Austinograea hourdezi Guinot & Segonzac 2018, n. sp.
Creators: name: Guinot, Danièle
name: Segonzac, Michel
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Bythograeidae
Austinograea
Austinograea hourdezi

description: Austinograea hourdezi n. sp.
(Figs 3A; 4A-E; 5A-H; 6A-E; 7A-H)
Austinograea sp. aff. williamsi Guinot, 1990: 898 (Addenda), 900, 901. — Guinot & Segonzac 2006b: 460, fig. 1. — Mateos et al. 2012: 1, 5, 6, 10, figs 1, 2, table 1.
TYPE MATERIAL. — Holotype. MNHN-IU- 2016-10737, ♂ 25.7 × 40.2 mm, southwestern Pacific, Lau Back-Arc Basin, TUIM06MV cruise, dive 142, Tow Cam site, 20°19.07’S, 176°08.24’W, 2719 m, 19.V.2005: right-handed individual, with left cheliped and all P2- P5 detached (Figs 4A-C; 6A-E).
Paratypes. MNHN-IU- 2016-10738, same data, 1 ♂ 29.8 × 48.1 mm (left-handed, two spots on both chelae, with weak heterochely and heterodonty) (Fig. 5A-H), 1 ♂ 24.7 × 36.0 mm (left-handed, with small regenerated right chela, bearing only one spot). MNHN-IU- 2016-10745 (= MNHN-B24060), 3 ♂ 21.0 × 32.8 mm, 18.7 × 28.0 mm, 18.3 × 29.2 mm, 5 ♀ 25.0 × 40.0 mm (two P1 lacking), 19.1 × 32.2 mm, 18.3 × 28.2 mm, 18.3 × 28.4 mm (Fig. 7A- H), cl 19.1 mm (bad condition), Lau Back-Arc Basin, BIOLAU cruise, BL 12, Vai Lili site, 23°13’S, 176°38’W, 1750 m, 24.V.1989. MNHN-IU-2016-10747 (= MNHN-B24059), 2 ♂ 18.0 × 31.0 mm, 17.0 × 28.0 mm, 1 ♀ 16.4 × 26.8 mm, Lau Back-Arc Basin, BIOLAU cruise, dive BL 03, Hine Hina site, 22°32’S, 176°43’W, 1853 m, 15.V.1989. MNHN-IU- 2016-10739, 1 ♀ (with two cutters) 28.4 × 46.8 mm, Lau Back-Arc Basin, Lau Basin 2009 cruise, dive 424, Kilo Moana site, 20°03.23’S, 176°08.01’W, 2623 m, 07.IX.2009. MNHN-IU- 2016-10741, 1 ♀ 25.3 × 40.0 mm, Lau Back-Arc Basin, TUIM06 MV cruise, dive 140, Kilo Moana site, 20°03.23’S, 176°08.01’W, 2623 m, 17.V.2005. MNHN-IU- 2016-10740, 1 ♂ 21.4 × 34.3 mm, Lau Back-Arc Basin, MGLN07MV cruise, dive 232, Tu’i Malila site, 21°59.34’S, 176°34.09’W, 1891 m, 11.IX.2006 (preserved in ethanol 85%). MNHN-IU- 2016-10743, 1 big damaged ♂ (with detached legs), Lau Back-Arc Basin, MGLN07MV cruise, dive 231, ABE site, 20°45.65’S, 176°11.45’W, 2130 m, 09.IX.2006 (preserved in formalin 10% then transferred to ethanol 70%). MNHN-IU- 2016-10746 (= MNHN-B27831), 1 ♀ cl 28.2 mm (left part broken), North Fiji Basin, STARMER II cruise, dive PL 16, White Lady site, 16°59.50’S, 173°55.47’E, 2000 m, 11.VII.1989. MNHN-IU- 2016-10742, 4 ♀ 19.4 × 39.3 mm, 20.5 × 33.2 mm, 19.0 × 30.0 mm, 25.0 × 40.0 mm, TUIM06MV cruise, dive 151, box 2, North Fiji Basin, White Lady site, 16°59.50’S, 173°55.47’E, 2000 m, 30.V.2005.
