Tymolus melanommus ( Doflein, 1904 )

Komai, Tomoyuki, 2023, Clarification of the identity of deep-sea crab Tymolus uncifer (Ortmann, 1892) and validation of Tymolus melanommus (Doflein, 1904) (Decapoda: Brachyura: Cyclodorippidae), Zootaxa 5352 (1), pp. 46-72 : 57-63

Tymolus melanommus ( Doflein, 1904)

[Japanese name: Ashiboso-mame-heike-gani]

( Figs. 3 , 9–13 , 14B )

Cyclodorippe uncifera .— Doflein 1902: 653; 1904: 34 (in part). Cyclodorippe uncifera forma melanomma Doflein, 1904: 34 , pl. 12, fig. 7. Tymolus uncifer .— Sakai 1937: 70, pl. 10, fig. 2; 1965: 21 (English text), 10 (English text), pl. 10, fig. 3; 1976: 33 (English text),

32 (Japanese text) (in part), pl. 8, fig. 3.— Tavares 1991: 444, figs. 2, 4, 8A, 9B, 10B; 1992: 205, fig. 2D.— Ikeda 1998: 21

(in part), 59, figs. 1, 2a, b.— Ng et al. 2008: 31 (list).—Spiridonov & Türkay 2007: 6–7, figs. 4D–E.— Komatsu & Komai

2009: 598, fig. 3F. Not Cyclodorippe uncifera forma melanomma Doflein, 1904 : pl. 12, fig. 6. = Tymolus globosus Spiridonov & Türkay, 2007 .

Material examined. Lectotype (designated herein). ZSM 393 /1, male (mm), Sagami Bay , 50 m, 1901, coll. A. Haberer.

Other material. CBM-ZC 8556 , 1 male (12.7× 12.5 mm), off Sohma , Fukushima Prefecture, 300–400 m, 14 October 2005, commercial trawler, coll. M. Fujiwara ; CBM-ZC 5253 , 2 ovigerous females (9.3×9.2, 10.0× 10.3 mm), off Choshi , Chiba Prefecture, 150–200 m, 24 November 1998, commercial trawler, coll . T. Komai ; CBM-ZC 6401 , 1 male, 1 ovigerous female (7.9× 7.9 mm) , RV “Tansei-maru”, KT-98-14 cruise, stn 17-1, Uraga Strait, S of Katsuyama-Ukishima Islet, Kyonan , Chiba Prefecture, 35°07.18’N, 139°49.11’E, 281–298 m, 30 August 1998, dredge, coll . T. Komai ; CBM-ZC 9213 , 1 male (5.8× 5.6 mm), Uraga Strait , SE of Katsuyama-Ukishima Islet, 200–250 m, 19 March 2007, commercial gill net for scampi, coll. S. Tsuzuki ; CBM-ZC 9485 , 1 male (10.7× 11.7 mm), Uraga Strait, off Kyonan , 200 m, commercial gill net for scampi, coll. S. Tsuzuki ; CBM-ZC 16563 , 3 males (9.3×9.1, 12.5×11.8, 13.0× 13.4 mm, DNA voucher), Uraga Strait , SW of Katsuyama-Ukishima Islet, 180–250 m, 2 December 2010, commercial gill net for scampi, coll . T. Komai ; CBM-ZC 17322 , 1 male (9.4× 8.9 mm), Uraga Strait, off Kyonan , 120–200 m, 24 October 2007, commercial gill net for scampi, coll . T. Komai ; CBM-ZC 17323 , 1 male (13.0×13.0 mm), similar locality, 200 m, 6 December 2009, commercial gill net for scampi, coll . T. Komai . CBM-ZC 6253 , 1 male (12.0×12.0 mm), Suruga Bay, off Toi , Shizuoka Prefecture, 34°52.06’N, 138°42.63’E, 550 m, 21 March 2001, commercial trawler, coll . T. Komai ; CBM-ZC 6260 , 1 male (7.7× 7.5 mm), 1 ovigerous female (8.8× 8.7 mm), Suruga Bay, off Toi , 34°54.02’N, 138°44.04’E, 300–350 m, 21 March 2001, commercial trawler, coll . T. Komai ; CBM-ZC 6272 , 4 males (11.2×11.2, 11.7×11.0, 12.1×11.8, 12.7× 12.9 mm), 1 female (8.0×8.0 mm), 1 ovigerous female (7.7×7.4 mmm), similar locality, 34°54.50’N, 138°44.20’E, 450–500 m, 21 March 2001, commercial trawler, coll . T. Komai ; CBM-ZC 16682 , 1 female (7.1× 7.1 mm; DNA voucher), 1 ovigerous female (8.0× 7.6 mm), TRV “Seisui-maru”, 2019 research cruise, stn 4B, Kumano Sea , SW of Kihoku, Mie Prefecture, 34°06.58’N, 136°27.66’E, 200 m, 2 October 2019, beam trawl, coll . T. Kimura .

