Microcodides chlaena Gosse 1886

Microcodides chlaena (Gosse, 1886)

This species was extremely common in the samples. It has previously been recorded in Europe (see e.g. Wulfert 1940; Berzins 1978), the former Soviet Union (Kutikova 1965; 1970) India (Sarma, 1988), Australia (Shiel & Koste 1979) and North­ and South America (Harring & Myers 1922; Koste 1986, 1988; Nogrady 1989). On Greenland it has been recorded in the Ilulissat region (Bergendal 1892). Koste and Shiel (1987) consider the species as a cosmopolitan.

The species is easily distinguished by the presence of toes with unequal length and lateral antennae in depressions located posterior to a pair of characteristic integumental elevations (Fig. 1 D).

The adult animals are gibbous in lateral view and conical in dorso­ventral view (Fig. 1 D); immature animals are considerably smaller, with S­shaped body (Fig. 1 B). The body is divided into a head, a trunk and a foot region. The head is large, especially in the immature specimens. The dorsal part of the trunk has distinct longitudinal folds in the integument and the foot is composed of two pseudosegments. The corona is complicated, consisting of a continuous circumapical band that encircles the buccal field. A pseudotrochus is formed by four rows of long, stiff cirri. All cirri curve away from the mouth opening. Two other paired rows of cirri are located closer to the mouth opening. These cirri are shorter and curve towards the mouth opening. The buccal field is small and comprises a group of motile cilia around the mouth. The brain is large and saccate. Cerebral glands were not identified. A large eyespot is located on the ventral side of the brain. A pair of dorsal antennae is located dorsally on the head. Lateral antennae are located laterally, slightly behind the mid length of the trunk. Each antenna opens inside a small depression in a prominent wing­shaped elevation formed by the integument (Fig. 1 D).

A short ciliated esophagus connects the pharynx and stomach. The stomach is large and contains a yellowish material. The gastric glands are granulated and unstalked.

Trophi from six specimens were prepared for SEM. The trophi are modified malleate. The rami are trapezoid, but with elongated, dorsally curved apices. The inner margins of the rami have six small teeth in the basal part; apical rami parts have paired combs with numerous fine denticles (Fig. 3 B). A pair of small, caudally pointed alulae is located on the lateral sides of the rami (Fig. 3 A). A pair of large basifenestrae is visible on the dorsal side (Fig. 3 A); smaller, slightly asymmetric subbasifenestrae are visible on the ventral side (Fig. 3 B). The ventral side furthermore has a pair of basal apophyses bearing a band of sarciopili (Fig. 3 B). A pair of delicate epipharyngeal plates is associated with the apical rami parts (Fig. 3). Fulcrum is short, broadest in distal half. Unci are large with 8 teeth. Principal tooth is bipartite (Fig. 3 B). Manubria are composed of a well­developed proximal head and a caudal rod. Proximal head contains three chambers, which all have large apertures.

Measurements: Body (adults): 190–240 µm; body (immature): 90–128 µm; right toe 27 µm; left toe 24 µm; trophi 27 µm; rami 20 µm; fulcrum 6 µm; manubria 16 µm; unci 14 µm.