Montanaxius mediumquod, Dworschak, 2016

Dworschak, Peter C., 2016, A new genus and species of axiid shrimp (Crustacea, Decapoda) from a southwestern Indian Ocean seamount, European Journal of Taxonomy 229, pp. 1-11 : 3-9

Montanaxius mediumquod gen. et sp. nov.

urn:lsid:zoobank.org:act:3758B050-140A-49A8-81A9-240DDFA486A6

Figs 1–4

Eiconaxius sp. – Stone 2012: 74 (colour figure) (photograph by David Shale, available from http://ngm. nationalgeographic.com/ 2012 /09/seamounts/img/image-02.jpg [accessed 19 Feb. 2016]).

Etymology

The specific epithet mediumquod is an arbitrary combination of the Latin words “ medium ”, meaning middle, and “ quod ”, meaning what, derived from the type locality ‘Middle of What’; the name is used as a noun in apposition.

Material examined

Holotype

SOUTHWESTERN INDIAN OCEAN: ³, seamount ‘ Middle of What’ , 37°57.915′ S, 50°24.426′ E, 1135 m depth, from hexactinellid sponge, coll. 1 Dec. 2011 (fcn: JC066-3498, parent# 2584) (23.3/7.6) ( NHMW 25677 ).

Paratypes

SOUTHWESTERN INDIAN OCEAN: 1 ♀, same data as holotype (23.8/7.6) ( NHMW 25676); 1 ♀, same data as holotype, rostrum damaged, minor P 1 missing, dissected (25.7/7.4) ( NHMW 25675).

Description

Rostrum straight, depressed below level of carapace, 0.37 times length of front-to-cervical groove, with 3 to 4 lateral spines, posteriormost in supraocular position, but not enlarged, continuing into short unarmed lateral carina on anterior carapace. Submedian carina absent. High median carina with two strong teeth and one low tubercle reaching almost to cervical groove. Cervical groove distinct ( Figs 1 A–B, 2A, 3A–B, 4A–B). No median carina posterior to cervical groove. Sternite 7 (pereopod 4) deeply divided in midline over posterior two-thirds and with sharp oblique lateral ridge ( Figs 1F , 2H , 3L ). Sternite 8 (pereopod 5) with setose triangular flap on anterior face at base of leg. Pleomere pleuron 1 1.5 times as high as middorsal length, ventrally rounded; pleuron 2 broad, lateral length 1.6 times dorsal length, anteriorly rounded, posteriorly rounded; pleura 3–5 ventrally rounded; pleuron 6 rounded ( Fig 2B ).

Eyestalks half as long as rostrum; cornea pigmented ( Fig. 2C ). Antennular peduncle reaching to middle of antennal article 4; basal article with lateral spine ( Fig. 2D ). Antennal article 2 with strong dorsolateral spine and small ventromesial spine; antennal acicle triangular, reaching to 1/3 length of penultimate article of antennal peduncle, mesial margin with strong spine ( Fig. 2E ).

Mouthparts similar to those of other species of the family, without specific characters (see Poore & Collins 2009). Third maxilliped ( Fig. 2 F–G) with ventral spine on coxa and basis, small spines on ischium lower border, prominent crista dentata; two strong spines on merus proximally, one spine on carpus lower border proximally; exopod as long as ischium-merus, flagellate distally.

First pereopods (chelipeds) significantly differentiated, major more swollen, with longer palm and shorter, more robust dactylus. Major cheliped on the right side in holotype ( Fig. 1D ) and paratype NHMW 25675, on the left side in the other female paratype ( Fig. 3C ); ischium as long as wide, one spine proximally on lower border; merus three times as long as high, three spines increasing in size on lower border, one subterminal spine on upper border; carpus short, ¼ length of merus, cup-shaped, unarmed; propodus with palm as long as merus, upper and lower borders smooth, curved, lower border with strong keel; small gap proximally between fingers when closed; fixed finger triangular, cutting edge with one strong triangular tooth at midlength and several smaller teeth distally, one large rounded tooth at 2/3 length mesially; dactylus with incision proximally, upper border strongly curved, cutting edge with low triangular blade at midlength, one corneous spine on upper border near tip ( Fig. 3D ).

Minor cheliped ( Figs 1C , 3E ) slightly thinner and shorter than major one; ischium as long as wide, one spine proximally on lower border; merus with four spines on lower border and one subterminal spine on upper border; carpus short, cup-shaped; propodus with curved borders, unarmed, keel on lower border reaching to beginning of fixed finger, short keel on upper border distally; no gap between fingers when closed; fixed finger triangular, with almost straight cutting edge and corneous tip; dactylus slightly curved on upper border, almost straight on lower border, one corneous spine on upper border near tip ( Fig. 3F ).

