Branchiura
Branchiura Beddard, 1892 (ref. ID; 1257, 3692, 5957, 6913, 6972, 7098)
Family Tubificidae (ref. ID; 1257, 1928, 5876, 5939, 6208, 7854)
Family Tubificidae: Subfamily Branchiurinae Hrabe, 1892 (ref. ID; 6913)
Family Tubificidae: Subfamily Rhyacodrilinae (ref. ID; 5857, 6648, 7824)
ref ID; 1663
Dorsal and ventral setae different. Ventral setae bifurcate, dorsal setae bifurcate or mixture of two or three types. 4 bundles of an indeterminate number each per segment. Worm usually reddish. Coelomocytes sparse or absent. With a dorsal and a ventral gill on each segment in the posterior 25 to 40 present of the body. 40 to 140 pairs of such gills. 20 to 185 mm long. Pinkish gray. Reported from many scattered stations, especially on lake bottoms. (ref ID; 1663)
ref. ID; 1923
Segments of the posterior portion of the body each with a dorsal and a ventral gill. (ref. ID; 1923)
ref. ID; 5957
Male effluent ducts with short vasa deferentia, atria covered with prostate cells, atrial diverticulae present, ejaculatory ducts enter eversible pseudopenis. Spermathecae paired, no spermatozeugmata. No coelomocytes. Dorsal and ventral gill filaments on each segment posteriorly. (ref. ID; 5957)
Remarks
The subfamily Branchiurinae was erected by Hrabe (1966) to hold this monotypic genus due to "absence of other typical signs of subfamily Rhyacodrilinae"; their one shared character was the diffuse prostate. The differences between these two subfamilies was expanded by Hrabe (1967) who suggested that the "peculiar coelomic sac surrounding the distal portion of the male duct ending with protrusible pseudopenis" was unique to the subfamily. Other distinguishing factors were said to be lack of coelomocytes, lack of postseptale on the nephridia, and the fact that the spermathecae open posterior to the ventral setae of X. Some of these characteristics were examined in sectioned material (Brinkhurst 1971) and details of the atria and glandular diverticulae noted. Examination of mature material from Japan and British Columbia has enabled some further amendments to be male. (ref. ID; 5957)
Type species
Branchiura sowerbyi Beddard, 1892 (ref. ID; 5957)
- Branchiura coccinea Michaelsen, 1900
See; Rhyacodrilus coccineus (ref. ID; 6208)
- Branchiura coccinea Vejdovsky (ref. ID; 1928)
- Branchiura sowerbyi Beddard, 1892 (ref. ID; 1257, 1923, 1928, 3692, 5939, 5957, 6208, 6648, 6913, 7098)
Syn; Kawamuria japonica Stephenson, 1917 (ref. ID; 7098)
Branchiura sowerbyi Beddard, 1892 (ref. ID; 1257, 1923, 1928, 3692, 5939, 5957, 6208, 6648, 6913, 7098, 7854)
Synonym
Kawamuria japonica Stephenson, 1917 (ref. ID; 7098)
Descriptions
This species is widely distribution. (ref. ID; 1923)
The worm live with their heads buried in the mud, whilst the tails wave actively about in water. Their tenacity of life is the very remarkable. The setae were more numerous than in Beddard's specimens. The anterior dorsal bundles contain 6-9 short, and 1-3 capillary setae. The ventral bundles contains 7-11 setae. In young forms there are usually three capillary setae in the dorsal bundles. The tips of the anterior ventral bundles are single. They gradually change into bifid setae behind the fifth segment. The clitellym occupies segments 1/210, 11, 12. The larger specimens are of a deep purple colour, the younger ones blood-red. (ref. ID; 1928)
Length to 185 mm, segments up to 270. Dorsal anterior bundles with 1-3 (6) short hair setae and (7-9) 11-12 pectinate setae (under oil immersion). Ventral bundles with 10-11 (14) bifid setae with reduced upper teeth. Spermathecal pores posterior to ventral setae of X, male pore single, a transverse median slit. Male system (all structures paired): vas deferens very wide behind sperm funnel, narrowing abruptly just before entry into atrium; vas deferens enters atrium subapicallly but runs to apex within atrial wall. Atrium covered with diffuse prostate cells. Glandular diverticulum joins atrium near base of prostate covered section; atrium and glandular diverticulum (often protruded into sperm sacs in XII) terminate in narrow ducts which gradually merge in XI and join eversible pseudopenis apically. Pseudopenis terminates on small median bursa. Pseudopenis and ducts contained in muscular sacs. Sperm in masses in the spermathecae. Cosmopolitan. (ref. ID; 5957)