Diagnosis. Carapace subpyriform; dorsal surface with sparse short setae, devoid of tubercles or nodules on protogastric and metagastric regions; anterolateral margin with 2 low tubercles (anterolateral and laterobranchial tubercles); pterygostomial area with minute granules, none spiniform; front with median projection distally bifurcate into short frontal submedian teeth by V-shaped median notch, triangular frontal lateral teeth falling far short of tips of frontal submedian teeth; frontal width approximately 0.3 of carapace width; exorbital teeth well produced; orbital notch deeply incised, V-shaped, relatively narrow. Ocular peduncle relatively long, slender, overreaching exorbital tooth by half-length of peduncle, constricted at midlength; cornea small (less than half distance between frontal submedian and lateral teeth), pigmented with light brown in life. Maxilliped 3 ischium-merus external surface microscopically granular, none of granules spinulose; merus tapering distally to subacute tip, lance-shaped. Pereopod 2 merus 1.3–1.6 times as long as carapace in males, 1.2–1.3 times as long in females, 9.3–11.7 times as long as distal width in males, 9.2–10.4 time as long in females, armed with 1 minute, hook-like spine at anterodistal angle or unarmed; carpus and propodus combined 0.6–0.9 times as long as merus in males, 0.7–0.8 times as long in females. Pereopod 3 merus 1.0–1.5 times as long as carapace in males, 1.0–1.2 times as long in females, 9.1–11.2 times as long as distal width in males, 6.7–9.8 time as long in females, always unarmed at anterodistal angle; carpus and propodus combined 0.8–1.0 times as long as merus in males, 0.9–1.0 times as long in females.

Redescription. Male. Carapace ( Figs. 9A , 10A , 11A, B ) subpyriform with lateral margins diverging posteriorly, 1.0–1.1 times as long as wide, greatest width at 0.7 length of carapace; surface finely granular, with sparse short setae (sparse on dorsal surface, more numerous on lateral sides). Regions on dorsal surface rather clearly indicated by shallow to deep grooves, without conspicuous tubercles or nodules on metagastric and protogastric regions; metagastric region widened posteriorly; protogastric regions each divided into two parts by shallow longitudinal grooves; epibranchial regions demarcated; cardiac region elevated, dome-like, clearly demarcated by deep gastric fossae and connected deep longitudinal grooves; intestinal region extremely narrow.Anterolateral margins not clearly delimited, with 2 low tubercles (anterolateral and laterobranchial tubercles) on each side; posterolateral margins each with row of minute, sharp granules. Front with median projection distally bifurcate by deep V-shaped median notch and triangular frontal lateral teeth falling far short of tips of bifurcated median projection, tips of frontal lateral teeth blunt or subacute; dorsal surface with shallow median groove, demarcated from carapace mesogastric region by shallow transverse groove extending to anteroventral margins. Frontal width approximately 0.3 of carapace width. Exorbital teeth laterally compressed, well produced, but falling short of frontal lateral teeth, separated from frontal lateral teeth by deep, narrow, V-shaped notch, each tip of frontal teeth bluntly pointed. Inferior orbital tooth ( Fig. 3C ) small, bluntly pointed, flanked by anteroventral angle of exorbital tooth and article 2 of antennal peduncle. Pterygostomial region gently inflated, divided into 2 unequal parts by shallow oblique groove.

Endostome ( Fig. 11C ) narrowing anteriorly to form deep efferent channel, anterior end reaching to median notch of frontal median projection.

Thoracic sternum ( Fig. 10B ) abruptly narrowed anteriorly, widest at sternite 5; surface microscopically granular, with median groove almost over entire length of sternites 3–5. Anteriormost sternite subtriangular with rounded anterior margin. Sternites 3–5 partially fused medially; sternite 3 subhexagonal; sternites 4 elevated along lateral margins, forming protuberance-like prominences posteriorly; sternite 5 lateral parts narrowing toward midline. Sternite 6 with posterolateral parts perpendicular against anterolateral parts (either side of sterno-pleonal cavity), extending dorsally to surround coxae of pereopods 3. Sternite 7 with lateral parts small, subtriangular in outline, weakly elevated. Sterno-pleonal cavity reaching nearly to anterior end of sternite 6, margins clearly delimited.

Ocular peduncles ( Figs. 10A , 11A, C ) slightly divergent, subcylindrical, relatively slender, constricted at midlength, inflated basally, reaching beyond tips of frontal submedian teeth. Cornea small (width less than half distance between tips of frontal submedian tooth and frontal lateral tooth), pigmented with light brown; minute ommatidia discernible.

