Orthoprotella bicornis, Lim & Othman & Takeuchi, 2015

Lim, Jacqueline Hui Chern, Othman, Bin Haji Ross & Takeuchi, Ichiro, 2015, Description of Orthoprotella bicornis, new species, and Paraprotella teluksuang, new species (Crustacea: Amphipoda) from Johor, Malaysia with special reference to unusual sexual bias towards females in Paraprotella, Raffles Bulletin of Zoology 63, pp. 33-48 : 34-41

Orthoprotella bicornis , new species

( Figs. 1–5 )

Material examined. Holotype: Male, 8.37 mm, UKMMZ-1502, Kampung Sebirah, Pulau Tinggi , TLSI, Johor, 02°18.490ʹN, 104°05.575ʹE; seagrass bed, SCUBA diving, 3 April 2009, depth 4.0 m; coll. Azman, B.A. R., Gan, S.Y., Lim, J.H.C., Chew, M.W.H., Shamsul, B. & Yoshida, T . Paratypes: 1 female, UKMMZ-1503; 3 males, 4 females, 7 premature males, 4 premature females, 28 juveniles, UKMMZ-1504; 3 males, 4 females, 6 premature males, 3 premature females, 28 juveniles, UKMMZ-1505; 2 males, 4 females, 6 premature males, 3 premature females, 28 juveniles; UKMMZ-1506; same station data.

Type locality. Kampung Sebirah, Pulau Tinggi, TLSI, Johor, Malaysia .

Description. Male. Body length 8.37 mm. UKMMZ-1502 ( Fig. 1 ). Head/pereonite 1 concave along dorsal margin, showing slight suture; head with a pair of mid-dorsal projections; eye large, distinctive. Head length 0.57 mm; pereonite 1 length 0.48 mm; pereonite 2 length 1.34 mm, with 1 small anterolateral triangular projection, 1 lateral projection above the insertion of gnathopod 2, 1 lateroventral triangular projection and 1 rounded dorsodistal projection; pereonite 3 length 1.73 mm, with 1 small anterolateral triangular projection; pereonite 4 length 1.62 mm; pereonite 5 length 1.76 mm, longest; pereonites 6 and 7 partially fused (dorsal suture oblique), combined length 0.87 mm. Antenna 1, 0.9 × body length; peduncular article 2 longest; peduncular article 3 with several small projections on anterodistal margin; flagellum 0.5 × peduncular length, with 16 articles, proximal article composed of 3 articles ( Fig. 1 : A1). Antenna 2 slender; 0.4× the length of antenna 1; peduncle with several feeble setae; flagellum 0.2 × of peduncular length, with 2 articles ( Fig. 1 : A2).

Mouthparts. Upper lip notched, forming rounded quadrilateral projections ( Fig. 2 : UL). Lower lip finely setose on inner and outer lobes ( Fig 2 : LL). Mandible right incisor with 5 teeth; lacinia mobilis with 2 distinct teeth and 3 small teeth; followed by 3 bundled setae; molar flake present; palp article 2 with 8 lateral setae; palp article 3 with setal formula 1-18-4-1 [ Fig. 2 : MD (R)]; left incisor with 5 teeth; lacinia mobilis with 5 teeth, followed by 3 bundled setae; palp article 2 with 8 lateral setae; palp article 3 with setal formula 1-19-4-1 [ Fig. 2 : MD (L)]. Maxilla 1 outer plate with 7 stout apical setal-teeth; palp distal margin with 5 triangular projections, with 7 setae and a row of 3 slender setae ( Fig. 2 : MX 1). Maxilla 2 inner plate triangular with about 8 apical setae; outer plate subrectangular with 12 apical setae ( Fig. 2 : MX 2). Maxilliped basal endite (inner plate) quadrilateral with 2 small teeth-like setae and 4 plumose setae on distal margin; ischial endite (outer plate) oval, 2.5 × length of inner plate, inner margin blade-like, with many fine setae, with 2 setae on inner margin and 3 setae on outer margin; palp article 2 setose on inner margin; palp article 3 with small triangular distal projection and 10 distal setae; palp article 4 (dactylus) falcate ( Fig. 2 : MXP).

Pereon. Gnathopod 1 basis shorter than ischium, merus and carpus combined (0.7 ×); ischium 0.3 × basis; merus subrectangular with several setae at ventrodistal corner; carpus subtriangular, with setae at distal and ventrodistal margin; propodus subtriangular, with 4 rows of submarginal setae (each row with 2–3 setae), palm begins 1/5 along posterior margin, with serriform teeth along entire margin, proximally with 1 robust seta; dactylus falcate, inner margin serrated, scarcely setose ( Fig. 1 : G1). Gnathopod 2 begins 1/3 along anterior margin of pereonite; basis length 5 × width, 0.8 × pereonite 2, distally with triangular projection with 1 seta near distal margin; carpus 0.2 × propodus length; propodus subovate, large, length 2 × width, dorsodistally with a small triangular projection, palm proximal projection with 1 robust (grasping) seta, and 2 smaller tooth-like setae apically, margin of palm heavily setose, proximal half of palm convex, mid-palmar projection with one seta followed by a deep sinus and a triangular projection, palm with serriform teeth between grasping proximal projection and mid-palmar projection; dactylus falcate, with fine setae along inner and outer margins ( Fig. 1 : G2).

