Sicyonella maldivensis Borradaile, 1910

Fukuoka, Kouki, Tamaki, Motoya & Kikuchi, Tomohiko, 2005, (Crustacea: Decapoda: Dendrobranchiata: Sergestidae), Zootaxa 833, pp. 1-31 : 20-28

Sicyonella maldivensis Borradaile, 1910 ( Figs. 12–16 , 17 C)

Sicyonella maldivensis Borradaile, 1910: 259 , 260, pl. 16, figs. 3, 3a; Hansen, 1919: 28, 29, pl. 2, fig. 4; Cecchini, 1933: 11, 12, fig. 4a–c; Chace, 1955: 4, fig. 3a.

Type locality. North Male Atoll, Maldives.

Type specimen. Lectotype: NHM (1987.10.1), male (cl 7.0 mm), one of syntype of S. maldivensis , North Male Atoll, Maldives, date unknown.

Material examined. [ USNM Collection] USNM­ 260757: 14 males (cl 6.1–7.2 mm) and 5 females (cl 7.3–9.5 mm), Sitanki, Sibutu Island, Sulu Archipelago, Philippines, surface, electric light, 25 Feb. 1908. USNM­94725: 1 female (cl 7.8 mm), Bikini Lagoon, light at night, 23 Apr. 1946, coll. Schultz and Morrison. USNM­94726: 1 male, Bikini Lagoon, marine light, anchorage, 25 Apr. 1946, coll. Schultz. USNM­105267: 1 female (cl 5.8 mm), Palau Islands (7°19’34.5’’N 134°28’05’’E), 16 Aug. 1955. USNM­105229: 1 male (cl 5.1 mm) and 1 female (cl 7.5 mm), Yoo Passage (7°12’00’’N 134°25’42’’E), west of Kasso Reef, Palau Islands, 27.5–32.9 m, dredge, 24 Aug. 1955. USNM­266986: 1 male (cl 5.0 mm), Parry Island, Marshall Islands, lagoon, 28 Aug. 1956.

[ MNHN Collection] MNHN: 1 male and 1 female, St. DW 1116, New Caledonia, date unknown.

[ NSMT Collection] NSMT­Cr 14115: 5 males (cl 3.9­4.5 mm), pier of Ishigaki Tropical Station of Seikai National Fisheries Research Institute (ITS), Urasoko Bay, Ishigaki Island, Okinawa, Japan, sand bottom, 2­3 m, light trap, 1 Sept. 2000, coll. K. Fukuoka. NSMT­Cr 16036: 1 male (cl 5.6 mm), dissected, Aka­shin­ko, Aka­jima Island, Okinawa, Japan, port, surface by hand­net under an electric light at night, 2 Oct. 2002, coll. K. Fukuoka. NSMT­Cr 16037: 1 female (cl 6.7 mm), dissected, Aka­shin­ko, Aka­jima Island, Okinawa, Japan, port, surface by hand­net under an electric light at night, 3 Oct. 2002, coll. K. Fukuoka. NSMT­Cr 16038: 3 males (cl 4.3–6.3 mm) and 1 female (cl 5.9 mm), Kise, Kasari, Amami­oshima Island, Kagoshima, Japan, fishing port, sand­mud bottom, 1 m, hand­net under an electric light at night, 23 July 2003, coll. K. Fukuoka. NSMT­Cr 16039: 1 female (cl 6.3 mm), Kise, Kasari, Amami­oshima Island, Kagoshima, Japan, fishing port, sand­mud bottom, 1 m, hand­net under an electric light at night, 25 July, 2003, coll. K. Fukuoka. NSMT­Cr 16040: 1 female (cl 6.6 mm), Aka­shin­ko, Aka­jima Island, Okinawa, Japan, port, surface by hand­net under an electric light at night, 24 Sept.

2003, coll. K. Fukuoka. NSMT­Cr 16041: 1 female (cl 5.7 mm), Aka­shin­ko, Aka­jima Island, Okinawa, Japan, port, surface by hand­net under an electric light at night, 26 Sept. 2003, coll. K. Fukuoka.

Description. Carapace with pterygostomian, postorbital and hepatic spines. Rostrum extending to base of antennular peduncle, with 2 teeth on dorsal margin ( Fig. 12 A­C).

Abdomen smooth; sixth somite twice as long as fifth one, with indistinct dorsolateral sulcus; pleuron of first to fifth somites expanded posteriorly, armed with setae on ventral margin. Telson tapering posteriorly, armed with 4 spines and numerous long, plumose setae on distal half of ventrolateral margin ( Fig. 14 M).

Eye elongate, 4.7–5.2 times as long as wide of base of stalk, 2–2.3 times as long as wide of cornea in male and 2.3–2.6 times as long as wide of cornea in female ( Fig. 12 A, B). Cornea of eye 2.1–2.6 times as wide as base of stalk in male, and 1.8–2 times as wide as base of stalk in female ( Fig. 12 A, B). Eyestalk gradually wider distally, without orbital spines ( Fig. 12 A–C).

