Fresnerhynchus crozeti D'Acoz & Degrave 2018, sp. nov.

Fresnerhynchus crozeti sp. nov.

(Figs 2–6)

Material examined. 1 female holotype, slope of a seamount situated NW of the Archipel Crozet, ship Ile Bourbon, reference ALC P 295 - 4, station 139, 44.653333333°S 47.9415°E, 1889 m, 24 May 2011, 02:58:00, coll. Eric Vicinati, MNHN-IU-2016-6297.

Description. A very large, robust-bodied shrimp with an elongated, narrow rostrum and large prominent eyes (Fig. 2).

Carapace (Fig. 3A–B): rostrum long and slender, longer than antennular peduncles and scaphocerite, but exact length not known, as its tip is broken; 14 dorsal movable teeth (5 post-rostral and 9 rostral teeth), close or very close to each other, the most distal one originating near the tip of article 2 of antennular peduncle, no dorsal teeth beyond this level (in the preserved part of rostrum); ventral border of rostrum with 16 (in preserved part of rostrum) well-developed styliform immovable teeth separate from each other by narrow slit; antennal spine present and large; pterygostomial spine well developed; supra-orbital, branchiostegal and hepatic spines absent; carapace posterodorsally not carinate behind post-rostral teeth; hepatic pit present, very distinct; long, faint and very blunt lateral carina behind hepatic pit.

Sternum (Fig. 3C): sternal surface between pereiopods very uneven, not forming a sternal plate.

Pleonites (Figs 2, 3A, 3D): dorsally not carinate, not produced posteriorly; posterodorsal border of pleonites 3–4 very minutely serrate; pleura 1–3 rounded; pleuron 4 ventrally nearly straight and posteriorly rounded, with confluence of borders forming blunt right angle; pleuron 5 posteroventrally produced into tooth and with welldeveloped tooth on anterior 0.3 of posterior border; pleonite 6 posterolaterally produced into tooth.

Telson (Fig. 3D–F): long and narrow, with median groove, equal in length to uropods, laterally spinose on distal 0.6 (with 7 spines on left side and 6 on right side), apically obtusely triangular, with median blunt protrusion (adorned with setae), with 3 pairs of stout apical spines (submedian the longest, median the shortest).

Eyestalks (Fig. 4A): large, globular, with cornea well developed, larger than stalk, dark grey in ethanol, with darker ill-defined band and darker diffuse circular spot along posterior border, posterodorsal margin of cornea with median protrusion oriented backwards; without independent ocellus.

Bec ocellaire (Fig. 4B): forming an elongate blunt-tipped projection pointing upwards.

Antenna 1 (Fig. 4C–E): peduncle setose; article 1 fairly stout, with distolateral blunt projection, with small tooth on midlength of ventromedial border, with narrowly triangular, acute-tipped stylocerite, almost reaching article 2, with small but very distinct projection at the base of stylocerite; article 2 and 3 stout, subequal and together about as long as first. Accessory flagellum absent.

Antenna 2 (Fig. 4F–G): scaphocerite long, about 3.2 × as long as broad, with straight lateral margin terminating in acute, slender tooth reaching tip of rounded apex of lamella.

Mandible (Fig. 5A–B): molar process normally developed, with 3 setose crests; incisor process large, bladeshaped, with 6 strong teeth on distal border, with medial border minutely serrate. Palp consisting of 3 robust articles; article 3 broadly elliptic.

Maxilla 1 (Fig. 5C): endopod produced into lobe adorned with short setulose setae [long straight subdistal medial seta presumed present but lost during dissection; small seta present at base of presumed insertion of lost long seta]; distal endite broadly elliptic, with row of slender mobile spines on medial border and with row of stout setae just behind; proximal endite subquadrate, with medial border adorned with row of short stout setae, with marginal surface adorned with very thin setae.

Maxilla 2 (Fig. 5D): anterior lobe of scaphognathite long and apically broadly rounded; posterior lobe long and very narrow, adorned with lash of very long setae; endopod with 3 distal setae; distal and proximal lobes of endite entire and broad; coxal endite broadly rounded.

Maxilliped 1 (Fig. 5E): epipod present, large, consisting of two elliptic lobes; exopod normally developed; endopod 3-articulate, strongly setose on medial border; basal endite triangular, much longer than coxal endite.

