Kallograea kulolasi n.

Guinot, Danièle & Ng, Peter K. L., 2025, Kallograea kulolasi n. gen., n. sp. and K. jolliveti (Guinot & Segonzac, 2018) from the hydrothermal Kulo Lasi Volcano Caldera, West Pacific; and a reappraisal of Austinograea Hessler & Martin, 1989 and Gandalfus McLay, 2007 (Decapoda, Brachyura, Bythograeoidea), Zoosystema 47 (33), pp. 773-797 : 778-783

Kallograea kulolasi n. sp.

( Figs 4-7)

urn:lsid:zoobank.org:act:

TYPE MATERIAL. — Holotype. Western Pacific • ♂ (right-handed) 7.3 × 12.7 mm; CHUBACARC 2019 cruise, Leg 1; Futuna Volcanic Arc, Kulo Lasi Caldera; 15°10.0692’S, 14°42.9563, 177°28.4632’, 177°00.5768’W (latitude minimum/maximum and longitude minimum/maximum, respectively); PL729 - GBT1; 1472 m; MNHNIU-2024-6067 .

Paratypes. Western Pacific • 1 ♂ (right-handed) 7.5 × 12.0 mm; same data as holotype; MNHN-IU-2024-6084 • 1♂ 9.7 × 15.4 mm (without chelipeds); MNHN-IU-2024-6035 [CHU 036] • 1 ♀ 8.1 × 12.6 mm (with detached chelipeds in tube); MNHN-IU-2024-6033 • 1 ♂ 9.6 × 16.4 mm; MNHN-IU-2024-6552 [CHU 035] • 1 ♂ (left-handed) 8.8 × 14.1 mm; ZRC 2024.0724 ( ex MNHNIU-2024-6085 ) .

TYPE LOCALITY. — Kulo Lasi Caldera, on periphery.

ETYMOLOGY. — Named after the Kulo Lasi Volcano where the species was discovered. Kulo lasi is a common name meaning ‘big cauldron’ in Futunian. Used as a noun in apposition.

DESCRIPTION

Carapace

Small size (carapace width 12.0- 16.4 mm). Carapace elliptical, very short, very elongated transversely, width-to-length ratio 1.59-1.74, flat; regions indistinct ( Figs 4A, C; 5A; 6A). Dorsal surface entirely smooth, glabrous ( Figs 4A, C; 5A; 6A). Anterolateral margin regularly rounded, with minute, barely discernible granules; supra-orbital margin with more obvious granules ( Figs 4A, C, E; 5A, C; 6A, E). Posterolateral margins convergent posteriad; posterior margin slightly concave ( Figs 4A, C; 5A; 6A). Subhepatic regions entirely glabrous ( Figs 4E; 5B, C; 6E). Front broad, not protruded, practically straight, not emarginate medially, barely pointed medially, with two indistinct lobes; margin without discernible granules ( Figs 4A, C, E; 5A; 6A, E). Infra-orbital region with scattered small granules ( Figs 4E; 6E). Eyes, antennules, antennae recessed below front ( Figs 4E; 6E). Orbit not delimited; orbital region extending as groove, lateral to area with vestigial eyestalks and antennae ( Figs 4E; 5A, C; 6E). Eyestalk absent; podophthalmite barely visible, as small fixed piece fused to floor of orbital region; cornea absent but a tiny dark pigment barely visible ( Figs 4E; 5A, C; 6E). Antennules folded horizontally ( Figs 4E; 5C; 6E). Antenna very small; urinary article fixed, recessed; basal article (2 + 3) cylindrical, moveable; article 4 slightly elongated, inclined; flagellum not long. Proepistome very thin ( Figs 4E; 5C, E; 6E). Posterior margin of epistome wide, with lateral margins distinctly concave, median projection obtusely triangular ( Figs 4E; 6E). Pterygostomial lobe with small granules; pterygostomial region smooth (except minute granules along lateral line), glabrous, except along lateral line ( Figs 4E; 5B, C; 6E).

