Mesopodopsis tenuipes Hanamura, Koizumi, and Sawamoto, 2008

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 : 2473-2480

Mesopodopsis tenuipes Hanamura, Koizumi, and Sawamoto , sp. nov.

( Figures 5 , 6 , 7 D–F)

Mesopodopsis orientalis: Tattersall 1960, p. 180 (in part, not Tattersall); Tattersall 1965, p. 91 (in part); Pillai 1968, p. 16, Figures 2b, h , 4b , 5b , 6a, f , 7a .

Material examined

Holotype. Sungai Batu Lintang , Sungai Merbok River, Malaysia, 15 February 2006, „ (BL 7.5 mm), medium sand sandy substrate, intertidal, hand net, coll. Y. Hanamura (NSMT-Cr 17921).

Paratypes. Numerous „„ (BL up to 7.5 mm) and ♀♀ including ovig. ♀♀ (BL up to 8.4 mm), data same as holotype (NSMT-Cr 17922, IORD In 07–003/004; FRI Cr 003) .

Additional materials examined

Malaysia. Kedah State: Sungai Pedang Lalang River, Langkawi Island , 31 July 2005, 23 „„ (BL 4.2–6.7 mm), 23 ♀♀ (BL 4.5–7.4 mm), one ovig. ♀ (BL 6.8 mm), medium sand sandy beach, intertidal, hand net, coll. Y. Hanamura ; Sungai Pedang Lalang River, Langkawi Island , 31 July 2005, 14 „„ (BL 4.2–5.7 mm), 17 ♀♀ (BL 4.3– 5.2 mm), 27 juv. (BL 2.0– 3.9 mm), medium to coarse sand sandy beach, intertidal, hand net, coll. Y. Hanamura ; Jeti Teluk Bayu, Sungai Merbok River , 16 December 2004, 168 „„ (BL 3.8–7.2 mm), 94 ♀♀ (BL 3.8–7.6 mm), 47 ovig. ♀♀ (BL 7.0– 8.1 mm), 12 juv. (BL 3.2–3.8 mm), medium to coarse sand sandy beach, intertidal, hand net, coll. Y. Hanamura. Perak State: Jeti Pantai Kechil, Matang mangrove estuary, 18 August 2005, five „„ (BL 5.5–7.0 mm), one ovig. ♀ (BL 7.9 mm), three juv. (BL 3.0– 4.0 mm), surface, coll. Y. Hanamura ; Jeti Jabatan Perikanan, Sungai Manjung River , 23 February 2006, one ovig. ♀ (BL 6.8 mm), sandy substrate, intertidal, hand net, Y. Hanamura ; Jetty Point, Lumut , 23 February 2006, one „ (BL 4.2 mm), one ♀ (BL 5.5 mm), fine sand sandy beach, intertidal, hand net, Y. Hanamura ; approximately 6 km up stream of Kuala Sepetang, Matang mangrove estuary, 25 May 2006, one ovig. ♀ (BL 8.2 mm), muddy substrate, intertidal, hand net, coll. Y Hanamura ; Kuala Sepetang, Matang mangrove estuary, 14 June 2006, 124 „„ (BL 4.1–7.5 mm), 110 ♀♀ (BL 4.0– 7.8 mm), 64 ovig. ♀♀ (BL 6.3–8.1 mm), 106 juv. (BL 3.1–3.8 mm), muddy substrate covered with cockle shells, intertidal, hand net, coll. Y Hanamura ; Kuala Sepetang, Matang , 11 July 2006, 15 „„ (BL 4.2–7.4 mm), 11 ♀♀ (BL 4.5–7.3 mm), five ovig. ♀♀ (BL 6.7–7.4 mm), 33 juv. (BL 2.3–3.9 mm), muddy substrate covered with cockle shells, intertidal, hand net, coll. Y. Hanamura ; Kuala Sepetang, Matang mangrove estuary, 8 August 2006, seven „„ (BL 4.2–6.8 mm), six ♀♀ (BL 4.5–6.7 mm), three ovig. ♀♀ (BL 6.7–7.3 mm), muddy substrate covered with cockle shells, intertidal, hand net, coll. Y. Hanamura ; Kuala Sepetang, Matang mangrove estuary, 1 March 2007, 61 „„ (BL 4.0– 7.8 mm), 65 ♀♀ (BL 4.0– 7.4 mm), 15 ovig. ♀♀ (BL 6.7–8.0 mm), 134 juv. (BL 2.3–3.8 mm), muddy substrate covered with cockle shells, intertidal, hand net, coll. Y. Hanamura ; off St. 4, Matang Mangrove estuary, 14 June 2006, one „ (BL 6.7 mm), 2.0 m, sledge, coll. Y. Hanamura. Malacca Strait (definite locality unknown): one „ (BL 5.5 mm), five ♀♀ (BL 5.6– 7.0 mm), one ovig. ♀ (BL 5.8 mm), three juv. (BL 3.9–4.1 mm), B68 1(C) (NHM 1964.1.21.3023/3046) ; three „„ (BL 4.5–6.5 mm), three ♀♀ (BL 5.3–7.0 mm), four ovig. ♀♀ (BL 6.5–7.5 mm) (NHM 1965.9.2.217–296).

