Anonyx nugax (Phipps, 1774)

Kim, Jun-Haeng Heo and Young-Hyo, 2021, Two new record of the genus Anonyx (Crustacea: Amphipoda: Uristidae) from Korean waters, Journal of Species Research 10 (3), pp. 267-275 : 271-274

Anonyx nugax (Phipps, 1774) ( Figs. 4-6 )

ǖṻnj나AEIJḖȁNjẹ (ljḏ)

Cancer nugax Phipps, 1774 , 192, pl. 12, fig. 2.

Anonyx kurilicus Gurjanova, 1962 , 242, fig. 78.

Anonyx nugax : Gurjanova, 1962, 216, fig. 67A, B.

Material examined. 1$( MABIK CR00248292 ), Gajin Port , Gajin-ri , Jugwang-myeon , Goseong-gun, Gangwon-do, Korea, 38°22 ʹ 05 ʺ N, 128°30 ʹ 45 ʺ E, 28 December 2019, J.H. Heo. The specimens were collected with a fishing net from subtidal zone and the remaining specimens in the collection of the corresponding author .

Description. Adult female, body ( Fig. 4 ) 19.07 mm long (MABIK CR00248292). Head ( Fig. 5A ) lateral cephalic lobe subacute; eye large, reniform, black. Epimeron 1 ( Fig. 5B ) produced anteroventrally, subrounded posteroventrally; epimeron 2 produced posteroventrally with large cusp; epimeron 3 round posteroventrally with prominent projection.

Antenna 1 ( Fig. 5C ), 0.89 times as long as antenna 2; peduncular article 1 stout, with a row of 10 penicillate setae dorsally; peduncular articles 2-3 strongly telescoping, short; length ratio of peduncular articles 1-3 = 1.00: 0.20: 0.15; flagellum 11-articulate, 1.55 times longer than peduncular articles, with 2-field short callynophore, calceoli absent; accessory flagellum 6-articulate, article 1 elongat- ed, expanded medial margin.

Antenna 2 ( Fig. 5D ) slender; peduncular article 4 subrectangular, 1.22 times as long as article 5, with a row of setules dorsally, ventral margin slightly expanded, with unequal simple and penicillate setea; flagellum 22-artic- ulate; calceoli absent.

Right mandible ( Fig. 5E ), incisor broad and smooth with 1 prominent tooth on the cutting edge; accessory spine row with 4 spines and setules; molar process well developed, columnar, distally truncate and triturative, densely pubescent; palp attached nearly midway, 3-articulate; article 1 short; article 2 longest, with 6 A2-setae, 3 C2-setae; article 3 weakly falcate, 0.76 times as long as article 2, with 4 B3-setae, 15 D3-setae, 3 E3-setae.

Left mandible ( Fig. 5F ) similar to left one, except for the bifid tooth on the cutting edge.

Gnathopod 1 ( Fig. 5G ) subchelate; coxa large, expand- ed anteriorly, 0.63 times as wide as long; basis with simple setae anteriorly; merus subequal in length to ischium, with setules posteriorly and 5 simple setae posterodistally; carpus with two clusters of simple setae distally, 0.47 times as long as basis; propodus subrectangular, concave posteriorly, slightly narrowing distally, subequal in length to carpus, palm transverse, weakly serrulate, defined by 2 bifid spines posterodistally; dactylus falcate, slightly exceeding palm, with an accessory tooth.

Gnathopod 2 ( Fig. 5H ), coxa subrectangular, 0.40 times as wide as long; basis linear, elongated, with simple setae anteriorly; ischium elongated, 1.35 times as long as merus, with 6 simple setae anteriorly and 3 simple setae posteriorly; merus 0.55 times as long as carpus, with a patch of setules posteriorly and a cluster of long setae posterodistally; carpus 0.52 times as long as basis, with setules and long simple setae posteriorly, clusters of long setae distally; propodus short, subquadrate, minutely chelate, with unipinnate setae anterodistally, 0.52 times as long as carpus, palm slightly concave, with small blunt spines on posterodistal corner; dactylus small, acute, fitting palm.

Pereopod 3 ( Fig. 6A ), coxa subrectangular, width 0.44 times length; basis narrowing proximally; merus produced anterodistally, 1.61 times as long as carpus, with unequal simple setae posteriorly and 2 simple setae anterodistally; propodus subrectangular, 1.50 times as long as carpus, with a row of paired long simple setae and 1 blunt spine hooked; dactylus falcate, 0.46 times as long as propodus.

Pereopod 4 ( Fig. 6B ) similar to pereopod 3 except coxa broader than that of pereopod 3, posterior margin excavate, posterodistal lobe produced.

