Sicyonella inermis (Paulson, 1875) (Figs. 7–11, 17 B)

Aphareus inermis Paulson, 1875: 123, tab. 18, fig. 3.

Aphareocaris elegans Calman, 1913: 219 –222, pl. 16, figs. 1–16.

Sicyonella inermis: Calman, 1914: 258 –260; Balss, 1915: 14, 15, figs. 10–15; De Man, 1922: 11 –13, fig. 7; Burkenroad, 1937: 506 –513.

Sicyonella elegans: Calman, 1914: 258 –260.

? Sicyonella aff. inermis: Kamezaki et al., 1988: 41, fig. (p. 41).

Type locality. Red Sea.

Type specimen. Location of specimen unknown.

Material examined. [NHM Collection] NHM (1912.2.10.135): 1 female (cl 7.2 mm), one of syntype of S. maldivensis, Cargados Carajos, Mauritius, date unknown. NHM (1913.5.19:8): 1 male (cl 5.1mm), holotype of Aphareocaris elegans, Thursday Island, Torres Straits, date unknown. NHM (1938.1.28:75–77): 5 females (cl 3.8–7.3 mm), near Biological Station of University of Egypt at Ghardaqa, Red Sea, on Halophila, Feb. 1936, coll. R. Gurney.

[USNM Collection] USNM­1026370: 2 females (cl 7.3 mm and broken), Sitanki, Sibutu Island, Sulu Archipelago, Philippines, surface, electric light, 25 Feb. 1908, separated from USNM­ 260757. USNM­89840: 1 male, Persian Gulf, Ras Tanura, Saudi Arabia, 26 Apr. 1948, coll. D. S. Erdman. USNM­89841: 2 males (cl 5.0 and 5.1 mm) and 4 females (cl 4.2–4.5 mm), Persian Gulf, Ras Tannurah, north of Bahrein, Saudi Arabia, 13 June 1948, coll. D. S. Erdman. USNM­89842: 1 female, Persian Gulf, Ras Tanura, Saudi Arabia, May­June 1948, coll. D. S. Erdman.

[NSMT Collection] NSMT­Cr 16028: 2 males (cl 6.0 and 6.2 mm), Nagura Bay, Ishigaki Island, Okinawa, Japan, seagrass bed, 2–3 m, light trap, 27 Dec. 1998, coll. M. Tamaki. NSMT­Cr 16029: 3 males (cl 4.1–4.8 mm), pier of Ishigaki Tropical Station of Seikai National Fisheries Research Institute (ITS), Urasoko Bay, Ishigaki Island, Okinawa, Japan, sand bottom, 2–3 m, light trap, 7 Nov. 2000, coll. K. Fukuoka. NSMT­Cr 14114: 4 males (cl 4.5–6.2 mm), pier of ITS, Urasoko Bay, Ishigaki Island, Okinawa, Japan, sand bottom, 2–3 m, light trap, 5 Dec. 2000, coll. K. Fukuoka. NSMT­Cr 16030: 1 male (cl 5.3 mm), dissected, pier of ITS, Urasoko Bay, Ishigaki Island, Okinawa, Japan, sand bottom, 2–3 m, light trap, 8 Dec. 2000, coll. K. Fukuoka. NSMT­Cr 16031: 1 female (cl 5.4 mm), pier of ITS, Urasoko Bay, Ishigaki Island, Okinawa, Japan, sand bottom, 2–3 m, light trap, 8 Dec. 2000, coll. K. Fukuoka. NSMT­Cr 16032: 1 female (cl 7.9 mm), pier of ITS, Urasoko Bay, Ishigaki Island, Okinawa, Japan, sand bottom, 2–3 m, light trap, 26 Mar. 2001, coll. K. Fukuoka. NSMT­Cr 16033: 4 females (cl 3.7–6.8 mm), Shiraho Coral Reef moat, Ishigaki Island, Okinawa, Japan, sand bottom among coral, 3 m, hand­net under an electric light at night, 16 July 2001, coll. K. Fukuoka. NSMT­Cr 16034: 3 females (cl 3.6–6.3 mm), Aka­shin­ko, Aka­jima Island, Okinawa, Japan, port, surface by hand­net under an electric light at night, 3 Oct. 2002, coll. K. Fukuoka. NSMT­Cr 16035: 1 female (cl 5.7 mm), dissected, pier of ITS, Urasoko Bay, Ishigaki Island, Okinawa, Japan, sand bottom, 2–3 m, light trap, 7 Nov. 2002, coll. K. Fukuoka.

