Mesopodopsis orientalis ( Tattersall, 1908 )

Hanamura, Yukio, Koizumi, Noriyuki, Sawamoto, Shozo, Siow, Ryon & Chee, Phaik Ean, 2008, Reassessment of the taxonomy of Mesopodopsis orientalis (Tattersall, 1908) (Crustacea, Mysida) and proposal of a new species for the genus with an appendix on M. zeylanica Nouvel, 1954, Journal of Natural History 42 (37 - 38), pp. 2461-2500 : 2464-2472

Mesopodopsis orientalis ( Tattersall, 1908)

( Figures 2–4 , 7 A–C)

Macropsis orientalis Tattersall, 1908, p. 236 , Plate 22, Figures 1–9 ; Tattersall 1914, p. 75 (in part, not Tattersall5 Mesopodopsis zeylanica ); Tattersall 1915, p. 159 (?in part).

Mesopodopsis orientalis: Tattersall 1922, p. 482 (?in part); Tattersall 1965, p. 91 (in part, not Tattersall5 Mesopodopsis tenuipes ); Pillai 1965, p. 1721, Figure 84; Murano 1988, p. 298; Pinkaew et al. 2001, Figure 7 a–d.

? Mesopodopsis orientalis: Nouvel 1957, p. 323 : Gupta and Gupta 1984, p. 185.

Not Mesopodopsis orientalis: Tattersall 1960, p. 180 (5 M. tenuipes); Pillai 1968, p. 16, Figures 2b, h , 4b , 5b , 6a, f , 7a . (5 M. tenuipes).

Material examined

India. Dhappa : near Calcutta (5Kolkata), 11 „„ (BL 4.8–5.5 mm), nine ♀♀ (BL ca 4.8–6.5 mm), three ovig. ♀♀ (BL 4.5–5.5 mm) (syntypes; NHM 1908.7.7.102–110); two „„ (BL 4.6, 5.3 mm), seven ♀♀ (BL 5.3–6.0 mm), one ovig. ♀ (BL 5.5 mm) (topotypes; NHM 1964.1.21. 2769/2962). Chilka Lake: Koh Kong, Nalbano, five „„ (BL ca 5.5–8.0 mm), three ♀♀ (BL ca 5.0– ca 7.0 mm), two ovig. ♀♀ (BL 7.5, ca 9.0 mm), one juv. (BL –), 25 January 1900 (NHM 1966.1.21. 3067/3116; slightly damaged). Madras (5 Chennai): five „„ (BL 5.6–6.7 mm), four ♀♀ (BL 3.8–6.8 mm), one ovig. ♀ (BL 6.5 mm) (slightly damaged), 21 May 1921 and 11 June 1921 (NHM 1964.1.21.2769/2962) .

