Stenothoe lowryi, Azman, 2023

Azman, Abdul Rahim, 2023, Description of Stenothoe lowryi sp. nov. (Crustacea: Amphipoda: Stenothoidae), from the Straits of Malacca, Malaysia, Records of the Australian Museum (Rec. Aust. Mus.) 75 (4), pp. 371-379 : 373-376

Stenothoe lowryi sp. nov.

urn:lsid:zoobank.org:act:27D7AC0F-003D-4D24-92D1-FFAB571B22BD

Figs 2–4

Holotype: Male , 5.3 mm (from tip of rostrum to apex of telson), UKMMZ-1133, Peninsular Malaysia, Pangkor Island, Teluk Nipah beach, 4°14'00.0"N 100°31'00.0"E, intertidal area, rock washing, 0–1 m depth, B. A. R. Azman, S. Y. Gan, J. H. C. Lim, C. F. Liong, 12 January 1996 ( UKM I.D. PKR 1.3923) . Allotype: Female, UKMMZ-1134, same station data as holotype; dissected appendages were kept in five semi-permanent slides mounted on glycerol.

Diagnosis. Stenothoidae with long antenna 1 (distinctly longer than head and pereonites 1–4) with peduncular article 1 2× longer than broad. Maxilliped palp article 3 short. Maxilla 2 well developed, with outer plate 2-articulate. Gnathopod 1 propodus about 2× as long as broad. Gnathopod 2 propodus with palmar margin moderately convex. Pereopod 7 basis proximally or slightly expanded (more than 1.5–1.8× as long as broad). Uropod 2 rami with single robust seta on medial margin. Uropod 3 article 2 distinctly longer than article 1, not rugose. Telson apically subacute.

Description. Male (based on holotype, 5.3 mm). Body smooth.

Head. Antenna 1 long (distinctly longer than head and pereonites 1–4), subequal in length to antenna 2; peduncle not geniculate; peduncular article 1 2× longer than broad, without anterodistal lobe, without posterodistal lobe; peduncular article 2 without anterodistal lobe; accessory flagellum absent; flagellum 20-articulate. Mandible palp absent; incisor process well developed. Maxilliped palp article 3 short. Maxilla 1 palp 2-articulate. Maxilla 2 well developed with outer plate 2-articulate.

Pereon. Gnathopods 1–2 dissimilar in shape; gnathopod 1 subchelate; merus enlarged, produced distally; carpus short (about as long as broad); propodus anterior and posterior margins subparallel (not expanded distally), about 2× as long as broad. Gnathopod 2 coxa posterior margin straight; basis anterodistal margin smooth; merus posterior margin convex, with setae; propodus narrow, oval, without posterodistal expansion, medium length (about twice as long as broad) (2.1), not transverse, palmar margin moderately convex, ventral margin with crenulation, (distally crenulate), with dense row(s) of fine setae; dactylus reaching distinctly further than half length of propodus, acute. Pereopod 3–7 setose. Pereonite 4 not elongate (similar length to pereonite 3); without dorsal carina. Pereopod 4 coxa ventral margin convex. Pereopod 5 basis not expanded. Pereopod 6 basis fully expanded; posterior margin straight. Pereopod 7 basis proximally or slightly expanded (more than 1.5× as long as broad), posterior margin convex (slightly), with crenulation; merus distally twice as wide as ischium, with ventral row of robust setae, expansion not reaching to mid-length of carpus; dactylus small (distinctly smaller than carpus).

Pleon. Epimeron 3 posteroventral corner subquadrate/ rounded. Uropod 1 peduncle with a distoventral spur; inner ramus well developed, subequal in length to outer ramus. Uropod 2 inner ramus well developed, subequal in length to outer ramus, rami with single robust seta on medial margin. Uropod 3 with peduncle and ramus; ramus subequal or longer than peduncle; peduncle longer than article 1; ramus 2 articulate; article 1 without marginal robust setae; article 2 distinctly longer than article 1, proximally swollen, not rugose. Telson laminar, with dorsolateral robust setae, apically subacute.

