(^) Euthecosome feeding apparently occurs in two modes. Internal filtration takes place
on a ciliated mucous gland inside the mantle cavity. Gilmer and Harbison (1986) have
observed an external mode of “filtration”: many euthecosomes actually hang
suspended from a mucous “bubble”, or float (Plate 6.7), which almost certainly also
serves as a food-gathering structure and is reeled in periodically. The floats explain
how pteropods can afford the energetic costs of keeping their weighty shells in the
upper water column. However, Gallager and Alatalo (pers. comm.) have reared
Limacina retroversa in tanks, and report that they survive and grow for long periods
without ever forming mucous floats, apparently feeding during active swimming with
the wings. Euthecomes are sequential hermaphrodites, the gonad switching from testis
ff
(ff)
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