Malaysia. Kedah State: mouth of Sungai Kedah River, Kota Kuala Kedah, 20 September 2005, 114 „„ (BL 3.7–7.0 mm), 78 ♀♀ (BL 3.8–7.8 mm), 72 ovig. ♀♀ (BL 6.4– 7.0 mm), 161 juv. (BL 2.2–3.4 mm), river bank is covered with cockle shells, intertidal, hand net, coll. Y. Hanamura ; Sungai Merbok River , 14 October 2004, St B, 4 m, two „„ (BL 6.4, 6.9 mm), sledge net, coll. Y. Hanamura ; Jeti Teluk Bayu, Sungai Merbok River , 16 December 2004, two „„ (BL 6.5, 6.5 mm), medium to coarse sand substrate, intertidal, hand net, coll. Y. Hanamura ; river bank situated off Pantai Merdeka, Merbok , 15 February 2006, 11 „„ (BL 3.6–6.7 mm), 10 ♀♀ (BL 3.6–7.4 mm), five ovig. ♀♀ (BL 7.1–7.4 mm), 11 juv. (BL 2.6–3.2 mm), fine sand sandy beach, intertidal, hand net, coll. Y. Hanamura ; Pantai Merdeka, Merbok , 12 March 2007, numerous specimens of „„ (BL up to 6.8 mm) and ovig. ♀♀ (BL up to 8.1 mm), fine sand sandy beach, intertidal, surf net for fish juveniles, coll. Y. Hanamura. Penang Island: Teluk Kumbar , 25 August 2004, numerous specimens of „„ (BL up to 6.3 mm) and ovig. ♀♀ (BL up to 6.7 mm), fine sand sandy beach, intertidal, hand net, coll. Y. Hanamura ; Teluk Kumbar , 9 September 2005, three „„ (BL 5.0– 5.5 mm), one ovig. ♀ (BL 6.5 mm), fine sand sandy beach, intertidal, hand net, coll. Y. Hanamura ; 13 September 2005, numerous specimens of „„ (BL up to 7.1 mm) and ovig. ♀♀ (BL up to 7.8 mm), fine sand sandy beach, intertidal, hand net, coll. Y. Hanamura (NSMT-Cr 17919, IORD In 07-001/002; FRI Cr 002) ; Kampong Sungai Betong , 2 March 2006, six „„ (BL 5.1– 6.5 mm), one ♀ (BL 3.7 mm), sandy–muddy beach, intertidal, hand net, coll. Y. Hanamura ; Gold coast, 13 March 2007, five „„ (BL 5.2–6.6 mm), two ♀♀ (BL 5.4, 5.7 mm), one juv. (BL 2.8 mm), fine sand sandy beach, hand net, coll. Y. Hanamura. Perak State: Jeti Pantai Kechil, Matang mangrove estuary, 18 August 2005, one „ (BL 6.6 mm), surface, hand net, coll. Y. Hanamura; Kuala Sepetang, Matang mangrove estuary, 17 May 2006, one „ (BL 6.4 mm), muddy-sand beach, intertidal, hand net, coll. Y. Hanamura; Kuala Sepetang, Matang, 1 March 2007, one „ (BL 7.2 mm), muddysand beach, intertidal, hand net, coll. Y. Hanamura. Malacca State: Pantai Kling Beach , 5 August 2005, 17 „„ (BL 4.2–6.7 mm), 19 ♀♀ (BL 3.7–6.7 mm), nine ovig. ♀♀ (BL 6.4–7.8 mm), fine sand sandy beach, intertidal, hand net, coll. Y. Hanamura ; Tanjung Kling , 5 August 2005, five „„ (BL 5.2–6.6 mm), two ♀♀ (BL 5.4, 5.7 mm), eight ovig. ♀♀ (BL 6.5–7.6 mm), fine sand sandy beach, intertidal, hand net, coll. Y. Hanamura ; Kampong Pantai Kemutang , 5 August 2005, nine „„ (BL 3.6–6.2 mm), seven ♀♀ (BL 4.0– 7.7 mm), one ovig. ♀ (BL 6.7 mm), five juv. (BL 2.7–3.4 mm), sandy beach, intertidal, hand net, coll. Y. Hanamura ; Pantai Kelembang , 5 August 2005, 12 „„ (BL 4.7–7.1 mm), four ♀♀ (BL 5–5.5 mm), three ovig. ♀♀ (BL 7.5–7.7 mm), intertidal, sandy beach, hand net, coll. Y. Hanamura.

Thailand. Samut Songkhram (Gulf of Thailand): off Khlong Khon, 18 October 2005, one „ (BL 6.8 mm), nine ♀♀ (BL 3.7–6.0 mm), one ovig. ♀ (BL 6.0 mm), 20 juv. (BL 1.9–3.5 mm), surface, scoop net, coll. Y. Fujioka; off Khlong Khon, 6 June 2006, numerous specimens of „„ (BL up to 7.3 mm) and ♀♀ (BL up to 7.8 mm), surface, scoop net, coll. Y. Fujioka; cultivation pond at Aquatic Research Station of Kasetsart University , 13 July 2005, 16 „„ (BL 5.8–7.6 mm), eight ♀♀ (BL 6.3– 7.6 mm), five ovig. ♀♀ (BL 5.6–6.8 mm), grab, coll. Y. Fujioka; cultivation pond at Aquatic Research Station of Kasetsart University , 27 July 2005, numerous specimens of „„ (damaged) and ♀♀ (damaged), grab, coll. Y. Fujioka. Chonburi (Gulf of Thailand): Muang Mai (salinity 13–15), 24 December 2003, four „„ (BL 5.3–7.1 mm), three ♀♀ (BL 5.6–7.1 mm), two ovig. ♀♀ (BL 6.2, 6.5 mm), coll. S. Ohtsuka; Bang Saen Beach, 30 August 2006, eight „„ (BL 6.2–6.5 mm), seven ovig. ♀♀ (BL 6.2–7.3 mm), sandy beach, intertidal, hand net, coll. Y. Hanamura (several specimens in separate samplings of the same site: NSMT-Cr 17920) .