Maxilliped 2 (Fig. 5F): epipod present, rounded; podobranch fully developed; exopod present, considerably longer than endopod; endopod as figured.

Maxilliped 3 (Fig. 5G): very long, slender, longer than pereiopods 1–2, penultimate article reaching tip of scaphocerite; 2 small but fully developed arthrobranchs; epipod L-shaped; exopod reaching midlength of antepenultimate article; antepenultimate article 2.6 × as long as penultimate and 1.2 × as long as ultimate, 10 × as long as wide, with 3 small subdistal spines arranged longitudinally; penultimate article 6 × as long as wide; ultimate article 2 × as long as penultimate, 12 × as long as wide, with 2 small apical spines.

Pereiopods, proximal appendices: 1 pleurobranch, 1 arthrobranch, 1 L-shaped epipod on pereiopods 1–4 (Fig. 2); 1 pleurobranch on pereiopod 5; exopod absent on all pereiopods.

Pereiopod 1 (Fig. 6A–B): fairly robust and rather short, 0.8 × as long as pereiopod 2, reaching about tip of scaphocerite; coxa as long as wide, with epipod; basis as long as wide; ischium 5 × as long as wide, without spines; merus 7 × as long as wide, 1.7 × as long as carpus, 1.3 × as long as propodus, 0.8 × as long as carpus and propodus combined; carpus 4 × as long as wide, slightly expanding distally; propodus 4.3 × as long as wide, 1.2 × as long as carpus, terminated in a strong, brown mobile spine, with lateral subdistal dense tuft of short setae; dactylus 0.4 × as long as propodus, 0.77 × as long as palm, with 15 styliform well-developed mobile spines lining flexor border, with lateral subdistal dense tuft of short setae with 2 strong, brown, distal spines interlocking with distal spine of propodus.

Pereiopod 2 (Fig. 6C–D): extremely slender, medium-sized, with minute chela, overreaching scaphocerite; coxa as long as wide, with epipod; basis as long as wide; ischium 6 × as long as wide, without spines; merus 12 × as long as wide, 0.8 × as long as carpus, 1.8 × as long as propodus; carpus 21 x as long as wide; propodus 8 x as long as wide, 0.4 × as long as carpus, terminated in a small but stout brown mobile spine, with lateral subdistal dense tuft of short setae; dactylus 0.2 × as long as propodus, 0.2 × as long as palm, with about 7 small, styliform, mobile spines lining flexor border, with lateral subdistal tuft of dense, short setae, with small but stout, corneous, distal spine.

Pereiopod 3 (Fig. 6E–G): coxa as long as wide, with epipod; basis as long as wide; ischium 4.5 × as long as wide, with large ventrolateral spine; merus 1.9 × as long as carpus, 1.4 × as long as propodus, 16 × as long as wide, with 5 large lateral and 6 large ventral spines; carpus 0.7 × as long as propodus, 11 × as long as wide, with about 5 short narrow spinules on flexor border (some missing); propodus 17 × as long as wide, with about 20 short narrow spinules on flexor border (some missing); dactylus 0.1 × as long as propodus, 4.2 × as long as wide (unguis included), with 1 large stout distal spine (unguis), 5 well developed spines on flexor border, with 1 seta on extensor border, with 2 setae at the base of unguis.

Pereiopod 4 (Fig. 6H–I): very similar to pereiopod 3; coxa as long as wide, with epipod; basis as long as wide; ischium 4.5 × as long as wide, with large ventrolateral spine; merus 1.9 × as long as carpus, 1.4 × as long as propodus, 16 × as long as wide, with 6 large lateral and 5 large ventral spines; carpus 0.7 × as long as propodus, 10.4 × as long as wide, with about 6 short narrow spinules on flexor border; propodus 24 × as long as wide, with about 20 short narrow spinules on flexor border (some missing); dactylus 0.10 × as long as propodus, 3.5 × as long as wide (including unguis), with large stout distal spine (unguis), 4 well developed spines on flexor border, with seta on extensor border, with 5 setae at base of unguis.

