Kiwa hirsuta, Macpherson & Jones & Segonzac, 2005

Macpherson, Enrique, Jones, William & Segonzac, Michel, 2005, A new squat lobster family of Galatheoidea (Crustacea, Decapoda, Anomura) from the hydrothermal vents of the Pacific-Antarctic Ridge, Zoosystema 27 (4), pp. 709-723 : 713-719

Kiwa hirsuta n. sp.

( Figs 3-8 )

HOLOTYPE. — Male, CL 58.6 mm, 51.5 mm (without rostrum), TL 88.4 mm (MNHN-Ga 5310). The holotype was collected by the slurp gun of the submarine Alvin, dive 4088, 22.III.2005, at the vent site area SEPR named Annie’s Anthill, 37°46.49 ’S, 110°54.72’W, 2228 m. On board, the left fifth pereopod and some seta were dissected and preserved in ethanol for DNA analyses by MBARI team. The specimen was fixed in formalin and transferred in ethanol 80° two days later.

ETYMOLOGY. — From the Latin, hirsutus, hairy, in reference to the abundance of setae on pereopods.

DESCRIPTION

Carapace, excluding rostrum, 1.3 times longer than broad, dorsal surface smooth and sparsely provided with fine uniramous setae. Gastric region extremely depressed, posteriorly separated from anterior branchial and cardiac regions by distinct depression; posterior gastric pit on either side. Cervical groove clearly distinct between gastric and anterior branchial regions; deep posterior branch of cervical groove between anterior and posterior branchial regions. Cardiac region small, depressed and separated from branchial regions by shallow grooves. Branchial regions slightly convex, separated by median longitudinal groove. Intestinal region well circumscribed and separat- ed from branchial regions by distinct grooves. Median W-shaped incision between anterior branchial regions. Lateral margins carinated, convexly divergent posteriorly, unarmed. Front margin slightly oblique, with small tooth near rostrum; anterolateral angle rounded. Rostrum broadly triangular, horizontal, slightly concave dorsally, lateral borders granulated, with long uniramous setae; ventral side slightly carinated ( Figs 3A ; 6A ).

Pterygostomian flap finely granulose, without setae, deeply excavated directly below midlength of anterior branchial region, anteriorly produced; two longitudinal carina between median depression and posterior border ( Fig. 6A ).

Sternite between third maxillipeds (sternite 3) large, strongly produced anteriorly, slightly concave, each lateral border with strong tooth at midlength, posterior margins convergent. Sternite 4 (between chelipeds), anteriorly concave, anterior margin as wide as sternite 3. Sternite 6 slightly wider than sternite 5, fifth slightly wider than sternite 4. Sternite 7 slightly narrower than sternite 6. Sternites with scattered uniramous setae, more dense at lateral borders ( Figs 4 ; 6E ).

Abdominal somites smooth, spineless, and sparsely setose. Somites 2-6 with two transverse carina at each lateral side, close to anterior and posterior margin; somites 2-5 each with median part delimited by shallow longitudinal groove at each side. Somite 6 with posterior border round- ed and produced, with median longitudinal, shallow groove ( Figs 3A ; 6A ). Uropods well developed, smooth, margins of outer and inner rami with numerous plumose setae, a few uniramous setae scattered on dorsal surface; basal segment short, wide and moderately flattened. Telson as wide as long, median transverse suture dividing telson in anterior and posterior portions, notched on each lateral border at level of transverse suture; posterior portion symmetrically bilobed, divided by single longitudinal suture, nearly half as wide as anterior part. Numerous plumose setae along lateral and posterior borders. A few uniramous setae scattered on dorsal surface ( Fig. 7A ).

Eyes strongly reduced, membranous remains, without pigment ( Fig. 6B ).

Antennule with slender, proximally inflated basal segment, articles 2 and 3 slender, basal segment slightly longer than article 2 and subequal to article 3. Dorsal and ventral flagella short, subequal in length, 0.5 time shorter than article 3; ventral flagellum with six segments, dorsal flagellum with two large basal segments and four small segments in terminal portion ( Fig. 6B, D ).

