Podocerus setouchiensis, Arai & Ohno & Tomikawa, 2022

Arai, Takanobu, Ohno, Yujiro & Tomikawa, Ko, 2022, A new species of the genus Podocerus from the Seto Inland Sea, Japan (Crustacea, Amphipoda, Podoceridae), ZooKeys 1128, pp. 99-109 : 99

Podocerus setouchiensis sp. nov.

Figs 2 , 3 , 4 , 5 New Japanese name: Setouchi-doronomi

Material examined.

Holotype: NSMT-Cr 30866, male (5.3 mm), intertidal zone of Tsuruduki , Etajima, Hiroshima Prefecture, Japan (34.1462°N, 132.4399°E), collected by K. Tomikawa on 18 April 2019 . Paratypes: NSMT-Cr 30867 (female 4.6 mm), NSMT-Cr 30868 (male 6.0 mm, G1527), NSMT-Cr 30869 (male 4.7 mm), NSMT-Cr 30870 (male 4.2 mm), data same as for holotype; NSMT-Cr 30871, 2 males (5.9 mm, 5.1 mm), intertidal zone of Gokan , Tamano, Okayama Prefecture, Japan (34.5263°N, 133.9893°E), collected by H. Ogawa on 9 April 2019 .

Diagnosis.

Body weakly rugose; pereonites 6-7 and pleonites 1-2 with dorsal carina. Head dorsally smooth. Antenna 1 accessory flagellum 1-articulate. Antenna 2 flagellar article 1 elongate. Uropod 3 rami with setae. Telson shorter than wide, with 2 long robust setae apically, lower margin with short lateral setae.

Description

(male, holotype, NSMT-Cr 30866). Body (Fig. 2A-C ) weakly rugose; pereonites 6-7 and pleonites 1-2 with dorsal carina. Head (Fig. 2A, C ) dorsally smooth; rostrum absent; lateral cephalic lobe squarish. Gnathopod 2 palm of propodus slightly convex with long plumose setae. Uropods 1 and 2 with distoventral projection.

Antenna 1 (Fig. 3A, B ) length 0.8 × body length; length ratio of peduncular articles 1-3 1.0: 2.1: 2.0; peduncular article 1 subquadrate, with long setae on posterior margin; peduncular articles 2 and 3 with 9 and 8 clusters of long setae on posterior margins, respectively; primary flagellum 6-articulate, 0.6 × peduncular articles 1-3 combined, article 1 long, 3.2 × article 2; accessory flagellum slender, 1-articulate. Antenna 2 (Fig. 3C, D ) 1.5 × antenna 1; peduncular article 4 with long setae on posterior margin; peduncular article 5, 1.4 × article 4, with short setae on anterior and posterior margins; flagellum 4-articulate, 0.2 × peduncular articles 1-5 combined, article 1 slightly longer than articles 2-4 combined.

Upper lip (Fig. 3E ) oval, ventral margin weakly concave, with minute setae. Lower lip (Fig. 3F ) outer lobe broad, setulose; inner lobes distinct. Left and right mandibles (Fig. 3G, H ) with 5-dentate incisor; molar process small, non-triturative, with a short plumose seta apically; accessory setal row with 3 setae; palp 3-articulate, length ratio of articles 1-3 1.0: 2.7: 1.9, article 1 bare, article 2 with 20 setae on ventral margin and submargin, ventral margin of article 3 lined with plumose setae, inner surface of article 3 with cluster of setae. Maxilla 1 (Fig. 3I ) inner plate indistinct; outer plate rectangular with 9 serrate robust setae; palp article 2 bearing 5 robust and 6 slender setae distally. Maxilla 2 (Fig. 3J ) with broad outer plate longer than inner plate, inner and outer plates bearing long plumose setae on apical margin. Maxilliped (Fig. 3K-M ) inner plate subrectangular, 3 small robust setae on apical margin and 1 on subapical margin; outer plate slightly exceeding half of palp article 2, medial margin with robust setae and long plumose setae; palp 4-articulate.

Gnathopod 1 (Fig. 3N ) coxa slender, subtriangular, longer than broad; basis length 3.7 × width, lacking setae on anterior and posterior margins; carpus 2.0 × broad, ventral margin weakly lobate with long setae; propodus subtriangular, length 1.9 × wide, anterior margin with 4 clusters of slender setae, posterior margin convex with 3 robust setae at palmar corner; posterior margin of dactylus 6-dentate with short setae. Gnathopod 2 (Fig. 3O ) coxa quadrate; basis 1.9 × broad, weakly concave anteriorly, anterodistal corner lobate; posterodistal corner of merus produced with simple and plumose setae; carpus indistinct, fused with propodus, with setae; propodus subovate, 2.1 × wide, anterior margin with 3 clusters of setae and single seta, medial surface with numerous plumose setae, palm slightly convex with long plumose setae, distal shelf well-developed, robust seta at palm defining corner; dactylus smooth, not reaching end of palm, with short setae.

Pereopods 3 and 4 (Fig. 4A-C ) basis lacking anterodistal lobe; ischium subrectangular; merus slightly shorter than carpus, anterodistal corner weakly produced; propodus longer than carpus, lacking robust setae marginally. Pereopod 5 (Fig. 4D ) basis without posterodistal lobe; posterodistal corner of merus weakly produced; length ratio of merus-dactylus 1.0: 1.2: 1.8: 1.0. Pereopod 6 (Fig. 4E ) basis subrectangular, length 1.4 × wide, posterodistal corner weakly lobate; posterodistal corner of merus weakly produced; length ratio of merus-dactylus 1.0: 1.2: 2.0: 0.9. Pereopod 7 (Fig. 4F ) basis length 1.2 × width, posterior margin expanded; merus produced posterodistally; length ratio of merus-dactylus 1.0: 1.2: 1.7: 1.2.

