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

Abstract

With 16 figures in the text)The shallow subtidal mactrid bivalve Muctrinulu 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 Lutruria lutruria. 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 biology and functional morphology ofArctica islandica(Bivalvia: Arcticidae) – A gerontophilic living fossil

“…It lacks the long siphons typical of deposit feeders such as the mactrids (Barnes & Morton 1997, Morton 2010) and species of the Tellinidae (Yonge 1949), but because the siphons are located virtually at the sedimentÁwater interface, it probably collects the rich surface film and suspended particles of epibenthic organic material Á the carbon sink Á that characterizes the seabed. It is, therefore, a specialized deposit feeder with large ctenidia and mediumsized labial palps, unlike surface-hoovering mactrids and tellinids, which possess small ctenidia and very large labial palps.…”

“…Particles of filtered potential food are then transported to the labial palps for final processing (Figure 7, ILP; OLP). The ctenidialÁlabial palp junction is of Category II (Stasek 1963) in which the anteriormost filaments are inserted into and fused with the distal oral groove, as in mactrids, for example, Mactrinula reevesii Gray, 1837 and Raetellops pulchella (Adams & Reeve, 1850) (Barnes & Morton 1997;Morton 2010). In comparison with Figure 7.…”

Form and functional morphology of Raetellops pulchella (Bivalvia: Mactridae): an example of convergent evolution with anomalodesmatans

“…The outer demibranch was also shorter in the anterior–posterior aspect than the inner demibranch. The ctenidia were also unusual in that they did not belong to the categories of bivalve gill structures and ciliation assigned to other members of the Mactridae, e.g., type C (1a) ( M. reevesii: Barnes & Morton 1996) or type C (2) [ Spisula subtruncata ( da C osta 1778) and L. lutraria: Atkins 1937a,b]. They were most similar, instead, to Atkins's type E (a), as also possessed by Tellina crassa (P ennant 1777) and Scrobicularia plana ( da C osta 1778).…”

“…With the exception of economically important species in the genus Spisula [e.g., Spisula solidissima (D illwyn 1817): Weinberg et al 1997], members of the diverse bivalve family Mactridae are virtually unstudied. One exception to this is the Indo‐West Pacific species Mactrinula reevesii G ray 1837 studied by Barnes & Morton (1996), who also provided a review of studies on representatives of the Mactridae up to that date. In this article, I report on the form and function of the rarely encountered deposit‐feeding mactrid bivalve Raetellops pulchella (A dams & R eeve 1850), with the aims of (i) elucidating aspects of its anatomy, (ii) seeing whether this would shed light on how the deposit‐feeding lifestyle in the Mactridae has evolved, and (iii) examining how their fragile shell functions.…”

Biology and anatomy of the ‘living fossil’Congeria kusceri (Bivalvia: Dreissenidae) from subterranean rivers and caves in the Dinaric karst of the former Yugoslavia

“…The intestine is similarly short in comparison to representatives of the other dreissenid genera and this is, again, a feature of a species with little access to large quantities of food. In comparison, representatives of the deposit feeding Mactridae have enormously long, complicated, intestines (Barnes & Morton, 1997) and those of Dreissena polymorpha and Mytilopsis sallei are also more complicated (Morton, 1969a(Morton, , 1981.…”