Stenothoe crenulata Chevreux, 1908

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 : 2320-2324

Stenothoe crenulata Chevreux, 1908

( Figures 3 , 4 ; Table 1)

Stenothoe crenulata Chevreux 1908: 471–475 , fig. 1–3; Shoemaker 1935: 237 fig. 2; Barnard JL 1955: 3–5, fig. 1.

Type locality

Gambier Archipel, Île Mangareva, Polynesia.

Material examined

Male 3 mm, Barbados, off Belairs Res. Inst., Holetown, Caribbean Sea, from corals, slide in the collection of SNM (illustrated).

Male 3 mm Pacific Ocean 4°30 ʹ N, 137°10 ʹ E, SNM .

Female 2 mm Venezuela (between Aruba and Blanquila), mud, summer 1936, NBCL ( PWH).

Male 2 mm (slide), females 2 mm, 1.5 mm Barbados offshore 02/1964, NBCL ( PWH).

Male Curaçao 1462, water-pipe, iron supports in tidal flow, with dense Pennaria , Didemnum , Styela and Microcosmus , 0–1 m depth, 02/01/1964, NBCL ( PWH).

About 70 males, females and juveniles, Sanur-Bali, Indonesia, algae of 2–4 m depth, July 1993 ( MVRCr) .

Diagnosis

Length 3 mm. Gn 2 male basis anteriorly widened; palm with dense but short setae, similar to those on dactylus inner margin.

Redescription

Based on Chevreux’ s original description, completing it:

Length 3 mm.

Head scarcely produced, with minute rostrum. Ocular lobe truncate. Eyes rounded, rather small. Antenna 1 longer than head and peraeonites 1–4, subequal to antenna 2; peduncle length of art 1> art 2; flagellum with about 17–22 articles; accessory flagellum absent. A 2 peduncle length of art 4> art 5, flagellum <peduncle, about 16–18 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 one. Maxilliped inner plate linguiform, with two distal setae; outer plate lacking.

Peraeon. Peraeonite 4 not elongate, wider than peraeonite 3. Gnathopods 1–2 dissimilar in shape. Gn 1 subchelate; length of propodus> merus + ischium together; length of propodus = 2× length of carpus; merus enlarged, produced distally, the tip reaching end of carpus; carpus triangular, l ≥ b; propodus 2× as long as broad, palm equal to remaining hind margin, group of defining setae small and not strong; palm rounded, oblique, propodus on palmar corner widest. Coxa 2 anterior margin rounded, posterior margin excavate, distally narrowing or rectangular. Gnathopod 2 male basis anteriorly widened, sometimes with crenulate margin; merus posterior margin rounded, crenate, with a setule in each notch; propodus posterior margin straight, palm reaching proximal end of propodus, thus no posterior margin remaining, palmar corner lacking, with two posterodistal humps, the proximal higher; propodus about 2.5–3× as long as broad, palm with dense row of fine short setae; dactylus reaching end of propodus, inner margin beset with setae of the similar length as on propodus. Peraeopods: Coxa 3 distally somewhat widening. P 3, 4: similar to each other.

Pleon. Uropods: U 1 reaching end of U 3; with prominent peduncular spur; peduncle> rami, rami subequal, spinose. U 2 shorter than U 1 or U 3, rami subequal. U 3 peduncle equal to ramus, ramus art 1 ≥ art 2, art 1 beset with 2–3 spines along the upper margin, with pair of distal spines, ramus art 2 upwards bent in the middle and regularly sculptured on the upper surface. Telson concave on the upper side, oblong, with three spines on the proximal half of each side.

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

Remarks

This species has been synonymized with S. gallensis and is herewith revived, belonging to the S. gallensis group. Difference to the above described S. gallensis : length only 3 mm; Cx 2 posteriorly somewhat excavated, distally narrowing, but this character probably changes with size; Gn 2 male basis anteriorly widened, sometimes with crenulate margin, merus posterior margin regularly rounded and densely beset with short setae; length of setae on dactylus and propodus similar; U 2 subequal; U 3 male ramus art 2 claw-like, regularly curved and sculptured; U 3 ratio peduncle ≤ ramus, ramus art 1> art 2.

J.L. Barnard (1955, p. 3–5, fig. 1) illustrates material of what he called S. gallensis collected from Hawaii which seems very similar, but the length of males is given as 5 mm (vs 3 mm in Chevreux for S. crenulata ), Cx 2 has a rectangular shape and no excavation on posterior margin, male Gn 2 merus has an acute posterodistal corner, and he does not mention nor illustrate the remarkably long peduncular spur on U 1 of S. crenulata , also not described by Chevreux, but always well visible in the present material.

The material of S. crenulata collected from Puerto Rico by Shoemaker (1935, p. 237 fig. 2) has no body length indicated, Cx 2 is drawn as regularly rectangular, and the setae on Gn 2 propodus are longer than the ones on the dactylus.

From Barbados and from Curaçao came two much smaller males, also illustrated here. The characters mentioned above are mixed, thus probably depending on allometry:

Length is 2 mm, Gn 2 male is very similar to the drawing by Barnard (1955, fig. 1; but body length less than half), Gn 2 merus is also strikingly acute distally, but the setae on the propodus are much longer than illustrated in Barnard, while the ones on the dactylus are extremely short and much less dense. Cx 2 is slightly excavate (vs straight in Barnard), U 1 has a long peduncular spur (not illustrated in Barnard).

More than 20 years ago, I collected quite a lot of stenothoids from Bali ( Indonesia): in the same samples there is S. frecanda Barnard, 1962 (described from California) and material very close to the original description of S. crenulata: Cx 2 is posteriorly slightly excavated or rectangular, Gn 2 male setae on the dactylus as long and dense as on propodus inner margin or somewhat longer. The difference between S. frecanda and S. crenulata is not very strong, besides the shape of U 3, but U 1 in S. frecanda is never straight, but bent upwards in the articulation between peduncle and ramus, and U 2 rami are clearly unequal.

I think all material discussed here matches S. crenulata Chevreux morphologically.

Distribution

Indonesia, Polynesia, Hawaii, Caribbean Sea.

Figures

Figure 3. Stenothoe crenulata Chevreux, 1908: male, Barbados, Caribbean Sea: Md = left and right mandible; Gn 1, 2 = first and second gnathopod with the same enlargement; Gn 1ʹ, Gn 2ʹ = both gnathopods partly enlarged; P 3 = third peraeopod; Us = urosome with uropods and telson; U 3 = third uropod; T = telson.

Figure 4. Stenothoe cf. crenulata Chevreux, 1908: male, 3 mm, Pacific Ocean 4°30ʹ N, 137° 10ʹE: A 1, 2 = antenna 1, 2; Gn 2 = male second gnathopod; U 3 = third uropod male; U 1, 2, 3 = uropod 1, 2, 3; T = telson.