Stylodactylus major Hayashi & Miyake, 1968

Cleva, Régis, 2004, Stylodactylidae And Bathypalaemonellidae From Taiwan (Crustacea: Decapoda: Caridea), Raffles Bulletin of Zoology 52 (2), pp. 497-511 : 497-499

Stylodactylus major Hayashi & Miyake, 1968

( Figs. 1 , 6a )

Stylodactylus major Hayashi & Miyake, 1968: 590 , Figs. 2 , 3 ; Hayashi, 1991a: 42; Cleva, 1994: 56, Fig. 1B .

Material examined. – 1 male (CL = 37 mm, TL without rostrum, broken, approx. 135 mm); 1 male (CL 32 mm, TL without rostrum, broken, approx. 118 mm) ( NTOU), “ TAIWAN 2001”, R. V. “OCEAN RESEARCHER1”, st. CD 136, 22 7.75N- 120 0.87E, 1211- 998 m, sticky mud, 22 Nov.2001 ; 1 male (CL 20 mm, TL with rostrum approx. 112 mm) ( NTOU), “ TAIWAN 2002”, st. CD 199, 24 25.38’N- 122 12.41’E, 1138-1187 m, 12 Sep.2002 ; 1 male (CL= 35 mm, TL without rostrum, broken, approx. 126 mm) ( NTOU), “ TAIWAN 2003”, st.CD 229, 22 13.35’N- 120 01.9’E, 1060- 880 m, 30 Aug.2003 .

Description. – Among these four interesting specimens the two from st. CD 136 have their rostrum broken and many appendages are missing. The male LC = 37 mm retains the two mxp3, the right P1 (dactyl missing), the right P2 (chela partly broken), the right P3, part of the right P4 (ischio-merus only), part of the left P3 (ischio-merus+carpus), and part of the left P5 (ischio-merus); the tip of the telson is missing. The male LC = 32 mm lacks all appendages, except the right mxp3 (ultimate segment broken) and the first segment of the left mxp 3. However, they display features which fit quite well with the description of the type material and allow their identification as Stylodactylus major with a reasonable degree of confidence; specimen from st. CD 229 has also its rostrum broken, but many pereiopods are still present. The following description is based on these three specimens:

Tegument firm; the whole cephalothorax and the abdomen, along with the telson and uropods, eyestalks, scaphocerites, stylocerites and antennular peduncles covered with numerous fine setae. Remaining part of the rostrum ( Fig. 1b ) bearing closely articulated spines of nearly equal size, six, eight or nine being situated on the postrostral carinae (seven, nine, ten, in the type material); first ventral rostral spine situated above the basal segment of the antennular peduncle and at the level of the 18 th, 19 th (as in the holotype), or 20 th dorsal rostral spine (including those situated on the postrostral carinae). Supra-orbital spine absent. Third abdominal somite produced backwards, bearing three, four or five marginal spines on the dorsal median line (one,three, four in the type material). Pleura of fourth and fifth abdominal somites acutely produced posteroventrally ( Fig. 1c ). Telson (excluding the two pairs of long terminal spines) about 1.8 times as long as the sixth abdominal somite, bearing eighteight, nine-ten and nine-ten dorsal spines (nine-ten and eightnine in the type material)( Fig. 1d ). Antennular peduncle and scaphocerite corresponding to those of the type material. Merus of the last three pairs of pereiopods bearing respectively: P3: 11-11,and 17; P4: 12; P5:eight or seven outer spines (15 or 16, 11 or 12 on the third and fourth pereiopods in the type material). Proportions of P3 articles close to those of the holotype: ischio-merus = 1.8 x propodus; propodus = 2.7 or 2.9 x carpus (terminal lobe of carpus excluded), and 5 or 5.4 x dactylus; dactylus bearing seven ventral spinules. Proportions of P5 articles: ischio-merus = 1.0 propodus; propodus = 3.0 x carpus and 9.0 x dactylus; dactylus bearing 11 spinules on its lower margin.

The specimen from st. CD 199, which is much smaller in size and has a less robust appearance, is in a very good state and corresponds well to the description of the type material, displaying the features listed above. Rostrum ( Fig. 1a ) 1.7 times longer than the carapace (holotype: 1.4 times) with 54 dorsal spines (seven of which situated on the carapace proper) and 34 ventral spines (holotype: 51(7)/30); first rostral ventral spine situated at level of 19th dorsal (as in the holotype); rostrum appearing to be less curved than in the female holotype, a characteristic linked with the sexual dimorphism observed in other species of the family; third abdominal somite with two marginal spines on the dorsal median line; telson with 10-11 dorsal spines; merus of left P3, P4, P5 respectively with 14, 13, 10 outer spines (right appendages missing); proportions of P3 articles: ischio-merus = 5 x carpus (distal lobe of carpus excluded); ischio-merus = 1.7 x propodus; propodus = 3 x carpus and 5 x dactylus; dactylus of P3 and P4 (that of P5 absent) with six ventral spinules.