Mxp3

Mxp3 completely closing buccal cavity, on all parts, especially between antero-external margin of merus and pterygostomial lobe. Ischium long, external margin oblique; longitudinal internal groove weak.Merus: external margin proximally straight, then obliquely directed; distal and external margins almost touching pterygostomial lobe; merus distal part markedly narrow, produced; internal margin bluntly angled medially. Carpus inserted on distal part of antero-internal margin of merus; propodus thick, short; dactylus long, reaching about three-quarters length of ischium; inner margins of propodus and dactylus with brush-like setae. Mxp3 coxa with only proximal portion visible, lateral projection hidden by junction of thoracic sternum (sternite 4) with pterygostome. Exopod thick, longer than endopod ischium ( Figs 4D, E; 5B; 6E).

Male chelipeds

Male chelipeds elongate, not clearly heteromorphic (weak heterochely in females, see below) ( Figs 4 A-C; 5C-F). Merus very long, slender, extending far beyond margin of carapace, subcylindrical, triangular in cross section, anterior border straight (without expansion), with regularly spaced small granules. Carpus covered with thick patches of thin soft setae on whole external surface; propodus of both chelipeds very long, with superior margin covered by thick patches of thin soft setae, appearing as a white down-like pubescence ( Fig. 4C) (more developed on major chela), partially extending on both outer and inner parts of palm (more on inner part) and extending partially to basal part of dactylus. Fingers distinctly shorter than palm, with dark colour extending along distal third- or quarter-length; no setae along occluding margins. No obvious spot at base of propodus. Dark pigmentation on fingers not extending to palm, confined to tips in males (as in females) ( Fig. 5 C-E).

In right-handed males (like holotype), major cheliped (crusher) stouter, slightly shorter than minor chela (cutter); both fingers very thick, distinctly blunt-tipped, weakly gaping; dactylus with small tooth, then molariform tooth on occluding margin; fixed finger thick, with some small denticles on occluding margin; dark colour extending dorsally on only distal part of fingers. Minor cheliped (cutter) with finger tips pointed. Merus as in major chela; palm rather long, outer surface slightly convex, smooth; both fingers not gaping at occluding margin, both tips curved, crossed; dactylus elongate, with occluding margin lined with some minute proximal teeth; fixed finger very thick, with thin extension bearing nearly straight occluding margin, with some small proximal teeth ( Figs 4A, B; 5C, D).

In left-handed male (e.g., ZRC 2024.0724, ex MNHNIU-2024-6085), chelae less developed; fingers of major chela much stouter than pointed fingers of minor chela; both fingers relatively thinner, only very weakly gaping, less blunt-tipped, slightly curved at tip; minor chela elongated, with less dense patch of thin soft setae on superior margin; fixed finger regularly teethed (medially granular in left-handed males) ( Fig. 5E, F).

Female chelipeds

Female chelipeds ( ♀ 8.1 × 12.6 mm mm, MNHNIU-2024-6033) not as developed as those of males, with merus distinctly shorter and narrower than in males ( Fig. 6A, B). Chelae slightly heteromorphic, not blunt-tipped, with both fingers not gaping, crossing at tips; major chela only a little stouter as minor chela. As in males, patches of thin soft setae, appearing as down-like pubescence, on superior margin of carpus, propodus, extending on both outer and inner part of palm. Dark pigmentation of fingers in most part confined to tips (as in males) ( Fig. 6C, D).

Ambulatory legs

P2-P5, in particular meri, distinctly long, slender. P2 much shorter than chelipeds; P3, P4 longest.Merus of P2-P4 smooth, without patches of setae, only with a few sparse setae; carpus, propodus and dactylus of P2-P5 with sparse setae on ventral margins ( Figs 4 A-C; 6A, B).

Thoracic sternum

Thoracic sternum very wide, short, extending laterally, elliptical; suture 2/3 complete; sutures 4/5-7/8 incomplete; sutures 6/7 and 7/8 medially less calcified ( Fig. 4D, F). Junction of sternite 4 with pterygostome represented by only short juxtaposition, without patch of setae. Median line at level of sternite 8 in both sexes, reaching to junction with sternite 7 ( Fig. 4F). In males, press-button of locking mechanism acute, on sternite 5 abutting against suture 5/6 ( Fig. 4F). Entirely smooth, glabrous in both sexes ( Figs 4D, F; 6B, F).

