Proscina stephenseni ( Pirlot, 1929 ), 2012

Zeidler, Wolfgang, 2012, A review of the hyperiidean amphipod families Mimonectidae and Proscinidae (Crustacea: Amphipoda: Hyperiidea: Scinoidea) 3533, Zootaxa 3533, pp. 1-74 : 8-10

Proscina stephenseni ( Pirlot, 1929)

( Fig. 1)

Parascina stephenseni Pirlot, 1929: 57–62 , fig. 4. Proscina stephenseni — Stephensen & Pirlot 1931: 544–545, fig. 17 (part). Pirlot 1932: 23. Barnard 1937: 179–180, fig. 21.

Vinogradov 1957: 208–209, fig. 13. Vinogradov 1970: 385 (table). Vinogradov et al. 1982: 123–124, fig. 52. Shih &

Hendrycks 1996: 591, 595, 596 (key), 599 (table), 600. non— Gasca et al. 2006: 239 (table), fig. 3e (here re-determined as Mimonectes sphaericus ) non— Mori et al. 2010: 4 (list), 8 (list) (see remarks).

Type material. This species was described from one immature female, measuring about 5 mm, from the North Atlantic (47°10’N 18°02’W); Armauer Hansen stn. 43, 2240 mw, 26 June 1922. The unique holotype is in the Aquarium-Muséum de l’Université de Liège, Belgium (RE 11979) .

Material examined. The specimens recorded by Barnard (1937), Gasca et al. (2006) and Mori et al. (2010), as detailed under remarks.

Diagnosis. According to Pirlot (1929) and Stephensen & Pirlot (1931). Pereon not inflated. Antennae 1 slightly shorter than pereon; relatively robust; callynophore with numerous, long aesthetascs. Antennae 2 reduced to two small, rounded articles. Gnathopod 1; basis relatively short, length 0.7x remaining articles combined, 1.4x carpus; propodus and carpus of similar length; propodus with numerous, long setae on anterior margin, distal corners produced slightly on either side of dactyl; dactyl thin, length 0.3x propodus. Gnathopod 2 similar in length to G1 but more slender; basis length 1.8x carpus; propodus length 1.5x carpus, armed with few long setae on both margins; dactyl like that of G1. Pereopoda all relatively slender. Pereopods 3 & 4 similar in structure, with P4 slightly longer; carpus much longer than merus but slightly shorter than propodus; dactyl a curved nail. Pereopod 5 slightly longer than P4; basis length 1.4x merus; merus, carpus and propodus of similar length, with few setae, mainly on posterior margin; dactyl thin, very short. Pereopod 6 marginally shorter than P5; basis length about 1.5x merus; carpus and propodus of similar length, marginally shorter than merus; dactyl like that of P5. Pereopod 7 marginally longer than P6, but all articles of similar structure and relative lengths. Uropoda with slender, relatively long, lanceolate rami, with serrated margins; all with inner ramus distinctly longer than outer, and much longer than peduncle, especially U1 & 2. Uropod 1; inner ramus length 1.6x outer, about twice peduncle. Uropod 2; inner ramus length 1.6x outer, and 1.8x peduncle. Uropod 3; inner ramus length 1.2x outer, and 1.7x peduncle; peduncle width 0.4x length. Telson with relatively blunt apex, slightly longer than broad, length about half peduncle of U3.

Colour not known for living specimens.

Remarks. Characteristic features of the type are the slender gnathopods and uropoda. In addition, the callynophore of the first antennae is furnished with numerous, long aesthetascs, a character usually associated with mature males, but the type is clearly a female with poorly-developed oostegites, as illustrated by Pirlot (1929) and Stephensen and Pirlot (1931). The propodus of gnathopod 1 is armed with long setae on the anterior margin, a character found in some males of Mimonectes , and the distal corners are produced slightly on either side of the dactyl. In this respect it resembles Mimonectes gaussi (Woltereck, 1904) , but in that species the projections are much more prominent, the pereopoda articles are of a different structure, and the uropoda have relatively short, wide peduncles and rami. The only other species with projections on the propodus of gnathopod 1, apart from Mimonectes diomedeae ( Woltereck, 1909) , which is similar to M. gaussi , is Mimonectes alexanderi sp. nov., but in that species the projection is only on the postero-distal corner, and the pereopods and uropoda are of a different structure. Thus, P. stephenseni would seem to be a valid species, and is here transferred to the genus Mimonectes .

In addition to the type there are five literature records of specimens as follows.

