Michaelimenes perlucidus ( Bruce, 1969 ), 2017

Octocorallia: Alcyonacea View in CoL : Nidaliidae ).

Holotype. Ovigerous ♀, CL 2.13 mm (examined by

C.H.J.M. Fransen), RMNH.CRUS.D.47760.

Distinguishing features. Small-sized, typical palaemonid form with slender ambulatory pereiopods ( Fig. 2 View Figure 2 ).

Carapace ( Fig. 3A View Figure 3 ), smooth, glabrous, without supraorbital spine; orbit feebly developed, inferior orbital angle produced, tip rounded; antennal spine marginal, reaching level of tip of inferior orbital angle; hepatic spine slightly ventrad to antennal spine; epigastric spine situated anterior fourth of median carina, separated from first rostral tooth by almost same gap as between first and second dorsal teeth. Rostrum ( Fig. 3A View Figure 3 ) straight, horizontal, slightly overreaching level of distal margin of antennular distal segment ( Fig. 2 View Figure 2 ), 1.0–1.3 times as long as carapace; dorsal carina armed with 6–8 equidistant teeth, first tooth situated just above posterior orbital margin; ventral margin straight, carina obsolete, armed with 1–3 teeth on distal third. Ophthalmic somite without interocular beak. Fourth thoracic sternite ( Fig. 3B View Figure 3 ) with low, transverse central ridge with median small notch, lacking fingerlike median process. Sixth abdominal segment ( Fig. 2 View Figure 2 ) stout, moderately short, 0.7–0.9 times as long as telson. Telson ( Fig. 3C View Figure 3 ) slightly tapering distally, with two pairs of small dorsolateral spines situated on posterior half, posterior margin with three pairs of spines.

Antennular peduncle ( Fig. 3D View Figure 3 ) with proximal segment armed ventromesially with a single acute tooth; lateral margin straight, terminating distally in acute tooth; stylocerite acute, reaching proximal two fifths of proximal segment. Antenna with scaphocerite ( Fig. 3E View Figure 3 ) well developed, lateral margin terminating in acute tooth falling short of bluntly angulate distal margin of lamella. Epistome ( Fig. 3F View Figure 3 ) with a pair of rounded, low, submedian eminences.

First pereiopod overreaching level of distal margin of scaphocerite by length of dactylus; cutting edges of both fingers unarmed, dactylus not subspatulate ( Fig. 1A View Figure 1 ). Second pereiopods unequal in length, dissimilar in shape. Major second pereiopod ( Fig. 4A, B View Figure 4 ) overreaching level of distal margin of scaphocerite by lengths of chela and part of carpus; carpus usually short ( Fig. 4A View Figure 4 ) (rarely slightly elongate as in Fig. 4B View Figure 4 ), feebly widening distally, 0.2–0.4 (usually 0.3) times as long as chela; chela with palm stout, elongate, subcylindrical, surface smooth, 2.4–3.1 times as long as dactylus, fingers short, slightly sinuous laterally; fixed finger with proximal excavation on the cutting surface ( Fig. 1B View Figure 1 ) for reception of proximal part of dactylar cutting edge, proximal part of cutting edge armed with 3–4 teeth, anterior tooth largest, triangular ( Fig. 1C, D View Figure 1 ); dactylus with distinct dorsomesial flange on distal two thirds, mesial surface ventrad to the flange oblique, cutting edge armed proximally with 2triangular teeth ( Fig.1C View Figure 1 ). Minor pereiopod ( Fig. 4C View Figure 4 ) overreaching level of distal margin of scaphocerite by length of chela; carpus moderately elongate, 0.2–0.4 times as long as chela; chela with palm slender, elongate, subcylindrical, surface smooth ( Fig. 4D View Figure 4 ), 1.4–2.6 times as long as dactylus, fingers somewhat elongate, slightly sinuous laterally; fixed finger with proximal excavation similar to major pereiopod, cutting edge armed proximally with 2–4 teeth (rarely unarmed), anterior tooth largest, triangular ( Fig. 1E View Figure 1 ); dactylus with feeble distomesial flange on distal two thirds ( Fig. 4D View Figure 4 ), cutting edge armed proximally with 1–2 triangular teeth (rarely unarmed) ( Fig. 1E View Figure 1 ).