Antennular peduncle ( Figs. 10A , 11A, C ) less than half-length of carapace. Basal articles stout, separated by anterior extension of endostome. Article 3 slightly longer and slenderer than article 2.

Antennal peduncle ( Fig. 11C ) much shorter than antennular peduncle. Article 1 in line with basal article of antennular peduncle. Articles 2 subcylindrical, slightly widened distally. Article 3 also subcylindrical, subequal to and slightly narrower than article 2. Terminal article very short, conical, bearing sensilia-like apical seta.

Maxilliped 3 ( Fig. 11D ) elongate, reaching distally to anterior end of endostome, upturned to fit anteriorly located buccal cavern; external surface of ischium and merus with covering of minute granules, none of granules spinolose. Ischium elongate subrectangular. Merus elongate, tapering to subacute tip, lance-shaped; lateral margin gently convex, mesial margin nearly straight. Palp (carpus-propodus-dactylus) partially hidden by merus; dactylus tapering distally, with brush-like setae. Exopod narrow, closely fit endopod ischium along entire length, lateral margin slightly convex; flagellum absent.

Chelipeds ( Fig. 9A , 11E, F ) equal and similar, surfaces of articles minutely granular. Merus upper surface rounded; lower surface flattened. Carpus upper surface gently convex; inner surface with blunt protuberance partially obscured by short setae. Palm widened distally, 1.1 times as high as long in adults; upper inner margin bluntly ridged; outer surface feebly convex; inner surface nearly flat; lower surface rounded. Fixed finger slightly deflexed, well compressed, terminating in subacute tip, occlusal margin irregularly denticulate; dactylus 1.3 times as long as palm, slightly curved, terminating in subacute tip, upper surface rounded with short setae along inner side, occlusal margin irregularly denticulate like opposite margin of fixed finger.

Pereopod 2 ( Figs. 9A , 12A ) elongate, surfaces of articles (except for dactylus) covered with minute granules and short setae (less granulate on propodus), but not particularly spinulose. Coxa large, without conspicuous armature. Ischium articulation to merus strongly oblique. Merus 1.3–1.6 times as long as carapace, 9.3–11.7 times as long as distal width, nearly straight, rod-like, slightly widened distally, with 1 minute, hook-like spine, or unarmed at anterodistal angle ( Fig. 12B ). Carpus and propodus combined 0.6–0.9 times as long as merus, both articles unarmed; carpus slightly widened distally. Dactylus slender, slightly flattened, gently arcuate, 1.0–1.2 times as long as propodus; upper and lower margins setose.

Pereopod 3 ( Figs. 9A , 12C ) generally similar to pereopod 2, but slightly shorter. Merus 1.0–1.5 times as long as carapace, 9.1–11.2 times as long as distal width, anterodistal angle always unarmed ( Fig. 12D ). Carpus-propodus combined 0.8–1.0 times as long as merus. Dactylus 1.0–1.1 times as long as propodus.

Pereopods 4 and 5 ( Figs. 10A , 12E, F ) located dorsally, much shorter and slenderer than pereopods 2 and 3. Meri extending well beyond posterolateral margin of carapace, subequal in length to ischium in pereopod 4, distinctly longer than ischium in pereopod 5. Dactyli slender, sickle-shaped, shorter than propodi, fully folded against propodi when flexed.

Pleon ( Figs. 9B , 11G ) consisting of 5 somites, pleomere 1 narrowest, pleomere 4 widest; pleomeres 1–3 visible in dorsal view; midline of pleomeres 1–4 elevated in blunt ridge, lateral margins also weakly elevated, separated from median ridge by shallow sulci. Pleotelson formed by fusion of pleomere 6 and telson, subtriangular with rounded apex, lateral margins slightly constricted proximally; outer surface with low median elevation near base.

Gonopod 1 ( Fig. 12G–J ) consisting of 3 articles; angle at articulation between ultimate and penultimate article about 30° in lateral view; ultimate article bean-shaped in general outline, cannulate, forming copulatory tube embracing gonopod 2 in situ, distal margin with setae extending onto proximal margins, ventral surface with deep longitudinal groove along over entire length; inner margin of penultimate article slightly expanded. G2 ( Fig. 12K ) strongly compressed laterally, lower distal end produced into very slender, chitinous projection, upper distal margin obliquely truncate, hollowed; upper margin slightly convex, while lower margin slightly sinuous.

