Worms by number

Abstract

This paper investigates alternation patterns in length, shape and orientation of dorsal cirri (fleshy segmental appendages) of phyllodocidans, a large group of polychaete worms (Annelida). We document the alternation patterns in several families of Phyllodocida (Syllidae, Hesionidae, Sigalionidae, Polynoidae, Aphroditidae and Acoetidae) and identify the simple mathematical rule bases that describe the progression of these sequences. Two fundamentally different binary alternation patterns were found on the first four segments: 1011 for nereidiform families and 1010 for aphroditiform families. The alternation pattern in all aphroditiform families matches a simple one-dimensional cellular automaton and that for Syllidae (nereidiform) matches the Fibonacci string sequence. Hesionidae (nereidiform) showed the greatest variation in alternation patterns, but all corresponded to various known substitution rules. Comparison of binary patterns of the first 22 segments using a distance measure supports the current ideas on phylogeny within Phyllodocida. These results suggest that gene(s) involved in postlarval segmental growth employ a switching sequence that corresponds to simple mathematical substitution rules.

Phylogeny of Syllidae (Polychaeta) based on morphological data

“…2C). Dorsal cirri of Syllidae demostrate a regular pattern of alternation in length, shape and orientation that matches with a mathematical rule, the Fibonacci string sequence: 1011 (0 meaning long cirri and 1 short cirri) (Glasby et al 2008). All the syllids also show alternation in the insertion of dorsal cirri (Glasby et al 2008), though in some taxa this alternation pattern is more evident (Fig.…”

“…2C). Dorsal cirri of Syllidae demostrate a regular pattern of alternation in length, shape and orientation that matches with a mathematical rule, the Fibonacci string sequence: 1011 (0 meaning long cirri and 1 short cirri) (Glasby et al . 2008).…”

“…2008). All the syllids also show alternation in the insertion of dorsal cirri (Glasby et al . 2008), though in some taxa this alternation pattern is more evident (Fig.…”

Systematics and evolution of syllids (Annelida, Syllidae)

“…The total evidence result ( Fig. 2) (molecular + morphology, no 18S regions excluded) indicates that Syllidae is monophyletic and well supported, defined by the presence of the proventricle, a thickened inner proboscis, and the dorsal cirri with a regular pattern of alternation in length, shape and orientation that matches a mathematical rule, the Fibonacci string sequence: 1011 (0 = long cirri, 1 = short cirri; Glasby et al, 2008). When including only molecular information, Syllidae is also a monophyletic group, although the support values are lower (Fig.…”

Two apparently unrelated groups of symbiotic annelids, Nautiliniellidae and Calamyzidae (Phyllodocida, Annelida), are a clade of derived chrysopetalid polychaetes

“…Phyllodocidae show foliaceous dorsal cirri, and some are elytra in scaleworms. Dorsal cirri are short in nautiliniellids and C. amphictenicola and they usually show alternation in length and orientation in the parapodia in most of the other terminals (Glasby et al., ). This alternation in the position of dorsal cirri has been observed in the genus Iheyomytilidicola Miura and Hashimoto in Nautiliniellidae (Aguado and Rouse, ).…”