Pleon

Both sexes with six free somites and telson. Male pleon rather wide, regularly triangular; pleonal somite 3 widest; pleonal somite 6 longest; telson very short, bluntly semicircular ( Fig. 4B, D). Press-button on narrow portion of sternite 5, absent in females ( Fig. 4F).

Female pleon almost round, covering most of thoracic sternites; telson semicircular ( Fig. 6B).

Gonopods

G1 almost straight, directed obliquely into sternopleonal cavity, never contiguous, and even distant throughout their entire length, including their tips which are apart, not recessed in medial depression at end of sternopleonal cavity. Only some setae along mid distal part ( Figs 4G; 7 A-D). G2 relatively long, flagellum slightly longer than basal part, curved, blade-like, distal part slightly dilated ( Figs 4H; 7E, F).

Vulvae

Vulvae distant from each other, subhemispherical; close to but separate from thoracic sternal suture 5/6, occupying 2/3 of surface of sternite 6 ( Fig. 6F).

REMARKS

Five males and one female of Kallograea kulolasi n. gen., n. sp., all small specimens, have been collected by the French CHUBACARC 2019 cruise on the periphery of the caldera of Kulo Lasi Volcano, through a unique dive in the north sector ( Figs 2; 3). Immediately suspected of being new by Stéphane Hourdez (pers. comm.), they are here confirmed to represent an undescribed species.

Kallograea kulolasi n. gen., n. sp. is a small-sized species, however, with well-developed gonopods and vulvae. It is also the smallest bythograeid known in the world. The smallest bythograeid previously was Bythograea microps Saint Laurent, 1984 ( Saint Laurent 1984: 356) from the East Pacific Rise (between 21°N and 9 ° 50 ’ N), which is indicated as having a maximum carapace width 40 mm according to Guinot & Segonzac (2006b: 468), but it seems that this size may be overestimated: the male collected during the Hot 96 mission measuring 13 × 24 mm likely represents the largest B. microps known to date ( Guinot & Segonzac 1997: 139; Guinot & Hurtado 2003: 437). Kallograea kulolasi n. gen., n. sp. is distinctly smaller, with specimens measuring 12 mm in carapace width already mature (e.g., MNHN-IU-2024-6084).

Kallograea kulolasi n. gen., n. sp. is characterised by a flat carapace, the males possessing distinctly elongate chelipeds, with especially blunt fingers on the major chela, and a prominent setal patch on the propodus that appears as a white down-like pubescence on the superior margin of the cheliped palm and extending on the inner and outer surfaces. This pubescence is best observed in water or ethanol, as the setae collapse and clump together when the specimen is studied dried (compare Fig. 4C with Fig. 5E, F). Since in most Austinograea species the setal patch is exclusively located on the inside of the palm, its presence on either side of the upper palm margin is a unique feature of K. kulolasi n. gen., n. sp. A setal patch is also present over the entire external surface of the carpus, which is not found in other bythograeoids, which have a glabrous carpus instead. The markedly thick and blunt-tipped fingers of the crusher cheliped is also a remarkable character of K. kulolasi n. gen., n. sp. The condition of these finger tips is unusual and perhaps functions similarly to the spoon-tipped fingers of other crabs. As indicated by Davie et al. (2015), not much is known about the precise function of spoon-tipped fingers, but they seem to be generally used for feeding on detritus, scooping up mucus from corals or picking up other soft foods, scraping off encrusting algae, effective gripping of filamentous algae, or scraping epilithic algae off coral rock. The rounded finger tips of the major chelae of K. kulolasi n. gen., n. sp. may be adapted for harvesting the filamentous bacterial matter in its habitat.

The palm and fingers of male adult chelipeds appear very heavy relative to the long and slender merus, in which the apodemes and attached muscles have little room, and together with the flat carapace, gives the crab a very distinctive appearance. Male Kallograea kulolasi n. gen., n. sp. clearly prioritises investing in strong chelipeds but in females, the chelipeds are proportionately shorter and the chelae are less strongly developed. This marked sexual dimorphism suggests the male chelipeds may have a role in reproductive selection.

DISTRIBUTION

Known only from the Futuna volcanic Arc, on the periphery of the Kulo Lasi Caldera.