Remarks. – Stylodactylus major is closely related to Stylodactylus brucei Cleva, 1994 , the largest species of the family, collected from Wallis Island (south-west Pacific) at 820-840 m depth, and from the north-west Australian shelf at 900-1000 m ( Cleva, 1994: 54). The two species can be separated by a series of differences ( Cleva, 1994: 56) that are repeated and augmented as follows:

i) Cephalothorax and abdomen glabrous in S. brucei ,

pubescent in S. major .

ii) Number, aspect, and disposition of rostral spines: 29-30

dorsal spines and 26-33 ventral spines in S. brucei versus

51-54 and 30-34 in S. major ; proximal dorsal spines of

S. brucei (including those on the postrostral carinae)

clearly longer than the others, those of S. major being of nearly equal size ( Figs. 1a, b ; Cleva, 1994: Figs. 1A, B ).

In addition, proximal dorsal spines clearly longer and more spaced in S. brucei than in S. major ; distal part of rostrum unarmed dorsally in S. brucei , in contrast to S.

major.

iii) Posteroventral margin of fourth abdominal pleuron rounded in S. brucei , pointed in S. major .

iv) Last three pairs of pereiopods less spinulous in S. brucei .

Proportions between the articles different in the two species: for example, comparison between the holotype of S. brucei (CL 37 mm) and the larger Taiwanese specimen, of equal size, of S. major , clearly shows that the propodus of P3 is significantly longer, and the dactylus shorter in the former.

Coloration. – Entirely red in the two large specimens from st. CD 136 ( Fig. 6a ), and somewhat orange-red in the smaller specimen from st. CD 199.

Distribution. – The type specimens (three females) were collected in the East China Sea (South Japan) at a depth of 122-124 m: as Dr. Komai has pointed out, the depth mentioned is doubtful in view of the other carideans caught at the same station: Heterocarpus dorsalis Bate , Pandalopsis sp. and Acanthephyra eximia Smith , all of which were collected beyond a depth of 500 m. It is worth noting that the four specimens caught in Taiwanese waters, between 880 and 1211 m, represent the second record for this species.

Figures

Fig. 1. Stylodactylus major Hayashi & Miyake, 1968: (a), (b), anterior part of cephalothorax; (c), abdomen (part); (d), telson; (a) male 20 mm, TAIWAN 2002, st. CD 199; (b) male 37 mm, TAIWAN 2001, st. CD 136; (c),(d), male 32 mm TAIWAN 2001, st. CD 136. Scale bars: b= 10 mm; a, c, d = 5 mm.

Fig. 6. (a) Stylodactylus major Hayashi & Miyake, 1968, male 37 mm, TAIWAN 2001, st. CD136; (b) Stylodactylus libratus Chace, 1983, male 11 mm, Su-Aou fishing Port; (c) Stylodactylus licinus Chace, 1983, female ov. 16 mm, TAIWAN 2001, st. CD132; (d) Stylodactylus tokarensis Zarenkov,1968, male 8.5 mm, TAIWAN 2001, st. CP115; (e) Bathypalaemonella hayashii Komai, 1995, female 12.5 mm, TAIWAN 2001, st. CP139; (f) Bathypalaemonetes brevirostris (Bruce, 1986), 8.5 mm, TAIWAN 2000, st. CP58; (g) Bathypalaemonetes pilosipes (Bruce, 1986), female 10.5 mm, TAIWAN 2001, st. CD139; (h) Bathypalaemonetes chani, new species, female ov.15 mm, holotype, TAIWAN 2001, st. CD132.

Fig. 2. (a), Stylodactylus libratus Chace, 1983, male 11 mm, Su-Aou fishing Port; (b), Stylodactylus tokarensis Zarenkov, 1968, male 8.5 mm, TAIWAN 2001, st. CP 115. Scale bars= 5 mm.

Fig. 3. (a),(d), Stylodactylus sp. aff. pubescens Burukovsky, 1990, female ov. 12.5 mm,“TAIWAN 2003”, st. CD 210: (a), anterior part of cephalothorax; (d), right third pereiopod; (b),(c), Stylodactylus pubescens Burukovsky, 1990: (b), male 11.5 mm, Paratype, anterior part of cephalothorax; (c), female 10.5 mm, Paratype, anterior part of cephalothorax. Scale bars = 5 mm.