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Diagnostic characters and definitions for enchytraeids

ampulla (-ae): the ental, enlarged portion of the spermatheca. Sperm donated by a mate is stored in this part of the spermatheca prior to intracocoon egg fertilization. The ampulla is connected to the exterior of the worm by the ectal duct and an epidermal ectal pore. In species ofGrania and of the other genera with marine taxa, except Achaeta, the ampulla is connected internally to the gut by the ental duct. In species ofGrania and some of Marionina, sperm rings form in the walls of the ampulla. The ampulla may itself have a single, or several, lateral outpocketings or diverticula.

bipartite penial sac: a complex sac at the terminus of the penial apparatus, in segment XII, found in species of Grania. It consists of two parts joined at a right or acute angle. The ectal or proximal part is an erect invagination of the male pore. The ental or distal part is a longitudinally oriented, muscular sac; when contracted, the walls of this part may be longitudinally ridged. A penial stylet extends into the ridged, ental sac. The term bipartite, saccate penial apparatus is used for the type of penial apparatus possessing such a sac, Type 6 (Locke & Coates 1999).

bulbous penial gland: a compact gland, associated with the male pore, in segment XII. Bulbous penial glands may lie alongside and open into an extended invagination of the male pore or may lie dorsal to and open into a simple, epidermal, male pore. The gland is penetrated by the ectal part of the vas deferens. In species of Grania, a penial stylet may extend through the bulbous gland to an extended invagination of the male pore. InRandidrilus there is an anterior and a posterior bulbous gland.

clitellum: a region of enlarged, secretory, epidermal cells (see Jamieson 1981) extending from about XI-XIII. The cocoon into which eggs are released is formed by secretions from the clitellum. In enchytraeids, the epidermal layer of the clitellum is just one cell thick; male (sperm) and female (egg) ducts and pores are within the region of the clitellum; no setae are present ventrally on segment XII once the clitellum is formed. Nielsen & Christensen (1959) classified enchytraeid specimens without a clitellum as immature and recommended that these never be used for species descriptions.

dorsal blood vessel bifurcation: anteriormost region of the dorsal blood vessel, where it divides to form two, lateral circumpharyngeal vessels which travel ventrally, then medially and posteriorly to unite as the ventral vessel. This bifurcation may lie posterior to the brain or near its anterior margin.

ectal duct: duct-like part of the spermatheca lying between the external spermathecal ectal pore and the ampulla. Sperm from a mate is transported through the ectal duct to the ampulla and, later, out to fertilize eggs. The ectal duct may have glandular cells along its length and/or at its junction with the ectal pore. The ectal duct may have distinctive dilations or regionation of cell types.

ectal gland: unicellular or multicellular gland at the spermathecal ectal pore; of epidermal origin.

ectal pore: opening of spermathecal ectal duct to the exterior, located dorsally or ventrolaterally in furrow between segments IV and V or just posterior to this on segment V and, rarely, VI, (see Randidrilus quadrithecatus). Usually paired, with the exception of Grania monospermatheca,which has a single, middorsal pore.

ental duct: duct-like part of the spermatheca between the ampulla and the esophagus; an open canal to the esophagus may be present. The specific function of an open connection is a matter of speculation (Westheide 1999; Locke 1999, p. 20). It could allow the flow of fluids and intestinal materials between the gut lumen and the spermatheca.

epidermal gland sac: found only in some species of Achaeta, all of which lack setae. The solitary sacs are laterally paired and there may be up to three pairs. They are either dorsolateral, or dorso- and ventrolateral, or dorso-, medio- and ventrolateral. Nielsen & Christensen (1959) referred to these as setal follicles or gland sacs but noted that "their true nature is doubtful" (op.cit., p. 16). Setal follicles is synonymous with seta-producing sac or setal sac (Stachowitsch 1992) so the use of that name for the glandular sacs of Achaeta implies an homology which is not substantiated.

head pore: unpaired, dorsal opening from body cavity to the exterior. Located on the anterior part of the peristomium, at the junction of the peristomium and prostomium, or near the anterior tip of the prostomium as in Achaeta and a number of terrestrial enchytraeid genera.

lobed testis sac: lobed, peritoneal, membrane enclosing testis, spermatocytes and sperm; originating ventrally on posterior face of septum between segments X and XI (septum 10/11) in the region of the testis. Individual lobes are drop- or pear-shaped. Found in species of Lumbricillus. There is one multi-lobed sac for each testis. Stephenson (1930), Coates (1987, 1989a) and Rota (1994) discussed differences between testis sacs and seminal vesicles or sperm sacs.

