Amynthas cruxus Tsai and Shen, 2007

Tsai, Chu-Fa, Shen, Huei-Ping, Tsai, Su-Chen & Lee, Hsun-Huang, 2007, Four new species of terrestrial earthworms belonging to the genus Amynthas (Megascolecidae: Oligochaeta) from Taiwan with discussion on speculative synonyms and species delimitation in oligochaete taxonomy, Journal of Natural History 41 (5 - 8), pp. 357-379 : 368-374

Amynthas cruxus Tsai and Shen , sp. nov.

( Figure 4 )

Type material

Holotype: a clitellate (dissected) collected 24 October 2000 from Tengchih (elevation 1500 m), Taoyuan, Kaohsiung County by H. P. Yang, S. T. Chang, C. Y. Chang, and H.

P. Shen (coll. no. 2000-71-Shen). Paratype: an amputated clitellate (same collection data as holotype) .

Other material

Three clitellates and three aclitellates collected 25 October 2000 along Shihshan Forest Road in natural forest near the Middle Altitude Experimental Station , Taiwan Endemic Species Research Institute (elevation 1700 m), Kaohsiung County (coll. no. 2000-75- Shen); one clitellate and one aclitellate collected 26 October 2000 along a forest road in the Chuyunshan Nature Reserve (elevation 1200 m) in Kaohsiung County near the border with Taitung County (coll. no. 2000-80-Shen); six clitellates (one dissected) collected 26 October 2000 along a forest road in the Chuyunshan Nature Reserve (elevation 900 m) in Kaohsiung County near the border with Taitung County (coll. no. 2000-81-Shen). All collections were made by the same collectors of the holotype .

Diagnosis

Medium earthworm; length (clitellates) 100–170 mm, segments numbering 91–120. Setae 27–37 in VII, 39–52 in XX, 11–13 between male pores. Spermathecal pores four pairs in 5/ 6–8/9, about 0.31 body circumferences ventrally apart. No genital papillae in the preclitellar region. Male pores 0.24–0.26 body circumferences ventrally apart, each on a teat-like porophore on a flat, diamond-shaped male disc, on which four genital papillae are arranged in the form of a cross around the porophore, each papilla about 0.2 mm in diameter with a slightly depressed centre. The male disc is surrounded by three to four diamond-shaped skin folds. Spermathecae large, four pairs in VI–IX. Seminal vesicles and prostate glands large. Prostatic duct large, U-shaped, occupying three segments in XVI– XVIII. Amphimictic.

External characters

Total length (clitellates) 100–170 mm. Segments numbering 91–120. Prostomium epilobous. Number of incomplete secondary annulets two to three per segment in VII– XIII. Setal number 27–37 in VII, 39–52 in XX, 11–13 between male pores. First dorsal pore in 11/12. Clitellum XIV–XVI, setae and dorsal pores absent, 2.1–3.42 mm long, 3.32– 4.76 mm wide. Spermathecal pores four pairs in intersegmental furrows of 5/6–8/9, each lip-like ( Figure 4B ), distance between paired pores about 0.31 body circumferences ventrally apart. No genital papillae in the preclitellar region. Female pore single, medioventral in XIV.

Male pores paired in XVIII, 0.24–0.26 body circumferences ventrally apart, each on a teat-like porophore on a flat, diamond-shaped disc (male disc), on which four genital papillae are arranged in the form of a cross around the porophore: one anterior, one posterior, one lateral, and one medial ( Figure 4A ). This male disc is surrounded by three to four diamond-shaped skin folds. Each of the genital papillae about 0.2 mm in diameter, white in colour, with a slightly depressed centre. No other genital papillae in the postclitellar region.

Preserved specimens light greyish brown on dorsum, light grey on ventrum and brown around clitellum.

Internal characters

Septa 5/6–7/8 and 10/11–13/14 thick, 8/9/10 absent. Gizzard in IX–X, large, bell-shaped. Intestine starting enlarged in XV or XVI. Intestinal caeca paired in XXVII, each simple, stocky, extending anteriorly to XXIV or XXV. Oesophageal hearts in XI–XIII.

Spermathecae large in VI–IX ( Figure 4C ), ampulla oval- to pear-shaped, 1.9–2.57 mm long, 1.4–1.83 mm wide, with a slender to stout spermathecal stalk of 0.6–0.95 mm in length. Diverticulum with a round or oval, iridescent seminal chamber, 0.45–0.8 mm in length, and a slender stalk of 0.92–1.15 mm in length. Diverticulum stalk slightly longer than spermathecal stalk. No accessory glands in the preclitellar region.

