Heterolepidoderma caudosquamatum, Grilli, Paolo, Kristensen, Reinhardt Møbjerg & Balsamo, Maria, 2009

Grilli, Paolo, Kristensen, Reinhardt Møbjerg & Balsamo, Maria, 2009, Heterolepidoderma caudosquamatum (Gastrotricha: Chaetonotida), a new species from brackish waters of Denmark, Zootaxa 2173, pp. 49-54 : 51-53

Heterolepidoderma caudosquamatum n. sp.

( Figures 2 , 3 )

Diagnosis. Heterolepidoderma species with slender, small-sized body. Five-lobed head with kephalion, pleuria, hypostomion and four ciliary tufts. 25-27 scale columns (19 dorsal), each composed of 27-29 hemielliptical keeled scales with a spiny process. The columns join together along the dorsal midline at the neck and narrow in the posterior trunk region. Two pairs of dorsal sensory bristles. At the dorsal posterior end are a median, large smooth plate, and two pairs of keeled scales that differ in shape. On each side of the ventral body are 3 ventrolateral columns of 27-29 scales similar to the dorsal ones, and one ventral column parallel to each ciliary band, composed of 27-29 smaller scales with a lamellar expansion (hydrofoil). The ventral interciliary area is covered with 9-11 columns of small, elongate keeled scales. At the ventral posterior end are four long, elliptical keeled scales.

TL 114–118 µm; fL 16–18 µm; phL 26–28 µm; kw 8.1 µm; hw 30–32µm; nw 23–26 µm; trw 41–46 µm; hscL 2.3–2.8 µm; trscL 6.1–6.4 µm; hhyL 3.6–3.9 µm; trhyL 7.6–7.8 µm.

Etymology. From the Latin cauda, tail, and squamatus, bearing scales, with reference to the peculiar dorsal scales at the caudal end.

Description. Small species, 114–118 µm in total body length, with a small and adhesive furca, 16–18 µm long. Five-lobed head with a large kephalion 8.1 µm wide, small epipleuria, well-developed hypopleuria and a trapezoidal hypostomion. Four tufts of cephalic cilia, the anterior two shorter than the posterior ones. The pharynx is 26–28 µm long; the PhIJ is at U28.

The body width varies from 30–32 µm at the head (U05), 23–26 µm at the neck (U26), 41–46 µm at the central part of the trunk (U35) and 25–26 µm at the furcal base (U91). The body is covered with 25–27 columns (19 dorsal), each of 27–29 juxtaposed scales (16–17 on the head region, 11–12 on the trunk region). The scale columns join together along the dorsal midline at the neck and at the posterior trunk region, and extend to cover the furcal base ( Figure 2 A). Scales are hemielliptical in shape, and bear a prominent, median keel extending into a very short spiny process, ca 1 µm ( Figures 2 B, 3 D). The length of the dorsal scales increases from 2.3–2.8 µm on the head to 6.1–6.4 µm on the trunk. Two pairs of sensory bristles are present on the neck and on the posterior trunk region, respectively. The posterior bristles, 13 µm in length, are inserted on two subtriangular, keeled scales. An unpaired large (4.4 x 4.9 µm), subtriangular, smooth plate lies at the furca indentation (U85): it appears much thinner than all the other body scales. Two small, keeled scales lie on the dorsal base of each furcal branch: the dorsolateral branch is roundish, ca. 3.2 µm in diameter, while the other is elliptical, 4 µm long, and lies just along the intrafurcal edge ( Figures 2 A, 3E). Three ventrolateral columns of 27–29 scales, similar to the dorsal columns and 2.8 µm long, extend along the external side of each ciliary band. One ventral column is adjacent to each ciliary band and composed of 27–29 scales bearing a well-developed lamellar expansion (hydrofoil). The hydrofoil length increases from 3.6–3.9 µm on the head to 7.6–7.8 µm on the trunk. The two ventral ciliary bands widen in the head region. Here, the interciliary area measures 12–16 µm in width and then expands on the trunk to 22–25 µm. Nine to eleven columns of small, elongate, keeled scales cover the ventral field from the neck region (U15) to the caudal end. Two pairs of long (6.6 – 6.7 µm), elliptical, keeled scales are located at the ventral posterior body end. The mouth, 4–5 µm in diameter, is surrounded by a thick cuticular ring with several protrusible processes. The mouth cavity is well developed and includes two cuticular rods. The pharynx, 26–28 µm long, is cylindrical, slightly widened at the posterior end. The intestine is 13 µm wide just after the pharyngo-intestinal junction, but clearly narrows at the posterior end to 5 µm. The anus opens at U88.

Almost all the specimens studied were in parthenogenic phase with one or two fully-grown oocytes. No spermatozoa nor X-organ were seen.

Figures

FIGURE 2. Heterolepidoderma caudosquamatum, n. sp.: A. Dorsal view; B. Details of dorsal scales from the head, neck and trunk; C. Ventral view; D. Cephalic plates.

FIGURE 3. Heterolepidoderma caudosquamatum, n. sp.: A. dorsolateral view; B. ventrolateral view; C. internal anatomy of an adult parthenogenic specimen; D. detail of the trunk dorsal scales; E. dorsal posterior end, showing the peculiar keeled scales.