An improbable opportunistic predator: the functional morphology ofPinna nobilis(Bivalvia: Pterioida: Pinnidae)

Abstract

The functional morphology ofPinna nobilisis described, with special reference to the uniquely pinnid pallial organ, the similarly unique buccal (formerly pallial) gland, the stomach and its contents. The pallial gland produces sulphuric acid which as well as functioning as a shell cleaning swab may be involved in prey capture. The buccal gland discharging into the oesophagus has proteolytic digestive functions while the stomach is adapted for the reception and digestion of captured, mucous-bound, mesozooplanktonic and epi- and endo-benthic, prey items.Pinna nobilisis thus not simply either an accidental or incidental predator of such species but is opportunistic. The buccal glands and stomachs of other Pinnidae are not so specialized as inP. nobilis,possibly indicating that in the particular, oligotrophic, environment of the Mediterranean and Adriatic Seas, and in which it is endemic,P. nobilishas, in addition to being a typical ctenidial suspension feeder, become an opportunistic predator. Although the deep sea representatives of the Septibranchia (Anomalodesmata) and Propeamussidae are obligate predators, this is the first record of any bivalve functioning as an opportunistic predator with unique morphological adaptations to facilitate this.

Stable isotope analyses reveal major nutritional deficiencies in captive vs. field juvenile individuals of Pinna nobilis

“…These results are in agreement with observations from previous studies suggesting the contribution of micro and mesozooplankton to pen shell diets (Davenport et al, 2011;Morton and Puljas, 2019) and support an overall central role of pelagic versus benthic food sources (Alomar et al, 2015). Our experiment with newly hatched Artemia nauplii also confirmed the actual ingestion of animal material, which was increased with the availability in the water column, thus supporting the description of opportunistic predator proposed by Morton and Puljas (2019). According to visual observations under the microscope, Artemia nauplii were only partly digested, which might also account for comparatively lower contributions of zooplankton vs. phytoplankton.…”

“…60.2%), but there may also be a significant contribution of the zooplankton fraction (up to 34.9%). These results are in agreement with observations from previous studies suggesting the contribution of micro and mesozooplankton to pen shell diets (Davenport et al, 2011;Morton and Puljas, 2019) and support an overall central role of pelagic versus benthic food sources (Alomar et al, 2015). Our experiment with newly hatched Artemia nauplii also confirmed the actual ingestion of animal material, which was increased with the availability in the water column, thus supporting the description of opportunistic predator proposed by Morton and Puljas (2019).…”

“…Similarly, the failure of larval cultures of P. nobilis (Trigos et al, 2018) due to an association between disease susceptibility and unbalanced diet formulation cannot be discarded. P. nobilis has been indicated to ingest a diversity of phytoplankton species (up to 68 different taxa), along with large quantities of detrital material (up to 95%), and some micro and mesozooplankton species (Davenport et al, 2011;Morton and Puljas, 2019), although the assimilation of the different fractions has not been assessed and dietary contributions are inferred from presence within stomach contents. For logistical reasons, most larval hatcheries including attempts conducted with P. nobilis (Trigos et al, 2018), only use 2-3 species of microalgae (at least one Haptophyceae and one Bacillariophyceae; Robert and Gérard, 1999) to feed the bivalves without a clear knowledge of their dietary requirements (Muller-Feuga et al, 2003).…”

Experimental tests of bivalve shell shape reveal potential tradeoffs between mechanical and behavioral defenses

“…The shapes of bivalve shells are often indicative of life mode: whether the organism lives above or below substrate, how it feeds, and how or if it locomotes 7 , 8 . The relatively simple but highly diverse shapes of bivalve shells are frequently used to illustrate the concept of functional morphology—the idea that morphology can be attributed to ecological role 9 – 13 . In fact, the ecological and evolutionary constraints on bivalve shell shapes are so restrictive that even very distantly related bivalves living in similar environments show convergence on a limited range of morphologies 7 , 8 , 14 , 15 .…”

Noble Pen Shell (Pinna nobilis) Mortalities along the Eastern Adriatic Coast with a Study of the Spreading Velocity

“…The live mollusks that were sent to the laboratory were opened by cutting the adductor muscle according to the methods described by Morton and Puljas [32]. The in situ appearance of the organs was evaluated.…”