Antennal peduncle without scaphocerite. Basal article unarmed; article 2 with strong lateral projection reaching midlength of article 4, dentate on distal portion, with additional distoventral spine; article 3 with distomesial spine; article 4 with two distomesial spines (dorsal and ventral), slighly longer than article 2 (without lateral projection); article 5 slightly shorter than preceding one, with three distal spines. Flagellum as long as carapace without rostrum ( Fig. 6B, C ).

Mandible with chitinous teeth on incisor process; palp 2-segmented ( Fig. 8E ). Maxillule with well developed endopod, with numerous setae; distal endite fringed with simple and plumose setae; proximal endite large with numerous simple and plumose setae ( Fig. 8G ). Maxilla with slender endopod, having several simple setae; distal endite bilobated, proximal lobe larger than distal; proximal endite bilobated, proximal lobe much larger than distal; both endites with numerous simple and plumose setae; scaphognathite large and flattened, margins with numerous single and plumose setae ( Fig. 8F ). First maxilliped with large bilobated exopod ( Fig. 8D ). Second maxilliped with exopod slightly longer than endopod; articles of endopod densely covered with simple and plumose setae, dactylus much longer than combined length of propodus and carpus ( Fig. 8A ). Third maxilliped well developed, with numerous long plumose setae, mostly in ventral and lateral sides of articles; coxae with distal bor- der strongly produced and denticulate, each tooth with corneous margin; basis and ischium fused, triangular, with ventral and lateral margins tuberculate; crista dentata in proximal half of ischium, with 24 small denticles on mesial ridge; merus and carpus triangular, similar in length; propodus 0.5 time length of carpus, with numerous plumose setae in distoventral border; dactylus moderately depressed, with dense plumose setae in distal portion ( Fig. 8B, C ).

Chelipeds (P1) and walking legs (P2-4) with numerous rows of spines, each spine with yellow corneal tip and tuft of long and dense plumose setae, only absent in cheliped fingers, setae denser and longer in mesial and ventral sides than in lateral and dorsal sides. Chelipeds nearly symmetric, slightly more than twice as long as carapace including rostrum; spines stronger in mesial and ventral sides than in lateral and dorsal sides. Merus and carpus subcylindrical, palm somewhat depressed. Ischium with some short but sharp distomesial spines. Merus 0.7 time carapace length, including rostrum, with additional row of strong spines along mesial margin. Carpus slightly shorter than merus, and 2.5 times longer than broad. Palm somewhat broadened distally, 0.8 length of carpus and 1.7 times as long as greatest width. Fingers somewhat triangular, 0.75 time length of palm, without setae, having numerous spines decreasing in size distally, distal areas of fingers unarmed; slightly gapping, and distally spoon-shaped; movable finger with proximal large denticulate tooth followed by cutting margin bordered with smooth, low, corneous scales, ending in acute corneous point; fixed finger with some proximal small teeth, followed by cutting edge similar to movable finger and ending in acute corneous point, additional row of mesial granules ending in acute corneous point; fingers distally crossing, corneous tip of movable finger crossing between two corneous tips of fixed finger ( Fig. 5 A-E).

P2-4 slender, slightly compressed laterally, decreasing in size posteriorly. P2 1.2 times carapace length including rostrum, merus half as long as carapace, more than four times longer than wide; carpus half as long as merus, slightly shorter than propodus. Propodi with row of 16 (P2), 11 (P3), 11 (P4) corneous movable spinules along flexor border. Each dactylus 0.6-0.7 time length of propodus, gently curving, flexor margin with 14 corneous movable spinules on P2, 14 on P3, 16 on P4, last spinule very close to corneous tip of terminal claw. Merus of P3 0.8 that of P2 and 1.5 that of P4 ( Figs 3 ; 7B ). P5 chelated, inserted below sternite 7, base not visible ventrally; hand and fixed finger strongly modified, flattened, as long as broad and clearly broader than carpus; fixed finger short; numerous and dense setae on extensor margins of palm and movable finger ( Figs 4A ; 7C ). Paired pleopods present.

Setae: the pereopods, and in particular the chelipeds, are densely covered with flexible setae (c. 15 mm, Fig. 5E ) having clusters of filamentous bacteria, mainly at distal part. The Figure 5F shows several morphotypes of probably sulfo-oxydizing bacteria, characterized by the presence of sulphide-like granulations. Other rigid chitinous setae (c. 13 mm; Fig. 5E ) are barbed in the distal part, ending in a rigid spine ( Fig. 5G ), and they are regularly inserted in pairs mainly on the merus of the chelipeds. They are deprived of bacteria.

