Thysanozoon brocchii ( Risso 1818 ) Grube 1840

Brusa, Francisco, Damborenea, Cristina & Quiroga, Sigmer, 2009, First records of Pseudocerotidae (Platyhelminthes: Polycladida: Cotylea) from Patagonia, Argentina, Zootaxa 2283, pp. 51-59 : 55-57

Species: Thysanozoon brocchii ( Risso 1818) Grube 1840

( Fig. 3 )

Synonyms: Tergipes brocchii Risso 1818 Planaria brocchii (Risso) Risso 1826

Planaria tuberculata Delle Chiaje 1828 Planaria verrucosa Delle Chiaje 1829 Stylochus papillosus Diesing 1836

Thysanozoon diesingi Grube 1840

Thysanozoon papillosum (Diesing) Grube 1840 Thysanozoon tuberculatum (Delle Chiaje) Grube 1840 Planaria dicquemaris Delle Chiaje 1841

Planaria dicquemaris var. verrucosa (Delle Chiaje 1829) Delle Chiaje 1841 Thysanozoon dicquemaris (Delle Chiaje) Oersted 1844 Eolidiceros panormus Quatrefages 1845

Eolidiceros brocchii (Risso) Quatrefages 1845 Thysanozoon panormus (Quatrefages) Diesing 1850 Thysanozoon fockei Diesing 1850

Thysanozoon spec. Schultze 1854

Planeolis panormus (Quatrefages) Stimpson 1857 Thysanozoon spec. Moseley 1877

Thysanozoon brocchii var. cruciatum Laidlaw 1906 Thysanozoon lagidium Marcus 1949

Material examined and locality. One mature specimen (25 mm X 15 mm) preserved in alcohol and as serial sagittal sections of the pharynx and the reproductive structures MPL 5958. Collected in March 2005 at Puerto Pirámides (42º 34 32.70 S, 64º 17 15.82 W), Península Valdés, Chubut, Argentina.

Distribution. Cosmopolitan. In the western Atlantic this species is known from the Lesser Antilles ( Marcus & Marcus 1968), the north coast of Brazil ( Marcus 1949, 1952) and recorded in this paper for the Península Valdés.

Description. External features. Form and Color: Oval, the edges of the body are slightly undulated. Live specimens are dorsally yellowish brown with papillae covering the entire surface. The papillae along the midline of the body are longer and they diminish in size towards the periphery of the body. These papillae are darker than the rest. The margin lacks papillae and it is delineated by a thin and discontinuous black line; the apical region of the pseudotentacles is white. The pseudotentacles are pointed, ear-like, and their anterior dorsal region is dark brown. The pharynx is located in the first fourth of the body and is formed by 4–5 simple and shallow folds. The sucker is large and located in the first half of the body, posterior to the female gonopore.

Eyes: The cerebral eyes are arranged in a horseshoe-shaped cluster. The dorsal pseudotentacular eyes are arranged in four separate longitudinal clusters, across the pseudotentacles. The ventral pseudotentacular eyes occur in two clusters.

Gonopores: Two male gonopores are present just posterior to the pharynx, one on each side of the midventral line. A female gonopore is positioned on the midventral line, immediately posterior to the male gonopores.

Internal features. Epidermis and musculature: The body wall is thicker on the ventral surface than on the dorsal surface. The body musculature is organized in three well-developed layers. The external one, which is the thinnest, is longitudinal and followed by circular fibers and a developed innermost layer of diagonal muscles. These three layers are more developed on the ventral surface. It is also possible to observe dorsoventral fibers along the body. The epidermis is not well developed, however; the dorsal epidermis includes the formation of the papillae which are conical and more robust in the midline of the body and slender towards the margins.

Reproductive anatomy: Male reproductive system – Numerous testes (60 µm in diameter) along the ventral surface of the body are arranged in 3–4 rows. This species has double male reproductive structures and their configuration is the same as previously described by Marcus (1949, 1952). The prostatic vesicle is oval (300 µm long X 150 µm wide) and has a well-developed musculature, its duct joining the ejaculatory duct before the papilla ends. The penis papilla bears a stylet (230–250 µm long). Female reproductive system – It is typical of pseudocerotids having a short and ciliated vagina, directed backwards and surrounded by numerous cement glands. A large number of ovaries are scattered dorsally.

Taxonomic remarks. In terms of taxonomy, Thysanozoon is one of the most difficult genera among pseudocerotids. In general, the shape and distribution of the papillae and the coloration are the most useful characters for the identification of the different species. T. brocchii was initially described for the coast of Nice in the Mediterranean Sea ( Risso 1818) and later recorded from the Western Atlantic. Marcus (1949, 1952) described T. lagidium from Ilha de São Sebastião, Brazil and considered it close to T. brocchii – to which he compared it. However, Marcus and Marcus (1968), after comparing specimens of T. brocchii from the Gulf of Naples with specimens of T. lagidium from Brazil and the Caribbean, and analyzing in detail internal and external features, concluded that the two nominal species were synonyms. The same criteria were applied by Faubel (1984) and followed by us herein. Prudhoe (1985), on the other hand, considers T. lagidium a separate species from T. brocchii .

Figures

FIGURE 3. Thysanozoon brocchii. A, dorsal view of live specimen. B, ventral view of live specimen. Arrow heads show male gonopores.