Description. Carapace with postorbital and hepatic spines; anterolateral corner produced into small pterygostomian spine. Rostrum extending to base of antennular peduncle, with 2 teeth on dorsal margin (Fig. 7 A–C).

Abdominal somite smooth; first to fifth somites with pleuron expanded posteriorly bearing setae on margin; sixth somite 2.2 times as long as fifth one, with indistinct dorsomedian carina. Telson elongate, triangular, 2.5–3.7 times as long as wide, armed with 4 spines and numerous long, plumose setae on distal 0.5 of ventrolateral margin (Fig. 9L).

Eye elongated, 2.4–2.9 times as long as wide of cornea (Fig. 7 A, B). Cornea of eye occupying 0.2–0.3 of eye in length, 1.8–2 times as wide as base of stalk (Fig. 7 A, B). Eyestalk gradually wider distally, without orbital spines (Fig. 7 A, B).

Antennular peduncle robust, elongate (Fig. 7 A, B). Stylocerite not reaching middle of first segment of peduncle (Fig. 7 A, B). First segment of antennular peduncle extending to distal 0.3 of scaphocerite, with anterolateral spiniform process (Fig. 7 A, B). Second segment of antennular peduncle rather short, 0.4–0.5 length of first segment in male and 0.4 length of first in female, 1.6–2 times as long as wide in male and 2–2.3 times as long as wide in female, with 1 or 2 short spines on anterolateral angle of dorsal surface (Fig. 7 A, B, D). Third segment of antennular peduncle rather short, 0.8–1 times as long as second segment in both sexes, 2.1–2.6 times as long as wide (Fig. 7 A, B). Distal two segments of antennular peduncle 0.7–0.9 of proximal segment in length (Fig. 7 A, B). Mesial antennular flagellum of male modified in proximal portion (Fig. 10 A); proximal 2 segments short, third segment armed with 2 long setae on anteromesial angle, fourth segment long, expanded laterally with scaly surface (Fig. 10 A–C).

Scaphocerite 3.3–3.6 times as long as wide, with rounded apical lobe (Fig. 7 E). Antennal peduncle robust, extending to proximal 0.4 of scaphocerite (Fig 7 E).

Mandibular palp flattened, divided into 3 segments; second segment expanded in middle; third segment 0.3 length of second one, 2–2.2 times as long as wide (Fig. 7 F).

Maxillule with proximal endite longer than wide, armed with 3 long, setose and several long, naked setae on distal part; distal endite expanded mesially; endopod narrow, 3.5 times as long as wide, armed with long, naked, spiniform seta on near apex of mesial margin and with 2 or 3 plumose setae on near apex of lateral margin (Fig. 7 G).

Maxilla with endopod tapering distally and armed with 8 or 9 spines on distal part; endite rudimentary; scaphognathite large, armed densely with plumose setae on entire margin (Fig. 7 H).

First maxilliped with endopod long, slender, 2­segmented, and armed with 3 long spines on proximal expanded part; exopod large; epipod no bilobed; distal endite broadened anteriorly, densely armed with setae on margin; proximal endite divided into two lobes (Fig. 8 A).

Second maxilliped without exopod and epipod; endopod similar to S. antennata (Fig. 8 B).

Third maxilliped long, robust, extending beyond distal end of antennular peduncle; ischium armed with short setae on mesial and lateral margins; merus 0.7–0.8 of ischium in length; carpus 1.1 times as long as merus; propodus 1.1 times longer than carpus, 3­subsegmented; dactylus 0.8 length of carpus, 4­subsegmented, with long, strong, spiniform claw on terminal end; distal 4 segments armed with short and long, robust setae on mesial and lateral margins (Fig. 8 C).

First pereopod extending to middle of merus of third maxilliped, chelate; carpus armed with brushing setae on distal 0.3 of mesial surface, these setae arranged in a V­shape; propodus slightly longer than carpus, armed on proximal 0.3 of lower side of mesial surface with double row of brushing setae, which are composed of short naked and rather long plumose setae; dactylus occupying 0.4 of propodus length, same size with propodal finger (Fig. 8 D, E).

Second pereopod 1.3–1.4 times as long as first pereopod, chelate; carpus 1.1–1.2 times longer than merus, armed with 5 or 6 small spines on distal 0.2 of lower margin; propodus 0.7–0.8 of carpus length, armed with 4 or 5 short spiniform setae on proximal 0.1 of lower margin; dactylus occupying 0.4 of propodus length (Fig. 8 F, G).