Second pereopod ( Fig. 3G ) slender, 0.84 times as long as first pereopods; ischium short, merus long, five times as long as ischium, 8.3 times as long as wide; carpus 0.6 times length of merus; palm same length as carpus, fingers half as long as palm, cutting edges with tiny spiniform setae in distal ¾ ( Fig. 1E ).

Third pereopod ( Fig. 3H ) slender, same length as second pereopod; coxa with median spine (except in female NHMW 25675), with gonopore in females; carpus half as long as merus; propodus 0.8 times

length of merus, with group of spiniform setae on lateral face distally; dactylus 0.4 times length of propodus, tapering to corneous tip, with row of spiniform setae on lateral face ( Fig. 3I ).

Fourth pereopod ( Fig. 3J ) slender, same length and article proportions as third pereopod; coxa with median spine; propodus with dense setae on lower border distally, lateral face with spinifrom setae, dactylus with rows of spiniform setae.

Fifth pereopod ( Fig. 3K ) slender, same length as P2–P4, precoxal lobe ovate, with small acute spine ventrally, coxa with small gonopore in male ( Fig. 1F ), small round plate laterally ( Fig. 1G ); merus 3 times as long as ischium; carpus as long as ischium; propodus twice as long as carpus, with dense stiff setae on lower border distally; dactylus as long as ischium, tear-shaped.

Epipods on Mxp1 to P4, podobranchs on Mxp2 (rudimentary) to P3, arthrobranchs on Mxp2 (rudimentary) to P4, pleurobranchs above P2–P4 (see Table 1 ).

Gonochoristic. Male first pleopod ( Figs 1 G–I, 4C) uniramous, two-articled; second article half as long as first, with indentation distally, lateral lobe with mesially directed spine, mesial lobe with cincinnuli (appendix interna). Second male pleopod ( Fig. 1 J–K) with appendix masculina and appendix interna of about the same length. Female first pleopod ( Fig. 2I ) uniramous, flagellate distally. Female second pleopod ( Fig. 2J ) with appendix interna. Third to fifth pleopods slender, with appendix interna, one third length of endopod.

Telson longer than wide, posterior margin with median spine, lateral edges with two to three spines at midlength and group of three spiniform setae proximally, two pairs of spines on dorsal surface. Uropodal endopod with curved posterior border and straight anterior border, median row of spines on dorsal surface. Uropodal exopod with spines distally on anterior border, one to two strong spiniform setae at transition to transverse suture, the latter distally beset with spines, posterior border smooth ( Fig. 3M ).

Colour

Body and appendages translucent, brownish, chelipeds brown, cornea light brown, reflective (after photograph in Stone 2012).

Ecology

The shrimps were associated with an unidentified hexactinellid sponge.

Distribution

Known only from the type locality: southwestern Indian Ocean, seamount ‘Middle of What’, 37°57.915′ S, 50°24.426′ E, 1135 m depth.

Figures

Fig. 1. Montanaxius mediumquod gen. et sp. nov., holotype, ³, NHMW 25677. A. Carapace in lateral view. B. Same, dorsal view. C. Minor cheliped in dorsal view. D. Major cheliped in dorsal view. E. Tip of pereopod 2. F. Sternites 6–8. G. Ventral part of coxa 5 and pleomere 1 with Plp1 (first article bent) in lateral view. H. Left Plp1 in anterior view. I. Terminus of left Plp1, posterior view. J. Left Plp2, mesial view. K. Right Plp2, anterior view. Setation omitted in C and D. Scale bars: A–H, J–K = 1 mm; I = 500 µm.

Fig. 2. Montanaxius mediumquod gen. et sp. nov., paratype, ♀, NHMW 25675. A. Front in lateral view (rostrum broken). B. Pleon in lateral view. C. Left eyestalk, dorsal view. D. Right antennule in mesial view. E. Right antenna in ventral view. F. Third maxilliped in lateral view. G. Same in mesial view. H. Sternites 6–8. I. Left first pleopod in lateral view. J. Right second pleopod in posterior view. All setation omitted except in F and I. Scale bars: 1 mm.

Fig. 3. Montanaxius mediumquod gen. et sp. nov., paratype, ♀, NHMW 25676. A. Front in lateral view. B. Same in dorsal view. C. Major cheliped in lateral view. D. Same, fingers in mesial view. E. Minor cheliped in lateral view. F. Same, fingers in mesial view. G. Second pereopod, lateral view. H. Third pereopod, lateral view. I. Same, detail of distal articles. J. Fourth pereopod in lateral view. K. Fifth pereopod in lateral view. L. Sternites 6–8 in ventral view. M. Telson and right uropods, dorsal view. Setation omitted in A–F. Scale bars: 1 mm.

Fig. 4. Montanaxius mediumquod gen. et sp. nov., holotype, ³, NHMW 25677. A. Front in dorsal view. B. Same in lateral view. C. Terminus of left first pleopod, posterior view. Abbreviations: c = cincinnuli (appendix interna); s = spine. Scale bars: A–B = 1 mm; C = 500 µm.