Prometopa cedrici, Krapp-Schickel, 2011

Krapp-Schickel, Traudl, 2011, New Antarctic stenothoids sensu lato (Amphipoda, Crustacea), European Journal of Taxonomy 2, pp. 1-17 : 3-12

Prometopa cedrici sp. nov.

Figs 1-6

Holotype

♂? 4.5 mm, fully dissected and mounted in slides in Faure's liquid; RBINS, I.G. 31071 2 slides: IG 31071 / INV 83816A and IG 31071 / INV 83816B ( Museum Brussels). R/V Polarstern, cruise ANTARKTIS- XXIII/8, Larsen B area, station 702-9 B_ South 65°57.85'S 60°28.42'W to 65°57.42'S 60°28.12'W, 12/01/2007, 215- 221 m, hard bottom with a lot of hydrocorals; gear: Agassiz trawl.

Paratype

♀, 4.8 mm, partly dissected, dissected parts mounted on 2 slides, registration numbers: RBINS, IG 31071 / INV 83816B and INV 83816C (Museum Brussels), same locality as above.

Etymology

Dedicated to Cédric d'Udekem d'Acoz (Brussels), extremely careful taxonomist for amphipods and decapods.

Description

HABITUS. Dorsal outline spiky from peraeonite 1-5, the next four body segments reinforced dorsally, appearing 'double folded', with rounded outline. Suture between urosomites not clear.

HEAD. A1 subequal to A2. A1 peduncle art. 1> art. 2, ratio art. 2:art. 3 = 2; art. 1 ordinary, without nasiform process; flagellum with 14 arts. A 2 art. 4> art. 5, flagellum with 8-9 arts.

Mouthparts: Md molar small; palp longer than Md body, ratio art. 2:art. 3 = about 3, sparse and regular setation on art. 2, only one distal seta on art. 3. Mx1 palp with 2 arts. Mx2 IP about half length of OP, both with long setae distally, next to them some short ones.

GNATHOPODS. Gn1 much smaller than Gn2. Cx1 semicircularly rounded distally. Basis robust and distally widening, on anterior margin long and short setae, on posterior one only short setae. Ischium longer than wide, with long setae distally. Merus distoposteriorly lengthened and beset with short and stiff setae, also two long setae and two spines distally. Carpus triangular, beset with long setae on anterior and posterior margin. Propodus 3-4 times as long as wide, on all margins some long setae, palm weakly rounded without any palmar corner, but defined by 5 spines.

Gn2 strong. Cx2 tongue-shaped, about twice as long as wide, with nearly parallel margins. Basis 3.5 times longer than wide, anterior margin densely beset with many fine setae, only 3 setae on posterior margin. Ischium somewhat longer than wide, like merus with few setae. Carpus triangular, shorter than wide, distally lobed with long distal and shorter marginal setae. Propodus subrectangular, distally a bit wider than proximally, with irregular setae anteriorly and posteriorly; palmar corner nearly rectangular, with prominent robust tooth, palm with U-shaped excavation medially and many small incisions. Dactylus short and strong, with many short setae on the inner side.

PERAEOPODS. P3 slender. Cx3 similar to Cx2, about 2.5 times as long as wide, with parallel margins. Basis and ischium about twice as wide as propodus and carpus, merus acutely lengthened anterodistally. Dactylus strong. P4 clearly stronger than P3: Cx4 subtrapezoidal, about as long as wide. Basis and ischium similar to P3. Merus much wider than in P3, acutely lengthened anterodistally. Carpus distad widening, with short spines. Propodus with spines and setae. Dactylus distally bifid. P5 similar to P4, strong and richly beset with spines and setae on both margins; basis rectangular, merus posteriorly lengthened, reaching about half length of carpus; dactylus robust, bifid. P6 similar to P5 but basis widened, posterior margin straight, merus posteriorly reaching end of carpus. P7 similar to P6 but basis posteriorly much more widened, margin rounded.

PLEON. Pl1-3 and Us1 dorsally thickened, with 'double pleat'.

Ep1 tongue-shaped lengthened posterodistally. Ep2, 3 with small upturned tooth posterodistally.

Us2 much narrower than Us1 or Us3.

U1 peduncle much longer than subequal rami, with small spines. U2 peduncle longer than longer ramus, ratio of length of rami about 3:2; with small spines. U3 very strong, peduncle shorter than in U2, but about twice as wide, with strong spines; ramus two-articulated, articles about the same length and also with strong spines on first article.

TELSON. Triangular, flappable, about 1.7 times longer than wide, with 4-5 strong spines marginally.

