Thysanozoon brocchii (Risso, 1818)

Bahia, Juliana, Padula, Vinicius & Delgado, Marlon, 2012, Five new records and morphological data of polyclad species (Platyhelminthes: Turbellaria) from Rio Grande do Norte, Northeastern Brazil, Zootaxa 3170, pp. 31-44 : 38-40

Thysanozoon brocchii (Risso, 1818)

( Fig. 5 )

Material examined and locality. Four specimens (12 mm x 11 mm, 13 mm x 10 mm, 13 mm x 11 mm and 17 mm x 14 mm) preserved in ethanol 70%, collected 9 March 2009 (MNRJ-PLAT 14). One mature specimen (16 mm x 12 mm) as sagittal sections of reproductive structures, collected 11 March 2009 (MNRJ-PLAT 15, 17 slides). Four specimens (12 mm x 9 mm, 17 mm x 16 mm, 15 mm x 15 mm and 14 mm x 12 mm) preserved in ethanol 70%, collected 11 March 2009 (MNRJ-PLAT 16). All specimens collected at Brazil, RN, Extremoz, Praia de Santa Rita, 0 5o 41’44’’S, 35o11’39’’W, intertidal, under rocks.

Distribution. Cosmopolitan. Described from Naples, Italy (Risso 1818) and known from other parts of the Mediterranean, Japan, South and West Africa, Florida, New Zealand, Brazil, and United Kingdom ( Prudhoe, 1985). This species shows feeding preferences on compound ascidians. We collected our specimens mainly near Didemnidae ascidians. The species T. brocchii is very active and swims when disturbed.

Diagnosis. Brown to yellowish dorsal region with a median longitudinal cream line; a transversal cream line may also be present, forming a cross. Dorsal surface papillate, smaller papillae toward the margin. Male apparatus doubled. Very active species.

Description. Color: Dorsal region whitish background color with pigmentation ranging from dark brown to yellowish brown. Longitudinal median line cream ( Fig. 5 A). Some papillae with white spots ( Fig. 5 A). Some specimens have a transversal line formed by lightly colored papilla. This pattern forms a whitish cross. Ventral surface white ( Fig. 5 B).

Form: Oval, elongated. Slightly undulated toward the edges. Papilla covering entire surface and ranging from 0.3 to 0.1 mm. Papilla size diminish toward the margin and absent from 0.5 mm up to the margin.

Tentacles: Pointed ear-like pseudotentacles 1 mm long.

Eyespots: Cerebral eyespots arranged in horseshoe shape. Cerebral cluster 0.9 mm distant from the anterior margin and bearing 32 – 50 eyespots. Pseudotentacular eyespots form four clusters dorsally and two clusters ventrally. Ventral clusters have more ocelli (65 – 70) than dorsal eyespots clusters (20 – 25).

Digestive system: Pharynx formed by shallow folds 3.5 mm long. Distance between anterior margin and pharynx is 2 mm. Mouth opens in the middle of pharynx extension. Digestive diverticula enter papilla body and might serve to increase digestion surface.

Epidermis and body wall: Body wall thickness mostly due to muscular layers. Body wall thickness greater on the dorsal surface (0.05 mm) than on the ventral surface (0.04 mm). Muscular layers disposed as follows: longitudinal, circular and diagonal layer. Pigmentation granules can be seen on the dorsal surface. Rhabdites are present on both surfaces but are more abundant on the dorsal epidermis. Muscular sucker 0.4 mm long located 0.9 mm from the female gonopore.

Gonopores: Two male and one female gonopore present. Each measures 0.5 mm in diameter. Male gonopores positioned right behind the pharynx. Female gonopore immediately posterior to male gonopores.

Male reproductive system: Doubled male structures. Seminal vesicle oval and somewhat pointed anteriorly and posteriorly ( Fig. 5 C). Prostatic vesicle (0.15 x 0.11 mm) oval and muscular situated ventrally from the 0.42 x 0.36 mm large seminal vesicle ( Fig. 5 C). Penis papilla 0.2 long, not fully developed. Penial stylet not visible on sections. Male atrium shallow (0.19 mm). Numerous testes arranged ventrally reaching 3.5 mm lenght ( Fig. 5 B).

Female reproductive system: Vagina 0.2 mm long, elongated backwards and surrounded by numerous cement glands ( Fig. 5 D). Female atrium 0.24 mm long and with pleated wall. Uteri branched and dorsal to male structures.

Taxonomic remarks. Thyzanozoon lagidium Marcus, 1949 was described from the Brazilian coast and was considered a synonym of T. brocchii by Marcus & Marcus (1968), followed by Faubel (1984). However, Prudhoe (1985) considered it as a separate species. The eyespot clusters of our specimens are different from T. brocchii material illustrated by Palombi (1928), from Suez Canal. The female atrium observed in the specimens here examined is more complex than is usually attributed to other Thysanozoon species. This characteristic was attributed to T. lagidium but then considered intraspecific variation among T. brocchii ( Marcus & Marcus, 1968) . As T. brocchii is a cosmopolitan species that has a distribution ranging from the Gulf of Naples (type locality) to Japan, including Brazil and Western Africa, we consider that this taxon should be revised. Also, Quiroga (pers. comm.) noted differences between T. brocchii specimens from different museums. The species T. brocchii may have a similar situation to the Pseudoceros bicolor complex, which consists of more than one species under the same pattern of coloration ( Litvaitis et al. 2010). Therefore, we assign our specimens to T. brocchii until a more detailed study is undertaken.

Figures

FIGURE 5. Thysanozoon brocchii (MNRJ-PLAT 14). A— in vivo, dorsal view. B – D (MNRJ-PLAT 15). B— ventral structures; C— sagittal section with indication of female reproductive structures; D— sagittal section with indication of male reproductive structures. cg: cement glands; fg: female gonopore; ma: male atrium; mg: male gonopore; ph: pharynx; pt: pseudotentacles; pv: prostatic vesicle; st: stylet; su: sucker; sv: seminal vesicle; ut: uteri; va: vagina; vs: vas deferens.