TYPE LOCALITY. — Southwestern Pacific, Lau Back-Arc Basin, Tow Cam site, 20°19.07’S, 176°08.24’W, 2719 m.
OTHER MATERIAL EXAMINED. — MNHN-IU- 2016-10748 (= MNHN- B27827), 1 ♀ cl 29.2 (damaged, left P1 lacking), North Fiji Basin, STARMER II cruise, dive PL 20, White Lady site, 16°59.50’S, 173°55.47’E, 2000 m.
MNHN-IU- 2016-10744, 2 ♀ 26.0 × 42.0 mm, 26.0 × 40.0 mm, Lau Back-Arc Basin, Lau Basin 2009 cruise, dive 427, ABE site, 20°45.65’S, 176°11.45’W, 2130 m, 28.V.2009 (preserved in ethanol 85%). This sample with two typical females devoid of spots on chelae palm also contains a female 27.1 × 44.6 mm with a spot (a unique spot) on each chela (see Individuals with regenerated chelae). MNHN-IU- 2016-10752, 1♀ 30.0 × 48.5 mm, Lau Back-Arc Basin, MGLN07MV cruise, dive 230, Kilo Moana site, 20°03.23’S, 176°08.01’W, 2623 m, 07.IV.2006 (preserved in formalin 10% and then transferred into ethanol 70%). This large right-handed female, with heterochely and heterodonty (Fig. 4D, E), is atypical due to the presence two spots on the chelae (on the crusher, one marked dark spot plus a faint another one, only discernible as yellow trace; on the cutter, two indistinct spots, only as yellow traces), conversely to typical females that are devoid of any spot. MNHN-IU- 2016-10768 (= MNHN-B27834), 1 ♀ 22.7 × 36.5 mm, North Fiji Basin, STARMER II cruise, dive PL 18, Mussel Valley, 18°50’S, 173°29’E, 2750 m, 13.VII.1989. This atypical female bears a spot on each chela. MNHN-IU- 2016-10765, only one big crusher chela (with two spots) and several pereopods, Lau Back-Arc Basin, no other data. Collection C. R. Fisher. 2 ♀, southwestern Pacific, Lau Back-Arc Basin, MGLN07MV, dive J2-232, Tu’i Malila site, 21°59.34’S, 176°34.09’W, 1891 m, 11.IX.2006 (preserved in formalin 10% and then transferred into ethanol 70%); 2 ♀, Lau Back-Arc Basin, MGLN07MV, dive 231, ABE site, 20°45.65’S, 176°11.45’W, 09.IX.2006 (preserved in formalin 10% and then transferred into ethanol 70%); 2 ♀, Lau Back-Arc Basin, Lau Basin 2009 cruise, dive 425, ABE site, 20°45.65’S, 176°11.45’W, 2130 m, 25.V.2009 (preserved in ethanol 85%).
ETYMOLOGY. — Dedicated to Stéphane Hourdez (CNRS, Station biologique de Roscoff, France) in recognition of his valuable contribution to the knowledge of hydrothermal fauna sites (taxonomy, ecology, physiology, adaptation, phylogeny). He actively participated in the taxonomic sampling during the C. R. Fisher’s cruises in the Lau Basin, suspecting the presence of new Austinograea.
DISTRIBUTION. — Austinograea hourdezi n. sp. is a widespread species encountered in the southwestern Pacific from numerous vent fields of the Lau and North Fiji Back-Arc Basins. It cohabits with A. alayseae at a number of sites, and the two species seem to share a similar distribution.
As A. alayseae, A. hourdezi n. sp. has not been found in the northwestern Pacific, at least after the revision of the MNHN collection and without, however, the examination of an extensive material from the Mariana Trough. For its part, A. williamsi seems to be confined to the northwestern Pacific, in the Mariana Back-Arc Basin, and vent sites of the Mariana Trough.