Remarks

This genus seems quite closely related to the following one, in partly sharing also a nasiform thickened A1 peduncle and varying humps dorsally. But the telson is flappable and horizontally inserted, as in ordinary stenothoids, and the propodi of the gnathopods are very different in size and shape.

For comparing this new species with other members of the genus, see key:

Key to Prometopa species

1. A1 peduncle article 1 without nasiform process...................................................................................2 – A1 peduncle article 1 with nasiform process..........................................................................................3

2. Gn2 palm smooth, oblique, not defined; Cx4 posteriorly excavated, Cx5 longer than broad; T2 pairs of spines; body segments dorsally smooth............................... Prometopa dorsoundata Bushueva, 1988

– Gn2 nearly rectipalmate, well defined by strong and prominent tooth; Cx4 posteriorly not excavated, Cx5 broader than long; T with 4-6 pairs of spines; posterior body segments dorsally 'pleated'......................................................................................................... Prometopa cedrici sp. nov

3. Strong sexual dimorphism, head with lacking prolongation, two acute dorsal protuberances on pleon segments........................................................................... Prometopa tuberculata Schellenberg, 1926

– Lacking sexual dimorphism, head with anterior prolongation, lacking dorsal protuberances on pleon segments...................................................................................... Prometopa edentata Rauschert, 1990

Barnard & Karaman (1991) called the stenothoid group with enlarged, thickened and vertically inserted telson 'subgroup thaumatelsonins'. In Krapp- Schickel (2006) as well as DeBroyer et al. (2007: 221) it is cited as 'subfamily Thaumatelsoninae' and Krapp- Schickel & Koenemann (2006) used various cladistic analyses in an effort to separate all thaumatelsonid members from the other stenothoids.

There is no doubt that thaumatelsonids are different, but the more stenothoids we discover, the less justified it seems to formally divide the huge number of stenothoid genera into different families or subfamilies with clearcut synapomorphies (something which I aimed at for long time), as there are always some bridging species with shared character states. However, the term 'Thaumatelsonin stenothoids' remains useful keeping in mind that this group most probably is not a completely natural clade.

Genus Antatelson J.L. Barnard, 1972

Type species: Thaumatelson walkeri Chilton, 1912

There are currently six included species: A. antennatum Bellan-Santini & Ledoyer, 1974 ; A. cultricauda (K.H. Barnard, 1932) , A. cuneatum Krapp- Schickel, 2006; A. rostratum Bellan- Santini & Ledoyer, 1974; A. tuberculatum Andres, 1989 ; A. walkeri ( Chilton, 1912) .

Diagnostic characters

A1 with nasiform process on art. 1. Flag. acc. minute to absent. Palp of Md usually with 3 arts., third art. sometimes reduced. Mx1 palp with 2 arts. Mxp IP well separated. Gn1, 2 subchelate, scarcely different in size and shape. Gn1 palm scarcely oblique, palm shorter or equal posterior margin. Gn2 propodus subrectangular, longer than wide, palmar corner nearly rectangular. P5-7 basis rectolinear. Peraeonite 4 much wider than segments 3 or 5 ( Barnard & Karaman 1991: 688 state that peraeonites 4-6 are coalesced, but this is never the case). Body dorsally smooth or with protuberances. Telson huge, vertically inserted, laterally compressed, fleshy.

Figures

Fig. 1. Prometopa cedrici sp. nov. Paratype: ♀, 4.8 mm. Photo by Cedric d’Udekem d’Acoz.

Fig. 2. Prometopa cedrici sp. nov. Paratype: ♀, 4.8 mm. Habitus a) laterally; b) dorsally; c) ventrally; d) frontally.

Fig. 3. Prometopa cedrici sp. nov. Paratype: ♀, 4.8 mm. A1, 2 = antennae; A1' first antenna partly enlarged; Mx1, 2 = maxillae; Mxp = maxilliped; Md = mandible.

Fig. 4. Prometopa cedrici sp. nov. Paratype: ♀, 4.8 mm. Gn1, 2 = gnathopods; Gn1' = propodus of first gnathopod enlarged.

Fig. 5. Prometopa cedrici sp. nov. Paratype: ♀, 4.8 mm. Cx7 = coxa 7 with peraeonite 7, showing the thickened dorsal part; outline: shape of middorsal bodyline (head on left side); P3-7 peraeopod 3-7; P4', P4'' distal part of peraeopod 4 enlarged; P5' dactylus of P5 enlarged.

Fig. 6. Prometopa cedrici sp. nov. Paratype: ♀, 4.8 mm. Ep1-3 = epimeral plates 1-3; Us = urosome with U1-3 = uropods 1-3; T = telson. Below right: Prometopa tuberculata head with Gn1.