Philarius rufulus, Mitsuhashi, Masako, 2012

Mitsuhashi, Masako, 2012, A new species of the genus Philarius (Crustacea: Decapoda: Palaemonidae) from Ryukyu Islands, Japan, Zootaxa 3481, pp. 82-88 : 82-88

Philarius rufulus sp. nov.

(figs. 1–4)

Material examined. Holotype ovigerous female (CL 4.5mm, BL 13.1mm), Cape Maeda, Okinawa Island, Japan, 5 m depth, from Acropora sp., coll. R. Minemizu, 11 Oct. 2011, RUMF-ZC-1896.

Etymology. From the Latin rufulus (reddish), referring to the characteristic brownish colour in the living specimen. Common name. Suo-midori-ishi-ebi (new Japanese name).

Description. A small-sized pontoniine shrimp with depressed body form (figs. 1A, 4).

Carapace (fig. 1A, B) smooth, glabrous; supraorbital eve present, evenly rounded; hepatic and supraorbital spines absent; inferior orbital angle produced, rounded, reaching middle of antennal spine; antennal spine acute, marginal; pterygostomial angle bluntly produced anteriorly.

Rostrum (fig. 1A–C) well developed, reaching distal margin of scaphocerite; dorsal carina with five acute teeth, posterior four teeth almost equidistant, posterior most tooth anterior to orbital margin, anterior most tooth somewhat separated from second tooth and near tip; ventral carina with two acute teeth, each on distal 0.3 and 0.4 of rostrum length.

Fourth thoracic sternite (fig. 1D) with broad triangular median process; fifth thoracic sternite (fig. 1D) with transverse ridge and median notch.

Abdominal somites (fig. 1A) smooth, glabrous; pleura of first to third somites broadly rounded; fifth somite posteriorly produced, angled; sixth somite about 1.5 times of fifth somite, 0.25 times of carapace length. Telson (fig. 1E) 1.8 times as long as sixth abdominal somite, tapering posteriorly, 2.3 times as long as greatest width; two pairs of slender dorsolateral spines situated at 0.6 and 0.8 of telson length; posterior margin with three pairs of spines, lateral spines small, intermediate spines longest, submedian spines slender.

Eye (fig. 1A, B) well developed, lacking ocellus, cornea globular, slightly narrower than widest part of peduncle; peduncle widens proximally, length about as proximal width.

Antennular peduncle (fig. 1B, F) reaching distal 0.25 of rostrum; stylocerite acute, reaching mid-length of basal segment; distolateral spine of basal segment overreaching intermediate segment; upper flagellum biramous, proximal 12 (right) or 11 (left) segments fused.

Antenna (fig. 1G) with stout basicerite armed with subacute lateral tooth; carpocerite extending to middle of scaphocerite; scaphocerite reaching tip of rostrum, 2.3 times as long as maximum width, broadest at proximal 0.4, lateral margin almost straight, distolateral tooth overreaching lamella by distal 0.25.

Epistome unarmed.

Mouthparts described based on right side. Mandible (fig. 2A) without palp; molar process with blunt teeth and bristles on tip; incisor process with three acute teeth, anterior somewhat larger than others. Maxillula (fig. 2B) with single curved palp; upper lacinia slender, distal margin truncated, armed with about ten simple spines; lower lacinia tapering, with long simple setae. Maxilla (fig. 2C) with simple palp, slender, slightly tapering distally, with three plumose setae on lateral margin; basal endite simple, about 1.5 times longer than palp, about ten simple setae on distal margin; scaphognathite well developed, with numerous marginal plumose setae. First maxilliped (fig. 2D) with short palp, slightly longer than width, medial margin with three short setae, medial seta plumose; basal endite with dense marginal setae, coxal endite distinctly produced medially, with short marginal setae; exopod with well developed flagellum, caridean lobe small; epipod large, triangular, feebly bilobed. Second maxilliped (fig. 2E) with normal endopod; dactylus segment broad, about three times longer than wide, medial slightly concave, with dense rows of setae medially; propodal segment with anteromedial margin bluntly produced, with long setae; carpus short, anteromedially angulate; ischium and basis complemtely fused; exopod with well developed flagellum; coxa inflated medially; epipod semi-quadrate, without podobranch. Third maxilliped (fig. 2F) with slender endopod reaching level of mid-length of scaphocerite; ischiomerus and basis almost completely fused, combined segment bowed, about four times as long as central width, medial margin with numerous long simple setae; terminal segment tapering distally, with transverse rows of long setae; penultimate segment about 1.4 times as long as ultimate segment and 1.5 times wider than ultimate segment, with sparse simple setae and several stout long setae dorsally; exopod with well developed flagellum, distally with long plumose setae; coxal plate oval, with several setae; arthrobranch absent.

First pereiopod (fig. 3A, B) moderately slender, overreaching distal margin of scaphocerite by chela and distal half of carpus; chela with palm slightly compressed, slightly longer than dactylus, with a dense setae on medial margin of fixed finger and sparse several transverse rows of setae; dactylus and fixed finger tapering; cutting edges entire, unarmed; carpus about twice of chela length, six times as long as distal width, slightly widening distally, longitudinal row of setae at subdistal margin; merus slightly shorter carpus, 5.5 times longer than width; ischium about half length of merus, disto-lateral margin roundly produced distally.