Antennular peduncle robust ( Fig. 12 A, B). Stylocerite not reaching middle of first segment of peduncle ( Fig. 12 A, B). First segment of antennular peduncle extending to distal 0.3 of scaphocerite, with anterolateral spiniform process ( Fig. 12 A, B). Second segment of antennular peduncle of both sexes 0.4–0.5 length of first segment, 1.9–2.4 times as long as wide, with 1–3 short spines on anterolateral angle ( Fig. 12 A, B, D). Third segment of antennular peduncle of both sexes 0.8–1.1 times as long as second segment, 2.5–3.3 times as long as wide ( Fig. 12 A, B). Distal two segments of antennular peduncle 0.8–1.1 times as long as proximal segment ( Fig. 12 A, B). Mesial antennular flagellum of male modified in proximal portion ( Fig. 15 A); first and second segments short, armed on upper margin with 5 and 2 robust setae, respectively, these setae branching in terminal end ( Fig. 15 A, B); third segment long ( Fig. 15 A), upper margin concave, pre­depression with 2 rather short, robust setae branching in terminal end, middle part naked, post­depression with 10 robust setae, proximal 8 setae gradually increasing in length anteriorly, scaly on posterior surface of distal part ( Fig. 15 C), anterior 2 setae without such structure ( Fig. 15 D).

Scaphocerite 3.5–3.6 times as long as wide, with triangular apical lobe ( Fig. 12 E). Antennal peduncle extending to proximal 0.4 of scaphocerite ( Fig. 12 E).

Mandibular palp flattened, divided into 3 segments; second segment expanded in middle; third segment 0.3 length of second one ( Fig. 12 F).

Maxillule with proximal endite longer than wide and armed with 3 or 4 long, robust, spiniform setae and several short setae on distal margin; distal endite expanded mesially; endopod tapering apically, armed with long, robust, naked, spiniform seta on near apex of mesial margin, and with 3–5 plumose setae on distal 0.3 of lateral margin to apex ( Fig. 12 G).

Maxilla with endopod tapering distally and armed with 8 short, robust spines on distal part; endite rudimentary; scaphognathite large, armed with plumose setae on entire margin ( Fig. 12 H).

First maxilliped with 3­segmented endopod armed with 2 long, stout spines on proximal expanded part; exopod leaf­shaped; epipod no bilobed; distal endite broadened anteriorly; proximal endite represented by two similar lobes ( Fig. 13 A).

Second maxilliped without exopod and epipod; similar to S. antennata and S. inermis ( Fig. 13 B).

Third maxilliped long, extending beyond distal end of antennular peduncle, similar to S. antennata and S. inermis ( Fig. 13 C).

First pereopod extending to middle of merus of third maxilliped, chelate; carpus armed with brushing setae arranged in a V­shape on distal 0.2 of mesial surface; propodus armed with double row of brushing setae on proximal 0.3 of lower side of mesial surface; dactylus occupying 0.4 of propodus length ( Fig. 13 D).

Second pereopod 1.3–1.4 times as long as first pereopod, chelate; carpus armed with 8–10 small spines on distal 0.2 of lower margin; propodus armed with 5 or 6 serrated, small spines on proximal 0.2 of lower margin ( Fig. 13 E, F).

Third pereopod 1.3 times longer than second pereopod, chelate; carpus 1.7–1.9 times as long as merus; propodus 0.7 of carpus length; dactylus 0.3 of propodus length ( Fig. 13 G).

Fourth pereopod 0.7 times as long as third pereopod ( Fig. 13 H). Fifth pereopod 0.8 of fourth pereopod in length ( Fig. 13 I). Fourth and fifth pereopods not chelate, armed with long plumose setae on lower and upper margins of ischium and merus and on only lower margin of carpus and propodus, terminating small claw on dactylus ( Fig. 13 H, I).

First pleopod without endopod ( Fig. 14 A); second to fifth pleopods with endopod and exopod ( Fig. 14 B, E, G, H). Endopod of second male pleopod with appendix interna armed with 2 long and 3 short spines on distal margin ( Fig. 14 B, C). Distomesial angle of sympod armed with 2 short, plumose setae in second pleopod ( Fig. 14 D), with tiny spiniform seta in third pleopod ( Figs. 14 F, 16A), with extremely long, robust, posteriorly curved, spiniform seta in fourth pleopod ( Fig. 14 G), and with 2–6 short and long, spiniform setae in fifth pleopod ( Figs. 14 H, I, 16B–D), setae on fourth and fifth pleopods serrated in distal half ( Fig. 16 C, D).

Uropodal endopod extending beyond apex of telson by 0.3 of its length; uropodal exopod 1.3 times longer than endopod ( Fig. 14 L).

