Umbilical Attachments

Of 655 known deformities caused by epizoa, only 12 or a little more than 1% have epizoa attached on or near the umbilicus. In one-half of these specimens there are more than one Placunopsis attached to the ammonite. As evidenced by the low

Fig. 16.11 (a) Placunopsis (9.5mm) near umbilicus of Quenstedtoceras (L.) lamberti causing "hunchback" and "depression" deformations (BHI-5346). (b) Placunopsis near the umbilicus and on the venter of Q. (L.) lamberti caused the deep depression in the dorsum BHI-5353) (xl). (c) Q. (L.) lamberti with the epizoon gone; note the deformation near the umbilicus BHI-5397) (xl.2).

Fig. 16.11 (a) Placunopsis (9.5mm) near umbilicus of Quenstedtoceras (L.) lamberti causing "hunchback" and "depression" deformations (BHI-5346). (b) Placunopsis near the umbilicus and on the venter of Q. (L.) lamberti caused the deep depression in the dorsum BHI-5353) (xl). (c) Q. (L.) lamberti with the epizoon gone; note the deformation near the umbilicus BHI-5397) (xl.2).

numbers, this is the most unusual place for attachment, yet the most easily to see and distinguish.

Deformity. One or more epizoa attached near the umbilicus of the ammonite (Fig. 16.11a-c). This phenomenon has also been described as occurring in Pavlovia (well illustrated by Keupp, 1996), although there are no illustrations with the epizoon attached. Keupp and Ilg (1992) referred to this deformity as forma aegra undatispirata.

Cause. Newly hatched Placunopsis attached themselves in or around the umbilicus of the ammonite and then continued to grow (Fig. 16.12a-f). It may have been impossible for the ammonite to remove epizoa from this location. This point of attachment, of all places, was probably the best for the Placunopsis and the least disfiguring for the ammonite. The bivalve was able to survive for a longer time, and, if there were multiple epizoa (Fig. 16.10b), they may have been able to spawn and colonize new areas of the ocean; this could account for different sizes of Placunopsis on the ammonites. Placunopsis may have been able to "infect" other ammonites after they released their spat (as in living bivalves) into the currents and thus onto other ammonites.

The umbilical attachment site was not too bad for the ammonite. It had an easier time compensating for the additional weight of the epizoon, and its shell growth did not become as contorted as in some of the other attachment places. As seen in Fig. 16.12b-f, there is still considerable distortion around the umbilicus, some on the flanks, and occasionally on the venter, as a result of epizoa attached near the umbilicus.

Fig. 16.12 (a) Placunopsis (8.3 x 9.7mm) attached on the umbilicus of Quenstedtoceras (L.) lamberti (BHI-5360). (b) Placunopsis (10.5mm across) attached on the umbilicus of Q. (L.) lamberti (BHI-5343). (c) Placunopsis (9.7mm across) attached near the umbilicus of Q. (L.) lamberti BHI-5488). (d) Two Placunopsis (large one 7.1 x 9.5mm) attached near the umbilicus of Q. (L.) lamberti (BHI-5467). (e) Placunopsis (5mm across) attached near the umbilicus of Q. (L.) lamberti (BHI-5466). (f) Two Placunopsis (large one 10 x 10.7mm) attached near the umbilicus of Q. (L.) lamberti causing deformities to the dorsum (BHI-5343).

Fig. 16.12 (a) Placunopsis (8.3 x 9.7mm) attached on the umbilicus of Quenstedtoceras (L.) lamberti (BHI-5360). (b) Placunopsis (10.5mm across) attached on the umbilicus of Q. (L.) lamberti (BHI-5343). (c) Placunopsis (9.7mm across) attached near the umbilicus of Q. (L.) lamberti BHI-5488). (d) Two Placunopsis (large one 7.1 x 9.5mm) attached near the umbilicus of Q. (L.) lamberti (BHI-5467). (e) Placunopsis (5mm across) attached near the umbilicus of Q. (L.) lamberti (BHI-5466). (f) Two Placunopsis (large one 10 x 10.7mm) attached near the umbilicus of Q. (L.) lamberti causing deformities to the dorsum (BHI-5343).

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