Marine Invertebrates of Bermuda Tiger Flatworm (Pseudoceros crozieri) By Katelyn Pisano and James B. Wood (Ed) Abstract Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links

Abstract


The tiger flatworm, Pseudoceros crozieri (Hyman 1939) is a marine polyclad flatworm that is named for its tiger-like stripes and orange coloration (Hyman 1939). It is generally small, growing up to about 40mm, and is found in colonies of its prey, the orange tunicate (Sterrer 1986). Although it is common in many areas, including Bermuda, there is little information known on this particular species as well as the entire class of Turbellaria (Karling 1978). The organism is sometimes identified as Maritigrella crozieri, and there is some debate of the family this organism belongs to, although most recent research indicates that it belongs to Euryleptidae.

Taxonomy


Phylum:Platyhelminthes

  Class:Turbellaria

    Order:Polycladida

      Family:Euryleptidae


Habitat


Pseudoceros crozieri, the tiger flatworm, can be found in most tropical waters, from South Carolina to Florida, and throughout the Caribbean and Bermuda. They can be found near colonies of mangrove tunicates, near the mangrove roots and any hard substrates in shallow, intertidal or subtidal waters. They are usually found in pairs on colonies of Ecteinascidia turbinata, the orange tunicate (Hyman 1939).


Ecology


Feeding:

Pseudoceros crozieri feed exclusively on orange tunicates, Ecteinascidia turbinata (Hyman 1939). To feed, the flatworm inserts its pharynx into the zooid of the tunicate and secretes proteases for external digestion. The tiger flatworm then sucks the digested parts from the test of the tunicate (Newman et. al 2000).

Reproduction:

Tiger flatworms are simultaneous hermaphrodites. They mate frequently, through hypodermic insemination. Organisms of this genus have one male copulatory complex (Hyman 1939). To find a mate, Pseudoceros crozieri relies on chemical compounds, which they can sense using their large pseudotentacles. Hypodermic insemination occurs when two individuals insert each other with their copulatory stylets (Sharer et. al 2004). Sperm is then transferred between individuals bilaterally in bundles (Newman et. al 2000). These sperm bundles travel up the parenchyma to the oviducts and fertilize the eggs, which are set down in egg masses. These eggs hatch into free swimming larvae in approximately 10 days. P. crozieri can also asexually reproduce through fission. When the individual divides into two or more parts, either on its own accord or due to predator interaction, it can regenerate the lost part. If a substantial amount of each part remains undamaged, more than one organism can grow back (Koopowitz and Holman 1988).

Anatomy:

P. crozieri can be identified by its obvious tiger-like stripes and coloration. On the dorsal surface, wavy black or dark brown stripes line the organism laterally from the center to the edge, and often end in a black dot. The background color of the animal can vary from whitish, to greenish, to orange, as it is dependent on the tiger flatworm’s prey, the orange tunicate (Hyman 1939). This bright coloration works as a visual defense against predators, indicating the unpalatability of the organism due to the chemical compounds absorbed from eating ascidians (Kicklighter and Hay 2005).
Marine flatworms all share the same general anatomy. They are dorsally flattened and very thin. All flatworms have bilateral symmetry and experience cephalization (Pechenik 2005). In the anterior region, the polyclad contains a cerebral ganglion knot, in which all nerve signals are received. To analyze its environment, the flatworm has mechanoreceptors along the epidermis, as well as photoreceptors on eyespots in the anterior region to sense light. The flatworm’s eyespots, or ocelli, are extremely simple and very little can be perceived besides light direction and intensity. Therefore, chemoreceptors are highly utilized by the organism to sense food and mates. P. crozieri are a very small species, only growing up to about 40 mm in length (Sterrer 1986). They are extremely delicate and smooth, and unlike many other polyclads, do not have dorsal papillae. Polyclads do not have gills, but breathe by diffusion through their skin. The edge of the flatworm’s body is lined with marginal ruffles, the amount of ruffles depending on the size of the organism. The epidermis is lined with thousands of cilia, and both inner and outer muscles helps to structure the animal. To further help form body structure, the flatworm has a hydrostatic skeleton. As a species of the family Polycladida, the tiger flatworm is characterized by a gut that contains multiple branches. This gut, along with the reproduction parts, takes up a large percentage of the flatworm’s body.

Growth Rate:

The regeneration of P. crozieri occurs very quickly. Often, individuals are completely regenerated after about ten days. After fission, wounds can begin to heal in as quickly as 15 minutes (Nentwig 1978). This regeneration is possible due to the organism’s possession of undifferentiated cells that can form a blastema and form the missing body region (Nentwig 1978).

Movement:

The tiger flatworm moves by crawling (or creeping), swimming, and looping. Movement occurs through undulations of the body, both by using muscles and body fluid in the mesoderm that is kept under pressure. The organism can also move across a substrate by beating the cilia on the ventral side of its body (Crozier 1918).