Holandry: testis sacs paired in X and XI, round, shiny. Seminal vesicles paired in XI and XII, large, finely folliculated, each with a round or cone-shaped dorsal lobe ( Figure 4E ). Prostate glands paired in XVIII, lobed, wrinkled, occupying three to four segments in XVII–XX. Prostatic duct unusually large, U-shaped, occupying three segments in XVI– XVIII, proximal half slender and distal half enlarged ( Figure 4D ). No accessory glands in the postclitellar region.

Etymology

The name cruxus (5cross) is given to the new species with reference to the cross formation of the genital papillae around the male pore.

Remarks

Amynthas cruxus sp. nov. from Taiwan belongs to the diffringens (5 corticis ) species-group of the genus Amynthas ( Sims and Easton, 1972) . It is closely related to Amynthas pingi (Stephenson, 1925) of China ( Chen 1933) and Amynthas hatomajimensis ( Ohfuchi, 1957) of the Ryukyus. These three species share a unique character in having a slightly elevated, flat, and smooth or granular male disc, on which there is a teat-like male porophore associated with genital papillae in a well-arranged pattern, and then surrounded by a groove or by one to few circular skin folds (rings) ( Figures 4A , 5A ). This male disc in the three species is easily distinguishable from the male pore region of A. corticis ( Kinberg, 1867) , that has a teat- or small disc-like elevated porophore, on which the male aperture is present, but its associated genital papillae if present (one or two) are located in an irregular pattern (not consistent arrangement) on first and second skin folds surrounding the porophore (not directly on the disc-like porophore) ( Figure 5D–F ). This flat male disc was noted for hatomajimensis by Ohfuchi (1957, p 246, Text-figure 20), and also for pingi by Chen (1933, p 230, Figure 15B). Gates (1938) compared characters between diffringens and pingi , and considered them as closely related species, but did not note this character for specific distinction.

Amynthas cruxus is easily distinguishable from A. pingi and A. hatomajimensis by the character of the genital papillae, length of spermathecal stalks, and shape and structure of the prostatic duct (Table III). Amynthas cruxus has four genital papillae on the male disc in the form of a cross (one anterior, one posterior, one lateral, and one medial, the latter two on setal line), whereas hatomajimensis has three papillae (one anterior, one posterior, and one medial on setal line), and pingi has two (antro-medial and postro-medial). Also, cruxus has an unusually large, thick, muscular, U-shaped prostatic duct, covering three segments from XVI to XVIII ( Figure 4D ), differing significantly from hatomajimensis and pingi that have a short duct covering from the posterior half of XVII to anterior half of XVIII ( Chen 1933; Ohfuchi 1957). Amynthas cruxus and A. hatomajimensis have a spermathecal stalk of which the length is about a third of the ampullar length, whereas for pingi the stalk is as long as the ampullar length. In addition, accessory glands associated with the genital papillae are absent in cruxus , present near spermathecae in hatomajimensis , and often present in VIII, IX (occasionally in X), XVIII, and XIX in pingi . Also, hatomajimensis is smaller in length and has lower segment number than cruxus and pingi . The three species have fully developed reproductive organs, suggesting that they are the bi-parental breeding populations.

Amynthas cruxus is also similar to Amynthas nanrenensis James et al., 2005 in having four pairs of spermathecae in VI–IX and small genital papillae around each male pore. However, nanrenensis has much higher setal number than cruxus with 60–64 in VII and 62–72 in XX for the former, and 27–37 in VII and 39–52 in XX for the latter.

Amynthas hatomajimensis from Hatomajima Island of Iriomote at the southern tip of the Ryukyu Archipelago ( Ohfuchi 1957) is given as a synonym with question mark of Amynthas corticis in the checklists of Japanese earthworms ( Easton 1981; Blakemore 2003), while Pheretima toriii Ohfuchi, 1941 from the cave of Shonyudo Shindo, Oita, Japan and Pheretima tajiroensis Ohfuchi, 1938 from Tajiro Island, Ojika, Japan are given as synonyms without question marks. There is no explanation on what the difference is between synonyms with question marks and those without question marks.

Amynthas hatomajimensis is easily distinguishable from corticis ; the former has a flat male disc on which genital papillae are arranged in a consistent pattern around the male aperture ( Figure 5A ) ( Ohfuchi 1957), whereas the latter has a small disc-like porophore, and genital papillae if present are one or two in irregular arrangement usually on the first skin fold or the second skin fold surrounding the porophore ( Figure 5D–F ). As mentioned above, hatomajimensis is neither synonymous with nor closely related to corticis , but is closely related to cruxus of Taiwan and pingi of China. The above three closely related species in China, Taiwan, and Iriomote Island at the southern tip of the Ryukyu Archipelago provide additional evidence for the zoogeographical association of the three areas ( Hikida and Ota 1997; Tsai et al. 2002).