It bears a large respiratory fan on the posterior segments, made up of a series of filiform processes, one dorsal and one ventral process per segment. When alive the worm undulates this fan rhythmically, which motion imparts an undulation along each of the individual processes, the whole combining to form an extremety graceful pattern. The hair chaetae being omitted as in most instances, unless they be at all modified. In the dorsal bundles there are 1-3 short hair chaetae in anterior segments, but none are present in the branchial region. There are in addition 11-12 simple ended or slightly bifurcate crotchets, and 10-11 similar chaetae in the ventral bundles. Ude (1929) states that there are 4-8 crotchets in both the dorsal and ventral bundles. There is no penis, although the terminal part of the atrium may be everted in which event it may resemble a penis. There are no specialised chaetae. (ref. ID; 6208)
Remarks
The muscular sac around the eversible male terminalia is quite normal in worms with eversible pseudopenes (i.e. M. evertus). A similar structure was noted by Chen (1940) in erecting the genus Littodrilus for M. aucklandicus. In Branchiura the muscule layer of the penial apparatus is divided with part forming the muscular outer sac and part the muscular walls of the eversible section of the male duct. The latter was not sufficiently emphasized in the illustration by Brinkhurst (1971). The muscle layer of the atrium is continuous along the length of the coiled duct within the muscular sac. The coelom lacks the large free coelomocytes of most Rhyacodrilinae but the peritoneum and chloragogen tissues are well developed. There are no modified penial setae, but although these are characteristic in the subfamily when present (with short curved ectal ends, long straight ental ends arranged fanwise), they are missing in other characteristic Rhyacodrilinae too. (ref. ID; 5957)
In Lake Biwa, the profundal population of Branchiura sowerbyi lacks posterior gills (Ohtaka & Nishino 1995). The present examination reveals that development of gill filaments is correlated with water depth in the lake. In the profundal region of the northern lake with depths deeper than 30 m, almost all individuals were devoid of gill filaments and only a few individuals had vestigial gills. In the sublittoral and littoral regions of the northern lake, worms with little developed gills occurred, but more than half of the individuals examined were still devoid of gills. In the shallow southern lake, worms with gills surpassed those without gills, however, the number and length of gill filaments were few and short. On the other hand, all worms in the adjacent lagoons had developed gills. These observations support the opinion presented by the previous authors (Chen 1940; Yamaguchi 1953; Ohtaka & Nishino 1995), that Kawamuria japonica Stephenson, which is devoid of posterior gill filaments and was originally described from profundal of Lake Biwa (Stephenson 1917), is an infraspecific variant of Branchiura sowerbyi presented. The form lacking gills has never been recorded from sites other than Lake Biwa. Chaetal morphology was examined for specimens from different localities within Lake Biwa and elsewhere. A hispid condition on the dorsal hairs was confirmed in all the material, and the distal form of the ventral chaetae did not vary much among populations, in which the upper teeth were almost absent or much shorter than lower teeth. On the other hand, considerable variation was detected between the populations in the number and length of dorsal hairs, and in the distal form of dorsal crotchets. The dorsal hairs in preclitellar segments were 1-5 per bundle (usually 2-3), and the longest hair was 2-3 times longer than the crotchets in the same bundle, in all specimens examined except those from Niigata and profundal Lake Biwa, which had