Second pereiopod (fig. 3C–E) well developed, robust, similar, overreaching distal margin of scaphocerite by chela and half length of carpus when extended anteriorly; right chela (fig. 3C, D) about 1.8 times CL, left chela (fig. 3E) about 1.7 times CL; palm smooth, subcylindrical, slightly compressed, without distinct setae, about 1.2 times as long as dactylus, three times longer than deep in medial view; fingers slightly curved medially, with long setae along cutting edges; dactyl four times longer than proximal deep, tapering distally, with well developed hooked tip, distal 0.3 of cutting edge unarmed, proximal margin armed with six low blunt teeth; fixed finger similar, with blunt six teeth proximal half of cutting edge; propodus with a small projection at dorsolateral proximal part; carpus widening distally, cup-shaped, twice as long as distal width, without distal tooth but distal concavity dorsally; merus 1.2 times as long as carpus, three times as long as width, distoventral margin feebly angulate; ischium 0.7 times as long as merus, twice as distal width.

Third pereiopod (fig. 3F, G) robust, tip reaching distal margin of scaphocerite when extended anteriorly; merus 2.2 times as long as carpus, three times as width; carpus 1.5 times as distal width, with distolateral lobe; propodus 2.1 times as long as carpus, four times as width, distal margin with dens of long setae covering dactylus, ventral surface with a few rows of tufts of setae on distal 0.2; dactylus about 0.2 of propodal length, simple, sinuous, unguis clearly demarcated. Fourth and fifth pereiopods similar to third, fifth propodus longer than others, three times as long as carpus.

Pleopods well developed, first pleopod with slender endopod, five times as long as width, half length of exopod; second to fifth pleopods with appendix interna at about mid-length of endopod.

Uropods (fig. 1E) with protopod posteriorly acute; exopod well overreached distal margin of telson, 2.4 times longer than broad, lateral margin almost straight, terminating with distolateral tooth and longer acute movable spine; endopod subequal to exopod length, 2.7 times as long as width.

About 200 eggs in early developmental stage present, diameter about 0.5–0.7mm.

Colour in life. (Based on the photograph, fig. 4) Body generally semi-translucence. Carapace and abdomen with bright olive and reddish brown patches. Eyes with reddish patch anteriorly. Antennule and antenna with dark purple flagellum. First and third to fifth pereiopods with a longitudinal reddish orange line. Second pereiopods with a dark blue line along carpus, palm and fingers; fingers with pale yellow cutting edges, proximal part of movable finger reddish brown. Early developmental stage eggs bright olive.

Remarks. Among the eight known species in the genus Philarius , P. lufulus sp. nov. can be referable to the “ P. gerlachei species complex” that was separated into six species by Marin & Anker (2011) and Marin (2012) by absence of supraorbital teeth and a strong tooth on the carpus of the second pereiopod. Philarius lufulus sp. nov. is easily distinguished from any of the others in the species complex by the two ventral teeth on the rostrum whereas all the species in the complex have a single ventral tooth. Variations of the number of ventral rostral dentition has been reported by Bruce (1982) in P. imperialis ( Kubo, 1940) (1–3 teeth) and P. lifuensis (Borradaile, 1898) (1 or 2 teeth) that are not member of this species complex, though this new species is distinct from closely similar species mentioned below.

Except for the two ventral teeth of the rostrum, P. lufulus sp. nov. closely similar to three species of the complex, P. gerlachei (Nobili, 1905) , P. polynesicus Marin & Anker, 2011 , and P. condi Marin, 2012 , that share the following morphological characters: the posterior most tooth of the rostrum anterior to orbital margin, the supraocular lobes absent, the tip of rostrum not reaching distal margin of the scaphocerite. Among them, P. lufulus sp. nov. is most similar to P. condi with the number of fused segments the antennular flagellum, relatively stout scaphocerite, sparse setae on the palm of the second pereiopods, and the stout telson shape ( Table 1 ). Philarius lufulus sp. nov. can be distinguished from P. condi by the fingers of the second pereiopod that is shorter than the palm (fig. 3D, E) that is as long as palm or slightly longer than palm in ovigerous female in P. condi ( Marin, 2012, fig. 3B, D). In addition, distal part of the fingers are fringed with long setae in P. condi , but that are not so long and dense in the intact holotype specimen of P. lufulus sp. nov. Although the colour pattern of the new species is also somewhat similar to P. c o n d i with shearing blue longitudinal line on the chelipeds of the second pereiopods (see Marin, 2012: figs. 4, 5), P. lufulus sp. nov. has characteristic reddish brown on the body, eyes and ambulatory pereiopods and is easily distinguished from P. condi .

This new species is also closely similar to Philarius sp. reported by Marin and Anker (2011). This new species differs from that specimen in having shallower rostral teeth, more numbers of fused parts of the antennal flagellum, and scaphocerite that is widest at proximal 0.4 (widest at mid-length in Philarius sp. Marin & Anker, 2011, fig. 20B).

P. gerlachei P. polynesicus P. condi Phiralius rufulus sp. nov.

Number of specimens 4 males, 2 ov. females 1 ov. female, 2 males 1 male, 2 ov. females 1 ov. female Shape of telson: length / Slender, 2.6 Stout, 2.2 Stout, 1.7 Stout, 1.8 proximal width

* According to description of Marin and Anker (2011) or Marin (2012), estimated ratio from the figures are in parenthesis.

Tables

TABLE 1. Morphological characters of Philarius rufulus sp. nov. and the three similar species.

Number of rostral dentition: 4/1 dorsal/ ventral	4, 5/1	4/1	5/2
Number of fused segments of At least 25 antennular flagellum	About 16	10–12	11, 12
*Shape of scaphocerite: 2.5 (2.9) length / greatest width	2.5 (2.4)	2 (2.7)	2.3
Palm of second pereiopod With dens setae	With dens setae	With sparse setae	With sparse setae