1. Barnard 1937: 179–180, fig. 21. One male, about 5.4 mm, ( NHM 1938.1.3.238); Southern Arabian Sea, near the Seychelles, John Murray stn. 131, 0–1500 m, 11 February 1934. I have examined this specimen ( Fig. 2) but have been unable to determine its specific status with confidence. It seems to be mature, judging by the numerous aesthetascs on the first antennae and the well-developed second antennae and genital papillae .

The specimen is in poor condition with the appendages missing from the right side, the urosome is badly damaged, and the buccal mass is also missing. The first antennae are relatively large and inserted near the ventral surface of the head, more so than in species of Mimonectes , contrary to one of the characters used to separate Proscina from Mimonectes .

It differs from the type (female) of P. stephenseni in the following characters, still discernible from the specimen, although some of these differences may be due to sexual dimorphism. Gnathopod 1; propodus lacks small projections on distal corners, adjacent to dactyl. Gnathopod 2; propodus relatively longer and broader, with slight, but distinct, postero-distal excavation. Pereopod 5; propodus is slightly shorter than carpus. Pereopod 7; merus is distinctly shorter than carpus (about half); in the type it is clearly longer than the carpus or propodus. Uropod 3; peduncle is relatively wide, about 0.6x length compared to 0.4x in the type.

The habitus is most similar to the three new species of Mimonectes described here, but the cuticle does not seem to be as thick, or opaque, and the pereon is without any discernible furrows; all of which may be because of its poorly preserved state. However, males of all of the three new species, which seem to be mature, and of a similar size to the present specimen, have the second antennae very much reduced. Of the three, it is most similar to M. neosphaericus sp. nov., except that the first antennae are about as long as the pereon and pleon combined, gnathopod 1 is simple, without pairs of strong setae on the palm, the peduncle of uropod 3 is relatively broader, and the telson is relatively shorter. The tiny outer ramus and odd rounded inner ramus of uropod three may be due to regeneration.

Thus, in view of the above, and considering its poor state of preservation, this specimen must be regarded as undeterminable, pending the discovery of more material of this, and allied, species.

2. Vinogradov 1957: 208–209, fig. 13. One female, 10 mm and one male, 9 mm, from the north-west Pacific , near the Kurile Islands (44°07’N 150°32’E); Vityaz, 0–3000 m and 0–2000 m respectively .

I have been unable to gain access to these specimens, but the illustrations provided by Vinogradov (1957) indicate that they are most likely Mimonectes sphaericus . The characters of the gnathopods and urosome, as illustrated, are typical of M. sphaericus and unlike the type of P. stephenseni , which has more slender uropoda, gnathopod 2 is very slender and simple, and gnathopod 1 has the distal corners of the propodus produced slightly on either side of the dactyl.

Shih & Hendrycks (1996) suggest that these specimens might represent their new species, P. vinogradovi , which is also very similar to M. sphaericus .

3. Shih & Hendrycks 1996: 591, 595, 596 (key), 599 (table), 600. It is not clear if the authors actually examined any specimens of this species, but in the table are listed records for the Atlantic (36°17’N 28°53W) (type locality for P. magna ) and the Arctic (85°53.5’N 136°47’W to 80°34’N 136°50’W), 300–900 m. However , no information is provided regarding how these records were obtained, whether or not specimens were examined, the sex and number of specimens, or their current depository, and the Canadian Museum of Nature could not provide any information regarding these records (Hendrycks pers. com.) .

4. Gasca et al. 2006: 239 (table), fig. 3e. One immature female, 8.0 mm, from the north-east Pacific, Monterey Canyon, California (36°68.5’N 122°06.3’W), ROV dive 843, 392 m, on the siphonophore Nectadamus diomedeae (Prayidae) .

I have examined this specimen and have re-determined it as Mimonectes sphaericus ; all characters being consistent with that species. This error in identification, and perhaps others, may have occurred as a result of following the record and illustrations of Vinogradov (1957) of specimens which are most likely M. sphaericus .

5. Mori et al. (2010), record this species from Sagami Bay and off Oshima, Japan. I have examined some of these specimens, from Sagami Bay, and three belong to the gammaridean family Stegocephalidae , one is M. gaussi and one is M. alexanderi sp. nov. Thus, this record should be ignored.

Distribution. Known only from the type locality and the south-western Indian Ocean ( Barnard 1937) as detailed above; the records of Shih & Hendrycks (1996) remaining unconfirmed.