Austinograea jolliveti, Guinot & Segonzac, 2018

Guinot, Danièle & Segonzac, Michel, 2018, A review of the brachyuran deep-sea vent community of the western Pacific, with two new species of Austinograea Hessler & Martin, 1989 (Crustacea, Decapoda, Brachyura, Bythograeidae) from the Lau and North Fiji Back-Arc Basins, Zoosystema 40 (5), pp. 75-107 : 89-90

Austinograea jolliveti n. sp.

( Figs 9A-H ; 10A-E; 11A-E )

TYPE MATERIAL. — Holotype. ♂ 12.8 × 20.0 mm (right-handed), western Pacific , North Fiji Basin, STARMER II cruise, dive 18 (PL 18), Mussel Valley site, 18°50’S, 173°29’E, 2750 m, 13.VII.1989 (MNHN-IU-2016-10769) ( Figs 9A-H ; 11A-E) . Paratypes. 1 ♂ 14.7 × 25.4 mm, 1 ♀ 12.4 × 21.6 mm ( Fig. 10A-E), same data ( MNHN-IU- 2016-10770) .

OTHER MATERIAL EXAMINED. — 1♀ 13.6 × 22.0 mm (left-handed), western Pacific , Lau Back-Arc Basin, MGLN07MV cruise, dive 237, ABE site, 20°45.65’S, 176°11.45’E, 2130 m, 25.IX.2006, MNHN- IU-2016-10751 (preserved in ethanol 85%).

TYPE LOCALITY. — Western Pacific , North Fiji Basin, Mussel Valley site, 2750 m.

ETYMOLOGY. — Dedicated to Didier Jollivet (CNRS, Station biologique de Roscoff, France), in recognition of his pioneering work on the ecology of the southwestern Back-Arc Basin hydrothermal communities in 1989 and for his valuable contribution to deciphering the delicate interplay of physical and biological factors in shaping the evolutionary history of hydrothermal vent fauna.

DISTRIBUTION. — Southwestern Pacific; only collected from one site in the Lau Basin (ABE site) and one site in the North Fiji Basin (Mussel Valley site).

DESCRIPTION (MALE)

Carapace

Carapace transversely elliptical, flat; regions indistinct. Dorsal surface nearly smooth, except for rare small granules on frontal region and tubercles on orbital region; numerous small pits. Anterolateral margin marked by rounded edge, slightly granulous. Posterolateral margins convergent; posterior margin slightly concave. Subhepatic region with dense setae mainly only at lateral edge. Front broad, not protruded, bluntly pointed medially and with two slightly convex lobes. Eyes, antennules and antennae recessed under front. Suborbital plate absent. Outer side of orbital region tuberculated. Proepistome incomplete. Orbital region deeply concave and open laterally, containing antennules, antennae and possible eye remnants. Eyestalk absent, podophthalmite fused to floor of orbital region; cornea absent, no visible pigment. Antennules folded horizontally, filling most of orbit. Antenna inserted in wide supraorbital notch; urinary article fixed, broad, recessed, basal article (2 + 3) cylindrical, moveable; article 4 elongated shorter, inclined. Margin of epistome projecting medially and formed of two markedly concave lobes, marked by row of low granules. Pterygostomial lobe granulous; pterygostomial region mostly smooth.

Thoracopods

Third maxillipeds completely closing buccal cavity. Ischium long, with marked longitudinal internal groove. Merus about half as long as ischium, narrow; external margin regularly curved, oblique, without marked angle; half distal part markedly narrow and much produced; half proximal internal margin with prominent median lobe. Carpus inserted in notch of anterointernal margin of merus; propodus thick; dactylus about as long as merus; inner margins of propodus and dactylus with brush-like setae. Exopod longer than endopod ischium. Wide mxp3 coxa with only proximal portion visible, its lateral projection hidden by junction of thoracic sternum (sternite 4) with pterygostome. Chelipeds long, heteromorphic. Palm of both chelipeds with inner surface bearing medially thick patches of setae, densely extending along occluding margins of both fingers, thus well dorsally visible along half of fingers. Dark colour extending on about whole fixed finger (the dark coloured of half posterior portion joins the coloured spot), and on two-thirds of dactylus of both crusher and cutter. Major cheliped (crusher) stouter than minor ones (cutter); merus notably elongated, largely extending beyond margin of carapace, narrow, anterior border entirely straight, with regular, small, distally reduced teeth; both fingers thick, blunt-tipped. Crusher: palm rather long, dorsal surface slightly convex, pitted; a conspicuous but hollow depression near base of fixed finger, appearing as pigmented spot, more or less in continuity with black area of fixed finger; dactylus elongate, thick, with only one blunt median tooth; fixed finger thick, with only one blunt proximal tooth on occluding margin; fingers thick, gaping, with blunt tips. Male cutter: palm elongate, nearly flat, smooth, with a conspicuous dark spot near base of fixed finger similar to that of the crusher; both fingers thick, more elongate, occluding, with blunt tips; dactylus with occluding margin smooth; occluding border of fixed finger with one proximal small tooth, and another one small more distally. P2-P5 shorter than chelipeds; P4 longest. Meri of P2, P3 with patch of dense setae on ventral margins, the patch being dense, thicker on inferior margin; meri of P4 and P5 and carpi, propodi of P2-P5 fringed on dorsal and ventral margins with short, stiff setae, mixed with longer setae. Dactyli elongate, with patches of short setae on anterior and posterior margins.

