August 4, 2001
From: Leslie Chan
During March and April of this year, in Hong Kong, I witnessed more than four species of nudibranchs being consumed by the same species of orange nudibranch (Gymnodoris inornata) which are fast moving and have a powerful suction to overcome their victims. All these photos are of natural occurrences, in no case did I offer the nudibranchs to the Gymnodoris as food. These photos show Chromodoris lineolata being eaten. [Ping Chau, Hong Kong. 8m depth. March 2001. Gymnodoris - 4 cm long].
In March and April I was staying underwater 7 hours a day and 4 days a week. I am skilled at scuba diving so I spend more than two hours a dive. I also have good patience while I wait for my subjects. During March and April I saw lots of feeding episodes from Ping Chau in the north of Hong Kong, to Trio Island in the south. Once in Trio Island I saw two Gymnodoris eating different species of nudibranchs at the same time and in the same area. And I also took a photo showing the killer eating a pair of mating nudibranchs. All the photos were taken in the natural environment.
Once in Ping Chau, I discovered the Gymnodoris was moving very fast in one direction towards a nudibranch two or three feet away. I guess the killer sensed its prey even 2-3 feet away. In two cases when I was watching nudibranchs being eaten - Doriopsilla miniata [Trio Island]; Dendrodoris fumata, - I saw the Gymnodoris attack the prey from the back, it extended something like a tube to suck the underneath of the prey. It seemed very powerful and even raised up the prey. But in the case of Doriopsilla miniata they struggled for too long so I could not wait underwater to see the end. But in another case where Doriopsilla miniata [Steep Island] was being eaten the picture shows the moment I discovered them so I had enough time to witness that the victim was swallowed completely after 1.5 hrs.
firstname.lastname@example.orgChan, L., 2001 (Aug 4) Gymnodoris inornata - feeding behaviour (1). [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/4989
Thank you for these wonderful photos of Gymnodoris inornata feeding. I have divided the photos of it eating Doriopsilla miniata and Dendrodoris fumata into separate messages. Your observations are an excellent addition to Helen Hughes's (1985) interesting account on feeding in Gymnodoris inornata in Hong Kong. Her studies were laboratory based and included a series of trials where individuals of
Successful attacks on both Chromodoris orientalis and Dendrodoris cf. miniata usually consisted of the prey being grasped under the mantle edge in the vicinity of the gills. Attacks in which the dorsal surface of the prey was grasped often led to the animals escaping. During successful feeding, the orange buccal tube enters the prey's body through a thick ring of everted oral tube. The internal organs are the first part of the animals to be consumed, being sucked out through the buccal tube. As this happens, the body progressively shrinks until the body wall is an empty wrinkled sac. In the final stage this empty sac is also eaten. Feeding time varied from 23min to 4hr 28min and was possibly related to prey size. A number of G. inornata were also recorded to feed twice within a 2-6 day period.
Most species of Gymnodoris which have been observed feeding grasp the prey with their teeth and engulf it whole. apparently bites a hole in the body wall of its prey so that it can insert its proboscis and eat the viscera first.
• Hughes, H.P.I. (1985) Feeding in Gymnodoris inornata (Bergh) and Gymnodoris alba (Bergh) (Opisthobranchia). In: Proceedings of the Second International Workshop on the Malacofauna of Hong Kong and southern China, Hong Kong, 1983. (Eds: Morton,B; Dudgeon,D) Hong Kong University Press, Hong Kong, 627-633.