Pleopods 1-3 (Fig. 4G ) peduncle with short setae, inner distal corner with 4 retinacula (Fig. 4H ).

Uropod 1 (Fig. 4I ) biramous; peduncle 3.4 × broad, medial and lateral margins each with 4 robust setae, distoventral projection length 0.3 × peduncle; inner ramus 1.2 × peduncle, with 7 medial and 2 lateral robust setae; outer ramus 0.8 × length of inner ramus, with 3 robust setae on lateral margin. Uropod 2 (Fig. 4I ) biramous; peduncle 1.3 × broad, with short distoventral projection; inner ramus 1.9 × peduncle, medial and lateral margins with 5 and 2 robust setae, respectively; outer ramus 0.7 × length of inner ramus, bearing 2 lateral robust setae. Uropod 3 (Fig. 4K ) uniramous, plate-like; with 4 apical, 1 medial and 1 lateral robust setae.

Telson (Fig. 4L ) length 0.9 × width, dorsal lobe with 2 long robust setae apically, lower margin with short lateral setae.

Female (paratype, NSMT-Cr 30867). Antenna 1 (Fig. 5A ) length ratio of peduncular articles 1-3 1.0: 2.1: 1.9; primary flagellum 5-articulate, 0.4 × peduncular articles 1-3 combined, article 1 long, 2.0 × article 2. Antenna 2 (Fig. 5B ) peduncular article 5, 1.4 × article 4; flagellum 3-articulate, 0.3 × peduncular articles 1-5 combined.

Gnathopod 1 (Fig. 5A ) basis almost straight; carpus 2.3 × broad; palmar margin of propodus bearing robust seta; posterior margin of dactylus 4-dentate. Gnathopod 2 (Fig. 5B ) basis with anterodistal robust setae; merus produced anterodistally with robust setae; carpus free, distinct from propodus; propodus ovate, length 1.4 × width, palm convex with 3 robust setae near palmar corner.

Etymology.

The specific name is derived from the Seto Inland Sea, where this new species is distributed.

DNA Sequence.

A sequence of COI (GenBank accession number LC719250; 658 bp) was determined from the paratype female (NSMT-Cr 30868).

Distribution.

Known from Hiroshima and Okayama Prefectures.

Remarks.

Podocerus setouchiensis sp. nov. is similar to P. andamanensis (Giles, 1890), P. casuarinensis Kilgallen, 2009, P. crenulatus Myers, 1985, P. fulanus J.L. Barnard, 1962, P. lazowasemi Baldinger & Gable, 1994, P. orontes Hughes, 2013, and P. walkeri Rabindranath, 1972 in having dorsal carinae on pereonites 6 and 7, and pleonites 1 and 2. However, this new species differs from these species by the features shown in the following key. Podocerus setouchiensis sp. nov. is also similar to P. ulreungensis Kim & Kim, 1991 from Ulleung Island in the Sea of Japan in having antenna 2 with elongate flagellar article 1, gnathopod 1 with weakly lobate carpus, male gnathopod 2 merus pointed distally, male gnathopod 2 propodus with convex palmar margin bearing long marginal setae and robust seta at palm defining corner, uropod 1 peduncle with distoventral projection, and telson with 2 apical setae. However, this new species is distinguished from the latter by the following features (features of P. ulreungensis in parentheses): pereonite 6 with dorsal carina (absent); antenna 1 accessory flagellum 1-articulate (2-articulate); antenna 1 flagellar article 1 length 3.2 times as long as article 2 (2.3 times); uropod 2 peduncle with a short distoventral projection (lacking projection); and telson shorter than wide (longer).

Figures

Figure 2. SEM photographs of Podocerus setouchiensis sp. nov. A habitus, lateral view (NSMT-Cr 30869, male 4.7 mm) B dorsal part of pereonites and pleonites, lateral view (NSMT-Cr 30869, male 4.7 mm) C habitus, dorsal view (NSMT-Cr 30870, male 4.2 mm).

Figure 3. Podocerus setouchiensis sp. nov., holotype male, NSMT-Cr 30866 A antenna 1, medial view B accessory flagellum of antenna 1, medial view C antenna 2, medial view D distal part of antenna 2, medial view E upper lip, anterior view F lower lip, posterior view G right mandible, medial view H incisor and lacinia mobilis of left mandible, lateral view I maxilla 1, medial view J maxilla 2, medial view K palp of maxilliped, medial view L outer plate of maxilliped, medial view M inner plate of maxilliped, medial view N gnathopod 1, lateral view (coxa omitted) O gnathopod 2, lateral view.

Figure 4. Podocerus setouchiensis sp. nov., holotype male, NSMT-Cr 30866 A pereopod 3, lateral view (coxa omitted) B dactylus of pereopod 3, lateral view C-F pereopods 4 - 7, lateral views (coxae omitted) G pleopod 1, posterior view H retinacula of pleopod 1, posterior view I-K uropods 1 - 3, dorsal views L telson, dorsal view.

Figure 5. Podocerus setouchiensis sp. nov., paratype female, NSMT-Cr 30867 A antenna 1, medial view B antenna 2, medial view C gnathopod 1, lateral view D gnathopod 2, lateral view.