Singapore: six „„ (BL 4.2–5.7 mm), three ♀♀ (BL 5.7–6.3 mm), one ovig. ♀ (5.8 mm), B60 1(C) (NHM 1964.1.21.3023/3046) .

Thailand (Gulf of Thailand). Samut Songkhram mangrove estuary: cultivation pond at Aquatic Research Center of Kasetsart University , 27 May 2005, one „ (BL ca 6 mm), grab, coll. Y. Fujioka ; cultivation pond at Aquatic Research Center of Kasetsart University , 29 June 2005, 37 „„ (BL 4.0–7.0 mm), 10 ♀♀ (BL 4.3–6.3 mm), 10 ovig. ♀♀ (BL 5.3–7.0 mm), 12 juv. (BL 2.5–3.7 mm), plankton haul, coll. Y. Fujioka ; cultivation pond at Aquatic Research Center of Kasetsart University , 13 July 2005, two „„ (BL ca 6.0, 6.5 mm), grab, coll. Y. Fujioka ; cultivation pond at Aquatic Research Center of Kasetsart University, October–November 2005, seven „„ (BL 3.9–8.0 mm), 13 ♀♀ (BL 3.8–8.2 mm), 25 juv. (BL 1.5–3.5 mm), plankton; cultivation pond at Aquatic Research Center of Kasetsart University , 29 August 2006, three „„ (BL 5.8–6.1 mm), near bank of waterway, surface, hand net, coll. Y. Hanamura.

Vietnam. Nha Trang : prawn culture pond, near Bihn Tan Bridge, 23 November 2005, seven „„ (BL 5.0– 6.4 mm), 27 ♀♀ (BL 4.8–7.5 mm), four ovig. ♀♀ (BL 6.9–7.3 mm), eight juv. (BL 1.8–2.7 mm), coll. N. Cho ; prawn culture pond, near Bihn Tan Bridge , 24 November 2005, 60 „„ (BL 5.1–6.9 mm), 59 ♀♀ (BL 6.2–7.8 mm), one ovig. ♀ (BL 7.5 mm), coll. N. Cho.

Philippines. Panay Island : Hamtik, 5 April 1976, 31 „„ (BL 3.6–6.5 mm), 34 ♀♀ (BL 3.6–6.7 mm), two ovig. ♀♀ (BL -, 6.0 mm), seven juv. (BL 2.7–3.4 mm), 08:15–08:25, 5 m (bottom) , CM net, coll. SEAFDEC (M-40-1); Banika , 15 August 1976, 32 „„ (BL ca 6.0– ca 7.5 mm), 23 ♀♀ (BL 4.5– ca 8.0 mm), 31 ovig. ♀♀ (BL 6.22– ca 8.0 mm), 14:00 , CM net, coll. SEAFDEC (M-40-2); Banika , 27 August 1976, one „ (BL 7.2 mm), 09:30 , CM net, coll. SEAFDEC (M-40-4); cultivation pond in Philippine University at Leganes, 23 November 1979, 38 „„ (BL 4.2–6.5 mm), 20 ♀♀ (BL 4.2– 6.7 mm), 36 ovig. ♀♀ (BL 5.2–6.4 mm), coll. M. Murano ; mouth of Altavas River , Batan Bay, 2 December 1979, four „„ (BL up to 5.2 mm), three ♀♀ (BL up to 6.5 mm), four ovig. ♀♀ (BL 6.5–7.5 mm), surface, coll. M. Murano ; mouth of Altavas River , Batan Bay, 2 December 1979, 112 „„ (BL 4.0– 7.5 mm), 127 ♀♀ (BL 4.0– 8.0 mm), 178 ovig. ♀♀ (BL 6.4–8.4 mm), 66 juv. (BL 1.7–8.4 mm), surface, coll. M. Murano.

