Research Article |
Corresponding author: Rofiza Yolanda ( padangers@gmail.com ) Academic editor: Sammy De Grave
© 2019 Rofiza Yolanda, Shozo Sawamoto, Vachira Lheknim.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Yolanda R, Sawamoto S, Lheknim V (2019) A new species in the genus Heteromysoides (Crustacea, Mysida, Mysidae) from Songkhla Lagoon, southern Thailand. Zoosystematics and Evolution 95(2): 535-542. https://doi.org/10.3897/zse.95.39214
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A new mysid, Heteromysoides songkhlaensis, is reported from shallow water in the Songkhla Lagoon, southern Thailand. The new species is closely similar to H. nana in having a triangular rostrum and the eyestalk without a process at the anteromesial corner. However, the new species can be readily distinguished from H. nana by three setae on the inner margin and five setae on distal margin of the second segment of the mandibular palp; the carpopropodus of the fifth and sixth thoracic endopod of the new species is composed of four articles, and the telson of the new species is distally rounded, shorter than the sixth abdominal somite, and 1.3 times longer than its basal width; the spines on the telson form elongated spines from the distal to posterior margin. The new species also resembles H. dennisi, H. simplex, and H. stenoura; however, it differs by (1) the presence of a rounded distal margin of telson, and (2) absence of a sharp process on the distolateral corner of the eyestalk.
Brackish water, Heteromysoides songkhlaensis, Thale Sap, Thale Sap Songkhla
In Southeast Asia, about 210 species in the order Mysida (Crustacea) have been reported (
During a study of variability of the recruitment abundance of Metapenaeus spp. in the hyperbenthos of Thale Sap and Thale Sap Songkhla in the Songkhla Lagoon system in 2018, several mysid specimens were collected. Among them, an undescribed species was discovered. The species showed morphological characteristics of the genus Heteromysoides Băcescu, 1968: (1) the cornea of the eye, which is restricted to the anterolateral part of the eyestalk, is reduced in size, and (2) the pleopods are not sexually dimorphic. The known species of the genus primarily occupy shallow marine waters, including marine caves, in the tropical and subtropical regions of the world.
To date, 10 species have been reported in the genus Heteromysoides: H. berberae Băcescu & Müller, 1985 from Somalia, east Africa; H. cotti Calman, 1932 from the Canary Islands; H. dennisi Bowman, 1985 from the Caribbean Sea; H. longiseta Băcescu, 1983 from Heron Island, eastern Australia; H. macrops Murano, 1988 from northern Australia; H. nana Murano, 1998 from Channel Island, Northern Territory, Australia; H. sahulensis Murano, 1998 from the Sahul Shelf, Australia; H. simplex Hanamura & Kase, 2001 from Okinawa, Japan; H. spongicola Băcescu, 1968 from Cuba and Grand Cayman; and H. stenoura Hanamura & Kase, 2004 from the Caribbean Sea.
In this paper, Heteromysoides songkhlaensis is newly described based on specimens collected in the Songkhla Lagoon system. This, the fourth mysid species known to occur in the Songkhla Lagoon and also the 49th in Thailand, is newly added to the Southeast Asian mysid fauna.
The Songkhla Lagoon system, also known as Songkhla Lake, is a large, shallow body of water located on the east coast of the Thai Peninsula in southern Thailand situated between 7°08'N and 7°48'N and between 100°07'E and 100°35'E. The lagoon system covers approximately 1,082 km2 and comprises four distinct bodies of water: Thale Noi, Thale Luang, Thale Sap, and Thale Sap Songkhla (Fig.
The map of the Songkhla Lagoon system, southern Thailand, shows seven sampling stations (black dot) where Heteromysoides songkhlaensis sp. nov. was collected. St. 1. Ban Bang Khiat; St. 2. Ban Koh Nang Kum; St. 3. Ban Laem Chak; St. 4. Ban Tai; St. 5. Ban Pa Khad; St. 6. Ban Bo Pab; St. 7. Ban Hua Khao.
Specimens were collected by using a modified Riley’s hand-pushed net. Its mouth frame was 30 × 50 cm (height × width), the mesh sizes were 2 mm and 0.5 mm, and its side length 2.5 m. The net was pushed forward for 30 m along the shallow zone of Songkhla Lagoon at seven stations (Fig.
Using a micrometer installed in the eyepiece of the microscope, body length (BL) was measured from the tip of the rostrum to the distal end of the telson, excluding apical denticles. Illustrations were made with the aid of a camera lucida. The marginal setae of some appendages, especially the antennal scale, thoracopodal exopods, and uropod, were omitted from the illustrations. Terminology was based mainly on
Holotype. Adult male (BL 3.2 mm) (NMST-Cr 26744), Thale Sap, 7°20'58.68"N, 100°25'31.56"E, Ban Bang Khiat, Tambon Bang Khiat, Singha-Nakhon District, Songkhla Province, Thailand, 19 January 2019, at 1.3 m of depth with salinity of 0.39 psu, over a muddy substrate, coll. V. Lheknim, N. Tubtimtong and R. Yolanda.