Pereopod 5 ( Fig. 6C ), coxa large, rounded quadrate, equilobate, width 1.33 times length; basis subquadrate, width 0.85 times length, posterior margin serrate, posteroventral lobe broadly rounded and expanded, with a row of spines along anterior margin; merus expanded posteriorly, anterior margin with spines accompanied by long seta, posterior margin with 3 spines; carpus 1.24 times as long as merus, with spines accompanied by a long seta; propodus slender, rectangular, slightly longer than carpus, anterior margin with a row of paired spines, dactylus falcate, 0.44 times as long as propodus.

Pereopod 6 ( Fig. 6D ) similar to pereopod 5, but each article longer in proportion than pereopod 5.

Pereopod 7 ( Fig. 6E ), coxa small, subquadrate; basis subovate, posterior margin serrate, round and convex, width 0.75 times length, anterior margin nearly straight, with a row of spines; ischium to dactylus similar to those of pereopod 6, except ischium and merus without simple setae anteriorly.

Uropod 1 ( Fig. 6F ), peduncle subrectangular, 1.23 times as long as outer ramus, with a row of 9 dorsolateral spines and 6 long dorsomedial spines; outer ramus 1.08 times as long as inner one, lateral margin with 6 spines, inner ramus with 4 medial and 1 lateral spines.

Uropod 2 ( Fig. 6G ), peduncle subquadrate, 0.85 times as long as outer ramus, with a row of 7 dorsolateral and 5 dorsomedial spines; outer ramus slightly longer than inner one, with 4 lateral spines, inner ramus constricted, with 3 lateral and inserted 1 spine on notch.

Uropod 3 ( Fig. 6H ), peduncle short, 0.55 times as long as outer ramus, with 4 lateral, 6 medial and 3 ventrodistal spines; outer ramus 1.14 times as long as inner ramus, biarticulate, proximal article with 6 plumose setae along medial margin, lateral margin with 5 spines, distal article short, 0.27 times as long as proximal one; inner ramus exceeding end of proximal article of outer ramus, medial margin with 6 plumose setae, lateral margin with 3 spines.

Telson ( Fig. 6I ) much longer than broad, cleft about 73 % of its length, each lobe with a deep apical notch bearing one stout spine and 3 stout spines, and a pair of penicillate setae dorsolaterally.

Distribution. Northern Hemisphere, Korea (East Sea).

Remarks. Anonyx nugax (Phipps, 1774) belongs to the A. nugax group that comprises A. makarovi Gurjanova, 1962 ; A. pacificus Gurjanova, 1962 ; A. sarsi Steele and Brunel, 1968 ; A. lilljeborgi Boech, 1870 ; A. beringi Steele, 1982 ; A. barrowensis Steele, 1982 ; A. schokalskii Gurjanova, 1962 ; A. comecrudus Barnard, 1971 ; A. debruyni Hoek, 1882 ; A. knipowitschi Gurjanova, 1962 ; A. epistomicus Kudrjaschov, 1965 ; and A. abei Takekawa and Ishimaru, 2001 , which has the constriction of the inner ramus of uropod 2 on the point of insertion of the distal spine ( Steele, 1982). This species is phenotypically similar to A. makarovi and A. pacificus in its armature of spines and setae ( Steele, 1982). The key to the identifica- tion of Anonyx species in the northwest Atlantic ( Steele & Brunel, 1968) is based on the more proximal position of the distal spine on the inner ramus of uropod 2 in A. makarovi . However, it is not possible to distinguish a species based on this single character because the characteristics of the two species overlap with each other ( Steele, 1982). Also, the newly recorded species, A. nugax , strongly resembles A. pacificus in general appearance. Steele (1982) mentioned that it is not easy to distinguish between the two species because there are overlapping characteristics. However, A. nugax is distinguished from A. pacificus based on the presence of a shorter and less acute epimeron 3 projection in mature specimens ( Steele, 1982). Our specimens are mostly consistent with the characteristics of A. nugax by the presence of a shorter, less acute projection on the epimeron 3. In future studies, it is necessary to establish the taxonomic account of species through molecular experiments because the Anonyx groups are very similar in morphology.

Figures

Fig. 4. Anonyx nugax (Phipps, 1774), adult female, 19.07 mm, habitus. Scale bar=2.0 mm.

Fig. 5. Anonyx nugax (Phipps, 1774), adult female, 19.07 mm. A, head; B, epimeral plates and urosomites; C, antenna 1; D, antenna 2; E, left mandible; F, right mandible; G, gnathopod 1; H, gnathopod 2. Scale bars:A, B, G, H=0.5 mm, C-F=0.2 mm.

Fig. 6. Anonyx nugax (Phipps, 1774), adult female, 19.07mm.A, pereopod 3; B, pereopod 4; C, pereopod 5; D, pereopod 6; E, pereopod 7; F, uropod 1; G, uropod 2; H, uropod 3; I, telson. Scale bars:A-H=0.5 mm, I=0.1 mm.