Processus unicifer (pu) of petasma of male less than half of lamina externa, broad, with rounded apex ( Fig. 14 J, K). Processu ventralis (pv) divided into 2 branches in near base ( Fig. 14 J, K); ventral branch divided into 2 secondary branches in near middle, lateral secondary branch slender, almost straight, terminating into hook, mesial one longer than lateral one, expanded and curved laterally in distal third, terminating into hook ( Fig. 15 F); dorsal branch shorter than ventral branch, expanded laterally. Lobus terminalis (lt) short ( Fig. 14 J, K). Lobus connectens (lc) short, tapering distally, terminating into hook ( Fig. 14 J, K). Lobus armatus (lar) strong, directed laterally, with strong hook on near apex of anterior surface and several small hooks on terminal part ( Figs. 14 J, K, 15E, G).

Thelycum of female with acute process on just posterior to base of third pereopod ( Fig. 16 E, F); coxa of third pereopod armed with several plumose setae on lateral surface, opened oviduct bearing several long, naked setae on lateral margin but smooth on upper margin ( Fig. 16 G).

Color. Body transparent with scattered red chromatophores. Antennular and antennal flagellums without red bands ( Fig. 17 C).

Distribution. This species has been recorded from the Maldives ( Borradaile, 1910), Indonesia ( Hansen, 1919), the Red Sea ( Cecchini, 1933), the Marshall Islands ( Chace, 1955), New Caledonia (MNHN collection), the Palau Islands, the Philippines (USNM collection), and Japan (this study).

This species has been collected from depths of 12–55 m ( Hansen, 1919; USNM collection data) by dredge, trawl, or plankton net, and from shallow water by dip net with an electric light at night (USNM collection data). The Japanese specimens were collected from a coral reef moat and fishing port at night using an electric light.

Remarks. Borradaile (1910) established S. maldivensis based on specimens collected from the Maldives and Cargados Carajos, Mauritius. Two syntype specimens, one male from the Maldives and one female from Cargados Carajos, were lodged in NHM. We reexamined these syntype specimens and identified the female specimen as S. inermis . Therefore, this study designates a lectotype of S. maldivensis based on the male specimen (NHM 1987.10.1) from the Maldives.

Borradaile (1910) briefly described S. maldivensis . Subsequently, Hansen (1919) recorded this species from Indonesian waters, and described several characters in detail. The Japanese specimens agree with these descriptions.

Chace (1955) first observed the thelycum of S. maldivensis in specimens from Bikini, and described and illustrated a prominent, bidentate structure immediately posterior to the coxa of the third pereopod. However, in our observation of specimens from Japan, the Philippines, and Palau, there is only a single denticle. The thelycum of a specimen from Bikini deposited in the USNM (USNM 94725) could not be observed because that portion has been dissected and is missing from the bottle.

Figures

FIGURE 12. Sicyonella maldivensis Borradaile, 1910. A, C, E­H, male (NSMT­Cr 16036); B, D, female (NSMT­Cr 16037). A, B, anterior part of body, dorsal; C, anterior part of cephalothorax, lateral; D, distal two segments of left antennular peduncle, dorsal; E, left antenna, ventral; F, left mandible, anterior; G, left maxillule, anterior; H, left maxilla, anterior.

FIGURE 13. Sicyonella maldivensis Borradaile, 1910. Male (NSMT­Cr 16036). A, left first maxilliped, anterior; B, left second maxilliped, anterior; C, left third maxilliped, lateral; D, left first pereopod, mesial; E, left second pereopod, mesial; F, segmented part of carpus and propodus of left second pereopod, lateral; G, left third pereopod, mesial; H, left fourth pereopod, mesial; I, left fifth pereopod, mesial.

FIGURE 14. Sicyonella maldivensis Borradaile, 1910. Male (NSMT­Cr 16036). A, left first pleopod; B, left second pleopod, lateral; C, appendix interna, lateral; D, setae on distomesial angle of sympod of left second pleopod, lateral; E, left third pleopod, mesial; F, seta on distomesial angle of sympod of left third pleopod, lateral; G, left fourth pleopod, mesial; H, left fifth pleopod, mesial; I, setae on distomesial angle of sympod of left fifth pleopod, mesial; J, left petasma, anterior; K, left petasma, posterior; L, left uropod, ventral; M, telson, dorsal. The arrows indicate lobus armatus (lar), lobus connectens (lc), lobus terminalis (lt), processus unicifer (pu), and processus ventralis (pv).

FIGURE 15. Sicyonella maldivensis Borradaile, 1910. Male. A­D, mesial antennular flagellum; E­ G, petasma. A, proximal part; B, distal part of robust seta on second segment; C, distal part of rather robust setae on post­depression of third segment; D, distal part of robust setae on post­depression of third segment; E, petasma, anterior; F, distal part of posterior branch of processus ventralis (pv); G, labus armatus (lar).

FIGURE 16. Sicyonella maldivensis Borradaile, 1910. A­D, male; E­G, female. A, seta on distomesial angle of sympod of left third pleopod; B­D, setae on distomesial angle of sympod of left fifth pleopod; E, thelycum, ventral; F, denticle (d) between base of right third and fourth pereopods, ventral; G, coxa of right third pereopod, ventral.

FIGURE 17. Color of proximal portion of antennal flagellum. A, S. antennata; B, S. inermis; C, S. maldivensis. The arrows indicate band of red pigments.