Tymolus uncifer ( Ortmann, 1892 )

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 : 49-57

Tymolus uncifer ( Ortmann, 1892)

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

( Figs. 2 , 4–8 , 14A )

Cyclodorippe uncifera Ortmann, 1892: 560 , pl. 26, fig. 6.— Doflein 1904: 34 (in part).— Parisi 1914: 197, pl. 13, fig. 2.

Tymolus uncifer .— Sakai 1965: 10 (Japanese text, in part).—1976: 32 (Japanese text, in part).— Ikeda 1998: 21 (in part), 59, fig. 3a–c.

? Tymolus brucei . — Spiridonov & Türkay 2007: 7. See “Discussion”.

Not Cyclodorippe uncifer .— Doflein 1902: 653 [= Tymolus melanommus ( Doflein, 1904) ].

Not Cyclodorippe (Cyclortmannia) uncifera .— Ihle 1916: 134, figs. 40, 43, 49, 50, 52, 57, 62. =? Tymolus glaucommus ( Alcock, 1894) .

Not Tymolus uncifer .—Huang & Liu 1979: 1 [= Tymolus brucei Tavares, 1991 ].— Dai et al. 1986: 31, pl. 3, fig. 13(2) [= Tymolus brucei ].— Takeda & Moosa 1990: 54, 58. [=?]— Dai & Yang 1991: 36, pl. 3, fig. 13(2) [= Tymolus brucei ].— Chen 1998: 231, fig. 2 [= Tymolus brucei ].—Tan & Huang 2000: 139.— Ho et al. 2004: 643, fig. 1C [=?].— Ahyong et al. 2009: 170, figs. 126–128 [=?].— Ng et al. 2017: 24 (list) [=?]. See “Discussion”.

Records remain to be verified.

Cyclodorippe uncifera .— Balss 1922: 286.

Tymolus uncifer .— Yokoya 1933: 103.— Takeda 1997: 232; 2001: 223.— Marumura & Kosaka 2003: 21.

Fossil records remain to be verified or in uncertain status (see “Discussion”).

Tymolus uncifer .— Karasawa 1993: 43, pl. 6, fig. 4.— Karasawa 1997: 16, 41, pl. 8, fig. 10.— Kitamura & Shiba 2008: 15.— Ando et al. 2020: 532 .

Material examined. Lectotype. MZS Cru 3187, male (5.0×5.0 mm), Sagami Bay, 100 fathoms (180 m), 1882, coll. L. Döderlein, designated by Tavares (1992).

Paralectotypes. MZS Cru 569, 1 male (8.6×8.2 mmm), Sagami Bay, 50–200 fathoms (90–360 m), 1882, coll. L. Döderlein ; MZS Cru 4224, 1 female (7.8× 7.8 mm), same data ; MZS Cru 570, Cru 4225–4228, 4 males (4.0×4.0, 4.2×4.2, 5.0× 5.2 mm), 1 female (4.0× 4.2 mm), same data as lectotype ; MZS 571 , 1 male (not measured), same data as lectotype .

Other material. CBM-ZC 4507 , 1 female (4.9× 5.1 mm), 1 ovigerous female (6.9× 7.2 mm), 1 juvenile (3.5× 3.6 mm), Tateyama Bay , Chiba Prefecture, TRV Shin’yo-maru, 1996 research cruise, stn 14, 34°59.89’N, 139°46.15’E, 260–390 m, mud, 24 October 1996, dredge, coll . T. Komai , examined by Tan & Huang (2000) ; CBM-ZC 16734 , 1 male (7.1× 6.7 mm), Sagami Bay , SW of Jogashima, Miura, Kanagawa Prefecture, 35°07.00’N, 139°34.20’E, 157–323 m, mud and sand, 15 February 2017, dredge ( RV Rinkai-maru), coll . T. Komai ; CBM-ZC 16943 , 1 female (cl 8.1 mm; infested by bopyrid), 1 ovigerous female (7.6× 7.6 mm), Sagami Bay , SW of Jogashima, Miura, Kanagawa Prefecture, 35°07.00’N, 139°33.52’E, 509–555 m, mud, 18 February 2016, dredge ( RV Rinkai-maru), coll . T. Komai ; CBM-ZC 16944 , 2 ovigerous females (7.2×7.6, 7.4× 7.5 mm), same data ; CBM-ZC 16951 , 5 males (5.0×5.0, 7.1×6.7, 7.3×7.3, 8.5×8.6, 9.8× 9.8 mm), 1 female (6.8× 7.4 mm), 1 ovigerous female (6.7× 6.9 mm), TRV Shin’yo-maru, 2002 research cruise, stn 21, SW of Izu-ohshima Island, Izu Islands , 35°00.51’N, 139°12.30’E, 549– 486 m, mud, 23 October 2002, dredge, coll . T. Komai ; CBM-ZC 16841 , 2 ovigerous females (6.6×7.0, 7.8× 8.1 mm; DNA voucher), Suruga Bay , off Ukusu, Nishi-izu, 300–400 m, 24 October 2021, commercial trawler .