DESCRIPTION (MALE)
Carapace
Carapace transversely elliptical, flat; regions indistinct. Dorsal surface nearly smooth, except for rare small granules on frontal region and small tubercles on orbital region; numerous small pits. Anterolateral margin marked by rounded edge, slightly granulous. Posterolateral margins convergent; posterior margin slightly concave. Subhepatic regions entirely covered by patches of dense setae. Front broad, not protruded, bluntly pointed medially and with two slightly concave lobes. Eyes, antennules and antennae recessed under front. Suborbital plate absent. Orbit not delimited, only an orbital region that extends as groove lateral to region containing vestigial eyestalks and antennae. Outer side of orbital region tuberculated. Eyestalk not moveable, showing as fixed piece fused to floor of orbital region; no cornea. Antennules folded horizontally. Antenna inserted in wide supraorbital notch; urinary article fixed, broad, recessed; basal article (2 +3) cylindrical, moveable; article 4 slightly elongated, inclined; flagellum of about 10 articles. Proepistome incomplete. Margin of epistome with moderate median projection and formed of two moderately concave lobes, marked by row of low granules. Pterygostomial lobe tuberculous; pterygostomial region smooth, except for small curved ridge.
Thoracopods
Third maxillipeds completely closing buccal cavity. Ischium long, with marked longitudinal internal groove. Merus: external margin regularly curved, oblique, without marked angle, with distal part markedly narrow and produced; internal margin with prominent lobe in half proximal portion. Carpus inserted in notch of antero-internal 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. Mxp3 coxa with only proximal portion visible, its lateral projection hidden by junction of thoracic sternum (sternite 4) with pterygostome. Chelipeds heteromorphic, marked heterochely (also in females, see below), with two types of chelae: major cheliped blunt-tip (crusher), stouter and shorter than pointed-tip minor chela (cutter). Carpus with setae on superior margin and inner surface; merus long, triangular in cross section, anterior border straight, with blunt teeth, smaller distally. Propodus of both chelae with two conspicuous, deep depressions at outer surface of palm near base of dactylus (absent in females), both as two dark spots, even well visible in specimens photographed in situ. Inner surface of both chelae dished on half posterior part; thick patches of dense setae largely extending on half anterior part of propodus and partially extending along occluding margins. Dark colour extending on about three-quarters of fixed finger and practically on whole part of dactylus of both crusher and cutter. Crusher: palm convex, inflated, smooth, except for two depressions located near base of dactylus: one horizontally directed and the largest; the other obliquely directed, smaller. Fingers thick, slightly gaping at occluding margins; two weak, blunt teeth, proximal and median, on occluding margin of dactylus; a blunt but marked subproximal tooth and smaller ones on occluding margin of fixed finger. Cutter: palm elongate, with subparallel borders, smooth, except for two depressions near base of dactylus, similar to those of the crusher; both fingers not gaping at the occluding margins; dactylus elongate, hollowed, with occluding margin smooth; fixed finger very thick, dished on inner surface; occluding margin nearly straight, with 2-3 small teeth, size progressively diminishing forwards. P2-P5 shorter than chelipeds; P3 and P4 longest; meri with patch of dense setae on ventral margins, carpi, propodi fringed on dorsal and ventral margins with felt of short, stiff setae, mixed with sparse longer setae, the patch being dense, thicker on inferior margin. Dactyli rather stout, with patches of short setae.
Thoracic sternum
Thoracic sternum with sutures 4/5-7/8 incomplete but separared by short gap; suture 2/3 complete. Median line only along sternite 8, hardly continuying along sternite 7. Junction of sternite 4 with pterygostome represented by only short juxtaposition, without patch of setae. Press-button of locking mechanism acute, very close to suture 5/6.
Pleon
Pleon of six free segments and telson regularly triangular; pleonal somite 3 widest; pleonal somite 6 longest, anterointernally delineated by raised, thick margin; telson triangular, rounded distally. Both G1 joining at tips. G1: slender, faintly curved, with only short, spiniform setae arranged in two rows along mid-part only. G2: about half the length of G1, with bend about two-thirds length at level of small setiferous area; flagellum rather long, curved, flattened, bladelike.
