A new earthworm of the genus pheretima (oligochaeta: megascolecidae) from the mekong delta of vietnam and taxonomical position of pheretima polychaetifera Thai, 1984

JOURNAL OF SCIENCE OF HNUE Natural Sci., 2011, Vol. 56, No. 7, pp. 152-159 A NEW EARTHWORM OF THE GENUS PHERETIMA (OLIGOCHAETA: MEGASCOLECIDAE) FROM THE MEKONG DELTA OF VIETNAM AND TAXONOMICAL POSITION OF PHERETIMA POLYCHAETIFERA THAI, 1984 Nguyen Thanh Tung Can Tho University E-mail: thanhtung@ctu.edu.vn Abstract. This paper describes a new species of earthworm (Pheretima paraalexandri sp.n.) which was found in the Mekong Delta, Vietnam. In addition, this paper also discusses the taxonomical position of Pheretima polychaetifera Thai, 1984. Pheretima paraalexandri Nguyen, sp.n. is the largest sized worm in the Mekong Delta. Firstly, dorsal pore in 12/13 or 13/14. Spermathecal pores four pairs in 5/6 - 8/9. Genital papillae present, paired in XIX. Genital papillae four pairs in VI - IX or less than. Behind genital papillae there is a setal zone (only present in XIX or both XIX and XX). Septa 5/6 - 7/8 and 10/11 - 12/13 thickened, 8/9 and 9/10 absent. Intestinal caeca, simple, in XXVII. Pheretima polychaetifera Thai, 1984 is a synonym of Pheretima alexandri (Beddard, 1901). Keywords: Pheretima paraalexandri sp. n., Pheretima polychaetifera Thai, 1984, new species, taxonomical position. 1. Introduction The earthworm fauna of the Mekong Delta has been researched extensively since 2007 [3]. We have collected many specimens of different species from various localities and have found a species of earthworms which are the largest size in this region. This species has morphologic characteristics similar to Pheretima alexan- dri (Beddard, 1901) but it also has some distinct taxonomic characteristics which are very stable for this species. Therefore, we believe that a new species close to Pheretima alexandri (Beddard, 1901). Taxonomic characteristics and some remarks of the new species will be presented in this paper. 2. Content 2.1. Study sites, materials and methods * Study sites and materials 152 A new earthworm of the genus Pheretima (Oligochaeta: Megascolecidae)... Figure 1. Collection sites of the new earthworm Specimens of the new species were col- lected from various localities in the Mekong Delta, Vietnam (see Figure 1). Holotype and Paratypes are deposited at the Zoology Labora- tory, Biology Department, Can Tho University. Holotype: Mature (clitellate) specimen, Cho Lach - Ben Tre (10◦1306.7 N; 106◦1014.6 E), on December 3rd 2007, Nguyen Thanh Tung, no. EWh001. Paratypes (all mature specimens): Two specimens, data as for holotype, no. EWp002 - EWp003; Four specimens, Vung Liem - Vinh Long (10◦0542.5 N; 106◦0328.2 E), on October 30th 2008, Nguyen Thi Nhi, no. EWp004 - EWp007; Nine specimens, Cai Be - Tien Giang (10◦1707.4 N; 105◦5331.2 E), on August 15th 2007, Nguyen Thanh Tung, no. EWp008 - EWp016. * Methods The earthworms were anesthetized in a 4% formalin solution. Details of the taxonomic characters required for classification of these species are available from sources such as Thai [9, 10], Gates [1], etc. According to the classification system of Sims and Easton [6], the new species is classified in the genus Amynthas. But there are some questionable problems in this classification system [7]. Now, some authors do not use it [2, 4, 9, 10]. Therefore, we still use the classification system of Kinberg, 1867. The new species is belonging to the genus Pheretima. In addition, when synthetizing materials related to the new species, we dis- covered that Pheretima polychaetifera Thai, 1984 has many characteristics similar to Pheretima alexandri (Beddard, 1901). We believe that Pheretima polychaetifera Thai, 1984 is a synonym of Pheretima alexandri (Beddard, 1901). 2.2. Results and discussion Pheretima paraalexandri Nguyen, sp. n. (Figure 2) 2.2.1. Description * External characters Length 164 - 248 mm, weight 6.0 - 12.1 g, diameter 6.41 - 7.93 mm, segment number 105 - 138; large - size; color: grey - brown with dorsal, light white with ven- tral and bluish mid-dorsal when they are alive, clitellum buff; prostomium epilobous (2/3); first dorsal pore in 12/13 or 13/14; setae 49 - 60 in VIII, 71 - 86 in XXX, between male pore 7 - 12, sometimes absent, aa ≥ 1.2 ab, zz ≥ 1.4 zy; clitellum XIV - 3 4 XVI or XVI, smooth, length 5.75 - 8.00 mm, diameter 5.02 - 6.50 mm, setae and dorsal pores absent. 