Gill 3 length 0.4 × of pereonite 3, oval. Pereopod 3 oval, 2-articulate, article 1 with 7 distal setae and 4 lateral setae; article 2 tiny, conical, with 1 apical plumose seta ( Fig. 3 : P3). Gill 4 length 0.4 × pereonite 4, oval. Pereopod 4 oval, 2-articulate, subequal in length to pereopod 3, article 1 with 7 distal setae and 5 lateral setae; article 2 tiny, conical, with 1 apical plumose seta ( Fig. 3 : P4). Pereopods 5–7 welldeveloped, progressively robust. Pereopod 5 carpus longest; propodus with 1 pair of grasping spine near proximal end of palm; dactylus falcate ( Fig. 3 : P5). Pereopod 6 merus and carpus subequal in length; propodus with a pair of grasping spine; dactylus falcate ( Fig. 3 : P4). Pereopod 7 merus and carpus subequal in length; propodus longest with a pair of grasping spine; dactylus falcate ( Fig. 3 : P7).

Pleon. Penes large, situated medially, Uropods 2 uniramous pairs. Uropod 1 biarticulate, peduncle with 8 setae on outer margin and 2 setae on inner margin; ramus slender, 1.4 × the length of peduncle, with 2 marginal setae and 1 apical seta. 2 setae present between penes and uropod 1. Uropod 2 ramus vestigial. Telson with 1 pair of normal setae and 1 pair of plumose setae ( Fig. 3 : ABD).

Female. Body length 6.16 mm. UKMMZ-1503 ( Fig. 4 ). Head length 0.43 mm, and pereonite 1 length 0.25 mm; head and pereonite 1 fused, with slight suture along dorsal margin (between head and pereonite 1). Pereonite 2 length 1.20 mm, with rounded dorsodistal projection, knob-like with fine setae. Pereonite 3 length 1.23 mm, with small dorsodistal projection. Pereonite 4 length 1.12 mm, distolaterally with a plate-like projection. Pereonite 5 length 1.25 mm, dorsally smooth. Pereonites 6 and 7 partially fused, combined length 0.68 mm. Antenna 1 length subequal with body length; peduncular article 2 longest, 2.8 × article 1; peduncular article 3 without distal projections; flagellum 0.8 × peduncular length, 15 articles, proximal article composed of 3 articles ( Fig. 4 : A1). Antenna 2, 0.6 × the length of antenna 1; flagellum 0.15 × peduncular length with 2 articles, proximal article 0.3 × distal article ( Fig. 4 : A2).

Pereon. Gnathopod 1 basis shorter than ischium, merus and carpus combined (0.8 ×)( Fig. 4 : G1). Gnathopod 2 begins 1/5 along anterior margin of pereonite; basis longer than ischium, merus and carpus combined (1.6 ×), length 5.5 × width, 0.8 × pereonite 2; carpus subequal in length with ischium, subtriangular; propodus subovate ( Fig. 4 : G2).

Gill 3 length 0.6 × of pereonite 3. Pereopod 3 length 0.4 × gill, oval, article 1 with 8 distal setae and 2 lateral setae. Oostegite 3 length 1.2 × width, setose along entire outer margin ( Fig. 5 : G1). Gill 4 length 0.7 × pereonite 4, oval. Pereopod 4 length 0.4 × gill, article 1 with 6 distal setae and 4 lateral setae. Oostegite 4 length 1.0 × width, sparsely setose along entire outer margin ( Fig. 5 : G2). Pereopods 5–7, progressively robust ( Figs. 5 : P5–7). Pereopod 5 carpus longest, slender; propodus with a pair of grasping spine near proximal end of palm ( Fig. 5 : P5).

Pleon. Uropod 1 absent in females. Uropod 2 ramus vestigial, degenerated into 2 setae [ Fig. 5 : ABD (V) and ABD (L)].

Remarks. Among the genera in the family Caprellidae , the genus Orthoprotella is distinguishable from its closest relative, the genus Protella Dana, 1852 (see Takeuchi et al., 2014) in terms of its uropod 1 ramus lacking a knob-like appendage (present in species of the genus Protella ).

Orthoprotella bicornis , new species, is unique in several distinctive characteristics; namely 1) dorsal and lateral projections (head with 1 paired projections; pereonite 2 with 1 small anterolateral triangular projection, 1 lateral projection above the insertion of gnathopod 2, 1 lateroventral triangular projection and 1 rounded dorsodistal projection; pereonite 3 with 1 small anterolateral triangular projection and 1 round dorsodistal projection); 2) antenna 1 peduncular article 3 with several distal projections (not present in females); 3) gnathopod 2 propodus with a small dorsodistal triangular projection; and 4) gnathopod 2 propodus proximal projection equipped with 1 robust seta (grasping spine) and 2 smaller tooth-like structures.

