Zootaxa, Taxonomy of Serpulidae (Annelida ... - Magnolia Press

adiole, whereas, in his opinion, it always is the first radiole in serpulins. He suggested, therefore, that
spirorbin operculum is not homologous to the serpulin operculum.
However, to determine which radiole is modified into the peduncle, ontogenetic studies are needed, and
these do not give a clear-cut answer. According to the embryological literature, the operculum is formed from
the 3 rd radiolar bud dorsally (e.g., Zeleny 1905 for Hydroides; Segrove 1941 for Pomatoceros; Vuillemin 1965
for Ficopomatus and spirorbins). Salensky (1884) is less clear for spirorbins, but contrary to Vuillemin (1965)
seems to indicate an origin from the second dorsal bud. According to Matjašič & Sket (1966), in Marifugia,
the operculum even may be formed from the 4 th radiolar bud dorsally. However, it cannot be excluded that the
differences in specifying the buds are due to confusion between radiolar and pinnular buds, such as the later
lip-associated pinnule (see different types of mouth-palps, p. 13). Another explanation for the differences in
numbering might be found in Smith (1985: 148): “The operculum arises completely independently of the
existing radioles. It starts as a small bud at the left side of the prostomium between radioles 2 and 3 [in Smith’s
perception radiole 1 becomes the dorsal palp of the mouth], but dorsal to them [thus outside the normal range
of radioles], in what is essentially the dorsal position. This bud grows out into a cylindrical opercular stalk
with distal swelling, … From the outset it is devoid of pinnules and no corresponding opercular stalk is found
on the right side.”
Partly based on the papers above, ten Hove (1984) argued that the peduncle in serpulids is actually the
modified second dorsal-most radiole, but in large-bodied serpulids the peduncle migrates during development
in such a way that it appears to be formed from the first radiole (or even completely outside the branchial
crown, such as the position in Pomatoceros).
Ten Hove (1984, 1989) distinguishes between indirect and direct opercular ontogeny. In some serpulids
(Hydroides, Serpula) juveniles develop an operculum on a pinnulated radiole; later, the peduncle loses its
pinnules and becomes smooth (= indirect development, e.g., Mörch 1863, ten Hove & Ben-Eliahu 2005).
When a functional operculum is lost, the rudimentary operculum develops into a functional one. Direct
development means that the peduncle and operculum develop directly from a knob, without a pinnule-bearing
stage (Segrove 1941: Pomatoceros; Vuillemin 1965: Ficopomatus, spirorbins; Matjašič & Sket 1966:
Marifugia; Smith 1985: 148 Spirobranchus). In the event of damage, a new operculum is regenerated from the
same peduncle (e.g., ten Hove 1970, figs 122, 123). Marsden & Anderson (1981) gave a figure of the
metamorphosing larva of Galeolaria; unfortunately they do not specify which of the 3 pairs of buds figured
will be the later operculum, but the figure does not essentially differ from that of Pomatoceros in Segrove
(1941 text/fig. 20). Most probably the opercular development in Galeolaria is direct, from a bud without a
pinnulate stage, just as in Pomatoceros, Marifugia, Ficopomatus, and spirorbids.
The opercular peduncle
In some serpulid taxa, the branchial radiole that bears the operculum is identical to the other radioles
(Filograna, Apomatus, Josephella (Fig. 3B; however, not in Josephella populations from the E.
Mediterranean (Ben-Eliahu & Payiatas 1999)) and in Protis). In most serpulids the operculum is borne on a
distinct peduncle (Fig. 3A, C, D, E, F). The peduncle may gradually merge into the basal fleshy part of the
operculum (Figs 3E, 5C), or be separated from it by a more or less clear constriction (Fig. 3F).
Morphologically, an opercular peduncle is usually inserted more or less below and between the first and
second normal radiole, outside the line of radioles (Fig. 3F). In some genera, the peduncle is located at the
base of branchial crown, covering several radioles (Pomatoceros, Spirobranchus, and Galeolaria). In other
taxa, such as Semivermilia, Metavermilia and Bathyvermilia, the peduncle is clearly positioned as the second
modified radiole (ten Hove 1975). In small specimens/species the insertion of peduncle may be very difficult
to observe. In Semivermilia pomatostegoides the peduncle is either the second radiole, or inserted below and
between first and second.
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