153 Nguyen Thanh Tung Spermathecal pores four pairs in 5/6 - 8/9, ventrolaterally, distance between paired spermathecal pores about 0.28 body circumference ventrally. Genital papillae four pairs in VI - IX or less than. Each papilla large, round, disk-like; distance be- tween paired genital papilliae about 0.30 - 0.35 body circumference ventrally. Some- times only 1 papilla present on some segments. Female pore is single, medioventrally in XIV. Male pores paired in XVIII, lateroventrally, distance between pores about 0.30 body circumference ventrally. Porophores round or oval on setal line, with a concave centre surrounded by 2 or 3 circular folds. Genital papillae present, paired in XIX. Behind genital papillae have setal zone (only present in XIX or both XIX and XX). * Internal characters Figure 2. Pheretima paraalexandri Nguyen, sp. n. A: Male pore area (mp: male pore, gm: genital papillae, sz: setal zone); B: Spermathecae (amp: ampulla, dv: diverticulum, ag: accessory glands); C: Prostate gland; D: Slide across on male pore area (mp: male pore); E: Slide across on longitudinal muscle of parietes; F: Ventral view of spermathecal pore area (gp: genital papillae); G: Mature individual; H: Pheretima paraalexandri cast. Septa 5/6 - 7/8 and 10/11 - 12/13 thickened, 8/9 and 9/10 absent. Gizzard 154 A new earthworm of the genus Pheretima (Oligochaeta: Megascolecidae)... round, large, in VIII - X. Intestine enlarged from XV or XVI. Intestinal caeca paired in XXVII, simple, margins with slight septal constrictions, grey-coloured, extending to XXIII or XXI. End lateral hearts in XIII. Pharyngeal micronephridia in 4/5 and more than in 5/6. Lymph glands start in XVI. Spermathecae four pairs in 5/6/7/8/9. Ampulla oval, large, yellowish. Diver- ticulum from anterior face of duct in parietes, longer than ampulla, variously looped wider portions internally. Accessory gland four pairs in VI - IX, round. Typhlosole, simply lamelliform, T% = 0.22 ± 0.03. Testes sacs paired in X and XI, large, separated, ventral, yellowish. Seminal vesicles paired in XI and XII, large, white. Ovaries paired in 12/13, ovisacs in 12/13 and 13/14. Prostate glands paired in XVIII, large, lobed, quite smooth, extending anteriorly to XVI and posteriorly to XXI or XXII with duct of prostatic U-shaped. Accessory glands fungi-shape. 2.2.2. Localities and habitats Most of Pheretima paraalexandri were collected in perennial gardens, some of them were collected near river banks. They often concentrate in places where humidity are high and live in the 1st layer (0 - 10 cm). Pheretima paraalexandri was found in various localities of the Mekong Delta such as Long An, Ben Tre, Vinh Long, Tien Giang, Hau Giang, Ca Mau, Adult specimens were not found at the end of the dry season and the beginning of the rainy season. Percent of Pheretima paraalexandri in different age classes in various localities of the Mekong delta from August to February which were shown in Figure 3. Figure 3. Percent of Pheretima paraalexandri in different age classes in the Mekong Delta from August to February 2.2.3. Remarks New species have many morphologic characters similar to Pheretima alexan- dri (Beddard, 1901) and Pheretima polychaetifera Thai, 1984 such as spermathecal pores four pairs in 5/6 - 8/9, first dorsal pore (12/13), shape of male pores paired 155 Nguyen Thanh Tung in XVIII, situation of septa (8/9 and 9/10 absent, 5/6 - 7/8 and 10/11 - 12/13 thickened), end lateral hearts in XIII, holandric, intestinal caeca paired in XXVII and simple, typhlosole simply lamelliform, etc. However, some taxonomic charac- ters of new species differ from Pheretima alexandri (Beddard, 1901) and Pheretima polychaetifera Thai, 1984 (see Table 1). Variation of setal zone behind genital papillae: among 155 individuals which were analyzed, only 59 individuals (38%) have setal zone in XIX and 96 individuals (62%) have this setal zone persent both in XIX and XX. Especially, 97% of sub- adult individuals have setal zone in XX but only remain 38% in juvenile and adult individuals which shows that the setal zone in XX may be absent when they mature. Variation of genital papillae in male pore and spermathecal pore area was analyzed in 108 adult and juvenile individuals. Results showed that genital papillae in male pore area is stable, almost all individuals have two papillae in XIX, only 5 individuals absent a papilla of right or left side of XIX. Conversely, genital papillae in spermathecal pore area has more complex changes. Figure 4 shows many types and the appearing percentage of each of genital papillae in spermathecal pore area of Pheretima paraalexandri. Table 1. Morphological differences between Pheretima paraalexandri and Pheretima alexandri (Beddard, 1901) and Pheretima polychaetifera Thai, 1984 Characters Ph. Pheretima Ph. paraalexandri Alexandri polychaetifera Source Above description Gates, 1972 Thai, 1984 Length 164 - 248 mm 105 - 290 mm 