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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Systematics of Oligochaeta

We thank following scientists for quoting text descriptions from their papers.

1. Morphological classification

[ref. ID; 3692 (O.B. Svtlov, 1982)]

Class Oligochaeta

Order Naidomorpha

Order Naidomorpha

Order Lumbricomorpha

[Another taxon]

2. Spermatology (Spermatozoon morphology)

[ref. ID; 6456 (Marco Ferraguti & S.G. Gelder, 1990)]

Superclass Clitellata

[Clitellata character]
Clitellate spermatozoa are long, filiform cells with an acrosome tube, a long thin nucleus, and mitochondria interposed between the nucleus and the tail. The acrosome tube has a wide range of shapes and dimensions. It contains the acrosome vesicle with subacrosomal material in which an acrosome rod (= perforatorium) is visible. A conventional centriole is not present in the mature spermatozoon, as a result of the high degree of modification that occurs during spermiogenesis (Ferraguti, 1984). The axoneme has a prominent central sheath apparently autapomorphic for clitellates, though absent in some of the more advanced forms of oligochaetes (Ferraguti 1984), and glycogen granules.

[Oligochaeta character] (See: ref. ID; 6453)
Oligochaete spermatozoa are distinguished from those of the other clitellates by three characters. (1) A straight or slightly bent acrosome is followed by a rectilinear flange or variously spiraled nucleus. (2) There is a species-specific number of cyclindrical, sectored mitochondria (2-8) in the mid-piece. (3) The basal cylinder of the flagellar central apparatus penetrates a variable distance into the centriole remnant (Jamieson 1986). The only known exception to this definition is a loosely spiraled acrosome in one species Phreodrilus observed by Jamieson (1981). Fertilization in Phreodrilus sp. is external, and thus contrary to that in most oligochaetes (Jamieson et al. 1987), therefore a spermatozoon model very different from that found in most oligochaetes is expected, following Franzen's rule (Franzen, 1956). The shape of the nucleus varies in the different branchiobdellidans as well as in oligochaetes. Branchiobdella spp. have a straight nucleus, as do all "megadriles". Bdellodrilus illuminatus has a nucleus that is anteriorly straight, becoming progressively more helical towards its posterior, as found in the tubificid Katetio sp. (Ferraguti et al. 1989). Xironogiton instabilis has a tightly coiled helical nucleus, closely resembling that of the lumbriculid Bythonomus sp. (Ferraguti and Jamieson 1987). Cambarincola fallax has a loosely coiled helical nucleus that differs from that of other oligochaetes with the possible exception of the megascolecid Pheretima hawayana, for which we have only optical microscope observations (Alderete de Mayo et al. 1979).

[Hirundinea character]
Seven characters distinguished the hirudineaen spermatozoon from the clitellate model as suggested by Wissocq and Malecha (1975). (1) A helical portion of the acrosome is located anterior to the acrosome tube and vesicle. (2) The acrosome tube has a lateral interruption, where the acrosome vesicle contacts the plasma membrane of the spermatozoon. This is possibly homologous to the apical button of oligochaetes spermatozoa (Garavaglia et al. 1974). (3) The acrosome tube has an external helical flange. (4) The nucleus forms one or more complex helices. (5) A single mitochondrion is present. (6) A conventional centriole, with the centriolar area penetrated by an extension of the central apparatus from the flagellum, is absent. (7) A long end-piece is present at the end of the flagellum.

[Branchiobdellida character]
The phylogenetic position of the Branchiobdellida in the Clitellata, based on anatomical characters, is debyable. Some authorities assign the taxon to the Oligochaeta (Avel 1959; Timm 1981), others assign it to the Hirundinea (Sawyer 1986) or support an independent group, equal in taxonomic rank to the former two (Holt 1989). Brinkhurst and Gleder (1991) currently accept the last theory, that the branchiobdellidans and lumbriculid oligochaetes do share a number of anatomical similarities in their reproductive organs (Avel 1959; Brinkhurst and Gelder 1989). However, Comparable similarities were not found in the ultrastructure of the spermatozoa and muscles between the two taxa (Franzen 1962; Ferraguti and Lanzavecchia 1977). The phylogeny with in the Branchiobdellida was addressed by Holt (1986), who arranged the genera into five families. Gelder and Brinkhurst (1990) demonstrated that the taxon was a monophyly by means of anatomical characters of the component genera in a Wagner analysis method (phylogenetic analysis using parasimony, of D. Swofford, Illinois Natural History Museum, Champaign). All branchiobdellidan spermatozoa examined so far are filiform, with an acrosome, a nuclues, a mid-piece containing only mitochondria, and a tail. The total length of the spermatozoa and the relative dimensions of the different portions vary among the species.