Type locality

Merbok mangrove estuary, Kedah State, Peninsular Malaysia.

Description

Body moderately large, surface smooth without folds, spines, or hairs.

Carapace ( Figure 5 A–E) produced anteriorly into evenly rounded rostral plate extending base of ocular peduncle, with sharp, feebly ridged spines at posterolateral parts of plate just behind ocular peduncles; shallow but distinct cervical groove present at about distal two-fifths of carapace; anterolateral corner sub-triangular with sub-acute apex; posterior margin slightly produced posteriorly at mid-dorsal part, excavated, leaving at least posterior two thoracic somites in dorsal view; posterolateral lobe moderately developed; pseudorostrum well marked.

Abdomen ( Figures 5A ; 7D, E ) with anterior five somites subequal in length; sixth abdominal somite 1.33–1.54 times as long as precedent. Telson ( Figure 5F ) 0.85–1.00 times as long as sixth abdominal somite, lateral margin slightly concave in dorsal aspect, armed with distinct spine at a point of distal one-third and also two to six, commonly three or four, short spines on each lateral margin ( Table 2); posterior onethird of telson linguiform, armed with closely set spinules of subequal length all round margin.

Eye ( Figure 5A, B, D, G ) with cornea well developed and pigmented, extending a little beyond second segment of antennular peduncle; cornea 1.17–1.44 times (mean: 1.26) as broad as stalk width as measured at mid-length.

Antennule ( Figure 5H, I ) dimorphic; in male, basal segment longest, subequal in length to combined length of distal two segments, armed with long sub-distal seta and a few setae at distolateral part; second segment shorter than third segment, with a few setae at distolateral part; third segment slightly widened distally, with a few setae at distolateral part; male lobe well developed, subequal in length to combined length of distal two segments of peduncle, fringed with fragile, dense setae along mesial margin; accessory flagellum with basal thickened part falling short of distal end of male lobe, then continuing somewhat short, slender lamus; lateral flagellum slightly thicker in basal part than that of mesial one, armed with several fragile, sensory setae along mesiobasal part; in female, antennular peduncle slightly slenderer than that of male, with several long setae at anterodistal part of third segment.

Antenna ( Figure 5J ) with scale extending beyond antennular peduncle by almost half length of distal lobe in male, somewhat lanceolate with obtuse apex, setose all around margin, about six times as long as basal width. In female, proportionately slightly longer than male and extending beyond antennular peduncle by whole length of distal lobe of antennal scale, about seven times as long as basal width; anterior end of peduncle in male extending as far as end of anterior end of second antennular peduncle, with distal segment 0.55–0.61 times as long as penultimate one; in female proportionately shorter than in male, anterior end of peduncle barely reaching midlength of second segment of antennular peduncle.

Labrum rounded anteriorly, without frontal spine.

Mouthparts as illustrated ( Figure 6 A–E).

Third to eighth thoracopods ( Figure 6 F–H) with eight- or nine-segmented lash on exopod; basal plate without ornamentation. Exopods with five to seven segmented carpopropodi; distodorsal setae on carpopropodus of eighth thoracic endopod with a series of minute, barbed spinules on distal one-third, but no such spinules on anterior endopods.

Penis ( Figure 6I ) rod-shaped, with several long setae at distolateral part of posterior margin and short, obtuse seta distally.

Marsupium composed of two pairs of oostegites.

