Stenothoe gallensis Walker, 1904

Krapp-Schickel, Traudl, 2015, Minute but constant morphological differences within members of Stenothoidae: the Stenothoe gallensis group with four new members, keys to Stenothoe worldwide, a new species of Parametopa and Sudanea n. gen. (Crustacea: Amphipoda), Journal of Natural History 49 (37), pp. 2309-2377 : 2316-2318

Stenothoe gallensis Walker, 1904

( Table 1)

Stenothoe gallensis Walker 1904: 261–62 , pl. 3, fig. 19 ( Sri Lanka); Nayar 1959: 17–18, pl- V, figs. 7–19 (Madras coast, India); Nayar, 1967: 144–45, fig. 5e ( Sri Lanka).

non Reid, 1951: 228 ff.

Stenothoe irakiensis Salman, 1985: 244–250 , figs. 1–4 (Arabian Gulf).

Type locality

Ceylon = Sri Lanka (7°N, 80°E) .

Material examined

Three males, 15 females in alcohol, one male slide; Dar es Salaam, Tanzania, coll. Stuhlmann 5/11/1902 ( MNHUB inv. Nr. 21544, slide 815) .

Diagnosis

Length 5–6 mm. Coxa 2 rectangular, with parallel margins, in hyperadult males posterior margin somewhat excavate. Gn 2 male propodus with two palmar humps near dactylus insertion; palm straight, beset with long, dense setae; no remaining posterior margin; dactylus also densely beset with setae of about half the length of the ones on palm, but they can be worn out and lacking; merus posteriorly rounded, with shallow incisions where long setae are inserted. Gn 2 female propodus triangular, similar to the shape of Gn 1. U 2 rami spinose; U 3 peduncle spinose, ramus art. 1 with one distal spine; ratio peduncle: ramus subequal, with geniculation and sculpture of second article in males.

Redescription

Based on Walker’ s original description, completing it:

Length of male 5–6 mm.

Head scarcely produced, with minute rostrum. Ocular lobe truncate. Eyes rounded, rather large. Antenna 1 longer than head and peraeonites 1–4, somewhat longer than antenna 2; peduncle length of art 1 and art 2 subequal; flagellum with about 22 articles; accessory flagellum absent. A 2 peduncle length of art 4 = art 5, flagellum> peduncle, about 18 arts.

Mouthparts: Mandible palp absent, with conical hump where insertion would normally occur. Maxilla 1 palp 2-articulate. Maxilla 2 outer plate sitting upon inner one. Maxilliped inner plate rectangular, with 2 distal setae; outer plate lacking.

Peraeon. Peraeonite 4 not elongate, similar in length to peraeonite 3. Gnathopods 1–2 dissimilar in shape. Gn 1 subchelate; length of propodus = length of merus + ischium together; length of propodus = 3× length of carpus; merus enlarged, produced distally, the tip reaching or surpassing end of carpus; carpus triangular, l ≥ b; propodus 2× as long as broad, palm equal to remaining hind margin, group of defining setae is small and not strong; palm rounded, propodus on palmar corner widest, distally narrowing. Gnathopod 2 merus posterior margin in both sexes crenate, with a setule in each notch. Propodus posterior margin straight, palm in male reaching proximal end of propodus, thus no posterior margin remaining, palmar corner lacking, with two posterodistal humps (Walker:‘double-pointed tooth’), the proximal higher, the irregular distal one with 6 intra-marginal setules; about 2.5–3× as long as broad, with few setae in female, dense row(s) of fine longer setae in males; dactylus reaching end of propodus in female, often surpassing it in male, both margins smooth and beset with setae.

Peraeopods: P 3, 4: similar to each other and to S. marina . P 5 basis after Walker l.c, ‘about half as wide as long, longer than the next 2’, which must be an error; merus only little produced distally; propodus nearly as long as carpus + merus together; dactylus strong.

Pleon. Pleonite 3 without dorsal elevation. Epimeron 3 posteroventral corner acute.

Uropods: U 1 reaching end of U 3; peduncle> rami, rami subequal, a spine in the middle of the inner one, 2–3 spines in the middle of the outer one. U 2 shorter than U 1 or U 3, rami subequal, spinose. U 3 peduncle ‘longer than the ramus’ in text of Walker; but in his illustration U 3 peduncle is equal to ramus art 1 + art 2, peduncle beset with 5–6 spines along the upper margin; ramus art 1 with one distal spine, ramus art 2 upwards bent in the middle and finely denticulate on the upper surface.

Telson concave on the upper side, oblong, with four spines increasing in size distally on the proximal half of each side.

Female. Gn 2 propodus palm convex, without palmar corner, but four nearly equidistant spines and some setae near the middle. U 3 last article straight and not rugose.

Remarks

The crucial characters after Walker are: length and shape of Gn 1 propodus, carpus, merus; Gn 2 two palmar humps near dactylus insertion; P 5 ‘basis wide, l:b = 2!’ (a character which Walker withdrew later, as based on an error), U 3 ratio of peduncle and ramus subequal, geniculation and sculpture of second article in males.

On the Madras coast ( India), Nayar (1959) found additional material of this species, and in 1967 again in the Gulf of Mannar ( Sri Lanka), which he redescribed and illustrated. In 1985, Salman erected a new species Stenothoe irakiensis (thoroughly guarded by Jerry Barnard) from the Arabian Gulf, and it matches perfectly in all described details, except that he describes and illustrates a peduncular spur on U 1, not mentioned before; thus, it is given in synonymy here.

The material from East Africa, that I examined at the Berlin Museum, also matches S. gallensis perfectly.

I do not offer an illustration of this species in the present paper, as two colleagues have detailed drawings ready for publication, and on the other hand the drawings by Nayar and especially by Salman (1985) give sufficient information.

Distribution

Indian Ocean: from East Africa to South China Sea.