Indonesia. Bali Island: Pegamentan Bay , 5 December 1996, 20 „„ (BL 5.6–6.3 mm), one ♀ (BL 5.9 mm), 31 ovig. ♀♀ (BL 5.7–6.8 mm), shrimp culture pond in mangrove forest, surface, hand net, coll. Y. Ogawa. (– indicates that precise measurement was impossible) .

Type locality

Brackish pond in Dhappa, near Calcutta (5Kolkata), India.

Description

Body smooth, without folds, hairs, or spines.

Carapace ( Figures 2A, B, D ; 3 A–E) anteriorly produced into rounded rostrum reaching base of ocular peduncle; rostral plate bearing minute but sharp spines, each placed at lateral parts just behind ocular peduncles; anterolateral corner nearly triangular with sub-acute apex; shallow but distinct cervical groove present at a point of anterior two-fifths; posterior dorsal margin nearly straight to slightly convex at median part, excavated dorsally, leaving at least last two thoracic somites uncovered in dorsal aspect; posterolateral lobe moderately developed; pseudorostrum well marked.

Abdomen ( Figures 2C ; 3A ; 7 A–C) with first five somites subequal in length; sixth somite longest, 1.38–1.63 times as long as fifth. Telson ( Figure 3F ) as long as or slightly shorter than sixth abdominal somite, 1.4–1.6 times as long as wide; lateral margin slightly concave, armed with sharp spine each at a point of posterior onethird and one to five (commonly two or three) small spines just anterior to the large lateral spine ( Table 2); posterior one-third linguiform bearing dense, close-set spinules of sub-equal length all around margin.

Eye ( Figures 2A, B, D ; 3A, B, D, G ) barely reaching end of second segment of antennular peduncle; cornea well pigmented, 1.00–1.17 times (mean: 1.09) as broad as stalk width when measured at mid-length; no ocular tubercle present.

Antennules ( Figure 3H, I ) sexually dimorphic; in male, first segment longest, subequal to combined length of distal two segments, armed with moderately stout seta and a few slender setae of unequal lengths at distolateral part; second segment slender and shortest; third segment slightly widened distally; male lobe well developed, subequal length to combined length of basal two segments of peduncle, armed with numerous fragile hairs along median margin; accessory flagellum with basal thickened part normally occupying seven-tenths of male lobe or more, then continuous to relatively short, slender flagellum; lateral flagellum slightly thickened at base, armed with several sensory setae on mesiobasal part; in female, peduncle is slightly slenderer than that of male, with several long setae at distoventral part of third segment.

Antenna ( Figure 3J ) with scale extending slightly beyond antennular peduncle in male, narrow and somewhat lanceolate, about 6.5 times as long as basal width, setose all around margin, and with distinct articulation separating distal lobe, latter occupying 0.11–0.14 length of scale; in female, slightly longer, about seven times as long as basal width, and extending beyond antennular peduncle by almost whole length of distal lobe of scale; anterior end of peduncle in male usually slightly to fully overreaching anterior end of second segment of antennular peduncle, while proportionately shorter, barely reaching or falling slightly short of that margin in females; distal segment of peduncle 0.55–0.61 times as long as penultimate one.

Mouthparts as illustrated ( Figure 4 A–E).

Third to eighth thoracopods ( Figure 4 F–H) similar in shape; exopod with eight- or nine-segmented lash; basal plate without ornamentation; endopod with five to seven segmented carpopropodi; distodorsal setae of carpopropodus of eighth thoracic endopod with a series of minute barbed spinules on distal one-third, but such spinules not present on anterior thoracic limbs.

Penis ( Figure 4I ) rod-shaped, with several long and short setae on posterior margin and two short, obtuse setae distally.

Marsupium composed of two pairs of oostegites.

