Thysanozoon brocchii ( Risso 1818 )

Velasquez, Ximena, Bolaños, D. Marcela & Benayahu, Yehuda, 2018, New records of cotylean flatworms (Platyhelminthes: Polycladida: Rhabditophora) from coastal habitats of Israel, Zootaxa 4438 (2), pp. 237-260: 248-250

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Thysanozoon brocchii ( Risso 1818 )


Thysanozoon brocchii ( Risso 1818) 

( Fig. 7 View Figure )

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 diesingii 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) Örsted, 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: Three mature specimens collected at Sdot-Yam , off Caesarea , Israeli eastern Mediterranean Sea (29° 30' N, 34° 55’ E). a) One specimen (16x 12 mm, live, ZMTAU-VR25137). ReproductiveGoogleMaps 

structures sagittally sectioned but no anatomical information from histological sections was obtained. The remaining portion of the specimen preserved in ethanol 70%. Collected on 8 July 2013. b) One specimen (17x 13 mm, live, ZMTAU-VR 25138), preserved in ethanol 70%. Collected on 8 July 2013. c) One specimen (16x 13 mm, live, ZMTAU-VR 25139), preserved in ethanol 70%. Collected on 20 August 2013.

Habitat: Specimens found on the rocky shore, during low tide, under rocks dominated principally by ascidians (1 m depth).

Distribution: Cosmopolitan species found in Naples, Italy, Western Mediterranean Sea (Type locality) ( Risso 1818; Lang 1884); Tunisia ( Gammoudi et al. 2011, 2017; Gammoudi & Tekaya 2012); Egypt, eastern Mediterranean Sea ( Palombi 1928); East London, South Africa, Indian Ocean, and Rio de Oro, West coast of Africa, Atlantic Ocean ( Palombi 1939a, b); Canary Islands ( Vera et al. 2009); Iberian Peninsula (Noreña et al. 2014); Caribbean Sea ( Quiroga et al. 2004); Brazil ( Bahia et al. 2012, 2014, 2015); Argentina ( Brusa et al. 2009; Bulnes et al. 2011); Japan ( Yeri & Kaburaki 1918); Borneo, Vietnam, New Zealand, and England ( Prudhoe 1989); Persian Gulf and Gulf of Oman, Iran ( Maghsoudlou & Rahimian 2014); West Coast of India ( Pitale & Apte 2017). In this study, the specimens were found at Sdot-Yam, eastern Mediterranean Sea, Israel.

External anatomy. Oval body with numerous papillae over the dorsal surface. Longer, thicker and more abundant papillae along the midline, decreasing in size and number towards the margin and becoming completely absent in the border ( Fig. 7A, B View Figure ). Dorsal background variable in color, ranging from yellow to light brown and dark brown to black. Presence of white dots extending towards the margin. A white longitudinal median line and some specimens with two transversal white lines formed by white pigment and lighter colored papillae ( Fig. 7A View Figure ). A faint yellow submarginal line bordering the entire body is present. The papillae along the midline line are darker than those close to the margin. Presence of a clear rim dotted with white ( Figs. 7A, B View Figure ). The ventral side is whitish-grey. Pointed, ear-like, pale yellow with white tip pseudotentacles, scattered with white and brown spots and a pinkish tinge at the margin ( Fig. 7C View Figure ). Cerebral eyes arranged in horseshoe shape. Small clusters of few pseudotentacular eyes ( Fig. 7C View Figure ). Short ruffled pharynx located anteriorly ( Fig. 7D View Figure ). Two conspicuous male gonopores close to each other located posteriorly to the pharynx. A prominent female gonopore in the midline, posterior and close to the male gonopores. Sucker located behind the female gonopore ( Fig. 7D View Figure ).

Taxonomic remarks. Thysanozoon brocchii ( RISSO 1818)  is the type species of the genus but it represents perhaps, the most doubtful species within the suborder Cotylea in terms of taxonomic identifications. The problem goes back to its original description as a nudibranch Tergipes brocchii  ( RISSO 1818). The author failed in presenting figures and detailed information of the newly described species; thus, to date, uncertainty even exists at the phylum level for this first original record. Based on the presence of dorsal papillae, Grube (1840) erected the genus Thysanozoon  , made the new combination Thysanozoon brocchi  , and created simultaneously the new species Thysanozoon diesingii GRUBE 1840  . However, during those 22 years before this new combination, multiple species with apparent papillae (called “tubercules” in the old literature) on the dorsal surface were described. Likewise, after the creation of the genus, numerous new species within the taxon have been erected (see synonyms above). To date, T. brocchii  has approximately 20 synonyms and many other still remain as Incertae  sedis ( Faubel 1984). Sadly, most of these records are unsatisfactory and ambiguous descriptions hindering the appropriate comparison and accurate placement of the species.

Another aspect that has contributed to the problem is the lack of internal and external morphological characters. The relative homogeneity of the reproductive system has limited researchers to mainly using differences in color and shape of dorsal papilla to distinguish Thysanozoon  related-species. However, we know that this is not a good practice due to the high degree of color variation and cases of species complexes seen in pseudocerotids ( Litvaitis et al. 2010; Bolaños et al. 2016). Again, DNA-based methods are needed for future studies to investigate the significance of these morphological details. Unfortunately, molecular and additional morphological information from most, if not all of the old records is not possible to obtain due to missing holotypes, misidentifications, and poor specimen preservation.

Based on the number of synonyms, T. brocchii  is considered a cosmopolitan species and it has been largely accepted that the color greatly varies according to its geographic location. The specimens found in this study are yellowish-brown and dark brown which is consistent with color descriptions of previous reports ( Marcus & Marcus 1968; Brusa et al. 2009; Bulnes et al. 2011; Bahía et al. 2014). In addition, our specimens exhibit a clear rim and an extremely delicate yellow submarginal band encircling the entire body. Differently, Bahía et al. (2015) mentioned that specimens from another locality in the Mediterranean show a red marginal band. Likewise, specimens reported for India showed a pink tint at the periphery ( Pitale & Apte 2017). Maghsoudlou & Rahimian (2014) indicated a purple band for animals from Iran. Brusa et al. (2009) reported a thin and discontinuous black line delineating the body in the specimens from Argentina; however, this feature was not observed in animals from a nearby location ( Bulnes et al. 2011) nor for animals from other localities. Brown dots on the pseudotentacles are apparently a general feature for this species ( Brusa et al. 2009; Bulnes et al. 2011; Bahia et al. 2012, 2014, 2015). T. brocchi  is a common species in the Mediterranean Sea and it represents a new record for the Israeli Mediterranean coast.