Larval and adult eyes in Capitella spec. I (Annelida, Polychaeta)

Abstract

Larval and adult eyes of the capitellid Capitella spec. I have been investigated by electron microscopy. Developing larvae possess one pair of eyespots. Each eyespot is composed of one sensory cell, one pigment cell, and one supporting cell. The sensory cell bears a photosensory apparatus, an array of parallel microvilli containing a striking form of submicrovillar cisternae (SMC). A single basal body was observed near the basal end of the SMC only in 3-4-day-old larvae. This basal body was not observed in older larvae. A special, thus far unreported feature of the pigment cell is a ring of microvilli-like structures that project from the edge of the pigment cup and form a kind of diaphragm around the head of the sensory cell. Each of these microvilli-like structures is covered with closely packed rows of tiny plates, giving them a fimbriated appearance. After metamorphosis, the larval eyespots are reduced. Adult specimens possess one pair of eyes. In juvenile worms the eye is built of 2-3 pigment cells and one sensory cell. The volume of adult eyes increases by the addition of 2-3 sensory cells. The pigment cells are deposited one upon the other, wrapping the sensory complex in the center. Each sensory cell forms a deep depression at its apical end where up to three cilia and numerous microvilli arise. The sensory processes project into a common ocular cavity. Long microvilli of the uppermost pigment cells project into an extracellular channel that reaches from the ocular cavity up to the cuticle. A single fourth sensory cell of identical structure may occur next to the eye directly beneath the cuticle and close to the opening of the ocular channel. Signs of progressive disintegration of the pigment cells can be observed in adult specimens. Sensory cells are not affected by this reduction process. Eyes resembling those of Capitella spec. I have never been reported before. Their functional qualities are discussed. © 1993 Wiley-Liss, Inc.

Pigmented eyes, photoreceptor‐like sense organs and central nervous system in the polychaete Scoloplos armiger (Orbiniidae, Annelida) and their phylogenetic importance

“…However, Capitella sp. is an exception within Scolecida, having multicellular eyes completely different in structure from any polychaete eye known so far, and thus most likely they are the result of convergent evolution (Rhode, 1993;Purschke et al, 2006). In Spionida the same larval-type ocelli are present as in Scolecida (Rhode, 1991;Purschke et al, 2006).…”

The larval ocelli of Golfingia misakiana (Sipuncula, Golfingiidae) and of a pelagosphera of another unidentified species

“…Bartolomaeus (1992a) added that the membranous tubes are continuous with the submicrovillar cisternae. Additionally, the micrographs presented by Rhode (1993;see Fig. 4) show that the tubuli of the SMC are united at their proximal ends and are also open.…”

“…Similar structures are found in the light sensitive cells of Pectinaria koreni Malmgren, 1865 (Polychaeta) and Capitella sp. (Polychaeta) where they are termed submicrovillar cisternae (SMC) (Bartolomaeus 1992a; Rhode 1993). Both authors pointed out that tubes or tubuli extend from the tip of the microvilli below these organelles.…”

“…One cilium with a striated rootlet between the micovilli is also found in the photoreceptive cells of several larvae of Polychaeta (Bartolomaeus 1987(Bartolomaeus , 1992aRhode 1993). In all these cases, the photoreceptors are considered to be rhabdomeric.…”

Phototaxis and the origin of visual eyes

“…References: Tripedalia cystopora [31], Autolytus prolifera [32,33], Capitella sp. [34,35], Harmothoe imbricata [36,37], Lanice conchilega [32,38], Neanthes succinea [39], Odontosyllis ctenostoma [40], Pectinaria koreni [32], Phyllodoce maculate [41], Phyllodoce mucosa [42], Platynereis dumerilii [43 -45], Polygordius appendiculatus [46,47], Serpula vermicularis [36,48] . Helical phototaxis is widespread among protists (not considered here, but see [104]) and metazoan larvae and relies on a direct sensory-motor coupling between a photoreceptor and an effector.…”