Thysanozoon nigropapillosum (Hyman 1959) (??mm)

Featured Invertebrate Data


Frequency on Okinawa: Collection Data (only a single collected specimen):
[brackets indicate range for all Okinawa-collected specimens of the species]

Species Account:

        Thysanozoon nigropapillosum is considered to be uncommon in the waters of Okinawa's main island as I have collected only a single animal, although I've photographed more than a half dozen individuals over a period of more than twenty years of Okinawa diving.

There are numerous images of T. nigropapillosum found on-line, one of these sites with numerous still photos is seen at this Google site. In addition, here's a a swimming individual photographed from the Red Sea via YouTube.

        The following short description of Thysanozoon nigropapillosum is taken from Wikipedia:

Thysanozoon nigropapillosum is a species of polyclad flatworms belonging to the family Pseudocerotidae. Some common names include gold-speckled flatworm, marine flatworm, yellow papillae flatworm, yellow-spotted flatworm, and yellow-spotted polyclad flatworm.

Description Thysanozoon nigropapillosum has a long body and broad shape. They grow up to 3 in (76 mm). The dorsal surface is deep black and covered with numerous yellow-tipped papillae varying in size. The ventral surface is dark brown. The outer margin of the body is slightly wavy and bordered in opaque white. They have small, ear-like pseudotentacles in the middle of the anterior end. They swim by propelling themselves through the water with a rhythmic undulating motion of the body.

        The following re-description of Thysanozoon nigropapillosum is from Wei-Ban Jie, Shih-Chieh Kuo & Hin-Kiu Mok. (2014).

Distribution and habitat. Thysanozoon nigropapillosum (Hyman, 1959) is not only abundant in Taiwan, but probably also in the Indian Ocean and tropical western Pacific. Gosliner et al., p. 111 (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.

During the day, it is often seen in coastal reef waters at depths between 1 and 20 metres, but is rarely seen at night. When water currents are strong or subjected to disturbance by a diver, these flatworms can swim quickly by rhythmic contractions and undulation of their body margin.

DISCUSSION We suggest that Thysanozoon nigropapillosum as described here is the most common shallow water marine flatworm species in Taiwan, because, since 1959, no scientist or diver has recorded flatworms that fit the original description of the colour pattern in the holotype of this species. Despite the loss of the original colour in the preserved holotype, the shape of the papillae and the colour proportion of the papilla´s tips remain visible in the holotype, and these are consistent with more recent observations made on living specimens. It is plausible that Hyman did not personally examine a fresh holotype, and the color pattern was reported according to the notes of the collector, Migel, who may have mistakenly described the color patterns. This paper therefore amends the description of this species.

The relationships between polyclad flatworms and nudibranchs have been studied (Newman & Cannon, 1994). Since both animals can bear toxins, the similarity of their colour patterns is generally believed to be due to a form of Mullerian mimicry. Both species benefit from being avoided by their predators. However, the extent to which this mimicry actually works in the sea still remains uncertain, as the potential common predators of polyclad flatworms and nudibranchs are unclear. Whilst nudibranchs are uncommon, the chances of encountering polyclad flatworms are even less. In eight years of observation (pers. unpubl. data), the most widespread and dominant nudibranch in Taiwan appears to be Phyllidiella pustulosa. It has a black dorsal coloration with pale-tipped compound tubercles. The colour of its dorsal surface has the same pattern as that of Taiwan´s most common flatworm, T. nigropapillosum. Considering the encounter rate for these two common species, Mullerian mimicry between Thysanozoon and Phyllidiella is much more possible than for other flatworms or nudibranchs.

Polyclad flatworms are benthic predators. They are known to feed on a wide range of invertebrates, including bivalves, gastropods, sessile tunicates and barnacles (Newman & Cannon, 2003). They generally occur where their specific food is abundant. In the case of T. nigropapillosum, they have been observed most often crawling over its favoured prey, colonial tunicates, and we report for the first time didemnid tunicate spicules in the food pellets and main intestine of T. nigropapillosum. These flatworms may well feed on other prey, but these have not been determined. When feeding, they stretch out the pharynx to engulf their prey. Their mouth opens just under their body so it is difficult to make direct observations. However, polyclads are mostly oligophagous animals, so if more pellets were available, the polyclad flatworm´s diet would be more fully understood.

Marine flatworms are hermaphrodites; each individual has fully functional male and female reproductive systems.


Literature Cited:

        I've added a second page w/ a series of images of the Okinawan material.

        In addition, I've added a link to the current and past featured invertebrates via a list and thumbnails.

Page Date: 01 Jun '18
Page Modification Date: 01 Jun '18
Digitally manipulated photo
Copyright © 2018 Robert F. Bolland