3. Phylogenetic classification

[ref. ID; 6423 (Ralph O. Brinkhurst & Amanda F.L. Nemec, 1987)]

Analytical method: Jaccard/Average Linkage cluster analysis and Wagner parsimony

Superclass Aclitellata

Superclass Clitellata

[ref. ID; 6451 (Marco Ferraguti & Christer Erseus, 1999)]

Phylogenetic analysis: PAUP (Phylogenetic Analysis Using Parsimony, version 3.1 for Macintosh computers)

Superclass Clitellata

Due to their possession of a clitellum (a cocoon-producing structure unique in the animal kingdom) and several other synapomorphic characters, clitellates are recognized as a monophyletic group of annelid worms (see Purschke et al., 1993). However, as many of their characters are distinctly different from those of e.g., polychaetes, few features can be used for inferring the direction of change in character states within the Clitellata. For the same reason, there is yet no clearly formulated hypothesis with regard to the sister group of Clitellata. There is no consensus whether Polychaeta and Clitellata are separate taxa, or whether Clitellata is merely a group within the paraphyletic former. This issue has recently been treated by several workers (Rouse & Fauchald 1995; Eibye-Jacobsen & Nielsen 1996; Westheide 1997; Westheide et al. 1999; McHugh 1997). The last author provided molecular evidence that polychaetes are paraphyletic unless clitellates, echiurans and pogonophorans are included. Within the Clitellata, the phylogenetic relationships between Oligochaeta (as this taxon has been traditionally conceived)), Branchiobdellida, Acanthobdellida and Euhirudinea (the true leeches) have long been debated. Recent phylogenetic studies of these groups by Purschke et al. (1993), Brinkhurst (1994), and Siddall & Burreson (1996) do not support the monophyly of Oligochaeta sensu stricto on the basis of morphological characters. The other groups all appear to be derived oligochaetes, which means that the names Oligochaeta and Clitellata could be regarded as synonymous (Siddall & Burreson 1996). So far, the low number of taxa investigated for gene sequence data (Moon et al. 1996 (see ref. ID; 6526); Kim et al. 1996), have not allowed a proper resolution of the phylogeny. However, a rapidly increasing number of such relevant molecular studies are expected to achieve this within the next few years. Purschke et al. (1993) have presented convincing arguments that the monotypic Acanthobdellida is a sister group of the Euhirudinea, the two together being regarded as the taxon Hirudinea. Branchiobdellidans exhibits both 'oligochaetoid' and 'leech-like' morphological features, but several contemporary authors hesitate to see them as an intermediate group between the (paraphyletic) oligochaetes and the hirudinean assemblage (Holt, 1989; Brinkhurst & Gelder 1989; Purschke et al. 1993; Valvassori et al. 1994; Brinkhurst 1994). On the other hand, Sawyer (1986) and Siddall & Burreson (1996) conclude that the Branchiobdellida are closley related to the Hirundinea. In several respects (gonadal sequence, semi-prosoporous male ducts, and body wall musculature) branchiobdellidans show similarities with the oligochaete family Lumbriculidae (Brinkhurst & Gelder 1989; Purschke et al. 1993; Valvassori et al. 1994). (ref. ID; 6451)

[ref. ID; 6526 (Seung Y. Moon, Chang B. Kim, Stuart R. Gelder & Won Kim, 1996)]

Analysis method: 18S ribosomal RNA gene sequences

The prime anatomical character in annelid taxonomy is the presence or absence of a clitellum, resulting in a species being placed in the superclass Clitellata or Aclitellata, respectively. Historically, annelids have been divided into three major classes, either the clitellate Oligochaeta or Hirudinea, or the aclitellate Polychaeta. However, the anatomical and embryological characters found in members of the branchiobdellidans and aphanoneurans prevent their unequivocal assignment to any of these major taxa. Branchiobdellidans, or crayfish worms, have a constant number of segments, a posterior attachment disc and jaws. These, and other characters, have been interpreted by some researchers to indicate that the branchiobdellidans are modified leeches (Sawyer 1986). However, others (Holt 1989; Brinkhurst & Gelder 1989) have argued convincingly that the characters listed are a result of evolutionary convergence in the two groups. In constrast, branchiobdellidans and lumbriculid oligochaetes both have their vasa deferentia and atria arranged in a semi-prospore condition, which would suggest that the branchiobdellidans are highly modified oligochaetes (Stephenson 1930; Timm 1991). The authors subscribe to the position that the branchiobdellidans form an independent taxon of equal rank to the oligochaetes and leeches (Holt 1965; Gelder & Brinkhurst 1989) at this time. However, the phylogenetic affinity of the branchiobdellidans with respect to the other taxa remains unresolved. The aeolosomotids have long been included with the oligochaetes (Vejdovsky 1884; Stephenson 1930), but with the understanding that the worms lack a clitellum. Although these freshwater, aclitellate worms have an oligochaete-shaped body, with dorsal and ventral bundles of hair chaetae, they also possess some non-oligochaete characters such as variable numbers of segments containing gonads, nephridia functioning as gonoducts, in additional to lacking a clitellum. This conflict in the definition of the Oligochaeta was addressed by Timm (1981) with the creation of a second aclitellate taxon, the Aphanonuera. (ref. ID; 6526)

[ref. ID; 6560 (R.O. Brinkhurst, 1990)]

Phylogenetic analysis of the Tubificinae: PAUP 2.4.1 (Phylogenetic Analysis Using Parsimony, by David Swofford)

[ref. ID; 6584 (Christer Erseus, 1987)]

Phylogenetic analysis of the aquatic Oligochaeta: Wanger parsimony analysis using PAUP 2.2
GLOBAL BRANCH SWAPPING: an algorithm for rearranging tree topologies in search of shorter trees
MULPARS: initiates a search for multiple equaly parsimonious trees
MAXTREEE=10: sets the maximum of equally parsimonious trees to be generated; limited set here to avoid long running times

Scientists list

We cannot still accept permission to quote some description from following articles. Please allow us to reproduce. (June 30, 2018)

ref. ID; 3692, 5859, 6208, 6533, 6578