fewer (0-2 per bundle) and distinctly shorter hairs (not exceeding twice the length of the crotchets). As for the distal ends of the dorsal crotchets, a bifurcate tip with a much shorter upper tooth was the most common condition in the Japanese populations, but pectinations or split lower teeth were often found in specimens from some Japanese localities including the southern lake of Lake Biwa. Pectinations were the most prominent condition in Chinese and Sumatran material. On the other hand, the distal end of the dorsal chaetae in the profundal Lake Biwa form were simple-pointed or cleft with parallel teeth. Such short hairs and simple-pointed dorsal chaetae as in the present material were previously described and figured in the original description of Kawamuria japonica from profundal population of B. sowerbyi in Lake Biwa is different from those of other localities, not only in terms of absence of gills, but also regarding chaetal characteristics. This suggests that speciation is progressing in the profundal population of Lake Biwa. However, it is also probable that the differences in chaetal forms between local populations depend on chemical condition of waters. To estimate the degree of differentiation in the profundal Lake Biwa population, critical comparison is needed for genital organs that could effectively isolate populations. (ref. ID; 6648)
It is justifiable that Chen (1940), and also Yamaguchi (1949, 1953) merged Kawamuria japonica originally described from Lake Biwa with Branchiura sowerbyi. This is because at the littoral of the lake, worms with variously vestigial gill filaments were often collected together with those completely devoid of gills which can be ascried to Kawamuria japonica. On the other hand, the profundal worms were almost all devoid of gills. Similar lack of gills can be caused by fish predation which removes the tails and gills (R.O. Brinkhurst, pers. comm.). However, in Lake Biwa, it is probable that the tail without gills is not a secondary modification by predation but an innate characteristics, because oligochaetes are seldom preyed upon by any fish at the profundal (Miura 1985). It is noticeable that Branchiura sowerbyi (gill absent form) inhabits even the deep profundal in Lake Biwa where water temperatures are almost constant (about 6-8 degrees C) throughout the year. The temperatures are lower than the threshold value for embryonic development (10 degrees C) estimated by Bonacina et al. (1994) for the Italian specimens. This species usually occurs in ponds or littoral regions of lakes with high temperatures and with large amount of plant debris (Ohtaka et al., 1991), and has never been recorded in such deep and cold habitats as Lake Biwa. Based on these reasons, it seems best to regard Kawamuria japonica as an infraspecific variant form of Branchiura sowerbyi endemic to Lake Biwa. (ref. ID; 7098)
Material examined
Japan, Dr. E. Kikuchi coll. Prospect Lake, Victoria, British Columbia, various dates, coll. H.R. Baker, P. Chapman. (ref. ID; 5957)
Over 1000 immature and mature individuals, many sites covering various areas in Lake Biwa, August 1988-January 1996. Sixteen immature and 29 mature individuals, two lagoons adjacent to Lake Biwa, 0.3-0.5 m depth, 9th March, 1994, 11th May, 1996. Two mature and 4 immature individuals, a pond in Sapporo, 23rd May, 1983. Three mature individuals, Niitsu, Niigata Pref., 19th May, 1996, N. Hayakawa collected. Two mature and 6 immature individuals, center of Lake Suwa, 6 m depth, 11th June, 1980. Twenty immature individuals, center of Lake Kitaura, 6.5 m depth, 5th January, 1985. Three immature individuals, a pond in Akashi, Hyogo Pref., 8th October, 1982. Four immature individuals, a pond in Takamatsu Kagawa Pref., 11th October, 1982. Two immature individuals, Kanna River, Okinawa, 8th August, 1990, M. Tsuchiya collected. Four immature individuals. Bao-an Lake, Hubei Prov., People's Republic of China, 8th April, 1987 (R.O. Brinkhurst collection). Twelve immature individuals, paddy fields at Padang, Sumatra, Indonesia, 4th August, 1988. (ref. ID; 6648)