Proboloides Della Valle

Krapp-Schickel, Traudl, 2011, On the Austral-Antarctic stenothoids Proboloides, Metopoides, Torometopa and Scaphodactylus (Crustacea Amphipoda) Part 2: the genus Proboloides, with description of two new genera and the transfer of two nominal species to Metopoides, ZooKeys 86, pp. 11-45 : 14-15

Genus Proboloides Della Valle

Della Valle, 1893: 907

Type species.

Metopa gregaria Sars, 1882: 93, t. 4, fig. 6

Proboloides mainly occurs in the Atlantic, but nominal Proboloides species have been reported also from the Pacific, Indian and Antarctic oceans. Its species are often found living in deep waters and show a clear sexual dimorphism, usually their gnathopods are quite different in size and shape, often with a strongly incised Gn2 palm, with palmar corner well defined in females, but not defined in males, and robust peraeopods.

Diagnostic characters.

A1 peduncle art 1 usually short, length <3 × width, subequal to cephalon; A1 usually shorter than 2/3 body length, A1 accessory flagellum lacking. Md palp with a very short or lacking art3, poorly setose; Mx1 palp 2 arts; Mx2 inner plate ordinary; Mxp inner plates well separated, outer plates usually reduced (less than 0.2 of merus length). Ratio Cx2:Cx1> 3. Cx2 length equal or more than 1.5 x the width. Gn1, 2 different in size and shape; Gn1 small, almost simple, rarely subchelate; carpus length equal to propodus; length of propodus Gn1 about half or less than half length of propodus Gn2; Gn2 palm has serrations or teeth, usually no incisions; Gn2 propodus is in males often, in females always smaller than Cx2; carpus shorter than wide, merus elongate. P5 basis linear, without posterodistal lobe; merus anterior margin shorter than 1.25 length of propodus anterior margin. P6, 7 basis expanded and lobate, merus tip reaching half to full length of carpus. Ep3 with acute posterodistal corner. U1 peduncle is longer than longer ramus. T length is shorter to equal the double width, triangular, laminar.

At the beginning of this study 16 species were known:

11 from the Atlantic, Pacific and Indian Ocean: Proboloides anophthalmus Ledoyer, 1986, Proboloides calcaratus (Sars, 1882), Proboloides clypeatus (Stimpson, 1853), Proboloides grandimanus (Bonnier, 1896), Proboloides gregarius (Sars, 1895), Proboloides holmesi Bousfield, 1973, Proboloides pacificus (Holmes, 1908), Proboloides schokalskii Gurjanova, 1946, Proboloides schuleikini Gurjanova, 1946, Proboloides tundus Barnard, 1962, Proboloides zubovi Gurjanva, 1951.

5 members from Antarctic-Subantarctic region: Proboloides porcellanus KH Barnard, 1932, Proboloides rotundus (Stebbing, 1917), Proboloides stephenseni Ruffo 1949, Proboloides typicamimus Andres, 1995, Proboloides typicus (Walker, 1906).

The differences between the current diagnoses of Metopoides , Proboloides , Scaphodactylus and Torometopa are still quite small and not satisfactory:

Metopoides . Mouthparts ordinary. Long antennae with 2-articulate flag. acc.; unspecialized gnathopods; short coxal plates; basis P6, 7 with weakly lengthened merus.

Proboloides . Md palp may have a shortened third article, the inner plates of Mxp may be fused. Antennae robust with 0-1 articulate acc. flag.; gnathopods with sexual dimorphism, Gn1 much smaller than Gn2; coxal plates enlarged; basis P6, 7 with strongly lengthened and widened merus.

Scaphodactylus . Mouthparts ordinary. Antennae with 2- articulate acc. flag.; gnathopods without or with sexual dimorphism (there are two groups within the genus); Gn1 dactylus spoon-shaped excavated; coxal plates small; basis P5 rectolinear with posterodistal lobe lengthened and widened; P6, 7 merus very weakly lengthened and widened.

Torometopa . Mouthparts ordinary. Antennae with 0-2- articulate acc. flag.; gnathopods without or with sexual dimorphism; coxal plates small or large; basis P5 rectolinear with posterodistal lobe lengthened and widened to varying degrees; P6, 7 merus weakly to strongly lengthened and widened. In short, characters of Metopoides and Proboloides together, but P5 basis with posterodistal lobe, which might have evolved independently. Thus this genus was the least convincing one.

To fill the gaps with question marks in the first matrix (see also Krapp-Schickel 2009), I studied the following species in detail: