Galathea chura , Osawa, Masayuki & Higashiji, Takuo, 2012

Osawa, Masayuki & Higashiji, Takuo, 2012, A new species of Galathea Fabricius, 1793 (Crustacea: Decapoda: Anomura: Galatheidae) from Okinawa, southern Japan, Zootaxa 3264, pp. 53-60: 54-58

publication ID

http://doi.org/ 10.5281/zenodo.208720

persistent identifier

http://treatment.plazi.org/id/E46AF814-534E-325E-FF25-FD656827D0A9

treatment provided by

Plazi

scientific name

Galathea chura
status

sp. nov.

Galathea chura  sp. nov.

( Figs 1–3View FIGURE 1View FIGURE 2View FIGURE 3)

[New Japanese name: Chura-koshioriebi]

Type material. Holotype male (cl 4.1 mm), off Onna Village, Okinawa Island, Ryukyu Islands, 26 ° 31.55 ´N, 127 ° 52.76 ´E, 188 m, on colony of unidentified species of Parisis  , 27 July 2011, research vessel Kuroshio-maru II, ROV, coll. Noboru Katagi (RUMF-ZC- 1731).

Diagnosis. Carapace, exclusive of rostrum, approximately as long as broad. Gastric region with rows of interrupted arcuate ridges; epigastric and hepatic dorsal spines absent. Lateral margins armed with 7 spines: 2 in front of and 5 behind anterior cervical groove. Rostrum 1.2 times as long as broad, with 4 deeply incised teeth on each lateral margin. Lateral orbital angle with small spine. Abdominal somites 2 and 3 with 2 transverse uninterrupted ridges. Basal article of antennular peduncle with 3 well-developed distal spines, distomesial spine shorter than distolateral. Antennal article 3 unarmed. Mxp 3 merus with 2 ventral (distal smaller) and 1 dorsodistal spines. P 1 about 2.0 times as long as carapace; carpus 1.4 times as long as broad; fingers not distally spooned. P 2 and P 3 propodi each with row of 3 or 4 spines on proximal half of dorsal margin. Epipods present on P 1 or P 1 and P 2 only.

Description. Carapace ( Fig. 1View FIGURE 1 A), exclusive of rostrum, approximately as long as broad; dorsal surface faintly convex from anterior to posterior; transverse ridges with short and somewhat long, stiff setae; cervical groove shallow but discernible, laterally bifurcated. Gastric region with 6 rows of interrupted and uninterrupted, transverse ridges; anterior first and second ridges long, interrupted medially; first weakly convex anteriorly, without epigastric spines; second sinuous; third short, scale-like, placed medially; fourth median straight ridge flanked by 2 pairs of arcuate ridges on each side (mesial arcuate ridge much shorter than lateral); fifth interrupted medially, moderately convex anteriorly; sixth uninterrupted, nearly transverse. Hepatic region unarmed. Anterior branchial region with 2 interrupted ridges directly behind anterior cervical groove and weakly arcuate ridge on median portion. Midtransverse ridge uninterrupted, preceded by cervical groove, followed by 4 interrupted (anterior first, third, fourth, fifth) and 3 uninterrupted (second, sixth, seventh) transverse ridges; fifth ridge broadly interrupted medially. Lateral margins convex medially, with 7 spines: 2 in front of and 5 behind anterior cervical groove; first anterolateral; second slightly smaller than first, located at midlength between first spine and anterior cervical groove; 2 spines on anterior branchial margin and 3 spines on posterior branchial margin, last smallest; additional small spine ventral to between first and second lateral spines. Rostrum ( Fig. 1View FIGURE 1 A) broad triangular, 1.2 times as long as broad, length 0.7 that of carapace and breadth approximately 0.6 that of carapace, nearly horizontal in lateral view; dorsal surface weakly concave, with sparse setules and 2 rows of short stiff setae along midline; lateral margin with 4 deeply incised sharp teeth, each bearing short stiff seta at mesial base. Lateral orbital angle ( Fig. 1View FIGURE 1 B) with small spine directed anterolaterally. Infraorbital margin ( Fig. 1View FIGURE 1 D) bluntly triangular anteriorly, minutely denticulate along lateral margin.

Pterygostomian flap rugose, unarmed on surface; anterior margin bluntly angular, with spinule dorsally ( Fig. 1View FIGURE 1 E, D).

Sternal plastron approximately as long as broad, lateral extremities gently divergent posteriorly. Sternite 3 ( Fig. 1View FIGURE 1 C) measured in midline 0.4 as long as broad, with median sinus bordering left and right lobes; anterior margin of each lobe convex, with minute denticles; surface with some minute striae. Sternite 4 (measured in midline from anterior margin to level of posterior lateral end) 2.6 times longer and 3.0 times broader (breadth including lateral lobes) than sternite 3, approximately 0.4 as long as broad; surface with 2 setiferous transverse ridges, anterior ridge medially interrupted; posterior ridge uninterrupted, situated medially. Sternites 5–7 smooth.

Abdominal somites 2–5 ( Fig. 1View FIGURE 1 A) with 2 transverse ridges each bearing row of short stiff setae, anterior ridge more distinctly elevated than posterior ridge on tergites 2–4, posterior ridge of tergite 4 interrupted medially, other ridges uninterrupted. Tergite 6 with 2 medially interrupted ridges, posteromedian margin nearly transverse, lateral lobes faintly produced posteriorly. Telson 0.6 as long as broad, incompletely subdivided; posteromedian margin with deep, broad incision. Male gonopods present on abdominal somites 1 and 2.

Ocular peduncle ( Fig. 1View FIGURE 1 A, B, D) 1.2 times longer than broad; eyestalk (other than cornea) with lateral margin nearly straight, dorsal rounded extension with 2 stiff setae distally; cornea not dilated.

Basal article of antennular peduncle ( Fig. 1View FIGURE 1 D) with well-developed, mucronated, distodorsal and distolateral spines, distodorsal larger; distomesial spine also well developed, shorter and more slender than distolateral spine. Ultimate article with few short fine setae not in tuft on dorsodistal margin.

Antennal peduncle ( Fig. 1View FIGURE 1 A, B, D, E) having article 1 with distomesial spine slightly overreaching ventrodistal margin of article 2. Article 2 with 2 well-developed distal spines; distolateral spine not reaching ventrodistal margin of article 3, subequal in size to distomesial spine. Articles 3 and 4 unarmed.

Mxp 3 ( Fig. 1View FIGURE 1 F) with basis bearing 5 denticles on mesial ridge, distal larger. Ischium with well-developed spine on ventrodistal margin; dorsal margin also with distinct distal spine; crista dentata with 12 denticles. Merus 1.2 times longer than ischium measured in midline; ventral margin with 2 spines, distal spine smaller than proximal; dorsal margin with small distal spine. Carpus unarmed, smooth on dorsal margin. Propodus 0.8 times length of carpus measured along dorsal margin. Dactylus elongate, somewhat inflated on ventroproximal margin, 0.7 length of propodus. Exopod with distal article distinctly overreaching distal margin of merus.

P 1 ( Fig. 2View FIGURE 2 A, B) 2.2 times carapace length, relatively short, subcylindrical, somewhat depressed on palm and fingers, spinose, with short ridges bearing short and moderately long, stiff setae. Merus 0.8 carapace length, 1.7 times as long as carpus, with spines arranged roughly in 5 rows: 1 dorsomesial, 1 ventromesial, 2 dorsal, and 1 ventrolateral, distal spines prominent; mesial surface also with subdistal strong spine. Carpus 0.8 length of palm, 1.4 times as long as broad; dorsal surface with small spines arranged roughly in 3 longitudinal rows continued on to palm, dorsomesial distal spine prominent; mesial surface with strong spines in midline, distal spine strongest; lateral surface with small median spine; ventromesial margin with small spines on distal half. Palm 1.6 times longer than broad; lateral and mesial margins subparallel; dorsal surface with 3 rows of small spines, dorsolateral row of spines irregularly continued on to entire lateral margin of fixed finger; ventromesial margin with small spines on proximal half. Fingers 0.7 length of palm, each distally ending in small blunt spine, without intermeshing spines; opposable margins nearly straight, with low, blunt teeth; dactylus (movable finger) feebly denticulate on dorsomesial margin, with spinules proximally and distally.

P 2–4 ( Fig. 2View FIGURE 2 C –F) relatively stout, with sparse, short stiff setae, P 2 overreaching distal margin of P 1 carpus by half length of dactylus. Meri successively shorter posteriorly (P 3 merus 0.9 length of P 2 merus, P 4 merus 0.8 length of P 3 merus); P 2 merus 0.7 carapace length, 3.4 times as long as broad (breadth measured at midlength), slightly narrower than P 3 merus, 1.3 times longer than P 2 propodus excluding rounded distal projection; P 3 merus 2.8 times longer than broad, slightly broader than P 4 merus, 1.1 times length of P 3 propodus; P 4 merus 2.6 times as long as broad, approximately as long as P 4 propodus. Dorsal margins with row of 8 proximally diminishing spines on P2, 6– 9 similar spines and on P 3, only with distal spine on P 4; lateral surface with sparse short ridges, unarmed on P 2 and P 3, with row of 3 spines slightly dorsal to midline on P 4; ventrolateral margin distally ending in strong spine followed proximally by small spines (P 2 and P 3) or slightly elevated ridges (P 4); ventromesial margin with small subterminal spine on P 2, unarmed on P 3 and P 4. Carpi each with 6 spines on dorsal margin, distal-most spine smaller than distal second; lateral surface with 1 or 2 and 2 or 3 spines sub-parallel to dorsal margin on P 2–3 and P 4, respectively; ventrodistal margin rounded, with small spine. Propodi subequal in length on P 2 and P 4, slightly longer on P 3; length-breadth ratio, 4.3 on P 2, 4.8 on P 3, and 4.2 on P 4; dorsal margin with 3 or 4 spines on proximal half on P 2 and P 3, with only 1 proximal spine on P 4; ventral margin with 7 slender movable spines including paired terminal spines, distolateral spine larger than ventromesial; lateral surface with sparse, short ridges. Dactyli subequal in length, 0.7–0.8 length of propodi, each terminating in curved strong spine; ventral margin with 6 or 7 proximally diminishing teeth, each with slender movable spine.

P 5 carpus with tuft of short setae on posterodistal margin; propodus with curved, hook-like setae on posterior surface.

Epipods present on P 1 and P 2 (left) or only P 1 (right), no pit for epipod on right P 2.

Color in life ( Fig. 3View FIGURE 3). Body and pereopods white in ground color. Carapace with 9 red blotches: 1 mesogastric, and 1 hepatic, 1 anterior branchial, and 2 posterior branchial on each side; pair of most posterior blotches largest. Rostrum red anterior to basal second lateral teeth, basal part deeply excavated in narrow wedge-shape in midline. Pterygostomian flap with 2 large red spots, one on anterior half and another on posterior half. Abdomen with broad, longitudinal red stripe on each side of tergites 2–4 and in midline of tergites 5 and 6 (faded on posterior part of tergite 5). Telson also with broad red stripe medially. Ocular peduncle red, with white broad mark on dorsal surface; cornea pale brown, covered with small red spots. Mxp 3 entirely white. P 1 with red bands or transverse blotches on dorsal surface: 1 each near distal parts of merus and carpus, median part of palm, and proximal part of dactylus. P 2–4 with broad red bands: 1 each on median parts of meri, propodi and dactyli.

Etymology. The specific name “ chura  ” corresponds to the Ryukyuan language for “beautiful”, referring to the coloration of the new species. The name is used as a noun in apposition.

Habitat. The holotype was collected from a colony of white-colored, unidentified species of the genus Parisis  (Octocorallia, Alcyonacea  , Parisididae  ) at a depth of 188 m. Although the bottom of the collection site was mud in general, there were some rocks which support sponges and octocorals. Water temperature was about 20–21 °C.

Remarks. Galathea chura  sp. nov. resembles G. magnifica Haswell, 1882  , G. spinosorostris Dana, 1852  , and G. tanegashimae Baba, 1969  in having scale-like or interrupted arcuate ridges on the gastric region of the carapace, four deeply incised teeth on each lateral margin of the rostrum, and epipods on the P 1 or P 1 and P 2 only (see Whitelegge 1900; Grant & McCulloch 1906; Baba 1969, 1988; Poore 2004; Baba et al. 2009). However, the absence of epigastric spines on the carapace and coloration in life immediately distinguish the new species from the three known species. Galathea magnifica  , G. spinosorostris  , and G. tanegashimae  all have a pair of epigastric spines, and lack distinct red markings on the carapace, abdomen and pereopods as seen in the new species (see Poore 2004; Baba et al. 2009; Macpherson & Cleva 2010). In addition to these differences, G. chura  sp. nov. differs from G. spinosorostris  and G. tanegashimae  in having much stouter and shorter P 1. In the new species, the P 1 is only 2.2 times as long as the carapace, whereas it is 2.7–3.8 times in G. spinosorostris  and G. tanegashimae  judging from the illustrations of the two species by Baba (1969), Baba et al. (2009), and Macpherson & Cleva (2010). Galathea spinosorostris  is further distinguished from G. chura  sp. nov. by the presence of some spinules on the hepatic dorsal surface of the carapace (no spinules in the new species). The dorsodistal spine on the Mxp 3 merus as seen in G. chura  sp. nov. is absent in G. magnifica  .

The presence of scale-like ridges on the anterior region of the carapace are also known for other four Indo- West Pacific species: G. longimana  Paul’son, 1875; G. squamea Baba, 1979  ; G. submagnifica Laurie, 1926  ; and G. subsquamata Stimpson, 1858  . However, these four species are readily distinguished from G. chura  sp. nov. by having epigastric spines on the carapace. There are two pairs of epigastric spines in G. longimana  and G. submagnifica  , whereas only one pair of epigastric spines are present in G. s q u a m e a and G. subsquamata  . The position of the epipods on the pereopods further discriminates G. chura  sp. nov. from G. s q u a m e a and G. subsquamata  . The new species has epipods on the P 1 or both P 1 and P 2 only, whereas the epipod on the P 1 is absent in G. squamea  and that on the P 3 is present in G. subsquamata  . The numbers of epipods in G. longimana  and G. submagnifica  are not cited in their original descriptions, and there are no definite records of the two species to date. Lewinsohn (1969) reported G. longimana  from the Red Sea, but Baba (1977) concluded that Lewinsohn’s material is identical with G. algae Baba, 1969  , which is currently regarded as a junior synonym of G. spinosorostris  (see Baba 1988, 1990). Galathea longimana  is distinctive in having very narrow rostrum (about 1.5 times as long as broad; see Paul’son 1875: tab. 12, fig. 2).