Rhopalophthalmus philippinensis Hanamura & Murano

Hanamura, Yukio, Murano, Masaaki & Man, Alias, 2011, Review of eastern Asian species of the mysid genus Rhopalophthalmus Illig, 1906 (Crustacea, Mysida) with descriptions of three new species, Zootaxa 2788, pp. 1-37 : 29-34

Rhopalophthalmus philippinensis Hanamura & Murano sp. nov.

( Figs. 18–21 )

Material examined. Holotype. Philippines. Banica, Panay Is.: male (BL ca. 11 mm); 15 Aug 1976, 2:00 p.m., coll. SEAFDEC ( NSMT Cr 21244).

Paratypes. Philippines. Banica, Panay Is.: 16 males (BL ca. 8–11.5 mm), 1 male abdomen, 1 female (BL 8.5 mm), 1 ovig. female (BL ca. 12 mm); data same as holotype ( NSMT Cr 21245).

Additional material examined. Philippines. Banica, Panay Is.: 5 males (BL ca. 10.5–ca. 11 mm), 3 females (BL ca. 10–11 mm), 6 ovig. females (BL ca. 10.5–12.5 mm); 27 Aug 1976, 9:30 a.m., coll. SEAFDEC ( NSMT Cr 21246). — 8 males (BL ca. 7.0– 10.5 mm), 1 female (BL 12.0 mm), 5 ovig. females (BL ca. 10.3–11 mm); 28 Aug 1976, 10:00 a.m., coll. SEAFDEC ( NSMT Cr 21247). — Mouth of Altavas River, Banga Bay, Panay Is.: 2 males (BL 7.5, 8.5 mm), 8 females (BL 7.5–9.5 mm), 1 ovig. female (BL 10.2 mm), 1 juv. (BL 4.0 mm); plankton net, 1– 2 m depth, 2 Dec 1979, coll. M. Murano ( NSMT Cr 21248).

South China Sea. Southern part of South China Sea: 1 male (BL 9.5 mm), 21 females (BL 7.5–11.6 mm), 62 ovig. females (BL 9.5–11.7 mm), 1 juv. (BL ca. 5.5 mm); RV Hakuho-maru cruise KH-72-1, St. 45, 05°13.5' N, 107°00.8' E to 05°13.7' N, 107°01.1' E, plankton net installed at mouth of 3 m beam trawl, 60 m depth, 10 July 1972, coll. M. Murano ( NSMT Cr 21249).

Description. Body moderately stout ( Fig. 18 a).

Anterior dorsal part of carapace between postorbital spines slightly produced and anterior margin weakly convex, forming wide, rounded rostral plate ( Figs. 18 a–d); postorbital spine sharp, supported by short carina; cervical groove marked dorsally and laterally around anterior one-third of carapace; anterior dorsal median nodule not present or occasionally represented by very feeble swelling just posterior to cervical sulcus, posterior nodule well protruded near posterior end; posterior dorsal margin excavate, leaving last 3 thoracic sometimes uncovered in dorsal view; cheeks evenly concave; antero-lateral spine sharp, extending as far as end of rostral plate.

Eyes ( Figs. 18 a–d) sub-pyriform, reaching second segment of antennular peduncle; cornea about two-thirds length of eye stalk. Antennules sexually dimorphic ( Figs. 18 f, g); male peduncle with first segment slightly longer than combined length of second and third segments, armed laterally with several long inwardly curving setae (slightly deformed in figure due to artifact); second segment shortest, shorter than its width; third segment as long as wide, with a few short hooked setae on mesial margin and several long ordinary setae around disto-mesial part, lateral flagellum basally swollen, forming male lobe furnished with dense slender hair. Female antennular peduncle more slender than that of males, first segment longer than combined length of second and third segments, armed with several long inwardly curving setae along mesial margin (somewhat deformed in figure due to artifact); second segment shortest, shorter than its width; third segment as long as or slightly longer than its width. Antenna ( Fig. 19 b) with scale extending well beyond antennular peduncle, about 6–7 times as long as wide, disto-lateral spine well advanced, overreaching anterior end of lamella; distal suture present; sympod with mesial second spine longest and considerably longer than most mesial one, and also 5–7 small lateral spines.

Labrum ( Fig. 19 c) truncated anteriorly, without median spine. Mouth parts as illustrated ( Figs. 19 d–h).

Thoracic appendages: endopod of third thoracopod ( Figs. 19 i, j) sub-equal in length to fourth one but slightly stouter than latter, carpo-propodus composed of 5–7 articles; fourth to sixth thracopod with endopods ( Figs. 20 a, b) similar in shape, extending to ocular peduncle, carpo-propodi composed of 7–9 articles; seventh thoracopod with endopod ( Figs. 20 c, d) reaching eye stalk, carpo-propodus with 8–10 articles, each with longest disto-ventral seta rather smooth, without marked setules around mid-length. Vestigial endopod of eighth thoracopod in males ( Fig. 20 e) composed normally of 3 articles, falling slightly short of end of basal plate; second article bearing several long setae; third article elongated, possessing short sub-distal seta. Vestigial endopod of eighth thoracopods in females ( Fig. 20 f) un-articulated, extending as far as or slightly beyond end of basal plate of exopod, with or without short seta at mid-length.

