PREZANT: ANTIPREDATION MECHANISM OF PHYLLODOCE MUCOSA 



were fed to the fish before and following be- 

 havioral experiments. These worms, which were 

 fi'om various size classes, included: Spio filicornis 

 (Spionidae) and Nephtys incisa (Nephtyidae) col- 

 lected from Nahant Bay: and Glyccra amencana 

 ( Glyceridae), Ner-eis virens iNereidae), 

 Scolecolepides viridis ( Orbiniidae), and Hydr-oides 

 dianthus (Serpulidae) collected from Henlopen 

 Flats. 



The feeding behavior of each species of fish, 

 e\c\uAmg Prioi^otuaevolans and Phol is giinnellufi, 

 was tested quantitatively viithPhyllodoce mucosa 

 and Scoloplos fragUis. Fish were starved for 24-48 

 h prior to testing. An individual fish was then 

 placed in a separate 4 1 glass aquarium or in a 

 small compartment on the seawater table and al- 

 lowed to acclimate for 60 min prior to experimen- 

 tation. Each test session was composed of two sets 

 of observations separated by a 5-min interval. A 

 set consisted of five 1-min trials each separated by 

 a 2-min interval. The trials entailed repeated ex- 

 posure of randomly chosen worms to potential 

 predation by each fish by dropping the worm from 

 a widemouthed glass pipette in close proximity to 

 the head of the fish. Since the fish were previously 

 fed from a pipette, they showed no hesitation m 

 accepting potential food items delivered in this 

 manner. Following release from the pipette, sev- 

 eral possible combinations of behavioral responses 

 of the fish were noted: 1) ingestion of the worm, 2) 

 rejection of the worm following an active attempt 

 at ingestion, 3) presence or absence of investiga- 

 tions of the worm by the fish (investigation is 

 defined here as an obvious "enticement" of the fish 

 to the worm without an attempt at ingestion), and 

 4) avoidance of the fish to the worm. The behavior 

 of P. mucosa was also noted following release from 

 the pipette and after rejection or avoidance by the 

 fish. 



If the worm sank to the floor of the aquarium, 

 either after rejection or without any contact with 

 the fish, it was taken off the bottom and again 

 dropped in front of the fish. This process was re- 

 peated as often as a l-min trial would allow. Dis- 

 counting delays due to behavioral interactions, 

 this averaged one exposure every 6 s. Prior to the 

 start of the first set of each test session and 1 min 

 after each trial ended, the fish was fed a small 

 portion of frozen brine shrimp to ensure active 

 feeding. If at any time during a test the fish re- 

 fused to eat the brine shrimp, the experiment was 

 terminated. Because of terminations, the number 

 of sessions per species offish varied. Initial qual- 



itative tests subjecting various other test or- 

 ganisms found on Henlopen Flats to potential 

 predation are also noted on Table 1. 



To test whether the mucoid secretion truly acts 

 as the predatory inhibitor in P. mucosa, two 

 further tests were carried out. First, mucus was 

 removed from the surface of P. mucosa by re- 

 peatedly sucking the worm in and out of a 

 narrow-mouthed glass pipette and then gently 

 dabbing it with a clean, lintless cloth. The worm 

 was then fed to a rock gunnel. Second, mucus from 

 P. mucosa was collected by placing several of the 

 worms in a small, dry stendor dish, allowing the 

 worms to physically irritate each other and thus 

 produce a copious supply of mucus. After the phyl- 

 lodocids were removed from the dish, a small 

 Nephtys incisa, which secretes very little external 

 mucus, was placed in it and allowed to accumulate 

 a thick mucoid coat. The nephtyd was then fed to 

 the rock gunnel. 



For histological .study of the mucus-producing 

 organs of P. mucosa, entire worms were fixed in 

 Zenker's or Hollande's fixatives and embedded in 

 polyester wax. Blocks were cut at 5 ixm and sec- 

 tions stained with Mallory's "Azan" or toluidine 

 blue in l.O'ii borax. 



To examine the ultrastructure of the parapodial 

 cirri of P. mucosa, small worms were fixed for 1 h 

 in cold Anderson's fixative, cut into 2 mm sections 

 with a razor blade, thoroughly rinsed with phos- 

 phate buffer (pH 7.2), and postfixed for 1 h in 2.0% 

 osmium tetroxide in a phosphate buffer. Following 

 dehydration in a gi'aded acetone series, the speci- 

 mens were embedded in Spurr's low viscosity 

 medium and polymerized at 60 C for 48 h. Thin 

 sections, cut on a Porter-Blum'' MTl ultramicro- 

 tome using glass knives, were stained with uranyl 

 acetate and Sato lead citrate. Sections were 

 examined with a Philips EM201 transmission 

 electron microscope at an accelerating voltage of 

 80 kV. 



RESULTS 



Response of Fish 



Results of the feeding experiments for the vari- 

 ous species offish being fed P. mucosa along with 

 the length of each are summarized in Tables 2 and 



^Reference to trade names does not imply endorsement by the 

 University of Delaware, College of Marine Studies or by the 

 National Mai'ine Fisheries Service. NOAA. 



607 