DESCRIPTION (FEMALE)
Chelipeds weakly dimorphic (versus dimorphic in males), having almost cutters on both sides. On both chelipeds: inner surface markedly dished on half posterior part of propodus and on fixed finger; thick patches of dense setae extending on half or anterior two-thirds part of propodus and along occluding margins of dactyli. Dark colour extending on about threequarters of fixed finger and on two-thirds of dactylus of both crusher and cutter. Weak heterochely and heterodonty; cutter however smaller than crusher. Crusher: palm hardly inflated, elongated, smooth, without depressions; fingers thick, not or only slightly gaping at the occluding margins; two tiny blunt teeth on occluding margin of dactylus; two tooth and a few smaller ones on occluding margin of fixed finger.Cutter: palm similar to crusher but fingers more elongated, not gaping at occluding margins; palm smooth, without depressions; both fingers; dactylus elongate, hollowed, with occluding margin practically smooth; fixed finger very thick, with occluding margin nearly straight, bearing small teeth, two being more marked. P2-P5 with felt of short, stiff setae, mixed with numerous longer setae. Median line along sternite 8, hardly continuying along sternite 7. Dense patches of setae on thoracic sternum near junction of sternite 4 with pterygostome. No pleonal locking mechanism in mature females. Margins of pleon densely fringed with setae. Vulvae large, rounded, with thick membranous area all around median opening.
REMARKS AND COMPARATIVE DIAGNOSIS
The two characteristic depressions on the propodus of both male chelae, crusher and cutter, of Austinograea hourdezi n. sp. (Figs 3A; 4A, B; 5E, G), typically absent in females (Fig. 7E, G), are similarly located in all the individuals examined, but they are variously delineated by a raised margin and thus may appear quite deep or shallower but practically always coloured as dark or coloured spots, always with a different texture and colour but commonly referred to as “dark spots”. The function of the pigmented pits or spots present on the palm of chelipeds (also on the subocular regions in others species) of certain bythograeids is supposed to be sensory.
For atypical specimens of A. hourdezi n. sp., see below Individuals with regenerated chelae.
Austinograea hourdezi n. sp. may be easily distinguished from A. alayseae (Fig. 8A, B), with which it cohabits in several sites, by:
1) subhepatic region covered by patch of dense setae in both sexes (no setae in A. alayseae); 2) mxp3: external border oblique, distal end strongly produced (in A. alayseae forming a marked angle:proximal portion vertically oriented, with slightly concave border, half distal portion abruptly tilted; distal end weakly produced); inner margin produced in marked lobe (without lobe in A. alayseae); 3) both male chelae with two deep, dark depressions, marked as spots (without any spot in A. alayseae); 4) in both sexes patches of dense setae on inner surface of palm and along fingers (without setae in A. alayseae); 5) marked heterochely: male crusher with short, stout propodus, and short, thick fingers; 6) fixed finger coloured; dactylus coloured on two thirds (in A. alayseae pronounced heterochely but propodus of male crusher more elongated; fingers more elongated, narrower); 7) male cutter with occluding margin of dactylus smooth; 8) fixed finger very thick, almost entirely coloured, occluding margin with three small teeth, size progressively diminishing forwards (in A. alayseae fingers elongated, armed on both occluding margins with several small teeth interspersed with smaller ones; dactylus coloured at distal end in males and only at tip in females); 9) thoracic sternum with median line at level of sternite 8 and practically not continuying along sternite 7 in both sexes (extending on most part of sternite 7 in both sexes of A. alayseae, see Guinot 1990: fig. 2C); 10) male pleon with triangular telson (rounded in A. alayseae); and 11) G1 rather straigt, with only minute setae along subdistal half (more curved, with several rows of rather long, acute setae along most of length in A. alayseae).