Female (sexually dimorphic characters). Gnathopod 1 propodus about 3× as long as broad. Gnathopod 2 propodus medium length (about 2 times as long as broad). Uropod 3 article 2 not swollen. Telson apically acute or subacute.

Etymology. This species is named after the late Dr J. K. Lowry, world-renowned amphipod taxonomist, in recognition for his outstanding taxonomic and systematic work on the amphipod fauna of the world.

Remarks. The material at hand is similar to Stenothoe gallensis Walker, 1904 , a distinctive species originally described from Galle, Sri Lanka. It should be noted, however, that in Walker’s original illustration, he mistakenly labelled pereopod 7 as pereopod 5. After thorough observation of the specimens from Pangkor Island, it is clear that they are not attributable to S. gallensis . Table 1 summarizes the characters and states reviewed from literature and the present study. Krapp-Schickel (2015) reviewed and reassessed most of the previously synonymized records of S. gallensis from various localities and placed S. irakiensis Salman, 1985 as a junior synonym of S. gallensis .

Comparing the descriptions and illustrations in the original texts ( Salman, 1985), this new species is most morphologically similar to Salman’s material of S. gallensis Walker, 1904 from the Arabian Gulf, in the shape of male gnathopod 2; outer plate of maxilla 2 with 2 articles; and article 2 longer than article 1 of uropod 2. Despite showing greatest morphological similarity, S. gallensis and S. lowryi sp. nov. have slight differences, with the latter having: 1) gnathopod 2 propodus with palmar margin moderately convex; 2) uropod 2 rami with only one robust seta on medial margin; 3) uropod 3 article 2 distinctly longer than article 1, proximally swollen, not rugose.

In S. lowryi , the separated articles of the outer plate of the Stenothoe irakiensis Salman, 1985 (junior synonym: S. gallensis Walker, 1904 ); S. irinae Marin & Sinelnikov, 2018 ; S. nhatrangensis Marin & Sinelnikov, 2018 ; S. andamanensis Krapp-Schickel, 2015 .

second maxilla is also present in S. andamanensis Krapp-Schickel, 2015 , but the new species can be recognized by: uropod 2 with only one robust seta on medial margin of rami (versus 2 or more robust setae in S. andamanensis ); uropod 3, article 2 distinctly longer than article 1 (length subequal in S. andamanensis ); and uropod 3 article 2 not rugose (article 2 rugose in S. andamanensis ).

From S. nhatrangensis Marin & Sinelnikov, 2018 , S. lowryi can be distinguished by the following features: maxilla 2 outer plate with separated articles (fused in S. nhatrangensis ); gnathopod 2 palmar margin of male moderately convex (concave in S. nhatrangensis ); coxa 2 posterior margin straight (rounded in S. nhatrangensis ); and uropod 2 with only one robust seta on the medial margin of the rami (with two or more robust setae in S. nhatrangensis ).

Finally, S. lowryi sp. nov. can be distinguished from S. irinae Marin & Sinelnikov, 2018 by: maxilla 2 outer plate with separated articles (fused in S. irinae ); coxa 2 posterior margin straight (rounded in S. irinae ); uropod 3 article 2 distinctly longer than article 1 (subequal in length in S. irinae ); and uropod 3 article 2 not rugose (article 2 rugose in S. irinae ).

Distribution. Pangkor Island, Peninsular Malaysia.

Figures

Figure 2. Stenothoe lowryi sp. nov., holotype male, 5.3 mm, UKMMZ-1133.

Figure 3. Stenothoe lowryi sp. nov., from Pangkor Island, Malaysia. Holotype male, 5.3 mm, UKMMZ-1133.Allotype female, 4.9 mm, UKMMZ-1134. Scales: A1, A2 = 0.4 mm; Mx2, Md = 0.1 mm; Mx1, Mp, G1 = 0.2 mm; remainder = 0.5 mm.

Figure 4. Stenothoe lowryi sp. nov., from Pangkor Island, Malaysia. Holotype male, 5.3 mm, UKMMZ-1133. Allotype female, 4.9 mm, UKMMZ-1134. Scales: P3–P7 = 0.5 mm; PL1–PL3 = 0.2 mm; remainder = 0.1 mm.