Thoracic sternum

Thoracic sternum with sutures 4/5-7/8 incomplete. Median line along sternite 8 and hardly continuying along sternite 7. Junction of sternite 4 with pterygostome via rather long juxtaposition; no patch of setae. Press-button of locking mechanism acute, close to suture 5/6, lacking on a side in holotype.

Pleon

Pleon of six free somites and telson, regularly triangular, third somite widest; telson short, bluntly triangular, rounded distally; pleonal somite 6 longest. G1: straight, with sparse, small and short setae, arranged in two rows along mid-part only. G2: about less than half G1’s length; flagellum very short, straight, flattened.

DESCRIPTION (FEMALE)

Subhepatic region without patches of dense setae. Chelipeds slightly dimorphic, both as cutters, major cheliped being hardly longer than minor cheliped; merus not elongated; chelae not markedly dissimilar; as in males, a pigmented spot near base of fixed finger on both propodi; both fingers not gaping, with acute tips. No pleonal locking mechanism. Pleon with margins densely fringed with setae. Vulvae rounded, closed by soft membrane.

COMPARATIVE DIAGNOSIS

The description of Austinograea jolliveti n. sp. is based on four, rather small specimens, from two vent sites. The species can be, however, distinguished from all other known Austinograea species by: 1) small size (to be checked on additional material); 2) subhepatic region with dense setae only at lateral edge (this feature needs to be checked on additional male material); 3) merus of male cheliped long, markedly extending beyond carapace margin, narrow on its whole length, regularly toothed on dorsal margin; 4) dorsal surface of propodus of both chelae in both sexes ( Figs 9E, G ; 10A, C) with a differently pigmented spot at the limit of the fixed finger (versus only one spot in male A. williamsi , and two spots in male A. hourdezi n. sp., moreover located on the anterior portion of the palm in both species, instead at the basis of fixed finger in A. jolliveti n. sp.); and 5) G2 much shorter than G1 and with a very reduced, straight flagellum ( Figs 9D ; 11E ) (compare with fig. 8 of Tsuchida & Hashimoto 2002, showing the two pairs of gonopods in A. alayseae , A. williamsi , and A. rodriguezensis ).

The unique spot near the base of dactylus on dorsal surface of both chelae in both sexes of A. jolliveti n. sp. ( Figs 9E, G ; 10A, C) is of a different nature from the two depressions of A. hourdezi n. sp. It shows as a differently pigmented “pustule” and is similar to the violaceous spot of Bythograea microps Saint Laurent, 1984 (from the East Pacific Rise) in about the same location, i.e., at the base of the palm of the male minor chela and of both female chelae ( Guinot & Segonzac 1997: figs 7C, 9D-F; 2006c: 468, fig. 5; Guinot & Hurtado 2003). This pigmented spot, supposedly sensory, easily allows distinguishing male and female A. jolliveti n. sp. from all other Austinograea species, and also from Gandalfus .

Figures

FIG. 9. — Austinograea jolliveti n. sp., holotype,♂ 12.8 × 20.0 mm (right-handed), North Fiji Basin,STARMER II cruise,dive 18 (PL 18), Mussel Valley site, 18°50’S, 173°29’E, 2750 m, MNHN-IU-2016-10769: A, dorsal view; B, C, ventral views; D, thoracic sternum with G1 and G2 in situ; E, G, both chelae with one coloured spot at fixed finger base and patch of setae at occluding margins of fingers; F, H, both chelae with patches of setae on inner surface and extending along oc- cluding margins of fingers; E, F, right crusher; G, H, left cutter. Note the long merus.

FIG. 11. — Austinograea jolliveti n. sp.,holotype,♂ 12.8 × 20.0 mm (right-handed),North Fiji Basin,STARMER II cruise,dive 18 (PL 18),Mussel Valley site,18°50’S, 173°29’E, 2750 m, MNHN-IU-2016-10769: A, mxp3; B, thoracic sternum; C, G1 and G2 in situ (reconstructed); D, G1, two views; E, G2, two views. Scale bars: B, 5 mm; D, 1 mm; E, 0.5 mm (note the scale bars of the two gonopods, the G2 being about half-length of G1); A, C, without scale.