The most distinctive character between Austinograea hourdezi n. sp. and A. williamsi is in the presence of a two spots in male chelae of A. hourdezi n. sp. (Figs 3A; 4A, B; 5E, G) ([versus one spot on the palm of crusher and cutter male chelipeds of A. williamsi, described by Hessler & Martin (1989: 651, figs 1b, 9a-c) as “small, often brown-stained, pitted area just proximal to, and in line with, ventral border of dactylus” in “larger males” and absent in females (see also Tsuchida & Fujikura 2000: fig. 2]). Heterochely and heterodonty are pronounced in males of A. hourdezi n. sp. and A. williamsi. The male cutter chela of A. hourdezi n. sp. has a thick, broad fixed finger, and an occluding margin armed with a few teeth. In A. williamsi the cutter chela is more elongate; the fixed finger is more inflated and broader, with a deeply dished inner surface, and a markedly convex, much toothed occluding margin that fits flush against dactylus. In A. hourdezi n. sp. the chelae show a sexual dimorphism that is distinctive from that of A. williamsi (see Hessler & Martin 1989: figs 9, 10), in which females have cutters for both chelipeds with a markedly concave propodal inner margin and a well dished fixed finger at occluding margin that bears numerous, sharper, delicate teeth. The mxp3 merus of A. hourdezi n. sp. is very similar to that of A. williamsi, both having an oblique external border, a produced ending and a pronounced inner lobe. Another marked difference is the subhepatic region: covered by dense setae in A. hourdezi n. sp., whereas the patch of setae is much more larger in A. williamsi, in which it considerably extends below the lateral line.
For the distinction between A. alayseae and A. williamsi, see the comparative illustrations in Tsuchida & Hashimoto (2002). The inner surface of palm and most inner surface of the dactylus of the two chelae bear patches of setae in both sexes of A. hourdezi n. sp. (Figs 3 A-C; 5A, F, H; 7A, B, F, H), as in A. williamsi, whereas in both sexes of A. alayseae the chelae of both sides are glabrous on palm and dactylus. The G1 and G2 of A. hourdezi n. sp. and A. williamsi (in which the G2 is about less than half the G1’s length) are similar, whereas in A. alayseae the G1 bears numerous long setae scattered over its entire length.
DISTINCTION OF FEMALES
As the spots on the cheliped propodus are typically absent in female A. hourdezi n. sp. and in both sexes of A. alayseae, the more useful significant character to differentiate the females of the two species is the patch of setae at the inner surface of the palm of females of A. hourdezi n. sp. (Fig. 7A, B, F, H), as in the males (Figs 3A; 5A, F, H). In contrast, in A. alayseae (Fig. 8A, B) the chelae are devoid of setae, in females as in males. The same character allows identification of females of A. williamsi, with setose patch at the inner chela surface (Hessler & Martin 1989: fig. 10), from females of A. alayseae, which have glabrous chelae. See the comparative illustration of female Austinograea chelae by Tsuchida & Hashimoto (2002: fig. 6), which does not show any spot in A. williamsi and A. alayseae, in contrast with A. rodriguezensis, which is shown bearing a spot, as in the males. In A. alayseae a thick posterior membrane may cover most of the vulva, leaving a variously developed opening, sometimes only a lateral slit, whereas in A. hourdezi n. sp. the medial opening is entirely surrounded by thick membrane (Fig. 7D).
INDIVIDUALS WITH REGENERATED CHELAE
A few male specimens that display most characters of A. hourdezi n. sp. (including mxp3 shape and patches of setae on inner surface of chelae) exhibit a single spot on the outer surface chelae palm, instead of two. The holotype (MNHN- IU-2016-10737), from the Lau Basin, Tow Cam site, a large right-handed male 25.7 × 40.2 mm, typically bears the two characteristic spots on each chela (Fig. 4A, B), such as most of other males that we have examined. Although left-handed and with weak heterochely and heterodonty, a larger male from the same site 29.8 × 48.1 mm, paratype, MNHN- IU-2016-10738, also shows the two typical spots on chelae, even on regenerated cheliped (Fig. 5E, G). But a smaller lefthanded male 24.7 × 36.0 mm, from the same sample, has an obviously regenerated minor chela that bears only one spot; its left chela, having become the major chela, shows the two typical spots.
