The biology and functional morphology of Pteria brevialata (Bivalvia: Pterioidea), epizoic on gorgonians in Hong Kong

Pteria brevialata characteristically attaches to Hicksonella princeps (Cnidaria: Gorgonoidea) at depths > 10 m in Hong Kong and the South China Sea. Attachment is by a stout byssus to the basal regions of the gorgonian colonies. The shell appears typical of the Pteriidae, but closer inspection shows that the antero-ventral margin, in particular, moulds itself to the form of the cylindrical gorgonian, which also changes its growth form, so that securer attachment is achieved. The margin of the right valve is not nacred so that the flexible outer prismatic layer adpresses firmly against the more extensively nacred left valve when they close; mantle and ctenidia also being withdrawn deeply. This is probably an anti-predation device. There are no mantle fusions, even between posterior inhalant and exhalant streams. The mantle margin is, however, complexly tentaculate. Pteria brevialata is monomyarian with reduced anterior byssal retractor muscles. The anterior face of the shell is thus greatly reduced whereas the posterior is inflated and postero-dorsally 'winged'.
Other features of the anatomy are described, including the ctenidial eyespot and simple photoreceptors in the inner component of the duplicated outer mantle folds, under the periostracum. Similar structures in other pterioideans and arcoideans suggest a close relationship between their respective orders.
It is concluded that gorgonian-associated pterioids can be derived from an epibyssate, crevice-dwelling ancestor, exploiting, as solitary individuals, the currents and clean oceanic waters above the substratum. This has three important advantages: (a) removal from surface-roving predators (the gorgonian providing additional protection); (b) exploitation of a niche hitherto unoccupied by bivalves and (c) removal of the animal from the sea-bed and exclusive exploitation of potential food held in suspension. Current stresses to attachment are avoided by modifications to the shell.     

The functional morphology of Mactrinula reevesii (Bivalvia: Mactroidea) in Hong Kong: adaptations for a deposit-feeding lifestyle

The shallow subtidal mactrid bivalve Mactrinula reevesii is a deposit-feeder in the southern and south-eastern oceanic waters of Hong Kong. Buried obliquely, large quantities of fine sediment are taken into the mantle cavity and sorted on enormous labial palps. The small ctenidia probably have little value in collecting material, amounts taken in being too large. The mid gut is long and complexly folded inside the visceral mass. It is also capable of distension, although superficial visceral muscles maintain internal tonus. The rectum is narrow and creates compact faecal pellets.
Most interest is in the ventral mantle margin which is, posterior to the pedal gape and the base of the inhalant siphon, united by a sheet of cuticle. There is no fourth pallial aperture. There are, however, two pairs of flaps extending along the posterior third of the internal ventral mantle surface. These arch over left and right mantle rejection tracts which transfer unwanted material to the base of the inhalant siphon for final expulsion. The mantle flaps prevent such material from being returned to the anterior end of the mantle cavity, for palp reprocessing, when new material arrives. They, thus, maximize sorting efficiency by separating unsorted from sorted and rejected material.
Other mactrids have similar mantle flaps which they use in different ways, including the channelling of unwanted material to a fourth pallial aperture for expulsion, as in Lutraria lutraria. The Mactridae have thus evolved a unique method of increasing the efficiency of pseudofaecal waste rejection which has thereby facilitated the deposit-feeding lifestyle by the diverse representatives of this family.     

The hydrodynamic characteristics of six scallops of the Super Family Pectinacea, Class Bivalvia

Measurements have been made in a recirculating water channel of the lift and drag forces on the plaster casts of six scallops of the Super Family Pectinacea, Class Bivalvia, namely Chlamys varia, Amusium pleuronectes, Pecten irradians, Pecten senatorius, Pecten pallium and Pecten alba . The results have shown that the shape of the lift curve for the bi-convex shells is similar to that of a comparable aerofoil shape, a discus, although with lower values. The piano-convex shell had similar lift values but a lower stall angle.
All the shells produced more induced drag than the discus and also had a higher form drag. Generally there was a correlation between the form drag coefficient and the thickness to chord ratio of the shell.
It is suggested that Amusium pleuronectes would be the best adapted for swimming flight, because of its low drag characteristics, followed by Pecten senatorius and Pecten irradians . It is thought that, although Pecten alba was likely to be the worst swimmer of those tested, it was also likely to be best able to escape by its ability to develop lift.     

