Crassimurex calcitrapa
Creators: name: Merle, Didier
name: Goldstein, Donald H.
name: Mckinney, Michael L.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Neogastropoda
Muricidae
Crassimurex
Crassimurex calcitrapa

description: PALEOECOLOGY OF CRASSIMUREX (S. S.) CALCITRAPA
Crassimurex (s. s.) calcitrapa is a euryhaline Lutetian species and clearly prefers intertidal or shallow subtidal brackish facies. In the middle Lutetian of the Paris Basin, it is common in several localities (La Ferme de l’Orme (at Beynes), Grignon, Villiers-Saint-Frédéric, Montchauvet, etc.).
At La Ferme de l’Orme (unit 6), the identification work allowed to recognize 46 species of mollusks (31 gastropopods and 15 bivalves) including only one driller, Crassimurex (s. s.) calcitrapa. It is the sole driller as no naticid and no other muricid is recorded in this paucispecific assemblage. This observation is very important, because in the absence of other predators, we can hypothesize that all the drill holes can only come from C. (s. s.) calcitrapa. In the same locality, it is associated with other euryhaline species. These include: Potamides lapidorum (Lamarck, 1804), Vicinocerithium calcitrapoides (Lamarck, 1804), Serratocerithium denticulatum (Lamarck, 1804) and Saxolucina saxorum (Lamarck, 1806). It is responsible for drill holes on V. calcitrapoides and S. serratum (Fig. 4 A-C). Crassimurex (s. s.) calcitrapa can be also a prey and traces of peeling by crabs are observed in seven specimens (Fig. 4D).
RESULTS
Different aspects of the growth of the shell of C. (s. s.) calcitrapa and the characteristics of the drill holes are developed below as follows: 1) growth and appearance of the sculpture is given to evaluate when the sculptural elements can protect the individuals; 2) prey size and predation pressure; 3) relationship of the size of the prey to the size of the predator based on the diameter of drill holes; 4) drill hole site selection; and 5) occurrence of multiple drill holes.
GROWTH AND APPEARANCE OF THE SCULPTURE
Adults of Crassimurex (s. s.) calcitrapa have small armoured shells and sculptural elements (spiral rows of cords, alignments of cord spines, reinforced varices) that can be considered as a deterrence to shell drillers. However, they are missing or thin in juveniles and appear during ontogeny. Therefore, an understanding of shell growth can help explain which areas of the shell were more easily drilled by predators during the life of individuals. We thus note that the ontogeny of these elements. Crassimurex (s. s.) calcitrapa bears a multispiral protoconch indicating planktotrophic larvae (Merle et al. 2011: text-fig. 61F) such that the protoconch is devoid of sculpture. The development of the spiral sculpture on the teleoconch was partly described byMerle & Pacaud (2002) who showed that all primary cords and cord spines on the convex part of the whorl (P1 to P5, see Merle 2001 for the terminology) are present on the 5th teleoconch whorl.
Observations of younger specimens demonstrate that P1 to P3 are already present on the third teleoconch whorl (Fig. 5A). More abapical cords on the siphonal canal (ADP, MP and ABP) appear during the fifth teleoconch whorl (Fig. 5C) and secondary cords appear later (Fig. 5D). Cord spines are present in the typical morphotype of the species present at La Ferme de l’Orme (unit 6). The ontogeny of the sculpture demonstrates a progressive appearance of its elements (spiral rows of cords and axial alignments of cord spines) and suggests that individuals become less vulnerable to predation as they grow, particularly when they reach the 5th whorl (see Fig. 5C). Also, the appearance of sculptural elements occurs with the thickening of the shell, which reinforces its resistance to drilling. In addition, cord spines and particularly P1 spine, which is more developed than the other cord spines, constitute an important mean of defense against predators.
PREY SIZE AND PREDATION PRESSURE
Sieving of samples from the unit 6 allowed us to collect 132 specimens of C. (s. s.) calcitrapa of which 14 specimens (Fig. 6; Table 1) display drill holes representing 10.61% of the total. The smallest specimen with signs of attack is 2.5 mm in length. The largest drilled specimen, an adult of 18.47 mm in height, has an incomplete hole, indicating an interrupted drilling process under unknown circumstances (e.g., another predator or perhaps abandonment from lack of success). Thus, 10.61% of all specimens are drilled during various ontogenetic phases ranging from very young specimens to young adults not exceeding 19 mm in height. Figure 7 illustrates the proportion of specimens not drilled versus drilled. These are divided into three size class intervals, one ranging from 0 to 9 mm in height (class I) and corresponding to juveniles very exposed to drilling, another ranging from 10 to 19 mm (class II) in which the drill holes are scarcer, and a class above 20 mm to 32 mm (class III) in which the specimens no longer have drill holes. The class I records 71% of the drill holes and clearly demonstrates that it is the most vulnerable class to this type of predation. In the class II, only four specimens, having a size varying from 10 to 19 mm, bear drill holes. This result is in accordance with observations demonstrating that the sculptural elements (cords and cord spines) appear in young adults and contribute to drill resistance via reinforcement of the shells by increasing its thickness.
RELATIONSHIP OF THE SIZE OF THE PREY TO THE SIZE OF THE PREDATOR
Based on the drill hole diameters, which can be correlated to the size of the attacker (Kowalewski 2004), individuals of all sizes drill conspecifics. On the bivariate plot Figure 8, we can observe that the class 0-7 mm displays the widest range of size hole ranging from 0.10 mm (for a specimen of 3.43 mm) to 1.2 mm (for a specimen of 7.06 mm). The hole of 0.10 mm is the smallest that we found and it was made likely by a very young individual.Conversely, 1.2mm corresponds to the largest hole encountered. Therefore, we can deduce that juveniles as well as adults were potential predators of juvenile and sub-adult individuals. In the class 7-32 mm, the size range of the holes is narrower, ranging from 0.95 mm to 1.2 mm, and seems to be the result of the action of larger individuals. This observation indicates that only adults only attack other adults. Furthermore, the two larger specimens of this class (H: 19.38 mm and 18.47 mm) bear unsuccessful attacks with unfinished holes, suggesting greater predation difficulty on larger individuals.
DRILL HOLE SITE SELECTION
All of the drilling attacks are based on an operating principle which consists of attacks systematically located between two varices (in the intervarices) and avoiding P1 spines that represent reinforcement of the shell. The only attack that does not follow this principle was made on the varix of an individual of 18.14 mm and ended in failure. On the spire of young specimens, the holes can be at different places (top of the whorl near the adapical suture, centre of the whorl or base of whorl, near the abapical suture). On the last whorl, holes are more commonly located on the centre of the whorl in the thinner part of the shell.
MULTIPLE DRILL HOLES
Three specimens have two drill holes. One is a small specimen of 4.45 mm in height and two, larger, are of 10.69 mm and 12.87 in height. We have also observed on C. (s. s.) calcitrapa prey species that multiple drill holes are a frequent occurrence (21.43% of the total) and that most swarming attacks involve predators of different sizes, determined by their drilling diameter; typically, one adult and several juveniles.
description: Published as part of Merle, Didier, Goldstein, Donald H. & Mckinney, Michael L., 2024, First evidence of cannibalism in Crassimurex (s. s.) calcitrapa (Lamarck, 1803) (Gastropoda, Muricidae) from the Lutetian of the Paris Basin (France), pp. 457-470 in Geodiversitas 46 (13) on pages 459-464, DOI: 10.5252/geodiversitas2024v46a13, http://zenodo.org/record/13789116