Ambulatory pereiopods similar to each other. Propodi armed with 4 small spines ventrally, without rows of tuft of long setae ( Fig. 4E View Figure 4 ). Dactyli ( Fig. 4F View Figure 4 ) biunguiculate, terminal unguis demarcated, distinctly longer and stouter than preterminal unguis.

Endopod of male first pleopod oblong, distally rounded, mesially with slender process. Endopod of male second pleopod with appendices masculina and interna, the former falling short of tip of the latter.

Color in life. Body and appendages generally translucent; anterior to ventral margin of carapace and ventral margins of abdominal somites bright yellow; antennal basicerite yellow ( Fig. 5 View Figure 5 ).

Distribution. Type locality: Macclesfield Bank, South China Sea, 16°06.5’N 114°38.3’E – 16°05.8’N 114°38.2’E, 78.7–80.5 m depth ( Bruce, 1969). Also known from Madagascar, La Réunion, Papua New Guinea, Philippines and Japan ( Bruce, 1978 a, 1996; De Grave, 2000; Kato and Okuno, 2001; Li and Bruce, 2006; present study). Bathymetrically known from 20 to 110 m. Boso Peninsula of Japan is the northernmost record in its known range.

Common name. Yaiba-kakure-ebi (new standard

Japanese name).

Remarks. Bruce (1969) originally described P. perlucidus on the basis of a single ovigerous female holotype collected from the South China Sea.Although no illustration was provided in the original description, subsequently, the original author re-described and fully illustrated P. perlucidus based on numerous specimens from Madagascar, western Indian Ocean ( Bruce, 1978a). As a result of the comparison with these previous studies, the present specimens from Japan can be identified as M. perlucidus on account of the straight and horizontal rostrum armed dorsally with 6–8 teeth and ventrally with 2–3 teeth ( Fig. 3A View Figure 3 ), the remarkably unequal second pereiopods in size and shape ( Fig.3A,C View Figure 3 ),the dactylus of the major second pereiopod with a distinct flange dorsomesially ( Fig. 1C, D View Figure 1 ), and the biunguiculate dactyli of the ambulatory pereiopods ( Fig. 4F View Figure 4 ). Although Bruce (1969) did not allude to the length of the dorsal flange of the major second pereiopodal dactylus, the holotype of P. perlucidus has it on the distal two thirds of the dactylar length as depicted in the present study ( Fig. 1C, D View Figure 1 ) (C.H.J.M. Fransen, in litt.). Some minor morphological differences exist between the present specimens and previous reports as mentioned below. I consider these gaps to be intraspecific variation. All the Japanese specimens possess an epigastric spine, and have the hepatic spine situated at a lower level than the antennal spine ( Fig. 3A View Figure 3 ) as in the holotype ( Bruce, 1969). The specimens from Madagascar reported upon Bruce (1978a), however, show variation in the absence or presence of the epigastric spine, and have the hepatic spine situated at the same level as the antennal spine. The carpus of the major second pereiopod is short in most of the present specimens ( Fig. 4A View Figure 4 ), but some of the examined specimens possess a relatively slender carpus being over one third of the length of the chela ( Fig. 4B View Figure 4 ), the proportion of which corresponds to the original description. In the herein examined specimens, the palm of the second pereiopod is 2.4–3.1 times as long as the dactylus, instead of 4.0 times in the holotype and 2.3 times in the specimens from Madagascar ( Bruce, 1969; 1978a).