The status of the Plicatulidae and the Dimyidae in relation to the superfamily Pectinacea (Mollusca: Bivalvia)

In the families Pectinidae and Propeamussidae (scallops) the massive rounded inner ligament layer which provides the opening thrust is bounded by long stretches of anterior and posterior outer ligament layer which, in the absence of teeth, maintain alignment of the valves. In the Spondylidae these outer layers migrate centrally to unite on either side of the inner layer, the primary ligament becoming transversely instead of longitudinally disposed. A secondary ligament of fused periostracum with no tensile strength unites the still long hinge line but secondary ball and socket teeth assume responsibility for alignment of the valves. In the Plicatulidae and the Dimyidae there is the same transverse disposition of the primary ligament but the mantle margins overarch this with production of a continuous longitudinal "external" secondary ligament above the "internal" primary ligament. Although resemblances with the Spondylidae are greater than with the Pectinidae and Propeamussidae, differences from all three are great enough to justify separation of the other two families into a new superfamily Plicatulacea. The monomyarian condition in the Plicatulidae could well have arisen from conditions similar to those in the Dimyidae, that is following cementation when dimyarian and not following byssal attachment as it does in the three families of the now proposed restricted Pectinacea.     

The ecology and functional morphology of Trigonothracia jinxingae (Bivalvia: Anomalodesmata: Thracioidea) from Xiamen, China

All anomalodesmatans are 'rare' but Trigonothrucia jinxingae is relatively common in Xiamen Harbour, Fujian Province, China. This is because the species has a life span of approximately one year and is a simultaneous hermaphrodite, probably with either a short or absent planktonic larval stage. That is, success results from rapid maturation, self-fertilization, direct development and within-habitat recruitment over an extended period in early summer.
Trigonothracia jinxingae is interesting in another way, however. The Thraciidae is the Mesozoic stem group of the Thracioidea which also contains the more modern (Caenozoic) Laternulidae and Periplomatidae. Features of the anatomy of T. jinxingae , such as the method of hydraulically moving the foot by the pumping of blood into a capacious pallial haemocoel, and the structure of the stomach, are reminiscent of the earliest (Palaeozoic) anomalodesmaans, i.e. the Pholadomyoidea, represented today by Pholadomya candida. The thraciid Asthenothaerus sp. (Pelseneer, 1911) even has, like P. cundida , an opisthopodium on its visceral mass. P. candida , however, fed on sub-surface deposits using its foot. T. jinxingae is also a deposit feeder, but on surface deposits using the inhalant siphon.
Modern periplomatids resemble thraciids in their separate siphons, but both representatives of this family and the Laternulidae are suspension feeders with extensive sorting areas on the wall of the stomach to process such material. The Thraciidae thus form a link between the oldest, pedal feeding, pholadomyoidean anomalodesmatan and the most advanced, suspension feeding, laternulids and periplomatids.     

The functional morphology of Sinonovacula constricta with a discussion on the taxonomic status of the Novaculininae (Bivalvia).

Sinonovacula constricta is representative of two genera of deep burrowing bivalves hitherto placed in the Novaculininae of the Tellinacea. This species, widely cultured in China, has not previously been critically examined. Aspects of its anatomy show that it should more properly be placed in the Solenacea. The presently accepted classification of this superfamily suggests that it should be placed close to Pharella in the Cultellidae but it is clear that the group requires more detailed re-examination.
Sinonovacula is somewhat posteriorly elongate with long separate siphons. The anterior pedal gape acts as a valve to the piston-like foot enabling rapid reburrowing to occur. Sensory tentacles around the pedal gape respond to mechanical disturbance and water can be squirted from the gape to, presumably, flush away the source of irritation. Modifications of this kind are rare in the Bivalvia.
The anatomy of Sinonovacula is described and related to its life style as a suspension feeder in soft intertidal muds. The ciliary currents of the mantle cavity are powerful, the labial palps in particular being large as compared with the relatively small ctenidia. The stomach is adapted for dealing with large amounts of food, though the sorting areas are not extensive; principal sorting is clearly the function of the labial palps. The style sac and mid-gut are separate (unlike the conjoined style sac and mid gut of the Tellinacea), and ensure separation of the style from the sediment loaded mid gut.
In many ways Sinonovacula foreshadows the highly modified true razor shells and conditions in these bivalves can be accounted for by further posterior elongation of a bivalve essentially similar to Sinonovacula.     

Inheritance of the general shell color in the scallop Argopecten purpuratus (Bivalvia: Pectinidae)

Although some external coloration and pigmentation patterns in molluscan shells may be attributable to environmental factors, most variation in these phenotypic characters depends on uncomplicated genetic mechanisms. Genetic research on inheritance of color variations in the north-Chilean scallop (Argopecten purpuratus) has now been expanded to analyze color segregation in juvenile scallops produced under controlled conditions employing self- and cross-fertilization. Calculations from the results were used for comparison with different numerical models based on Mendelian inheritance, and results were also obtained on the inheritance of a dorsoventral white line often observed on the left (upper) valve in this species. The results confirmed the hereditary basis for color variation in the shell of this scallop, suggesting a simple, dominant model of epistasis to explain the distribution of the different color variants observed (purple, brown, orange, yellow, and white). The presence of the white line may be controlled by a recessive allele with simple Mendelian traits on a locus distinct from those that control color variation.