110 - 150 mm Diameter 6.41 - 7.93 mm 4 - 9 mm 6 - 9 mm Weight 6.0 - 12.1 g - 2.8 - 5.6 g Segment number 105 - 138 90 - 141 128 - 175 Setae between male pore 8 - 11 9 - 28 0 Setal zone on male pore area Present, in XIX or XIX and XX Absent Present, XIX and XX Ratio of setal distance aa ≥ 1.2 ab, - aa = ab between aa and ab, zz and zy zz ≥ 1.4 zy - zz = zy Prostomium Epi (2/3) Rudimentary Epi Genital papillae + Spermathecal pore area 4 pairs or 3 pairs Absent Absent + Male pore area 1 pairs in XIX Absent Absent Pharyngeal micronephridia In 4/5 and 5/6 - In 5/6 and 6/7 Diverticulum and ampulla Longer than ampulla Longer than main axis - Testes sacs Unpaired Paired or unpaired - 156 A new earthworm of the genus Pheretima (Oligochaeta: Megascolecidae)... Figure 4. Many types and the percentage of each type appearance of genital papillae in spermathecal pore area of Pheretima paraalexandri Nguyen, sp.n. Pheretima Polychaetifera Thai, 1984 as a synonym of Pheretima alexandri (Beddard, 1901) In 1984, Thai Tran Bai published a new species to science among specimens collected in Long An Province. This new species has setal zone behind male pore areas, which is a very specific characteristic. Therefore, he called it Pheretima poly- chaetifera. When comparing this species with some different species which have similar setal zones, we believe that Pheretima polychaetifera Thai, 1984 is a syn- onym of Pheretima alexandri (Beddard, 1901). Table 2 shows the similarity between Pheretima polychaetifera and its synonyms. Table 2. Comparison of characteristics between Pheretima Polychaetifera Thai, 1984 and its synonyms Characters Ph. alexandri Ph. suctoria Ph. lignicola Ph. polychaetifera Length 113 - 165 mm 75 - 135 mm 105 - 165 mm 110 - 150 mm Diameter 4.8 - 5 mm 4 - 7 mm 4 - 6.5 mm 6 - 9 mm Segment number 78 - 126 103 - 123 90 - 130 128 - 175 Setae - XXX/VIII > 1 > 1 > 1 > 1 - Between male pores 18 4 - 8 12 0 - Setal zone behind male pore area Absent Present Present, Present, - XVII - XIX XIX - XX - aa & ab; zz & zy - aa = ab; zz = zy aa = ab; zz = zy aa = ab; zz = zy Prostomium Rudimentary Epi Epi, almost tany Epi, open Genital markings Absent Absent Absent Absent Spermathecal pores 4 pairs, 4 pairs, 4 pairs, 4 pairs, 5/6 - 8/9 5/6 - 8/9 5/6 - 8/9 5/6 - 8/9 Fist dorsal pore 12/13 12/13 12/13 12/13 157 Nguyen Thanh Tung Male pores in XVIII In rather circular area On small papillae In large depressions In slightly depressions 8/9/10 aborted; 8/9/10 aborted; 8/9/10 aborted; 8/9/10 aborted; Septa 6/7/8; 10/11/12 6/7/8; 10/11/12 6/7/8; 10/11/12 6/7/8; 10/11/12 thickened thickened thickened thickened Diverticulum From median face of duct at parietes, shorter than ampulla From median face of duct at parietes, shorter than ampulla From origin of duct at parietes, shorter than ampulla - Gizard VIII - IX - VIII - End heart XIII - - XIII Testes sacs Holandric, unpaired or paired Holandric, - Holandric, unpaired -, unpaired Seminal vesicles Large, Large, In XI and XII - in XI & XII in XI &XII Intestine origin XV or XVI - XIV or XVI XV Intestinal caeca Simple, Simple, Simple, Simple, in XXVII in XXVI in XXVI or XXVII in XXVII Typhlosole Simply lamelliform - - Simply lamelliform Source Somniyam, 2008 Stephenson, 1923 Stephenson, 1923 Thai, 1984 * According to Gates, 1972 Pheretima lignicola Stephenson, 1914 and Pheretima suctoria Stephenson, 1923 were synonyms of Pheretima alexandri (Beddard, 1901) According to the descriptions of Gates for specimens collected in Myanmar, Kosavititkul and Somniyam for specimens collected in Thailand, Pheretima alexan- dri did not have setal zones behind male pores area [1, 3, 4, 7]. But the description of Setephenson for specimens collected in India and England, setal zones present in or behind male pores area [8]. In addition, Gates believed that Pheretima ligni- cola Stephenson, 1914 and Pheretima suctoria Stephenson, 1923 were synonyms of Pheretima alexandri (Beddard, 1901), both these species also had setal zone in male pores area [1]. That shows setal zone is an unstable characteristic and can not use it as a special characteristic for Pheretima polychaetifera. Therefore, we believe that Pheretima polychaetifera Thai, 1984 is a synonym of Pheretima alexandri (Beddard, 1901). 3. Conclusion Pheretima paraalexandri Nguyen, sp. n., which a new species of earthworms, have many characteristics closing to ones of Pheretima alexandri (Beddard, 1901). Pheretima polychaetifera Thai, 1984 is the synonym of Pheretima alexandri (Beddard, 1901). 158 A new earthworm of the genus Pheretima (Oligochaeta: Megascolecidae)... REFERENCES [1] Gates, G. E., 1972. 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