Functional morphology, biology and sexual strategy of the circumboreal, adventitious crypt-building,Crenella decussata(Bivalvia: Mytiloidea: Crenellidae)

Abstract

The anatomy ofCrenella decussata(Mytiloidea) is described. Individuals of this circumboreal species occupy granular crypts composed of sand grains held in place by mucus. The swollen basal region of the tubule is occupied by an individual, which connects to the sediment surface by two posterior tubes accommodating the inhalant and exhalant streams. There is reduction in musculature and, most importantly, anterior foreshortening of the outer ctenidial demibranchs and loss of the labial palps. This creates an anterior space in the mantle for the initial brooding of fertilized ova by females to the prodissoconch stage. Subsequently, these larvae are transferred to the exhalant tube of the crypt wherein they attach by a single fine byssal thread and are further brooded until the crawl-away juvenile stage is attained. Experimental studies of larval behaviour suggest that parental pheromones sustain the female/offspring bond. Newly hatched individuals responded to parental exhalant water by actively attaching themselves using a byssal thread. This response persisted for 28 days, but not after 55 days when, we suggest, the pheromonal response ceases and offspring are developed sufficiently to take up life in their own nests. Offspring retrieved from parental crypts and fed continuously reached an average shell length of 500 μm after 7.5 months. Brooded offspring thus appear to rely on embryonal energy resources until post-metamorphosis, after which suspension feeding becomes essential for further growth and development before the parental crypt is vacated.

Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, Part II: The pteriomorphs

“…1, 2) is well represented in museum collections, although it is likely a species complex based on considerable variation observed by this author. This is consistent with a major difference in life habit between a North Atlantic population, described by Morton et al (2016) as lacking a byssus and occupying crypts built of mucus-cemented sand grains, and the Northeastern Pacific forms that construct a network of fine byssal threads (Fig. 2A).…”

“…Gray, 1840 This family-group of small to minute mussels (<10 mm) is represented in the Paleogene fossil record of the Northeastern Pacific by a single genus, Crenella T. Brown (1827). Following the proposal of Morton et al (2016), the group is elevated here to family status. Five additional genera have been recognized in the living fauna of the Northeastern Pacific (Coan et al 2000).…”

“…The unsettled state of mytiloid systematics has been characterized more colorfully as a "taxonomic farrago" and as "nomenclatural chaos" (Morton et al 2016). Convergent miniaturization of the shell associated with infaunal nestling (Harper and Skelton 1993) masks potentially significant anatomical differences.…”

Functional morphology ofCardiomya cleryana(d'Orbigny, 1842) (Bivalvia: Anomalodesmata: Cuspidariidae) from Brazilian waters: new insights into the lifestyle of carnivorous bivalves

“…Left and right halves of the septum are united by the septal membrane (sm), which separates anteriorly to create the siphonal gape (~1.5 mm in length) through which the foot can protrude. Unlike in Grippina coronata Machado & Passos, 2015 (Spheniopsidae) (Morton et al ., 2015b) no cilia were observed along the margin of this membrane. The septum is perforated ventrally by four pairs of pores (sep 1–4) more or less equally spaced and measuring ~250 µm in diameter (Figure 4I).…”

“…A similarly long foot has, however, been described for species of the Mytilidae such as Modiolarca subpicta (Cantraine, 1835) (= Musculus subpictus Cantraine, 1835) and is similarly responsible for the planting of byssal threads in the juvenile (Morton & Dinesen, 2011). Another example is provided by Crenella decussata (Montagu, 1808) which has a long foot mainly used to construct an adventitious tube within which an individual resides (Morton et al ., 2015a). Some representatives of the Lucinoidea such as Diplodonta punctata (Say, 1822) (Domaneschi, 1979), Lucina pectinata (Gmelin, 1791) = Phacoides pectinatus (Gmelin, 1791) (Narchi & Assis, 1980), Anodontia philippiana (Reeve, 1850) = Pegophysema philippiana (Reeve, 1850) (Taylor & Glover, 2006, figure 4) also have a long, highly extensible, foot.…”