Male first, second, and fifth pleopods ( Figure 4J, M ) unsegmented, simple lobe, increasing in length posteriorly. Third pleopod ( Figures 2F ; 4K ) moderately robust and bilobed; endopod shorter than exopod, unsegmented, bearing several setae around margins; exopod slender, straight or sometimes curving near base, normally unsegmented but occasionally with incipient articulation above mid-length, with moderately long seta distally. Fourth pleopod ( Figures 2G ; 4L ; 7 A–C) bilobed and strongly elongated, 1.53–2.21 times (mean: 1.79) as long as sixth abdominal somite; sympod 0.53–0.66 times as broad as maximal width of cornea; endopod rudimentary, unsegmented with short terminal seta; exopod stout and elongated, barely reaching or slightly overreaching end of sixth abdominal somite except for terminal setae, usually two-segmented, but rarely with incipient articulation near basal part; distal segment much shorter than penultimate, with basally stout, short and long, slender setae distally.

Uropod ( Figure 3K ) about 1.8 times as long as sixth abdominal somite; endopod slightly more than two-thirds length of exopod, bearing several setae along lateral and mesial margins and also with several spines along lateral margin.

Colour

Semi-transparent when alive, with dark, thin vertical and transverse posterior lines present on each ventral surface of anterior five abdominal somites and sixth abdominal somite with slightly thickened transverse line on posterior end.

Size

Maximum body size in male 8 mm, ca. 9 mm in female ( Chilka Lake ), and 4.5 mm in smallest ovigerous female (syntype), while those found in annual survey on the west coast of Malaysia were 7.1 mm, 8.3 mm and 5.2 mm, respectively (see also Hanamura et al. 2008). The maturation size may vary depending on locality and habitat .

Remarks

Tattersall’s syntypes are slightly damaged but the major diagnostic features were as follows: (1) male fourth pleopod barely extending to end of sixth abdominal somite or slightly overreaching end of sixth abdominal somite, its sympod less than half as broad as width of cornea; (2) antennal peduncle in male extending to mid-length of third segment of the antennular peduncle; in females, barely reaching or falling slightly short of anterior end of second antennular segment; and (3) telson possessing two to four, commonly two or three, spinules on lateral margin except for large spine ( Table 2). The syntypes and topotypes appeared to have smaller body size and, inversely, comparatively slightly longer fourth pleopods in males as compared with those usually obtained in the coastal waters including India (cf. Figures 2A ; 3A ; 7 A–C).

In the revision of Mesopodopsis, Pillai (1968) examined M. orientalis from specimens collected from the Malacca Strait (NHM 1965.9.2, collected in July 1962) because he did not have access to either the type specimens of M. orientalis or the topotypic materials. From the published data, these specimens were assumed to refer to those obtained in June 1962 in the inshore water of Panshor (definite locality unknown:? Basan Panchor in Perak State) at salinity of 23‰ (see also Tattersall 1965). A re-examination of M. orientalis with the same reference number housed in the Natural History Museum revealed that they could be attributed to M. tenuipes sp. nov.; hence, it is highly probable that the specimens examined by Pillai would belong to the latter species. Similarly, M. orientalis specimens recorded by Tattersall (1960, 1965) from a fish cultivation pond in Singapore as well as those from the Malacca Strait (NHM 1964.1.21.3023/3046) were referred to M. tenuipes because they possess a long fourth male pleopod.

Pillai (1968) suggested in his review that some early records of M. orientalis in India should be reconfirmed. Indeed, early records of this species ( Tattersall 1914, 1915, 1922; and those cited by Gordan 1957) should be read with caution because a re-examination of selected loan samples revealed confusion with M. zeylanica Nouvel, 1954 (see also the section under ‘‘ M. zeylanica ’’).

For the distinction between M. orientalis and M. tenuipes sp. nov., refer to the ‘‘Remarks’’ under the latter species and also ‘‘Discussion’’.

Distribution

Known from the southeastern coast of India, Madras (5Chennai), Gulf of Bengal, west coast of Malay Peninsula, Gulf of Thailand, and Indonesia (present study, Biju personal comm.) ( Figure 10 ).

Habitat

Mesopodopsis orientalis is a euryhaline species collected in our survey from a salinity range of 13–32. In northwestern Peninsular Malaysia (and probably in Thailand), this species usually inhabits the shallow coastal waters as well as the lower reaches of the river, but a small number of individuals were occasionally encountered in upper streams of estuarine rivers (see also ‘‘Habitat’’ under M. tenuipes ). Almost all specimens examined herein were collected from surface waters.

Figures

Figure 1. Morphometric measurements in eye (A), posterior part of abdomen (B), and male fourth pleopod (C). wc, width of cornea; ws, width of stalk; lsas, length of sixth abdominal somite; lfmp, length of fourth male pleopod; wfps, width of fourth pleopodal sympod of male.