Females. Carapace generally similar to that of male, but pereopods 2 and 3 proportionally shorter ( Fig. 9B ). Thoracic sternum ( Fig. 13A ) narrowing anteriorly, widest at sternite 5; surface microscopically granular, medially depressed on sternites 3–5. Anteriormost sternite roundly subtriangular with rounded anterior margin. Sternites 3–5 demarcated by transverse furrows; sternite 3 subhexagonal; sternites 4 with paired rounded elevations, lateral margins accommodating coxae of chelipeds substantially elevated. Sternite 5 posteriorly with transverse ridge forming anterior boundary of sterno-pleonal cavity. Entire sternite 6 forming deep sterno-pleonal cavity, steeply sloping, medially with blunt transverse ridge adjacent to sternite 5; suture demarcating sternites 5 and 6 distinct laterally, faded away medially; suture demarcating sternites 6 and 7 also distinct laterally, fairly oblique against longitudinal axis.

Chelipeds ( Fig. 9B ) slenderer than those of males. Chela ( Fig. 13B ) 2.5 times as long as high; palm widened distally, 1.1 times as wide as long; fingers terminating in acute tips, fixed finger gently deflexed; denticles on occlusal margins sharper than those of males; dactylus twice as long as palm.

Pereopod 2 ( Fig. 9B ) merus 1.2–1.3 times as long as carapace, 9.2–10.4 times as long as distal width; carpus and propodus combined 0.7–0.8 times as long as merus. Pereopod 3 ( Fig. 9B ) merus 1.0–1.2 times as long as carapace, 6.7–9.8 times as long as distal width; carpus and propodus combined 0.9–1.0 times as long as merus; gonopore on each coxa.

Pleon ( Fig. 9B , 13C ) large, consisting of 5 somites, pleomere 6 fused with telson (= pleotelson). Pleomeres 1–5 each with low, rounded protuberance on midline; pleomeres 1–4 visible in dorsal view; pleomere 1 narrowest, subtrapezoidal; pleotelson widest. Pleotelson semicircular, 1.7–1.8 times as long as wide.

Eggs spherical, diameter 0.7–0.8 mm.

Size. Largest male 13.0× 13.4 mm; largest female 10.0× 10.3 mm, ovigerous female 7.9×7.9–10.0× 10.3 mm.

Colouration in life. Carapace white or gray-white; appendages entirely white; cornea pigmented with light brown ( Fig. 14B ).

Distribution. Known with certainty only from the Pacific coast of Japan, from Iwate Prefecture to Tosa Bay; at depths of 50– 550 m.

Figures

FIGURE 3. Tymolus melanommus (Doflein, 1904), lectotype, male (7.5×7.0 mm), ZSM 393/1. A, cephalothorax and pleon, dorsal view; B, detached left cheliped and pereopods 2 and 3.

FIGURE 9. Tymolus melanommus (Doflein, 1904), habitus in dorsal view. A, male (13.0×13.0 mm), CBM-ZC 17323; B, ovigerous female (8.8×8.7 mm), CBM-ZC 6260. In preservative.

FIGURE 10. Tymolus melanommus (Doflein, 1904), male (13.0×13.0 mm), CBM-ZC 17323. A, carapace and cephalic appendages, dorsal view; B, thoracic sternum, ventral view. In preservative.

FIGURE 11. Tymolus melanommus (Doflein, 1904), male (13.0×13.0 mm), CBM-ZC 17323. A, anterior part of carapace, ocular peduncles and antennae, dorsal view (setae omitted); B, left anterolateral part of carapace (setae omitted); C, left anterior part of carapace and cephalic appendages, ventral view (setae omitted); D, right maxilliped 3, external view; E, carpus of right cheliped, dorsal view; F, right chela, outer view; G, pleon, external view (setae omitted).

FIGURE 12. Tymolus melanommus (Doflein, 1904), male (13.0×13.0 mm), CBM-ZC 17323.A, right pereopod 2, dorsal view; B, same, distal part of merus, dorsal view; C, right pereopod 3, dorsal view (setae omitted); D, same, distal part of merus, dorsal view; E, right pereopod 4, dorsal view; F, right pereopod 5, dorsal view; G, left gonopod 1, mesial view; H, same, ventral view; I, same, lateral view; J, same, dorsal view; K, left gonopod 2, lateral view.

FIGURE 13. Tymolus melanommus (Doflein, 1904), ovigerous female (8.8×8.7 mm), CBM-ZC 6260. A, thoracic sternum, ventral view; B, right chela, outer view; C, pleon, external view. Setae omitted.

FIGURE 14. Habitus showing living colouration.A, Tymolus uncifer (Ortmann, 1892), ovigerous female (7.8×8.1 mm), CBM- ZC 16841; B, Tymolus melanommus (Doflein, 1904), male (13.0×13.0 mm), CBM-ZC 17323.