Allotype.
Adult female with empty marsupium (BL 3.7 mm) (
Paratypes.
1 adult male (BL 3.6 mm, dissected) (
Head and cephalic appendages.
Carapace with anterior margin obtusely produced into wide, triangular rostrum (Fig.
Heteromysoides songkhlaensis sp. nov. Holotype, male (BL 3.2 mm, A, C, E, F, G, I) (
Thoracopods.
Flagelliform part of first and eighth thoracopodal exopods composed of 8 segments (Figs
Heteromysoides songkhlaensis sp. nov. Paratype, male (BL 3.6 mm, A–I) (
Pleon and pleopods.
Abdominal somites smooth, without hairs, spines or folds, ventral sternites without process, anterior 5 somites subequal in length, sixth somite 1.3 times as long as preceding somite (Fig.
Uropod and telson.
Uropodal endopod slightly shorter than exopod, without spine on ventral side of statocyst region (Fig.
Heteromysoides songkhlaensis sp. nov. Holotype, male (BL 3.2 mm, D–H, K), (
Body length and the number of spines on the telson of Heteromysoides songkhlaensis sp. nov. from Songkhla lagoon, southern Thailand.
No. | Type of specimen | Sex | Body length (mm) | Number of spines |
---|---|---|---|---|
1 | Holotype | Male | 3.2 | 15 |
2 | Paratype | Male | 3.4 | 12 |
3 | Paratype | Male | 3.5 | 13 |
4 | Paratype | Male | 3.6 | 14 |
5 | Paratype | Male | 3.6 | 11 |
6 | Paratype | Male | 4.0 | 18 |
Range | 3.2–4.0 | 11–18 | ||
7 | Allotype | Female | 3.7 | 15 |
8 | Paratype | Female | 3.1 | 12 |
9 | Paratype | Female | 3.2 | 17 |
10 | Paratype | Female | 3.6 | 19 |
11 | Paratype | Female | 3.6 | 17 |
12 | Paratype | Female | 3.7 | 16 |
Range | 3.1–3.7 | 12–19 |
This species is named after the locality, Songkhla Lagoon, where of the specimens were found.
This species was captured in brackish waters above a muddy substratum at Thale Sap and Thale Sap Songkhla, Songkhla Lagoon, southern Thailand.
Heteromysoides songkhlaensis is closely similar to H. nana in (1) having a triangular rostrum of the carapace, and (2) lacking a process at the anteromesial of the eyestalk. However, the new species can be distinguished from H. nana by several features: (1) the mandibular palp displays three setae on the inner margin and five setae at the distal margin of the second segment as opposed to two setae on the inner margin and three setae at the distal margin of the second segment in H. nana; (2) the carpopropodi of the fifth and sixth thoracic endopods of the new species is composed of four articles compared to five articles in H. nana; (3) the telson of the new species is distally rounded, shorter than the sixth abdominal somite, and 1.3 times longer than its basal width, while in H. nana the telson is slightly concave, longer than the sixth abdominal somite, and 1.6 times longer than its basal width; and (4) the spines on the telson are noticeably different in their arrangement from those of H. nana.
The new species also exhibits similarities to several other Heteromysoides species, e.g. H. dennisi, H. simplex, and H. stenoura, in having (1) the telson without a cleft or sinus at its distal end, and (2) the uropodal endopod without a spine on the inner mesial margin. However, the new species differs from them in having (1) the eyestalk without a sharp process at the disto-lateral part, and (2) the telson rounded, not truncated, at the distal margin.
Several species from the family Mysidae in Southeast Asia have been found from brackish to full-strength seawater, e.g. Mesopodopsis orientalis (e.g.,
The present study is part of a research project on “Distribution patterns and variability in abundance of post larvae and juvenile of Metapenaeus spp. for fishery status and management guidelines in Thale Sap Songkhla, southern Thailand” which is supported by a grant (SCI 6003643) from Prince of Songkhla University. The first author expresses his deep gratitude to the Graduate School, Prince of Songkla University for the scholarship award on Thailand’s Education Hub for ASEAN Countries (TEH-AC) (contract no. TEH-AC 042/2017) and for financial support of this research. We also thank Mr Naratip Tubtimtong for the fieldwork and Mr Sompong Pachonchit for driving us during this study. Finally, we thank an anonymous reviewer and Dr Yukio Hanamura for their useful comments which improved the manuscript.