Diagnosis. Carapace subcircular in outline with subparallel lateral margins, approximately as long as wide; dorsal surface with short setae (sparse on dorsal surface, more numerous on lateral sides), devoid of conspicuous tubercles or nodules on protogastric and metagastric regions; anterolateral margin with 1 small tubercle (laterobranchial tubercle); pterygostomial region with minute granules, none spiniform; front with median projection distally bifurcate by V-shaped median notch and triangular frontal lateral teeth falling far short of tips of frontal submedian teeth; frontal width approximately 0.4 of carapace width; exorbital teeth slightly produced; orbital notch deeply incised, V-shaped, relatively narrow. Ocular peduncle relatively stout, short, overreaching exorbital tooth only by length of cornea, not constricted; cornea large (width more than half distance between frontal submedian and lateral teeth), poorly pigmented even in life. Maxilliped 3 ischium-merus external surface microscopically granular, none of granules spinulose; merus tapering to rounded distal margin, subovate in outline. Pereopod 2 merus 1.7–2.3 times as long as carapace in males, 1.5–2.0 times as long in females, 14.3–17.0 times as long as distal width in males, 10.1–16.3 time as long in females, armed with cluster of 3–7 small, hook-like spines at anterodistal angle; carpus and propodus combined 0.4–0.6 times as long as merus in males, 0.5–0.8 times as long as merus in females. Pereopod 3 merus 1.6–2.0 times as long as carapace in males, 1.2–1.8 times as long as carapace in females, 12.9–15.8 times as long as distal width in males, 10.0–14.5 time as long as distal width in females, armed with single or cluster of 2–4 hook-like spines at anterodistal angle; carpus and propodus combined 0.6–0.7 times as long as merus in males, 0.6–0.9 times as long as merus in females. No fringe of setae on flexor margins of propodi of pereopods 2 and 3.

Redescription. Male. Carapace ( Figs.4A , 5A , 6A,B )subcircular with lateral margins subparallel, approximately as long as wide, greatest width at 0.6–0.7 length of carapace; surface finely granular, with short setae (sparse on dorsal surface, more numerous on lateral sides). Regions on dorsal surface rather clearly indicated by shallow 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 obsolescent tubercles (anterolateral and laterobranchial tubercles) on each side; posterolateral margins each with row of minute, sharp granules. Front with median projection distally bifurcate by wide V-shaped median notch and triangular frontal lateral teeth falling far short of tips of submedian teeth on 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 0.4 of carapace width. Exorbital teeth laterally compressed, falling far short of frontal lateral teeth, separated from frontal lateral teeth by deeply incised, V-shaped orbital notch, each tip bluntly pointed. Inferior orbital tooth small, blunt, flanked by anteroventral angle of exorbital tooth and article 2 of antennal peduncle ( Fig. 6C ). Pterygostomial region gently inflated, divided into 2 unequal parts by shallow oblique groove, covered with minute granules.

Endostome ( Fig. 6C ) narrowing anteriorly to form efferent channel, anterior end reaching to median notch of frontal median projection.

Thoracic sternum ( Fig. 5B ) narrowing anteriorly, widest at sternite 5; surface granular, with median groove almost over entire length of sternites 3–5. Anteriormost sternite subtriangular with blunt or subacute anterior end. Sternites 3–5 partially fused medially; sternite 3 subhexagonal; sternites 4 elevated along lateral margins, forming protuberance-like prominences posteriorly. Sternites 5 and 6 partially fused mesially, lateral parts of former narrowing toward midline; groove separating sternites 5 and 6 deep, oblique, ending mesially in deep depression far remote from 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 very deep, reaching nearly to anterior end of sternite 6, margins clearly delimited.

Ocular peduncles ( Figs. 5A , 6A, C ) slightly divergent, subcylindrical, relatively stout, not constricted, slightly inflated basally, overreaching exorbital teeth only by lengths of corneas. Cornea large (width more than half distance between tips of frontal submedian tooth and frontal lateral tooth), poorly pigmented even in life; ommatidia apparently absent.

Antennular peduncle ( Fig. 6A, C ) about half-length of carapace. Basal articles stout, separated by anterior extension of endostome. Article 3 subequal in length and slenderer than article 2.

Antennal peduncle ( Fig. 6A, C ) 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. 6D ) elongate, reaching distally to anterior end of endostome, upturned to fit anteriorly located buccal cavern; external surface of ischium and merus minutely granular, none of granules spinulose. Ischium elongate subrectangular. Merus tapering distally to rounded tip, elongate subovate; lateral margin gently convex, mesial margin nearly straight. Palp (carpus- propodus-dactylus) partially hidden by merus; dactylus small, tapering distally, with brush-like setae. Exopod narrow, closely fit endopod ischium along entire length, reaching distal margin of ischium, lateral margin slightly convex; flagellum absent.

Chelipeds ( Figs. 4A , 6E, F ) equal and similar, surfaces of articles minutely granular. Merus upper surface rounded; lower surface flattened. Carpus upper surface gently convex; inner surface weakly produced with few spinules. 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 1.1 times as long as palm, slightly curved, terminating in blunt or subacute tip, upper surface rounded with short setae along inner side, occlusal margin irregularly denticulate like opposite margin of fixed finger.