Species of Orthoprotella have a wide range of dorsal projections; therefore, observations of its dorsal and lateral body projections can be used to easily distinguish one species from another. Among the 11 recorded species of Orthoprotella ( Haswell, 1880; Barnard, 1916; Guiler, 1954; Quitete, 1975; Mori, 1996; Arimoto, 1981; Guerra-García, 2004, 2006; Guerra-García & Takeuchi, 2004; Takeuchi & Lowry, 2007), the status of two species, O. melloi Quitete, 1975 and O. hamata Arimoto, 1981 , is unclear due to their limited descriptions and insufficient figures. According to Laubitz (1991), O. hamata could be synonymous with Monoliropus falcimanus Mayer, 1904 , but further examination of specimens is needed. Due to their unresolved taxonomy, these two species are considered nomina dubia and omitted from comparisons below.

The remaining nine species can be further divided into two groups based on the presence or absence of dorsal projections on the body. The first group consists of four species, which are dorsally smooth (this includes O. mayeri Barnard, 1916 ; O. tasmaniensis Guiler, 1954 ; O. pearce Guerra-García, 2006 ; and O. berentsae Takeuchi & Lowry, 2007 ). The second group consists of five species, which are equipped with dorsal projections ( O. gordoni Guiler, 1954 ; O. australis ( Haswell, 1880) ; O. spinigera Mori, 1996 ; O. nana Guerra-García, 2004 ; and O. tuberculata Guerra-García & Takeuchi, 2004 ).

Orthoprotella bicornis , new species, belongs to the second group (based on paired dorsal projections on its head and a single dorsodistal projection on pereonites 2) and appears most similar to O. australis ( Haswell, 1880) recorded from New South Wales, Australia. Descriptions and figures of mouthparts were not provided in Haswell’s (1880) original record. Mayer (1903) illustrates the whole body (lateral and dorsal view), maxilliped, mandibular palp and abdomen of mature and premature male. Orthoprotella bicornis , new species, is similar to O. australis ( Haswell, 1880) in the following characteristics: 1) antenna 1 length almost as long as body length; 2) gnathopod 1 with propodus subtriangular in shape; 3) gnathopod 2 propodus longer than head and pereonite 1 and suboval in shape; and 4) palmar margin of gnahopod 2 marginally setaceous. The abdomen of O. australis from Mayer (1903) shows close similarity with the present specimen in the distinct peduncle of uropod 1. However, O. bicornis , new species, differs from O. australis in 1) the presence of several small projections on the anterodistal margin of antenna 1 peduncle article 3 (not stated in O. australis ); 2) the shape of pereopods 3 and 4 oval, and expanded medially (pereopods 3 and 4 slender, not expanded medially in O. australis ); 3) the pereopod 7 propodus proximal projection with 1 pair of grasping spines (proximal projection equipped with several robust setae in O. australis ); 4) the distal region of uropod 1 peduncle lacking fine setae (present in O. australis ); and 5) ramus of uropod 2 lacking setae (1 seta in O. australis ).

The second group is distinct in the number of dorsal projections on the body. Orthoprotella tuberculata Guerra-García & Takeuchi, 2004 has numerous dorsal projections from head to pereonite 5; O. nana Guerra-García, 2004 is dorsally smooth with a small dorsal hump on its head. Orthoprotella nana is close to O. mayeri Barnard, 1916 but differs in body length as well as the absence of an anterolateral projection on pereonites 2 and 3 (present in O. mayeri ).

Etymology. This species was named based on the two prominent projections on the head.

Distribution. Currently known only from Johor, Malaysia.

Figures

Fig. 1. Orthoprotella bicornis, new species, male holotype, 8.37 mm, UKMMZ-1502, Kampung Sebirah, Pulau Tinggi, TLSI. Scale bars A1, A2 and G2 = 0.2 mm; G1 = 0.1 mm; whole body = 0.5 mm.

Fig. 2. Orthoprotella bicornis, new species, male holotype, 8.37 mm, UKMMZ-1502, Kampung Sebirah, Pulau Tinggi, TLSI. Scale bars MD (R), MD (L) and MXP = 0.1 mm; MX1, MX2, LL and UL = 0.05 mm.

Fig. 3. Orthoprotella bicornis, new species, male holotype, 8.37 mm, UKMMZ-1502, Kampung Sebirah, Pulau Tinggi, TLSI. Scale bars ABD (L), ABD (V) = 0.1 mm; P3, P4, P5, P6 and P7 = 0.2 mm.

Fig. 4. Orthoprotella bicornis, new species, female paratype, 6.16 mm, UKMMZ-1503, Kampung Sebirah, Pulau Tinggi, TLSI. Scale bars A1, A2 and whole body = 0.5 mm; G1 and G2 = 0.2 mm.

Fig. 5. Orthoprotella bicornis, new species, female paratype, 6.16 mm, UKMMZ-1503, Kampung Sebirah, Pulau Tinggi, TLSI. Scale bars ABD (L) and ABD (V) = 0.1 mm; P3, P4, P5, P6 and P7 = 0.2 mm.