Amynthas morrisi (Beddard, 1892)

Shen, Huei-Ping & Yeo, Darren C. J., 2005, Terrestrial Earthworms (Oligochaeta) From Singapore, Raffles Bulletin of Zoology 53 (1), pp. 13-33 : 24

Amynthas morrisi (Beddard, 1892)

Perichaeta morrisi Beddard, 1892a: 166 ; Rosa, 1896a: 516. Perichaeta barbadensis Beddard, 1892a: 167 (part). Perichaeta pallida Michselsen, 1892: 227 (part). Perichaeta amazonica Rosa, 1894: 14 . Perichaeta insulae Beddard, 1896: 204 . Perichaeta cupulifera Fedarb, 1898: 445 . Amyntas hawayanus – Beddard, 1900a: 645 (part). Pheretima morrisi – Michaelsen, 1900: 287; Ude, 1905: 434; Chen,

1931: 148; 1933: 267; Gates, 1936b: 437; 1968: 253; 1972: 202. Pheretima hawayana (Rosa) subsp. barbadensis (Beddard) –

Michaelsen, 1909: 187; Ude, 1932: 155. Pheretima hawayana var. lineata Gates, 1926a: 154 ; 1931: 385;

1932: 434. Pheretima hawayana – Stephenson, 1932: 45; Gates, 1933: 529;

1935: 92. Amynthas morrisi – Sims & Easton, 1972: 236; Easton, 1981:55;

1982: 729.

Material examined. – 9 mature (clitellate) and 3 immature (aclitellate) specimens ( ZRC), Rifle Range Rd. opposite to Murnane Reservoir, 5 Mar.2003 ; 1 mature (dissected) and 1 immature specimens ( ZRC), Kent Ridge Campus of National University of Singapore, 6 Mar.2003 ; 3 mature and 2 immature specimens ( ZRC), Sungei Buloh , 7 Mar.2003 ; 1 mature specimen ( ZRC), Turut Track , Kranji Wireless Station, 7 Mar.2003 ; 7 mature (1 dissected) and 2 immature specimens ( ZRC), Rifle Range Rd. opposite to Murnane Reservoir, 25 Jun.2003 . All the above specimens were collected by K. K. P. Lim, D. C. J. Yeo & K. L. Yeo.

Description. – Length 77-100 mm, weight 0.61-0.87 g. Segments numbering 74-95. Prostomium epilobous. First dorsal pore 10/11. Setae small, number 47-52 in VII, 45-59 in XX, 8-15 between male pores in XVIII. Clitellum XIV-XVI, 2.86-3.6 mm in length, 2.79-3.83 mm in width, anterior edge of XIV and posterior edge of XVI slightly coloured, not glandular, dorsal pores absent, 8-19 setae on ventral XVI. Spermathecal pores two pairs in 5/6/7, ventro-lateral, distance between paired pores 0.32-0.34 body circumferences ventrally apart. One or two papillae ventro-medial to each spermathecal pore at the anterior edge of VII, often an additional presetal papilla on medio-ventrum of VII, an additional presetal papilla on medio-ventrum of VIII for one mature specimen. Each papilla round, about 0.35 mm in diameter, with a conspicuous dark centre. Female pore single, medio-ventral in XIV. Male pores paired in XVIII, about 0.36 body circumferences ventrally apart, each on a small, papilla-like protuberance which often the fusion of two. Two round genital papillae immediately medial to each male pore, one presetal and the other postsetal; the above papillae within porophore surrounded by five or six circular ridges. The whole male area sometimes slightly elevated. Often one to three presetal papillae on medio-ventrum of XVIII or additional papillae above and/or below male porophore adjacent to 17/18 or 18/ 19 segmental furrow. Each papilla round, centre concave, about 0.3 mm in diameter. Preserved specimens with dark grey dorsum, greyish ventrum and dark brown clitellum.

Septa 5/6-7/8 and 10/11-13/14 thickened, 8/9 and 9/10 absent. Gizzard in IX-X, large, round, yellowish white. Intestine enlarged from XIV or XV. Intestinal caeca paired in XXVII, each simple, short, extending anteriorly to XXV, with a white distal end. Esophageal hearts XI-XIII. Meronephridia bush-like mass in intersegmental spaces anterior to 6/7. Spermathecae two pairs in VI and VII, ampulla round, 0.97- 1.4 mm long, 1.04-1.52 mm wide, with a long, slender stalk of 1.26-1.35 mm in length. Diverticulum vestigial or normally developed, stalk slender, straight or slightly bent, 0.88-2.09 mm long, seminal chamber absent, or in the form of an elongated end about 0.8 mm in length, or a normal ovalshaped seminal chamber of 0.25-0.52 mm in length. Accessory glands sessile, white, each in the form of an irregular tissue-like mass, 0.8-0.9 mm long, 0.55 mm wide. Holandry: testis sacs paired in X and XI, round, smooth, yellowish. Seminal vesicles paired in XI and XII, large, follicular, yellowish. Prostate glands paired in XVIII, racemose, follicular, extending posteriorly to XX or XXI. Prostatic ducts large at the middle, narrow and coiled at distal end. Accessory glands small, stalked or sessile, whitish and irregularly shaped.

Remarks. – Amynthas morrisi is a holandric and quadrithecal earthworm belonging to the morrisi species-group of the genus Amynthas (sensu Sims & Easton, 1972) . It is a peregrine species and has often been considered conspecific to or a subspecies or variety of A. gracilis (see Beddard, 1900a; Michaelsen, 1909; Stephenson, 1912, 1932; Gates, 1926a, 1931, 1932, 1933). However, the two species are easily distinguishable by the number and position of spermathecae and genital papillae. Amynthas morrisi is quadrithecal with spermathecae paired in VI and VII, whereas A. gracilis is sexthecal with spermathecae paired in VI, VII and VIII. In addition, A. morrisi has one presetal and one postsetal papillae immediately medial to each male pore in the male porophore and presetal papillae in VII, whereas A. gracilis has a simple male pore with postsetal papillae in oblique row outside the male porophore and small postsetal papillae absent or present in VII. Ude (1905) and Chen (1931, 1933) have also made detailed comparisons between the two species.

All specimens of A. morrisi examined from Singapore exhibit the typical papilla arrangements in segment VII and within the male porophore except one mature worm collected from the NUS campus (6 March 2003), which has only two small sunken papillae in the male porophore. In the Oligochaeta collection of the Raffles Museum, specimens of ZRC 1974.11.25.20 and ZRC 1974.11.25.21 identified by Stephenson (1932) as P. hawayana are actually A. morrisi . This species is the most common pheretimoid earthworm in Singapore (see Table 2).