Abdomen ( Fig. 18 a) smooth, without any ornamentation, first 5 somites sub-equal in length; sixth somite 1.25–1.45 times as long as fifth one; first somite in male rounded ventrally to form pleuron with shallow excavation near anterior part.

Pleopods in males ( Figs. 21 a–d) biramous: first pleopod with endopod un-articulated, possessing several short marginal setae, exopod multi-articulated; exopod of second pleopod greatly elongated, reaching or slightly overreaching mid-length of sixth abdominal somite, composed of about 13 articles, distal segment with pair of apical setae and proportionately long sub-apical seta, several basal articles with long seta while several unarmed articles present between these armed articles, endopod multi-articulated; third to fifth pleopods similar in shape, with multi-articulated endopods and exopods of sub-equal length, their length slightly decreasing posteriorly. Pleopods in females ( Figs. 21 e–g) un-articulated, length increasing on posterior somites.

Uropod ( Fig. 19 a) 2-segmented in both exopod and endopod, exopod with distal segment about half-length of basal one; endopod reaching around mid-length of distal segment of exopod, several scattered short setae along lateral margin, distal segment about two-fifths length of basal one, latter with stout seta on ventral surface near midlength.

Telson ( Fig. 18 e) sub-equal in length to sixth abdominal somite, falling far short of articulation of uropodal endopod, about twice as long as basal width and again about 3 times as long as broad at sub-basal constricted part, widest at basal part and abruptly narrowing near base, forming no discernible waist owing to parallel lateral margins, then gradually narrowing from mid-length toward distal; rounded posterior end of telson with 2 pairs of spinose setae, lateral pair distinctly longer than mesial pair, each with rather sharp setules throughout margins; lateral margin of telson armed with somewhat short 7–9, commonly 8, setae on posterior half, most of them possessing a few to several setules on posterior margin.

Body length. Largest recorded male: BL 11.5 mm, largest female: BL 12.5 mm.

Egg size. Stage I embryos (eggs) oblong, 0.70–0.90 mm along longest axis (N=3). Etymology. The name of the species “ philippinensis ” is selected for the type locality.

Remarks. Rhopalophthalmus philippinensis is remarkable in the genus in having 1) a proportionately short telson without a discernible waist, 2) a unique spine arrangement on the antennal sympod armed with the longest mesial second spine flanked by a shorter most mesial spine in addition to 5–7 much short lateral spines, and 3) the carpo-propodus articles of the third to seventh thoracic endopods are also larger in number than those of other members of eastern Asian Rhopalophthalmus .

The general appearance of R. philippinensis shows some resemblance to that of R. africana O. Tattersall, 1957 captured from the Sierra Leone estuary, western Africa, but the African species possesses a single prominent spine and a single small spine on the antennal sympod instead of having several small spines in R. philippinensis . Furthermore, the carpo-propodi of the third to seventh thoracic endopods are composed of four sub-segments in R. africana as opposed to five or more in the new species.

The new species also resembles R. dakini O. Tattersall, 1957 from Australia, but the antennal sympod spines of Australian species are arranged to form a perfect cone.

Distribution. Recorded from the Philippines and southern part of South China Sea (present study).

Figures

FIGURE 18. Rhopalophthalmus philippinensis Hanamura & Murano sp. nov. Holotype male (BL ca. 11 mm) (a), paratype male (BL 10.5 mm) (b, c, e, f), and paratype ovigerous female (BL 11.5 mm) (d, g) collected from Panay Island, Philippines: a, entire body of male (lateral view); b, carapace and cephalic appendages of male (lateral view); c, anterior part of carapace and cephalic appendages of male (dorsal view); d, anterior part of carapace and cephalic appendages of female (dorsal view); e, telson (ventral view); f, right antennule of male (dorsal view); g, right antennule of female (dorsal view).

FIGURE 19. Rhopalophthalmus philippinensis Hanamura & Murano sp. nov. Paratype male (BL 10.5 mm) collected from Panay Island, Philippines: a, right uropod (ventral view); b, right antenna (ventral view); c, labrum; d, right mandibular palp; e, right maxillule; f, right maxilla; g, right first thoracic limb; h, right second thoracic limb; i, j, right third thoracic limb and carpo-propodus of endopod.

FIGURE 20. Rhopalophthalmus philippinensis Hanamura & Murano sp. nov. Paratype male (BL 10.5 mm) (a – e) and paratype ovigerous female (BL 11.5 mm) (f) collected from Panay Island, Philippines: a, b, right sixth thoracic endopod and carpopropodus of endopod; c, d, right seventh thoracic limb and carpo-propodus of endopod; e, right eighth thoracic limb of male; f, rudimentary endopod of right eighth thoracic limb of female.

FIGURE 21. Rhopalophthalmus philippinensis Hanamura & Murano sp. nov. Paratype male (BL 10.5 mm) (a – d) and paratype ovigerous female (BL 11.5 mm) (e – g) collected from Panay Island, Philippines: a – d, right first, second, third, and fifth pleopods of male; e – g, right first, third, and fifth pleopods of female.