Perionyx violaceus Horst, 1893

Shen, Huei-Ping & Yeo, Darren C. J., 2005, Terrestrial Earthworms (Oligochaeta) From Singapore, Raffles Bulletin of Zoology 53 (1), pp. 13-33 : 25

Perionyx violaceus Horst, 1893

Perionyx violaceus Horst, 1893b: 72 ; Michaelsen, 1900: 209; 1922: 22; 1923: 1; 1928: 10; 1932: 602; Stephenson, 1930: 3; 1931: 262; 1932: 51; Gates, 1935: 89; 1937: 197.

Material examined. – 1 mature (clitellate), amputated specimen (dissected)( ZRC), Hindehe Drive, Bukit Timah, coll. H. K. Lua, 19 Mar.1989 ; 1 mature specimen ( ZRC), Rifle Range Rd. opposite to Murnane Reservoir, coll. K. K. P. Lim, D. C. J. Yeo & K. L. Yeo, 5 Mar.2003 .

Description. – Length (amputated) 19+ mm. Segments numbering 33+. Prostomium epilobous. First dorsal pore 5/ 6. Setal number 44 in VII, 50 in XX. Clitellum XIII-XVII, 2.9 mm in length, 3.04 mm in width, setal ring present on each segment. Spermathecal pores two pairs in 7/8-8/9, medio-ventral. Female pore single, medio-ventral in XIV.

Male pores closely paired in medio-ventral XVIII, on round protuberances within a transversely depressed area with distinct anterior and posterior margins but indistinct lateral margins. Penial setae absent. Genital papillae absent in both preclitellar and postclitellar regions. Preserved specimens with purplish red dorsum, much lighter ventrum, and yellowish clitellum.

No septa specially thick. Gizzard invisible. Intestine enlarged from XV. Caeca absent. Last hearts in XII. Spermathecae two pairs in VIII and IX, large. Ampulla oval, 0.9-1.0 mm long, 0.75 mm wide, duct short and stout; two small, sessile lobes about 0.2 mm in diameter at the junction of the first ampulla and its duct, several tiny protuberances at the junction of the second ampulla and its duct. Diverticulum absent. Holandry: testis sacs in X and XI. Seminal vesicles in XI and XII, large, second seminal vesicle on the left occupying segments XII-XIV. Prostate glands confined to XVIII, compact. Prostatic ducts short and stout. Accessory glands absent.

Remarks. – According to Gates (1937), Perionyx excavatus Perrier, 1872 and P. violaceus were considered to be different species, owing to the presence or absence of diverticulum and penial setae. However, in the key to Perionyx species provided by Horst (1893b), neither one of the two species had penial setae; the only difference between them was that P. excavatus had no diverticulum while P. violaceus had small, stalked diverticula. According to Beddard (1892b), the group of setae of each male pore of P. excavatus might withdraw from the exterior of the body. This phenomenon might explain Horst’s (1893b) observation, and while this happens, there is hardly any difference in the external appearance between P. excavatus and P. violaceus .

In Michaelsen’s (1900) description, four to six setae were present between male pores for P. excavatus . Michaelsen (1900) also provided a key for the Perionyx species in which P. excavatus had very small diverticula while P. violaceus had round or club-shaped diverticula and had no penial setae. Michaelsen (1909: 176) noted that the appearance of diverticulum was very different in different states of spermathecae, and characteristic penial setae was a principal diagnostic feature for distinguishing species. However, Gates (1972: 140) stated that penial setae, to which so much systematic importance was attributed in the past, seemed to be of much less significance in Perionyx as well as in certain other genera.

According to Horst (1893b), P. violaceus was very common in Java and Sumatra. It was also found in Borneo ( Michaelsen, 1928, 1932) and Pulau Berhala, Straits of Malacca ( Stephenson, 1930). Gates (1935, 1937) described the P. violaceus specimens from Malay Peninsula and Bukit Timah, Singapore as having diverticula. However, the Perionyx specimen collected from Bukit Timah in 1989 had no diverticulum but only two small, sessile lobes at the junction of the first ampulla and its duct. Therefore, we agree with Michaelsen (1909) on the importance of penial setae for species identification.