Thysanozoon brocchii ( Risso 1818 )

Bahia, Juliana, Padula, Vinicius, Lavrado, Helena Passeri & Quiroga, Sigmer, 2014, Taxonomy of Cotylea (Platyhelminthes: Polycladida) from Cabo Frio, southeastern Brazil, with the description of a new species, Zootaxa 3873 (5), pp. 495-525 : 509

Thysanozoon brocchii ( Risso 1818)

( Figs. 11 and 12 )

Material examined. Two specimens (MNRJ-PLAT 41, 12 x 8 mm; 23 x 12 mm), the bigger as sagittal sections of reproductive structures (23 slides) collected 0 9.12.2007 at Enseada 2, Ilha do Papagaio, Cabo Frio, Brazil (22°53'45.43"S, 41°59'5.54"W). One specimen in ethanol 70% (MNRJ-PLAT 42, 16 mm x 12 mm) collected 30.03.2008 at Enseada do Mimi, Ilha do Papagaio, Cabo Frio, Brazil (22°53'30.85"S; 41°59'9.52"W). One specimen (MNRJ-PLAT 43, 13 mm x 9 mm) collected 21.04. 2008. One specimen (MNRJ-PLAT 44, 7 x 6 mm) collected 13.12.2008. One specimen (MNRJ-PLAT 45, 23 mm x 15 mm) collected 0 7.02.2009. One specimen (MNRJ-PLAT 46, 13 mm x 9 mm) collected 10.04.2009. One specimen (MNRJ-PLAT 47, 25 x 19 mm) collected 17.04.2010. All specimens or parts preserved in ethanol 70%. All collected at Praia das Conchas, Cabo Frio, Brazil (22°52'33.05"S, 41°58'39.27"W).

Distribution. Originally described from Naples, Italy (type locality; Risso 1818). It is considered a cosmopolitan species, reported from other regions of the Mediterranean Sea, United Kingdom, south and west of Africa, Florida, Caribbean coast of Colombia ( Quiroga et al. 2004b), Brazil, Japan and New Zealand ( Prudhoe 1985). Recently reported from Canary Islands ( Vera et al. 2008), Argentina ( Brusa et al. 2009) and from Northeastern Brazil (Bahia et al. 2012).

Diagnosis. Brown to yellowish brown with longitudinal median line cream colored; cream transversal line can also be present, forming a cross. Dorsal surface papillated, papillae size decreased toward the margin, some being spotted with white. Male system duplicated. Seminal vesicle elongated and located diagonally to the body.

Taxonomic remarks.

We have found specimens both larger and smaller (from 25 x 19 mm to 7 x 6 mm) than described originally from Brazil (13 x 7 mm), and specimens with similar size as specimens from Argentina (25 x 15 mm). They all fit the original description ( Risso 1818) and the description of the Brazilian variation ( Marcus 1949; Marcus & Marcus 1968). As observed by Marcus (1949), Brazilian specimens of T. brocchii have more invaginations in the female atrium than other Thysanozoon species. Also, T. brocchii differs from other Atlantic species, such as Thysanozoon nigrum , T. flavotuberculatum , in the coloration pattern and eyespot groups ( Hyman 1939a). The color variation found is illustrated in Figure 12 . The papillae size varies from 0.5 to 0.3 mm and decreases toward the margin, being absent only in a 0.5 mm area near the margin were there are black pigmentation spots ( Fig. 11 B and D). Because of the worldwide distribution of this species we recommend the use of molecular markers in a future study, to test if it is really a single species or a complex of morphologically similar species.

Ecology. Specimens of Thysanozoon brocchii were collected over ascidians in the family Didemnidae in several ocasions. This species, together with Lamellaria molluscs, was observed frequently near colonies of this type of ascidians, especially at Praia das Conchas ( Fig. 11 H and I). The relationship between these animals was reported both in the original description of T. lagidium ( Marcus 1949: pg 83) and later ( Marcus & Marcus 1951). In some specimens we found uterine ducts containing oocytes that reach 100 µm diameter. The species T. brocchii was observed to be very active and presented swimming behavior when disturbed.

Figures

FIGURE 11. Thysanozoon brocchii (MNRJ-PLAT 46). A. in vivo; B. dorsal view, highlighting dorsal papillae; C. detail from the anterior dorsal region; D. detail from the anterior region; E. sagittal section of dorsal papillae; F. sagittal section of male reproductive structures; G. sagittal section of female reproductive structures; H. T. brocchii in situ over Didemnidae ascidians; I. tipical environment found under rocks at Praia das Conchas. as: ascidians; ce: cerebral eyespots; cg: cement glands; cp: cement pouch; dp: dorsal papillae; fa: female atrium; fg: female gonopore; la: Lamellaria; ma: male atrium; mg: male gonopore; pa: penis papilla; ph: pharynx; pt: pseudotentacle; pv: prostatic vesicle; st: stylet; sv: seminal vesicle; te: tentacular eyespots; va: vagina.

FIGURE 12. Color pattern variation in Thysanozoon brocchii. A. MNRJ-PLAT 43; B. MNRJ-PLAT 41; C. MNRJ-PLAT 46; D. MNRJ-PLAT 44; E. MNRJ-PLAT 47; F. MNRJ-PLAT 45.