Pleopod dimorphic ( Figures 6 J–O, 7D–F). In male, first, second and fifth pleopods unsegmented, increasing in length posteriorly. Third pleopod moderately long and bilobed; endopod slender and unsegmented but occasionally imperfectly articulated above mid-length, often slightly curving near base, bearing moderately long terminal seta; exopod distinctly longer than endopod. Fourth pleopod much stouter than others and elongated, 1.83–2.43 (mean: 2.11) times as long as sixth abdominal somite, very unequally bilobed; sympod 0.36–0.52 times (mean: 0.44) as broad as width of cornea; endopod rudimentary, simple, unsegmented lobe; exopod strongly elongated, posterior end excluding terminal setae fully or overreaching statocyst area of uropodal endopod, normally two-segmented, but sometimes imperfect articulation is visible near basal part; distal segment very short, with basally stout, shorter and long slender terminal setae; in females, all pleopods unsegmented, increasing in length posteriorly.

Uropod ( Figure 5K ) with expod somewhat narrow, lateral margin slightly concave; endopod two-thirds or slightly more length of exopod, armed laterally with several widely spaced spines.

Colour

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

Body size

Maximum male 8.0 mm, maximum female 8.6 mm ( Malaysia), and smallest ovigerous female 5.2 mm (brackish aquaculture pond on Panay Island, Philippines) and 5.6 mm (mangrove estuary in Malaysia; see also Hanamura et al. 2008, as M. orientalis ). As in M. orientalis , the size at maturation may vary depending on locality/habitats.

Etymology

The species name ‘‘ tenuipes ’’ refers to a long fourth male pleopod, slenderer than in its congener M. orientalis : it is an adjective that agrees with the feminine gender of the genus.

Remarks

Mesopodopsis tenuipes sp. nov. closely resembles M. orientalis so that both species were previously treated as a single species. At first glance, the new species differs from M. orientalis , which has a longer fourth male pleopod than the latter. The length ratio (length of fourth pleopod vs length of sixth abdominal somite; mean ¡SD, 2.11¡0.021) was significantly greater than that of M. orientalis (1.79¡0.014) (t 516.01, p,0.05; n 5174), although the length appeared to vary slightly from one population to another (see Figure 7 ). In addition, differences were also noticed in the following particulars: (1) the cornea of M. tenuipes (mean width of cornea versus width of stalk ¡SD, 1.26¡0.005) is significantly broader than that of M. orientalis (1.09¡0.003) (t 523.62, p,0.05; n 5320); (2) the antennal peduncle is proportionately short in male M. tenuipes , barely reaching the anterior end of the second segment of the antennular peduncle (extending well beyond that margin in M. orientalis ), while, in the female, it falls far short of that margin (barely reaching it in M. orientalis ); (3) the fourth male pleopod of M. tenuipes (width of sympod versus width of cornea, 0.44¡0.019) is much narrower than that of M. orientalis (0.59¡0.026) (t 523.15, p,0.05; n 5120). The major features distinguishing the two species are summarized in Table 3.

The DNA sequence data supported the findings in morphology, and the populations with a long and slender fourth male pleopod attributable to M. tenuipes were determined to be genetically isolated from those with a short and stout fourth male pleopod, which were assigned to M. orientalis (see ‘‘Results of DNA analysis’’).

The specimens from the aquaculture ponds in Singapore and Panay Island in the Philippines appeared to have a smaller body and, inversely, a proportionately longer pleopod in males than those from open waters (cf. Figures 5A ; 7D ). There is a slight possibility that environmental conditions, such as food availability, contribute to the maturation size and some morphological characteristics.

Mesopodopsis orientalis studied by Hanamura et al. (2008) for the life history traits in the Merbok mangrove estuary, Malaysia, was referred to this new species.

Distribution

Known with reasonable certainty from the west coast of Peninsular Malaysia, Gulf of Thailand, southern Vietnam, and Philippines ( Figure 9 ). The presence of M. tenuipes in India is not clear. However, from a general distribution pattern of other

estuarine crustaceans in the region, it is highly probable that this species is present there.

Habitat

This species primarily occurs in inner waters of the estuarine system as compared with M. orientalis . In the Merbok River, Malaysia, M. tenuipes was normally found in the middle to upper reaches (e.g. Sts B and C in Hanamura et al. 2008, as M. orientalis ) and very occasionally in the river mouth (St. A), where M. orientalis is usually found. A small number of individuals of M. tenuipes were rarely encountered in mangrove-related coastal waters. This species has a wide range of salinity tolerance, i.e. from 8 to 32 in the collected specimens. The majority of samples treated herein were obtained from the surface layer close to the riverbank or land (see also Hanamura et al. 2008).

Figures

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 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 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.