Epizoa

D. Seilacher (2005, personal communication) tentatively identified the majority of the epizoa attached to the ammonite shell as Placunopsis, with occasionally some Ostrea (Fig. 1). Placunopsis were living, attached "guests" that seem to have interacted only with Quenstedtoceras (L.) lamberti, while leaving the other ammonite species in the zone alone. Seilacher (1960) referred to Placunopsis as a false oyster, based on the attachment of the right valve rather than the left valve, as in true oysters (such as Ostrea). In Placunopsis, the lower valve is flat, the upper valve is rounded, and the ornamentation is barely visible. Sometimes the shell structure seems to mimic the ornamentation of Q. (L.) lamberti, perhaps because the ammonite grew over the bivalves while they were still living and growing.

Placunopsis found at the Dubki Quarry seem to have been almost a plague on Quenstedtoceras (L.) lamberti, and are inferred to be the cause of shell deformations

Fig. 16.5 (a) Placunopsis (10 x 11 mm) exposed on Quenstedtoceras (L.) lamberti (BHI-5352). (b) Epizoa are missing in exposed void on the venter of Q. (L.) lamberti (BHI-5396) (x1). (c) Two small Placunopsis (6mm across) on Q. (L.) lamberti (BHI-6000). (d) Two large Placunopsis (5 x 7mm and 6 x 9mm) on Q. (L.) lamberti (BHI-5357). (e) Placunopsis (10 x 15mm) exposed on Quenstedtoceras (L.) lamberti (BHI-5470). (f) Placunopsis (10.5 x 15mm) exposed on ventrolateral shoulder of Q. (L.) lamberti (BHI-5383).

Fig. 16.5 (a) Placunopsis (10 x 11 mm) exposed on Quenstedtoceras (L.) lamberti (BHI-5352). (b) Epizoa are missing in exposed void on the venter of Q. (L.) lamberti (BHI-5396) (x1). (c) Two small Placunopsis (6mm across) on Q. (L.) lamberti (BHI-6000). (d) Two large Placunopsis (5 x 7mm and 6 x 9mm) on Q. (L.) lamberti (BHI-5357). (e) Placunopsis (10 x 15mm) exposed on Quenstedtoceras (L.) lamberti (BHI-5470). (f) Placunopsis (10.5 x 15mm) exposed on ventrolateral shoulder of Q. (L.) lamberti (BHI-5383).

in more than 700 specimens in our collections, although the overall percentage is unknown. By comparison, Ostrea were found on only eight specimens. While most Placunopsis are assumed to be juveniles, some seem to have approached adult size. Attached Placunopsis (that were able to be measured on Q. (L.) lamberti) range in size from 2.5 x 3 mm (Fig. 16.4b) to 16 x 18.5 mm (Figs. 16.1, 16.4b, 16.5). Most attached Placunopsis are probably smaller than 2 mm, but, if they are, they tend to be destroyed during preparation.

Fig. 16.6 (a) "Hunchback " deformity on Quenstedtoceras (L.) lamberti (BHI-5376) (x0.8). (b) "Hunchback" effect on the venter of Q. (L.) lamberti (BHI-5342) (x0.6). (c) Typical "hunchback" on the venter of Q. (L.) lamberti (BHI-5383) (x0.7). Note that this is the same specimen as Fig. 5b, but before preparation.

Fifteen Quenstedtoceras (L.) lamberti have serpulid worm tubes attached to them. Some of the worm tubes appear to have also grown on the ammonites while the ammonites were still alive (Fig. 16.2). Two specimens have large worm tubes that grew on both flanks and across the venter. There are no shell deformities observed resulting from worm-tube attachment, so even though some of the worms grew in a manner that suggests that the ammonites were alive, their attachment to empty ammonite shells could still be a possibility. There are no other types of epi-zoa detected on Q. (L.) lamberti or any other ammonite genus.

Schindewolf (1936) illustrated four specimens of Arietites and Schlotheimia from the Jurassic with individual worm tubes (serpulids) growing from one side of the venter to the other. These worms grew larger as the ammonite grew, and their placement on the ammonite shell was determined by how the ammonite shell rotated as the serpulid grew. Landman et al. (1987) observed serpulids, bryozoans, barnacles, and scyphozoans all attached on living Nautilus. If present-day serpulids and other epizoa can attach to living Nautilus, it is probable that, in the past, serpulids and other epizoa could and did attach to living ammonites (at least in some species).

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