Thysanozoon nigropapillosum ( Hyman, 1959 )

Jie, Wei-Ban, Kuo, Shih-Chieh & Mok, Hin-Kiu, 2014, Re-description of Thysanozoon nigropapillosum (Polycladida: Pseudocerotidae) from the South China Sea, with observations on a novel pre-copulatory structure, sexual behaviour and diet, Raffles Bulletin of Zoology 62, pp. 764-770 : 765-767

Thysanozoon nigropapillosum ( Hyman, 1959)

( Figs. 2 , 3 )

Acanthozoon nigropapillosus – Hyman, 1959: 581–583 (Type locality: Falarik Islet, Ifaluk Atoll, central Pacific Ocean). Thysanozoon nigropapillosum – Faubel, 1984: 213 (New combination).

Material examined. 1 specimen (35 × 20 mm) ( TMPL000001 ), subtidal zone at Hejie, Hengchun , Pingtung County. coll. W. B. Jie, 1 February 2012 ; 1 specimen (33 × 18 mm) ( TMPL000002 ); subtidal zone at Hejie, Hengchun , Pingtung County. coll. W. B. Jie, 2 February 2012 . 1 specimen (24 × 16 mm) ( TMPL000003 ); subtidal zone at Longdong Bay , New Taipei City. coll. W. B. Jie, 6 July 2012 . 1 specimen (10 × 9 mm) ( TMPL000004 ), subtidal rhabdites, which were concentrated more at the tip of the papillae than on the surface between the papillae ( Fig. 4A, B ). These rhadites purportedly have either a defensive or a secretory role in all polyclad flatworms ( Martin, 1978) .

Rhabdites were also present on the surface of both the male and female reproductive organs. The inner surface of the male genital atrium ( Fig. 4C ) contained more rhabdites than the female pore ( Fig. 4D ).

Distribution and habitat. Thysanozoon nigropapillosum ( Hyman, 1959) is not only abundant in Taiwan ( Fig. 5A ), but probably also in the Indian Ocean and tropical western Pacific ( Fig. 5B ). Gosliner et al. (1996) posted a picture of a flatworm having a white margin with yellow-tipped papillae that was labelled T. nigropapillosum ( Hyman, 1959) and offered their collecting distribution including Maldives, Sri Lanka, Indonesia, New Guinea and Solomon Islands.

July 2011, from 1530 hours to 1541 hours, 12 m depth, in Longdong bay (121°27ʹ56ʺN, 25°0ʹ43ʺE), northeast Taiwan. At the beginning of the encounter, two individuals circled each other. Subsequently one of the individuals extended its paired penis towards its partner and then gripped its partner’s lateral outermost margin, in a chopstick-like fashion. In this unilateral insemination, after the spermatophore has been deposited on the epidermis, the sperm donor left, without receiving any sperm from its partner ( Fig. 9A, B ) .

Figures

Fig. 2. Thysanozoon nigropapillosum (Hyman, 1959). Anterior is to the right. A, dorsal view; B, ventral view. ce, cerebral eyespots; fp, female pore; m, mouth; mp, male pore; ph, pharynx; pt, pseudotentacle; s, sucker.

Fig. 3. Diagrammatic representation of the reproductive anatomy of Thysanozoon nigropapillosum (Hyman, 1959). A, male. e, ejaculatory duct; in, intestine; ma, male pore; pr, prostate gland; se, seminal vesicle; sp, sperm; st, stylet; v, vas deferens. B, female. c, cement gland; f, female pore; mi, main intestine; p, pharynx; v, vagina.

Fig. 4. Thysanozoon nigropapillosum (Hyman, 1959): rhabdites on epidermis (indicated by arrows). A, B, on the tips of papillae; C, distributed on the inner surface of the male atrium; D, distributed on the female pore.

Fig.5. Distribution of Thysanozoon nigropapillosum (Hyman, 1959) A, around Taiwan; B, type locality (hollow square), and the probably distribution of Newman et al. (2003) collection (filled triangles), the distribution of Gosliner et al. (1996) collection (filled circles) in Indo-west Pacific.

Fig. 9. Thysanozoon nigropapillosum (Hyman, 1959): copulation observed at Longdong bay, northeast coast of Taiwan, 25 July 2011. A, Dermal impregnation for unilateral insemination; B, One individual (right), with the paired penis stretched, gripping its partner (left) at the outermost margin. (spermatophore is indicated by an arrow)