Two samples of female A. hourdezi n. sp., instead of being devoid of any spot on the chela, bear a spot on both chelae: they are left-handed, which means that one chela was regenerated. These females that bear a spot on each cheliped, crusher and cutter, are:
MNHN-IU- 2016-10744, 1 ♀ 27.1 × 44.6 mm (left-handed), Lau Back-Arc Basin, Lau Basin 2009 cruise, dive 427, ABE site, 20°45.65’S, 176°11.45’W, 2130 m, 28.V.2009 (preserved in ethanol 85%). It belongs to the same sample that contains two typical females devoid of spots on chelae palm;
MNHN-IU- 2016-10768 (= MNHN-B27834), 1♀ 22.7 × 36.5 mm, North Fiji Basin, STARMER II cruise, dive PL 18, Mussel Valley, 18°50’S, 173°29’E, 2750 m, 13.VII.1989 (was found with a typical male of A. alayseae).
A large, right-handed ♀ 30.0 × 48.5 mm (MNHN- IU-2016-10752) from the Lau Back-Arc Basin, MGLN07MV cruise, dive 230, Kilo Moana site, 20°03.23’S, 176°08.01’W, 2623 m, 07.IX.2006, and identified as A. hourdezi n. sp. on the basis of other characters, has the right chela of a crusher type with one marked spot plus a second spot only as a yellow trace, and the cutter with two yellowish spots (Fig. 4D, E), This male chela pattern is unusual for female A. hourdezi n. sp., which are generally devoid of any spot (Fig. 7E, G).
A bythograeid that bears only a left cheliped, photographed in situ (Fig. 8C) at the site Kilo Moana during the Lau Basin 2009 cruise and with a single dark spot on the chela could be A. hourdezi n. sp., based on the patches of setae discernible just at the suface of the inner chela palm and on setose patches on the right subhepatic region. This could be an atypical specimen of A. hourdezi n. sp., with a regenerated cheliped. It was found associated with mussels Bathymodiolus brevior Cosel, Métivier & Hashimoto, 1994 (see Cosel et al. 1994), gastropods Ifremeria nautilei Bouchet & Warén, 1991, sea anemone Cyananthea hourdezi Zelnio, Rodríguez & Daly, 2009 (see Zelnio et al. 2009; E. Rodríguez, pers. comm. 2017). Due to the same features, the seemingly right-handed crab collected at Tow Cam site, dive 240, and photographed in situ (Zelnio et al. 2009: fig. 14B) associated with an unidentifiable actiniarian zoanthidean, could be also identified to A. hourdezi n. sp., but it is difficult to discern the presence of spots on the chelae.
All of these specimens with atypical spot(s) on the chelae exhibit all other morphological traits of A. hourdezi n. sp., and are not A. williamsi nor A. rodriguezensis, both of which are characterised by one spot on the outer chela palm, near the dactylus base. We assume that most of these atypical crabs were initially right-handed and that left-handers represent individuals whose asymmetry has been reversed following autotomy and regeneration of the lost cheliped (see Chelae: crusher and cutter. Regenerated chelae). This reversion of chelipeds, which causes a dramatic rearrangement and triggers a new allometric growth, is thought to have induced a novel implantation of the spots on the chelae, mainly when autotomy or loss occurs at a large size of crabs. These atypical individuals, without other equivocal morphological evidence and presumably not genetically cryptic, are here treated as A. hourdezi n. sp. subject to their recognition by molecular sequences (in study).
MOLECULAR ANALYSIS
In the early 2000s fragments of Austinograea from the Lau Back-Arc Basin, Valu Fa Ridge, recognised by Guinot (1990) as “ Austinograea aff. williamsi ” and here described as A. hourdezi n. sp. were sent by D. Guinot to L. A. Hurtado (Texas A&M University, USA) and V. Leignel (Université du Maine, Le Mans, France) for molecular analyses. Genetic divergence warranted recognition of a new species. The sequences obtained for the 16S rDNA, Cytb, and 28S rDNA recovered that the uncorrected nucleotide divergence for the mitochondrial 16S rDNA gene was 5.5% between A. hourdezi n. sp. and A. williamsi; 7% between A. hourdezi n. sp. and A. alayseae; and 5.9% between A. williamsi and A. alayseae (Mateos et al. 2012: 1, 3, 5, 6, 10, fig. 2, table 1, as Austinograea aff. williamsi).
description: Published as part of 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, pp. 75-107 in Zoosystema 40 (5) on pages 80-89, DOI: 10.5252/zoosystema2018v40a5, http://zenodo.org/record/3738100