta on the posterior margin, three apical setae on the anterior margin; dactylus subequal to that of pereopod 2. Pereopod 4 (Fig. 4, P4) coxa widest with posteromarginal subacute lobe; basis expanded posterodistally, straight anterior margin with two medial setae; mid diameter of ischium is 0.8× the width of distal basis, one apical seta each on the posterior and anterior margin; merus with straight posterior margin and convex anterior margin, distal margin oblique, two medial setae on the posterior margin, one apical seta each on the posterior and anterior margin; carpus expanded anterodistally with one apical seta, two medial seta on the posterior margin; propodus longer than wide, almost as long as merus and carpus combined, two medial, two apical, and one apical robust seta on the posterior margin, one medial and two apical setae on the anterior margin; dactylus subequal to that of pereopod 3. Pereopod 5 (Fig. 4, P5) basis posteromarginally weakly convex with rounded posterior lobe, expanded ventrally and partly covering the ischium, three medial and two apical setae on the posterior margin; ischium almost as long as wide, two medial and four apical setae on the anterior margin; merus drawn out into slightly rounded posterodistal lobe with three apical setae, one medial and one apical seta on the anterior margin; carpus almost as long as merus, slightly expanded posterodistally with one apical, one medial, and one apical seta on the anterior margin; propodus subequal to the shape of pereopod 4, longer than wide with 2× the width, two medial and three apical setae on the posterior margin, one medial, two apical, and one apical robust seta on the anterior margin; dactylus falcate, slightly longer compared to that of pereopod 4, with long unguis, six medial setae on the posterior margin and one apical seta on the anterior margin. Pereopod 6 (Fig. 4, P6) basis with straight anterior margin, posteromarginally weakly convex with rounded posterior lobe, expanded ventrally and partly covering the ischium and merus, distal margin oblique, two medial and apical setae on the anterior margin; ischium subrectangular with two medial and apical setae on the anterior margin; merus expanded posterodistally with one medial and three apical setae; carpus longer than wide as the distal merus, two medial setae on the anterior margin, one apical seta on the posterior margin; propodus longer than wide, 3× the width, one medial and two apical setae each on the posterior and anterior margin, one apical robust seta on the anterior margin; dactylus is as the same as pereopod 5, one medial seta on the posterior margin and one apical seta on the anterior margin. Pereopod 7 (Fig. 4, P7) basis posteromarginally weakly convex without rounded posterior lobe with one apical seta on the anterior margin; ischium slightly expanded posterodistally, longer than wide, with one apical seta on the anterior margin; merus expanded posterodistally with one apical seta, one apical seta on the anterior margin; carpus almost as long as merus, longer than wide, with one apical seta on the posterior margin, two apical setae on the anterior margin; propodus as long as that of pereopod 5, longer than wide, two medial and apical setae on the posterior margin, one medial and apical seta, and one apical robust seta on the anterior margin; dactylus falcate, with long unguis, as long as pereopod 5 with one apical seta on the anterior margin.
The new species shows significant differences from other known species of Pereionotus. However, Pereionotus tinggiensis sp. nov. appears to have some similarities to the neighbouring Australian species, namely P. dieteri, P. hartmuti, P. thomsoni, and P. yongensis. Nonetheless, certain distinct characters were observed, including, i) the presence of additional robust seta half-way on the posterior margin of propodi of pereopods 1-4 and, ii) similar robust setae on the anterior margin of the propodi of pereopods 5-7, distinguishing P. tinggiensis sp. nov. from P. thomsoni. Besides, P. hartmuti and P. yongensis were found to exhibit a dense fringe of long slender setae on the distal margin of coxa 1-4. This unique characteristic is lacking in P. tinggiensis sp. nov. The new species is similar to P. dieteri in having robust subterminal lateral lobe of peduncular article 1 of antenna 1; not having additional robust seta half-way on the posterior margin of propodi of pereopods 1-4; and lacking robust seta on the anterior margin of the propodi of pereopods 1-7, but can be distinguished from P. dieteri by the absence of one or two short robust setae on the anterodistal corner of merus and carpus of pereopods 6 and 7.
Etymology. This species is named after the type locality, Pulau Tinggi, Johor, Malaysia.
Key to the species of Pereionotus (female)