Pheretima toriii is a small cave earthworm, 37–43 mm in length, and has setal number of 43–45 in VIII, 56–58 in XX, teat-like porophore surrounded by six or eight skin folds (rings) without setae and genital papillae ( Figure 5B ), and prostatic duct slender and straight ( Ohfuchi 1941), whereas corticis is larger, 45–170 mm in length, and has setal number of 26–46 in VIII, 39–54 in XX, a small disc-like porophore surrounded by a few skin folds often with one or two genital papillae, and U- or C-shaped muscular prostatic duct ( Gates 1972). Ohfuchi (1941, p 246) already recognized a slender, straight prostatic duct as a unique character of toriii that is not seen in other species of the genus. Also, both species are different in ecological niches and migratory behaviour: toriii is cave dwelling and endemic, and corticis is terrestrial and peregrine. Unquestionably, toriii is a valid species distinguishable specifically from corticis .

Pheretima tajiroensis has a large (about 0.6 mm in diameter) and circular male porophore, deeply sunk down and surrounded by an elevated skin fold ( Figure 5C ) ( Ohfuchi 1938, p 48, Text-figure 12), which differs greatly from the small disc-like porophore of corticis ( Figure 5D–F ). Based simply on the male porophore structure, tajiroensis is a valid species distinguishable specifically from corticis .

The above three species, hatomajimensis , toriii , and tajiroensis , have unique, specifically distinctive characters. It is difficult to imagine or to speculate that they are synonymous among each other, and also synonymous to corticis as suggested by Easton (1981) and Blakemore (2003). The former two species have fully developed reproductive organs, so they are bi-parental H morphs. If hatomajimensis and toriii were synonymous to corticis , then they would be the ancestral H morph of parthenogenetic, aprostatic corticis and also the ancestral H morph of sheni speculated by Gates (1972) and Blakemore (2003). This would be too much speculation.

The original description of Perichaeta corticis Kinberg, 1867 is very simple as ‘‘ P. corticis n. Setae ubique c. 40: nae, minutae aliaeque crescentes majores; segment. 114; longitudo 68 mm. Oahu, sub cortice arborum’’ ( Kinberg 1867, p 102). Easton (1982, p 726) gave a diagnosis of A. corticis also very simply as ‘‘ Amynthas with paired spermathecal pores c.1/3 of the body circumference apart in furrows 5/6/7/8/9; genital markings as Fig. 4 a .’’ Later Blakemore (2003, p 16) redefined the diagnosis but still very loosely (not specific) as ‘‘ Amynthas with four pairs of spermathecal pores ca. 0.3 body circumference apart in furrows 5/6/7/8/9. Genital markings small paired or variable near spermathecal and male pores. Intestinal caeca simple with smooth or incised margins, originating near segment 27. Parthenogenetic morphs common (e.g., prostates and/or spermathecal diverticula aborted). Size range given as 45–270 mm ( Sims & Gerard 1985: 128, 1999: 128); cf. 45–170 mm ( Gates 1972: 178), (cf. Amynthas fuscatus given as 100–450 mm).’’

In addition to use of uncertain, speculative synonyms (with question marks), the oversimple original description ( Kinberg 1867), over-simple diagnosis ( Easton 1982), and loosely defined diagnosis ( Blakemore 2003), may be one of the reasons for so many synonyms for corticis in the checklists of Japanese earthworms ( Easton 1981, p 49; Blakemore 2003, p 14–16). If there were more detailed verification with more definitive, specific diagnostic characters with clear species concept, many of the synonyms (with and without question marks) of corticis and other species in the Japanese earthworm checklists ( Easton 1981; Blakemore 2003) might have been found to be valid nominal species, and their nominal status should not have been rejected at all from the Japanese earthworm fauna (biodiversity).

Figures

Figure 4. Amynthas cruxus sp. nov., holotype, 170 mm. (A) Ventral view of right male pore region (gp, genital papilla; ma, male aperture; md, male disc); (B) spermathecal pore; (C) dorsal view of right spermathecae (amp, ampulla; dv, diverticulum); (D) dorsal view of right prostate gland (pg) (pd, prostatic duct); (E) dorso-lateral view of right testis sacs (ts) and seminal vesicles (sv) of a 122-mm specimen (coll. no. 2000-81-Shen) (dl, dorsal lobe; vd, vas deferens; ve, vas efferens).

Figure 5. Comparison of male pore regions, ventral views. (A) A. hatomajimensis (Ohfuchi 1957, p 246, Figure 20- 1, Ryukyus, Japan); (B) A. toriii (Ohfuchi 1941, p 246, Figure 2-1, Kyusyu, Japan); (C) A. tajiroensis (Ohfuchi 1938, p 48, Figure 12-2, Honshu, Japan); (D, E) A. corticis (5P. diffringens, Taiwan); (F) P. heterochaeta (5A. corticis) (Chen 1933, p 235, Figure 16B, C, China).