HABITAT AND DISTRIBUTION

The new species occurs at densities of one to two individuals per 10 m 2, more or less regularly spaced on the zone of pillow basalt surrounding active hydrothermal vents ( Fig. 2 ). The species co-occurs with galatheid squat lobsters (genus Munidopsis Whiteaves, 1874 ), crabs (genus Bythograea Williams, 1980 ), vent mussels (genus Bathymodiolus Kenk F Wilson, 1985 ) and buccinid gastropods. Specimens of Kiwa hirsuta n. gen., n. sp. were also observed on extinct chimneys and at the base of black smokers, among vent mussels, where shimmering milky water emanates. Like other vent decapod crustaceans Kiwa hirsuta n. gen., n. sp. is probably omnivorous. Specimens were observed in situ consuming tissues of mussels damaged by submersible sampling activities. The “Yeti” crab was observed on three hydrothermal sites distributed on nearly 1.5 km along the Pacific-Antarctic Ridge segment ( Fig. 1 ): Sebastian’s Steamer (37°47.48’S, 110°54.85’W, 2204 m), Pâle Étoile (37º47.36’S, 110º54.85’W, 2215 m) and Annie’s Anthill (37°46.49’S, 110°54.72’W, 2228 m), 1.2 km northern. This site is the northern boundary known of the “Yeti” crab.

Figures

FIG. 3. — Kiwa hirsuta n. gen., n. sp. male holotype (MNHN-Ga 5310); A, dorsal view; B, ventral view.

FIG. 4. — Kiwa hirsuta n. gen., n. sp. male holotype (MNHN-Ga 5310); A, sternal plastron, showing fifth pereopod; B, sternal plastron.

FIG. 5. — Kiwa hirsuta n. gen., n. sp. male holotype (MNHN-Ga 5310), chelipeds; A, left, mesial view; B, left, lateral view; C, right, mesial view; D, right, lateral view; E, spines of the carpus, with flexible setae and two pairs of rigid setae located on the left and on the right; F, filamentous bacteria fixed on a flexible seta (microscope picture); G, apical part of a rigid seta showing barbula (SEM picture). Scale bars: E, 3 mm; F, 20 µm; G, 100 µm.

FIG. 6. — Kiwa hirsuta n. gen., n. sp. male holotype (MNHN-Ga 5310); A, carapace and abdomen, lateral view; B, antennule and antenna, right, and anterior part of pterygostomian flap included, ventral view; C, right antenna, dorsal view; D, right antennula, dorsal view; E, sternal plastron, third and fourth sternites. Scale bars: A, 10 mm; B-E, 5 mm.

FIG. 7. — Kiwa hirsuta n. gen., n. sp. male holotype (MNHN-Ga 5310); A, sixth segment of abdomen, telson and uropods, dorsal view; B, dactylus and propodus, left P2; C, right P5. Scale bars: 5 mm.

FIG. 8. — Kiwa hirsuta n. gen., n. sp. male holotype (MNHN-Ga 5310), left mouthparts; A, second maxilliped, ventral view; B, third maxilliped, ventral view; C, basis-ischium of third maxilliped, mesial view; D, first maxilliped, ventral view; E, mandible, ventral view; F, maxilla, ventral view; G, maxillule, ventral view. Scale bars: A-D, F, G, 5 mm; E, 2 mm.

FIG. 2. — Kiwa hirsuta n. gen., n. sp., in situ observations; A, two specimens on vent site Annie’s Anthill, with crabs Bythograea sp., on mussel bed Bathymodiolus sp.; B, one specimen on pillow lava, near the vent site Pâle Étoile. Photographs taken by the submarine Alvin in March 2004 (SEPR), copyright MBARI/PAR 5/B. Vrijenhoek.

FIG. 1. — East Pacific Rise and Pacific-Antarctic Ridge showing the hydrothermal vent sites, the vent sites visited during the PAR 5 cruise (L), and the distribution of the new species at 38°S site (detail in rectangle).