Bruce (1996) described P.involens as a new species on the basis of 1 male and 3 female specimens from the depths of 92–97 m off Mindoro, Philippines. This species has also been recorded from La Réunion, western Indian Ocean by Li and Bruce (2006). In the original description, Bruce (1996) compared P. involens with Periclimenes vaubani Bruce, 1990 and Periclimenes richeri Bruce, 1990 , described from considerably deeper waters at 445–650 m in New Caledonian waters ( Bruce, 1990). However, P.involens appears closest to M. perlucidus rather than P. vaubani and P.richeri on account of the form of the rostrum and the development of the dorsal flange of the dactylus and the proximal excavation of the fixed finger in the major second pereiopod. The present study reveals that the proportion of the major second pereiopod is intraspecifically variable within M. perlucidus , and that of P. involens is closely similar to the typical form of the present specimens of M. perlucidus ( Fig. 4A View Figure 4 ). Therefore, P. involens is considered a synonym of M. perlucidus .

The host of the P. perlucidus holotype was indicated as “gorgonian” in the original description ( Bruce, 1969). Later, Bruce (1978a; 1979) identified the host as Verrucella sanguinolenta (Gray) (Octocorallia: Alcyonacea : Ellisellidae , now called as Phenilia sanguinolenta Gray, 1859 ). In addition, Bruce (1978a) listed three species of soft corals included in the family Nephtheidae , viz., Roxasia speciosa (Kükenthal) , Morchellana gilva (Henderson) , and Morchellana nova Tixier Durivault. The valid names of the former two species are now applied as Dendronephthya speciosa Kükenthal, 1905 and Dendronephthya gilva Henderson, 1909 respectively, and Morchellana nova sensu Bruce (1978a) possibly belongs to the same taxon as Dendronephthya novaezeelandiae Kükenthal, 1905 since the specific name “nova ” is not known for any species of alcyonacean (Yukimitsu Imahara, in litt.). Furthermore, De Grave (2000) indicated the host of P. perlucidus from Hansa Bay, Papua New Guinea as Dendronephthya sp. From these previous records, the preferred hosts of M. perlucidus appear to be species of the genus Dendronephthya Kükenthal, 1905 , and P. sanguinolenta is possibly considered as an alternative host. Therefore, Chironephthya spp. associated with the present specimens examined represents a new host record. In Japanese waters, the relationship between M. perlucidus and Dendronephthya has not been observed, nevertheless colonies of Dendronephthya are abundant at the collection sites of the present shrimp specimens. A hypothesis for this host selection seems to be that the relationship appeared only in the warm temperate waters of the Western Pacific.More observations from other areas in the Indo-West Pacific are required to be more conclusive with regards to the host specificity of M. perlucidus .

The color pattern of M. perlucidus has only been previously recorded by De Grave(2000) as “transparent with a yellow hue”. The coloration of the present specimens agrees with this indication on account of the transparent body and appendages and yellow markings on the anterior and ventral margin of the carapace and ventral margins of the abdominal somites ( Fig. 5 View Figure 5 ). This color pattern is characteristic, and differs from other palaemonid shrimp species associated with alcyonaceans. In the popular guidebook on the decapod and stomatopod crustaceans from Hachijo-jima Island, Japan, Kato and Okuno (2001) reported a palaemonid shrimp associated with Chironephthya sp. under the name of “ Periclimenes sp. B ”. Although a voucher specimen was not collected, the color pattern of the photographed individual corresponds to those of the specimens examined in this study, and part of these were captured from the same island. Therefore, Periclimenes sp. B sensu Kato and Okuno (2001) can be identified without hesitation as M. perlucidus .

Fransen (1994) reported two male and two ovigerous female specimens of P. perlucidus from the Seychelles, western Indian Ocean. However, the illustrated male and female have the symmetrical and slender second pereiopods as in the minor pereiopod of the Madagascar specimens reported upon by Bruce (1978a). The examined specimens from Japan contain the similar sized individuals to the Fransen’s (1994) specimens, and showed the markedly unequal second pereiopods and the distinct flange on the dactylus of the major pereiopod. Thus, I consider the specimens from the Seychelles being a species outside of Michaelimenes .