Recent Research


Recently, there have been many studies concerning the role of Maritigrella crozieri in antitumor medicine. The tunicate, Ecteinascidia turbinata, that P. crozieri feeds exclusively on is known to produce the chemical compound Ecteinascidin-743, or ET-743 (Proksch et. al 2003). When the flatworm ingests the tunicate, it absorbs this chemical as well. In nature, the compound deters predators from eating both organisms, but research has shown that it can also fight against tumors of various cancers (Scarpa and Wright 2004). Unfortunately, it is currently nearly impossible for scientists to reproduce the compound at its natural effectiveness in the lab. This would mean massive harvesting of P. crozieri and E. turbinata, destroying habitats and endangering populations. However, even harvesting these organisms would not be enough to produce effective amounts of the drug. In order to produce one gram of the drug, about one metric ton of ascidians would have to be harvested. This is an amount much more than current populations can provide (Proksch et. al 2003).
In 2003, studies were conducted on the light sensitivity of larvae of P. crozieri (Johnson and Forward 2003). P. crozieri produce Muller’s larvae, which is a form of free swimming larvae that somewhat resemble ctenophores. The studies show that as the larvae develop, they become more sensitive to light. The larvae are deterred by high intensities of light, and are attracted to blue-green light wavelengths, and avoid yellow-red regions of light (Johnson and Forward 2003).

Commercial Importance


Although there is currently no commercial importance assigned to Maritigrella crozieri, there may be in the future. P. crozieri may be able to provide sufficient amounts of ET-743 without depleting the population with future medical advancements. Exposure to ET-743 can help to cure a menagerie of diseases, possibly including breast cancer, sarcoma, ovarian cancer, and melanoma (Izbicka et. al 1998).

Bermuda Laws

There are no Bermudian laws concerning Maritigrella crozieri.

Personal Interest

While learning about the regeneration of flatworms in Marine Invertebrate Zoology, I became fascinated with the amazing abilities of the turbellarian class and wanted to conduct my independent research project on them. I proceeded to read Sterrer to find a specific species to study, and came upon the tiger flatworm, which was said to be fairly common in the area. After finding one during a field trip to the boat channel near Ferry Point to collect tunicates, I became increasingly interested in this beautiful, remarkable organism.

References

Crozier, W.J. 1918. On the method of progression in polyclads. Proceedings of the National Academy of Sciences 4:379-381.

Hyman, L.H. 1939. Acoel and polyclad Turbellaria from Bermuda and the Sargassum. Bull. Bingham. Oceanogr. Collec. 7: 1-26.

Izbicka, E., R. Lawrence, E. Raymond, G. Eckhardt, G. Faircloth, J. Jimeno, G. Clark, and D. D. Von Hoff. 1998. In vitro antitumor activity of the novel marine agent, Ecteinascidin -743 (ET-743, NSC-648766) against human tumors explanted from patients. Annals of Oncology 9: 981-987.

Johnson, K.B. and R.B. Forward Jr. 2003.Larval photoresponses of the polyclad flatworm Maritigrella crozieri (Platyhelminthes, Polycladida) (Hyman). Journal of Experimental Marine Biology and Ecology 282: 103-112.

Karling, T.G. 1978. Anatomy and Systematics of Marine Turbellaria from Bermuda. Zoologica Scripta 7: 225-248.

Kicklighter, C.E. and M.E. Hay. 2005. Integrating prey defensive traits: Contrasts of marine worms from temperate and tropical habitats. Ecological Monographs 76: 195-215.

Koopowitz, H. and M. Holman. 1988. Neuronal repair and recovery of function in the polyclad flatworm, Notoplana acticola. American Zoology 28: 1065-1075.

Koopowitz, H., D. Silver, and G. Rose. 1976. Primitive nervous systems. Control and recovery of feeding behavior in the polyclad flatworm, Notoplana acticola. Biol. Bull. 150: 411-425.

Nentwig, M.R. 1978. Comparative morphological studies of head development after decapitation and after fission in the planarian Dugesia dorotocephala. Trans. Amer. Micros. Soc. 97: 297-309.

Newman, L.J., Norenburg, J.L., and Reed, S. 2000. Taxonomic and biological observations on the tiger flatworm, Maritigrella crozieri (Hyman, 1939), new combination (Platyhelminthes, Polycladida, Euryleptidae) from Florida waters. J. Nat. Hist. 34: 799–808.

Pechenik, J.A. 2005. Biology of the Invertebrates (Fifth Ed.) Boston, MA: McGraw Hill.

Proksch, P., R. Ebel, R.A. Edrada, P. Schupp, W.H. Lin, Sudarsono, V. Wray, and K. Steube. 2003. Detection of pharmacologically active natural products using ecology. Selected examples from Indopacific marine invertebrates and sponge- derived fungi. Pure Appl. Chem. 75:343-352.

Scarpa, J and A. Wright. 2004. Culture of the tiger flatworm Maritigrella crozieri for anti-tumor compound harvesting. Global Aquaculture Advocate. In press.

Sharer, L., G. Joss, and P. Sadner. 2004. Mating behavior of the marine turbellarian Macrostomum sp.: These worms suck. Marine Biology 145: 373-380.

Sterrer, Wolfgang. 1986. Marine Fauna and Flora of Bermuda. Canada: Wiley Interscience. 203.


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