penial apparatus: the part of the male reproductive system located in segment XII, lying between the ectal end of the vas deferens and the external opening of the male reproductive system. The penial apparatus of marine enchytraeids may have a penial stylet protruding from the vas deferens, a bipartite sac, a bulbous gland, and an epidermal infolding or invagination at the male pore. Gustavsson & Erséus (1997) provided a discussion of atria and prostate glands of aquatic oligochaetes, in general, in which they refer to the penial apparatus of all enchytraeids as the penial bulb. Evolution from a simple male pore to a complex invagination and glandular apparatus at the male pore has occurred within the enchytraeid lineage (Coates 1987, 1989a) so that they do not have homologues of atria and prostates of, for example, tubificid oligochaetes. However, the terms atrium (or genital atrium) and prostate are applied to structurally and functionally comparable or analogous elements of the male reproductive systems of many lineages of animals (Abercrombie et al. 1992), including enchytraeids (Rota 1994). The complex forms of penial apparatus seen in species ofGrania (Coates 1984; Locke & Coates 1999) were not known when the term penial bulb was first applied to the male pore apparatus of enchytraeids, and does not adequately encompass these forms or the simplest forms of the penial apparatus (see Rota 1994).

penial stylet: slender, tapering, tube-like structure in the penial apparatus, reported for some Grania species; extends from ectal portion of vas deferens into bulbous penial gland or bipartite penial sac; possibly cuticular.

penial gland: a general term for a gland associated with the penial apparatus. In enchytraeids penial glands are usually located, with ducts opening, near or at the male pore. See comments on prostate under penial apparatus.

peptonephridia: a pair of tubular organs extending from the posterior of the pharynx; free floating in the coelom. According to Nielsen & Christensen (1959, 1963) peptonephridia are a particular type of salivary gland, found only in species of Enchytraeus, Enchylea, and Fridericia, and just one of many types of esophageal appendages known for enchytraeids. There is no evidence for a definite digestive function or of an ontogenetic relation of these organs to nephridia but the name peptonephridia is, unfortunately, entrenched. At one time there was confusion about the presence of peptonephridia in species of Grania and this led to the erection of the genus Hemigrania for Grania-like species which did not have peptonephridia (see Locke & Coates 1999). It is now clearly recognized that no species of Grania have peptonephridia. The terrestrial genusHemienchytraeus has an unpaired pharyngeal appendage which Nielsen & Christensen (1959) specifically did not call peptonephridia and which Coates (1989a, 1989b, 1987) showed had independent origins from the peptonephridia of species of Fridericia, at least. The organ found inHemienchytraeus is sometimes referred to as an unpaired peptonephridium.

pharyngeal gland: compact glandular mass which may occur on the septa at the posterior of segments from IV to VI, or VIII in some species of the freshwater Cognettia, and ventrally in the same segments. Pharyngeal glands are laterally paired in each segment in which they are present. The ducts of these glands run ventrolaterally in a compact strand of tissue, anteriorly from the gland masses to the dorsal pharyngeal pad.

seta(e): chitinous bristles which project from secretory setal sacs in the body wall; with special epidermal musculature allowing complex movements. Ectal tip single-pointed for all but one freshwater (Barbidrilus) and one terrestrial (Aspidodrilus) genus of enchytraeid, variously shaped shaft. General distribution pattern is in four groups or bundles on each segment posterior to the peristomium and anterior to the pygidium. In enchytraeids, the setal bundles are located two ventrolaterally and two more or less laterally on each segment. Setae are never found on what is called body segment I of oligochaetes, and some or all bundles may be missing from various or all other segments. Among marine species, setae occur singly, rather than as bundles, in Grania, Randidrilus, and some species of Marionina. Jamieson (1981) and Gustavsson (1999) discussed the structure and formation of oligochaete setae.

sperm ring: ring-like bundle of spermatozoa embedded in the walls of the spermathecal ampulla. Sperm rings are seen in species of Grania and marine species of Marionina. Mechanism and reason for formation are unknown. Also see ampulla.

spermatheca(e): female reproductive structure which receives and stores sperm from a mate. Consists of two or three main parts: ectal duct and ampulla, and sometimes an ental duct; with ectal origin in V and, rarely, also in VI; may be paired or single in species of Grania.

statocyst: vesicular, ciliate organ with globular inclusions or statoliths, located anterior to the brain (Locke 2000), thought to be a geotactic or equilibrium organ; reported only in Grania species; lies below head pore and dorsal to the anterior bifurcation of the dorsal blood vessel.

vas deferens (vasa deferentia): duct connecting sperm funnel to penial apparatus; with ciliated canal through which sperm travel to the male pore. In species of Grania, muscular modifications may be present as bandlike constrictions, knots (short spirals), elongate spirals, and longitudinal bands.

© Copyright 1999-2017, K.A. Coates


{page update: 8 July 2003}

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