Third pereopod 1.2–1.3 times as long as second pereopod, chelate; carpus 1.6 times longer than merus; propodus 0.7 length of carpus, 11 times as long as wide; dactylus occupying 0.3 of propodus in length (Fig. 8 H).

Fourth and fifth pereopods developed, 7­segmented, not chelate, armed with long plumose setae on lower and upper margins in ischium and merus and on only lower margin in carpus and propodus, terminating into small claw on dactylus (Fig. 8 I, J).

First pleopod without endopod (Fig. 9A); second to fifth pleopods with endopod and exopod, exopod longer than endopod (Fig. 9B, E, G, I). Distomesial corner of sympod of second pleopod armed with 1 or 2 tiny setae (Figs. 9D, 11A); that of third pleopod with rather short, spiniform seta (Fig. 9F); that of fourth pleopod with long, robust, posteriorly curved, spiniform seta, which is serrated in distal half (Figs. 9H, 11B, C); that of fifth pleopod with long, robust, almost straight, spiniform seta (Figs. 9J, 11D). Appendix interna present on base of exopod of second male pleopod, armed with 4 long spines on distal margin (Fig. 9B, C).

Uropodal endopod extending beyond telson by 0.3 of its length; exopod 1.3 times longer than endopod (Fig. 9L).

Processus unicifer (pu) of petasma of male short, 0.1 of laminal externa in length, tapering to rounded apex (Fig. 9K); pars media (pm) simplified, tip of capitulum curved mesially, mesial surface from tip to posterior 0.3 with hooks (Figs. 9K, 10D, E).

Thelycum of female not modified (Fig. 10 F); coxa of third pereopod smooth on lateral surface, with oviduct opening armed with several long, naked setae on lateral margin and several plumose setae on upper margin (Fig. 10 G).

Sicyonella inermis (Paulson, 1875) . A­C, E, G, I, K, L, Male (NSMT­Cr 16030); D, F, H, J, male (NSMT­Cr 16028). A, left first pleopod, mesial; B, left second pleopod, mesial; C, appendix interna of second pleopod, lateral; D, seta 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, mesial; G, left fourth pleopod, mesial; H, seta on distomesial angle of sympod of left fourth pleopod, mesial; I, left fifth pleopod, mesial; J, seta on distomesial angle of sympod of left fifth pleopod, mesial; K, petasma, posterior; L, uropod and telson, dorsal. The arrows indicate pars media (pm) and processus unicifer (pu).

Color. Body transparent with scattered red chromatophores. Antennal flagellum with 2–5 red bands in the stiff proximal portion (Fig. 17 B).

Distirbution. After reexamining two syntype specimens of S. maldivensis, one male from the Maldives and one female from Cargados Carajos, Mauritius, lodged in NHM, the female specimen (NHM 1912.2.10.135) was identified as S. inermis from the shape of the thelycum and the setation of the sympod of the pleopods.

This species is recorded from the Red Sea (Paulson, 1875; Balss, 1915; Burkenroad, 1937), Mauritius (Borradaile, 1910), the Torres Strait (Calman, 1913), Indonesia (De Man, 1922), Sri Lanka (Burkenroad, 1937), the Persian Gulf (Chace, 1955), the Philippines (USNM collection), and Japan (this study).

This species was collected in offshore water with a plankton net (Balss, 1915; De Mann, 1922), in a dredge at night, and from a seagrass bed, Halophila, at a depth of 7 m (Burkenroad, 1937). Japanese specimens were collected from a seagrass bed or the sandy bottom area of a coral reef moat, shallower than 10 m.

Remarks. Sicyonella inermis was established by Paulson (1875) under the name Aphareus inermis, and was briefly described on a single specimen (sex unknown) collected from the Red Sea. Subsequently, Calman (1913) described this species in detail based on a single male specimen, which was named Aphareocaris elegans, collected from Thursday Island, Torres Straits. Calman (1914) degraded A. elegans into the junior synonym of S. maldivensis because he considered A. elegans an immature form of S. maldivensis . Hansen (1919) doubted its state, but retained it. In 1937, Burkenroad examined specimens of S. inermis collected from Sri Lanka and the Red Sea, and synonymized A. elegans with S. inermis .

The number of teeth on the dorsal margin of the rostrum has been given as one (Paulson, 1875) or two (Calman, 1913; Balss, 1915; De Mann, 1922). All of the specimens that we examined have two teeth.

The telson was described with four pairs of marginal spines in Paulson (1875) and De Mann (1922), and with five pairs in Calman (1913). All of the specimens that we examined have four pairs of marginal spines.