Aktedrilus parvithecatus ( Erséus 1978 )

Pinder, Adrian M., Eberhard, Stefan M. & Humphreys, William F., 2006, New phallodrilines (Annelida: Clitellata: Tubificidae) from Western Australian groundwater, Zootaxa 1304 (1), pp. 31-48 : 36-37

Aktedrilus parvithecatus ( Erséus 1978) ( Fig. 3 )

Bacescuella parvithecata Erséus, 1978: 264

Bacescuella pilicrepus Erséus, 1984b: 153

Aktedrilus parvithecatus ( Erséus, 1978) ; Erséus (1987: 117); Erséus (1992: 21)

Material examined. WAM V 4446 . Two specimens whole­mounted on same slide, from a small anchialine karst window (#C­510) about 500 m from the sea, Cape Range , Western Australia ( Fig. 1 ), 22°20'S 113°49'E, 8 Aug 1993. Conductivity 3.30 mS cm ­1, total dissolved solids 1800 mg L ­1. Coll. W.F. Humphreys and R. D. Brooks ( WAM collection # BES 2502) .

Description of new material. Length and number of segments 6.3–6.6 mm and 48–53 respectively, width of slide­mounted worms 0.15–0.21 mm at segment XI. Clitellum from posterior 1/3 of X to 12/13, more glandular, but not distinctly thicker than epidermis of other segments. Male pores ventro­lateral on XI, about one third of the distance between 10/11 and 11/12. Single spermathecal pore mid­dorsal behind 9/10. Female funnels ventrolateral on 11/12.

Prostomium bluntly oval, length:height at base 1.1–1.3, with large round clusters of cells below the epidermis, projecting into, and occupying up to half of the prostomial coelom. Pharynx in II/III. Pharyngeal glands, consisting of large irregular cells, associated with gut in IV–V (or anterior of VI). Rest of ciliated digestive tract narrow anteriorly, wider from XIV–XVII. Dorsal and ventral blood vessels connected by commissural vessels in at least IV and V and by a plexus of capillaries surrounding the gut from about VI. Large chlorogogue cells with non­staining cytoplasm almost filling coelom from VI or VII. Coelomocytes not observed. Chaetae bifid with sharp teeth, the upper tooth about half as long as the lower, 4–7/bundle in pre­genital segments and 3–5/bundle posteriorly, located at about two–thirds of the distance between anterior and posterior septa, 33–48 µm long x 1.3–1.5 µm wide at nodulus, largest in pre­genital segments, the nodulus slightly distal. Ventral chaetae present but not modified on X, absent on XI.

Genitalia paired, except for spermatheca. Testes antero­ventral in X with sperm sacs extending posteriad to XIV. Ovaries antero­ventral in XI, egg sacs not present. Sperm funnels ventro­lateral on 9/10 leading to very short thin (8 µm) vasa deferentia (ciliation uncertain) joining apical end of tubular atria. Atria about 300 µm long, width about 17 µm with sperm present in the lumen (not shown on Fig. 3 ). Cytoplasm of atrial lining cells with numerous vesicles, much more so in ectal 2/3 rds, of a similar size and shape to those in the prostate glands. Muscle layer of atrium mostly thin, but in one specimen this is somewhat thicker around the ental part of the atrium with less abundant cellular vesicles. Atria joining ovoid penes apically, leading to a pore on the inner side of the penes. Penis sacs opening to exterior ventro­laterally. Two large prostate glands associated with each set of male ducts. Anterior prostates lying medial to the atria but connection to male duct not visible. Posterior prostates lying medial to penis sacs in front of 11/12, almost as tall as the segment and connected to the male duct where the atria join the penis sacs, sometimes protruding into XII. One spermatheca present with a small ampulla (28–31 x 16 µm) connected to mid­dorsal pore by thick duct (25–32 µm long, 13–14 µm wide) narrowing towards pore with narrow lumen. Loose sperm present in ampulla.

Remarks. Apart from lacking external spermatophores, the new specimens conform well to descriptions and illustrations of A. parvithecatus by Erséus (1978; 1984a; 1984b; 1987) and Erséus and Cantú­Martínez (1984). The spermatophores are placed on the exterior body wall during reproduction in some species of Aktedrilus , including A. parvithecatus , although their absence in these three specimens is not of great significance: they were absent on 4 of 8 specimens from Rottnest Island collected by Erséus (1993). This species has mostly been collected from intertidal and barely subtidal sands (Erséus 1987,1993), although Erséus (1992b) also recorded it from brackish anchialine waters in the Cabo Verde Islands off north­west Africa. This species is obviously capable of living in a wide range of salinities as the population described above was collected in water with tds only 1800 mg L ­1. Occurrence in both marine littoral and brackish hypogean water (a mineral spring) has similarly been reported for Aktedrilus cuneus Erséus, 1984 . Aktedrilus parvithecatus is circumtropical in distribution, with records from Pacific Mexico, Galapagos, France, Canary and Cabo Verde Islands, Saudi Arabia, Hong Kong, Bermuda and south­western Australia (Rottnest Island).

Figures

FIGURE 1. Map of Western Australia showing major geological units and localities for 1) Pectinodrilus ningaloo, 2) Aktedrilus parvithecatus, 3) Aktedrilus podeilema, 4) Aktedrilus leeuwinensis and 5) Aktedrilus sp.

FIGURE 3. Aktedrilus parvithecatus (Erseus, 1978). Genitalia (scale bar 100µm).