Pereopod 2 ( Figs. 5A , 7A, B ) markedly elongate, surfaces of articles covered with minute granules (except for dactylus) and short setae, but not particularly spinulose. Coxa large, with condyle at anteroventral distal angle. Ischium articulation to merus strongly oblique. Merus 1.7–2.3 times as long as carapace, 14.3–17.0 times as long as distal width, nearly straight, rod-like, slightly widened distally, with cluster of 3–7 small, mesially curved, hook-like spines at anterodistal angle. Carpus and propodus combined 0.4–0.6 times as long as merus, both articles unarmed; carpus slightly widened distally. Dactylus slender, slightly flattened, gently arcuate, subequal in length to propodus; upper and lower margins setose.

Pereopod 3 ( Figs. 5A , 7C, D ) generally similar to pereopod 2, but slightly shorter. Merus 1.6–2.0 times as long as carapace, 12.9–15.8 times as long as distal width, anterodistal angle with cluster of 3 or 4 small, hook-like spines. Carpus-propodus combined 0.6–0.7 times as long as merus. Dactylus subequal in length to propodus.

Pereopods 4 and 5 ( Figs. 5A , 7E, F ) located dorsally, much shorter and slenderer than pereopods 2 and 3. Meri extending well beyond posterolateral margin of carapace. Dactyli slender, sickle-shaped, shorter than propodi, fully folded against propodi when flexed.

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

Gonopod 1 ( Fig. 7G–J ) consisting of 3 articles; angle between ultimate and penultimate article 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. 7K ) stout, fairly compressed laterally, lower distal end extending into slender, chitinous projection, upper distal margin truncate, hollowed; upper margin gently convex, while lower margin gently concave.

Females. Carapace generally similar to that of male, but pereopods 2 and 3 proportionally shorter ( Fig. 4B ). Thoracic sternum ( Fig. 8A ) narrowing anteriorly, widest at sternite 5; surface microscopically granular, medially sulcate on sternites 3–5. Anteriormost sternite subtriangular with blunt 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, flange-like; small deep pit on either side just proximal to base of maxilliped 3. 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 ( Figs. 4B , 8B ) slenderer than those of males. Chela 2.5 times as long as wide; palm widened distally, 1.1 times as wide as long; fingers terminating in acute tips, fixed finger somewhat deflexed; denticles on occlusal margins obsolescent or blunt; dactylus twice as long as palm.

Pereopod 2 ( Fig. 4B ) merus 1.5–2.0 times as long as carapace, 10.1–16.3 times as long as distal width; carpus and propodus combined 0.5–0.8 times as long as merus. Pereopod 3 ( Fig. 4B ) merus 1.2–1.8 times as long as carapace, 10–14.5 times as long as distal width; carpus and propodus combined 0.5–0.8 times as long as merus; gonopore on each coxa.

Pleon ( Figs. 4B , 8C ) 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; pleomeres 4 and 5 widest. Pleotelson semicircular, 1.6 times as long as wide.

Eggs spherical, diameter 0.7 mm.

Colouration in life. Entirely white; corneas opaque, poorly pigmented ( Fig. 14A ).

Distribution. Known with certainty only from the Pacific coast of Japan, Sagami Sea to Suruga Bay, at depths of 157–555 m (see below “Discussion”).

Remarks. One juvenile (CBM-ZC 4507, 3.5× 3.6 mm), the smallest among the examined specimens, differs from adult specimens in having proportionally shorter carpus+propodus (0.9 times as long as merus in the pereopod 2, 0.7 times in the pereopod 3), approaching the condition seen in T. melanommus . As discussed below, morphometric characters of the pereopods 2 and 3 are useful in differentiating T. uncifer and T. melanomma in adults, but careful observation will be necessary when identifying juvenile or young specimens.

Figures

FIGURE 2. Tymolus uncifer (Ortmann, 1892), lectotype, male (5.0×5.0 mm), MZS Cru 3187. A, cephalothorax and pleon, dorsal view; B, same, ventral view.

FIGURE 4. Tymolus uncifer (Ortmann, 1892), habitus in dorsal view. A, male (9.8×9.8 mm), CBM-ZC 16951; B, ovigerous female (7.6×7.6 mm), CBM-ZC 16943. In preservative.

FIGURE 5. Tymolus uncifer (Ortmann, 1892), male (9.8×9.8 mm), CBM-ZC 16951. A, carapace and cephalic appendages, dorsal view; B, thoracic sternum, ventral view. In preservative.

FIGURE 6. Tymolus uncifer (Ortmann, 1892), male (9.8×9.8 mm), CBM-ZC 16951. A, anterior part of carapace, ocular peduncles, antennules and antennae, dorsal view; 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 7. Tymolus uncifer (Ortmann, 1892), male (9.8×9.8 mm), CBM-ZC 16951.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 8. Tymolus uncifer (Ortmann, 1892), ovigerous female 7.6×7.6 mm), CBM-ZC 16943. 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.