Figure 2. Mesopodopsis orientalis Tattersall, male syntype [body length (BL) ca 5.5 mm] (A– C), female syntype (BL 6.6 mm) (D), and male topotype (BL ca. 5.5 mm) (E–G) from Dhappa, India. (A) Carapace and cephalic appendages, dorsal; (B) same, lateral; (C) posterior part of abdomen, lateral; (D) anterior part of carapace and cephalic appendages, lateral; (E) right antennule, dorsal; (F) right second pleopod, anterior; (G) right fourth pleopod, posterior.

Figure 3. Mesopodopsis orientalis Tattersall, male [body length (BL) 7.1 mm] (A–C, F–H, J, K) and ovigerous female (BL 7.8 mm) (D, E, I) from Penang, Malaysia. (A) Entire body, lateral; (B, D) anterior part of carapace and cephalic appendages, dorsal; (C, E) posterior part of carapace, dorsal; (F) telson, ventral; (G) eye, dorsal; (H, I) antennule, dorsal; (J) antenna, ventral; (K) uropod, dorsal.

Figure 4. Mesopodopsis orientalis Tattersall, male [body length (BL) 7.1mm] (A–M) and ovigerous female (BL 7.8 mm) (N, O) from Teluk Kumbar Beach, Penang, Malaysia. (A) Right mandible, ventral; (B) right maxillule, ventral; (C) left maxilla, ventral; (D) right endopod of first thoracopod, ventral; (E) right second thoracopod, ventral; (F) right endopod of sixth thoracopod, posterior; (G, H) right seventh and eighth thoracopods, ventral; (I) right penis, mesial; (J–M) right, male second to fifth pleopods; (N, O) right, female second and fifth pleopods.

Figure 5. Mesopodopsis tenuipes sp. nov., paratype male [body length (BL) 7.5 mm] (A–C, F– H, J, K) and paratype ovigerous female (BL 8.0 mm) (D, E, I) from Sungai Batu Lingtang, Merbok, Malaysia. (A) Entire body, lateral; (B, D) anterior part of carapace and cephalic appendages, dorsal; (C, E) posterior part of carapace, dorsal; (F) telson, ventral; (G) eye, dorsal; (H, I) antennule, dorsal; (J) antenna, ventral; (K) uropod, dorsal.

Figure 6. Mesopodopsis tenuipes sp. nov., paratype male [body length (BL) 7.5 mm] (A–M) and paratype ovigerous female (BL 8.0 mm) (N, O) from Sungai Batu Lingtan, Merbok, Malaysia. (A) Right mandible, ventral; (B) left maxillule,internal; (C) right maxilla, internal;(D) right endopod of first thoracopod, ventral; (E) right second thoracopod, ventral; (F) right endopod of sixth thoracopod, posterior; (G, H) right seventh and eighth thoracopods, ventral; (I) right penis, mesial; (J–M) right, male second to fifth pleopods; (N, O) right, female second and fifth pleopods.

Figure 7. Posterior part of abdomen and length variations in fourth male pleopod of Mesopodopsis orientalis Tattersall (A–C) and M. tenuipes sp. nov. (D–F). (A) Syntype, Dhappa, India [body length (BL) ca 5.5 mm]; (B) Teluk Kumbar Bach, Penang, Malaysia (BL 7.1 mm); (C) Pantai Merdeka Beach, Merbok, Malaysia (BL 6.6 mm); (D) Sungai Batu Lintang, Merbok, Malaysia (BL 7.5 mm); (E) aquaculture pond of Kasetsart University, Samut Songkhram, Thailand (BL 8.0 mm); (F) aquaculture pond of Philippine University at Legares, Panay Island, Philippines (BL 5.5 mm).

Figure 8. Maximum parsimony tree of the cytochrome c oxidase subunit I (COI; left) and 16S recombinant RNA

Figure 9. Mesopodopsis zeylanica Nouvel, male [body length (BL) ca. 6.0 mm] from Madras (5Chennai), India. (A) Carapace and cephalic appendages, dorsal; (B) posterior part of abdomen, lateral; (C) right fourth male pleopod.

Figure 10. Distribution of the Indo-Australasian species of Mesopodopsis in the south and southeastern Asian coastal waters. Filled symbols are based on the present study and open symbols are from published literature including personal communications.