Zoological Studies

Vol. 61, 2022

(update: 2022.5.5)

Predation of Oysters Using an Autonomic Pharynx in the Oyster Leech Cryptostylochus sp. (Polycladida: Stylochidae)

Ching-Jung Teng1, Ying-Jung Su1, Chih-Yu Yeh1, and Wei-Ban Jie1,*

1National Experimental High School at Hsinchu Science Park, No.300, Jieshou Rd, East Dist., Hsinchu City 300, Taiwan. *Correspondence: E-mail: wbjie@nehs.hc.edu.tw (Jie).
E-mail: ally901119@gmail.com (Teng); h611119@nehs.hc.edu.tw (Su); rubyyehmail@gmail.com (Yeh)

Received 27 May 2021 / Accepted 28 January 2021
Communicated by Benny K.K. Chan

Oyster farming has been threatened by marine flatworms for over 40 years, but few studies have been done to address this issue. Here, we examine the predatory behavior of the polyclad flatworm Cryptostylochus sp. from Penghu, Taiwan. Its predation process consists of three parts: the attack, invasion, and ingestion period. During the attack period, which begins 4 or more hours before the invasion, protruding pharynges form fragments that we call “autonomic pharynges”. The autonomic pharynx is translucent white, membrane-like, and variable in length. Using time-lapse photography, we show that the pharynx moves around slowly and independently for roughly 10 hours before losing mobility. The autonomic pharynx moved toward the edge of the oyster shell and increases the frequency at which the oyster or clam opens and closes compared to the control group. The passageway demonstrates negative phototactic behavior in petri dishes. Linear regression showed a positive correlation between the number of autonomic pharynges and the clam mortality rate. Histological dissections showed that clam mantle tissue is externally digested by the autonomic pharynx. The fragments of multi-branched ruffled pharynxfrom polyclad flatworms slowly detach and play a critical role during the period of the attack on bivalves.

Key words: Stylochid flatworms, Polyclad, Predatory behavior, External digestion, Oyster farming.

Citation: Teng CJ, Su YJ, Yeh CY, Jie WB. 2022. Predation of oysters using an autonomic pharynx in the oyster leech Cryptostylochus sp. (Polycladida: Stylochidae). Zool Stud 61:7. doi:10.6620/ZS.2022.61-07

Supplementary Materials: Video S1 | Video S2