Pereiopod 5 (Fig. 6J–K): similar to pereiopods 3–4 except for ornamentation of ischium and merus, and carpus slightly longer (1.2 × as long as carpus of pereiopod 3); coxa as long as wide, without epipod; basis as long as wide; ischium × as long as wide, without spine; merus 1.6 × as long as carpus, 1.3 × as long as propodus, 15 × as long as wide, with 7 large lateral spines and no ventral spines; carpus 0.8 × as long as propodus, 13 × as long as wide, with at least 2 narrow spinules on flexor border (some missing); propodus 21 × as long as wide, with at least 14 short narrow spinules on flexor border (some missing); dactylus 0.11 × as long as propodus, 3.3 × as long as wide (unguis included), with 1 large stout distal spine (unguis), 4 well developed spines on flexor border, with 1 seta on extensor border, with 4 setae at the base of unguis.

Uropods (Fig. 3D): normal; subdistal tooth of outer ramus robust.

Colour pattern. Body and appendages uniformly scarlet red; cornea anteriorly blackish, posteriorly fading to pale grey (photograph made on board by COPEC, not reproduced here as of insufficient quality).

Size. Given the broken rostral tip of the holotype, the total body length cannot be estimated, but the total length of the broken specimen is about 150 mm, with a postorbital carapace length of 38.5 mm.

Etymology. The species name crozetus, -i (Latin noun: masculine, second declension) alludes to the type locality of the species, which is close to the Crozet Islands. The name is a genitive.

Distribution and ecology. NW of Crozet Islands, 44.653333333°S 47.9415°E, at 1889 m depth. A Google Earth plot (30 Jan. 2017) indicates that the collecting station is located on the steep slope of an isolated seamount. The species is presumably benthic and associated with hard substrates (see remarks). The locality is situated between the Subtropical Front and the Sub-Antarctic Front (e.g. Koubbi et al. 2016: 7, figs 2–3).

Remarks. The holotype and only specimen of Fresnerhynchus crozeti sp. nov. available for study was caught with long lines [palangres] by a commercial fishing boat operating on the deep slopes of the Crozet Islands and surrounding seamounts, and preserved by French fishery observers. Specimens collected by the observers largely consist of large vagile (e.g. starfishes) and sessile (e.g. corals) organisms, which are hooked on or entangled in the long lines, when they hit the seafloor (Alexis Martin, pers. comm.). It is unlikely that the holotype of F. crozeti itself was hooked on a line and its state of preservation suggests that it does not come from a fish stomach. Rather, it was most likely clinging to substrate, perhaps corals that were taken by the hooks or entangled in the line and then hauled to the surface. The small robust spinose dactyli of the ambulatory pereiopods (reminiscent of those of Rhynchocinetidae) suggest that they are adapted for clinging onto hard (biotic or abiotic) substrates. At least, they give to the shrimp the capacity to firmly grasp hard substrates and to be hauled with a line from the abyss to the surface without losing its foothold. The occurrence on legs and mouthparts of a substance resembling coagulated mucus produced by gorgonians and antipatharians supports this assumption. In assuming that this hypothesis is correct, the occurrence of the shrimp on coral-like organisms might likely be the consequence of either an obligate symbiosis or a looser facultative association, although a fortuitous occurrence cannot be ruled out.

The absence of previous records of such a large and characteristic shrimp as Fresnerhynchus crozeti might be explained by two factors. First of all, deep-sea sampling around the Crozet Islands and in nearby areas is infrequent (Koubbi et al. 2016) and rare species may have easily escaped capture until now. However the most important factor is, in our opinion, its putative habitat. The sub-Antarctic French long line fisheries specifically target the steep slopes of islands and seamounts. Steep slopes are difficult to sample with trawls and dredges and the skippers of research vessels often refuse to operate on such risky grounds. As such, it is possible that F. crozeti was only collected so recently, simply because it occurs on bottoms almost impossible to sample with conventional gears. Only a fortunate chance (entanglement of benthos in long lines and the perspicacity of the fishery controllers) allowed its discovery. Should the inferred habitat be correct, this opens the possibility that F. crozeti might actually be more widely distributed in sub-Antarctic waters and even temperate parts of the Indian Ocean. It seems even possible that further unknown decapod species await their discovery on deep-sea steep bottoms of similar areas of the southern hemisphere.