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Abstract Macaronichnus segregatis degiberti , a relatively large ichnosubspecies of Macaronichnus segregatis , is an almost straight to gently curved, cylindrical, fossilized burrow, oriented horizontal to oblique to the bedding plane. It is interpreted as a pascichnial trace fossil formed through selective sand feeding and excretion of a free-living polychaete, such as a relatively large travisiid (formerly classified as opheliid or scalibregmatid) polychaete Travisia. While the other ichnosubspecies, i.e., M. s. segregatis , M. s. lineiformins , M. s. meandriformis , and M. s. spiriformis , are commonly 2–5 mm in diameter and occur exclusively in foreshore deposits, M. s. degiberti attains a diameter of up to 15 mm and shows wide environmental distribution, ranging from tidal channels, tidal sand bars, tidal sandridges, tidal flats, upper to lower shorefaces, bioturbated sandy shelves, shelf storm-sheets, to shelf sand ridges. The core of M. s. degiberti , consisting mainly of light mineral-rich sand grains, is composed of alternating lamellae of light mineral-rich and heavy mineral-rich sands, arranged oblique to the bedding plane. On the other hand, the mantle, composed mainly of heavy mineral-rich sands, has a smooth outline, or evenly spaced lobes flanked on both sides. The morphology of the mantle lobes and core lamellae suggests repeated pulses of sediment probing and excreting behaviour of the tracemaker. Two or more burrows of this ichnosubspecies tend to occur adjacently, sometimes intertwining. As Travisia develops directly, lacking any planktic larval stages, aggregations of the burrows can be interpreted to reflect the burrowers' interindividual exploratory behaviour with the aim of copulation. Travisia , also known as a "stink worm", secretes volatile chemical substances that might act as sex pheromones to attract other individuals for reproduction within the substrate. Therefore, a new category of ethological classification of trace fossils "sequorichnia" (sequor , follow; and ichnia , traces), for exploration of other individuals, is proposed here. This is the first record of interindividual exploratory behaviour of infaunae. Highlights • Macaronichnus segregatis degiberti is likely formed by locomotion, selective feeding and egestion of a travisiid polychaete. • It occurs in sandy deposits in a variety of shallow-marine environments, but never does those in a wave-dominated foreshore. • The travisiid, without planktic larval stage, often followed other individuals' burrows for a probable reproductive purpose. • Such an exploratory behaviour likely guided by residual sex pheromones in their burrows. • A new category of ethological classification "sequorichnia" (sequor , follow; and ichnia traces) for exploration is proposed. [ABSTRACT FROM AUTHOR]

Opheliid polychaetes collected by the United States Antarctic Research Program and additional material from South America were made available for study through the Smithsonian Institution, Washington, D.C., USA. The Opheliidae from Antarctic seas were treated by Hartman (1966, 1967, 1978), who summarized earlier work and also described several new species. Of the five genera she recorded, two (Travisia and Kesun) have since been synonymized and one, Ammotrypane, has been referred to Ophelina; Hartman’s records therefore encompass four genera, three of which are represented in the present collections. No representatives of Euzonus (Thoracophelia) were found. The following species were recorded from Antarctica in the present study: Ophelia algida n. sp., Ophelina breviata (Ehlers, 1913), Ophelina cf. cylindricaudata (sensu Hartmann-Schröder and Rosenfeldt, 1989), Ophelina nematoides (Ehlers, 1913), Ophelina scaphigera (Ehlers, 1900), Ophelina cf. setigera (Hartman, 1978), Ophelina syringopyge (Ehlers, 1901), Travisia antarctica Hartman, 1967 (emended 1978), Travisia kerguelensis McIntosh, 1885, Travisia kerguelensis gravieri Monro, 1930, Travisia palmeri n. sp. and Travisia tincta n. sp. The new species of Ophelia is distinguished by having branchiae starting on chaetiger 2 (rather than on or after chaetiger 8 as in most species of this genus). Travisia palmeri has 22 chaetigers and is distinguished by long branchiae. Travisia kerguelensis gravieri is raised to full species status and renamed T. monroi. Travisia tincta n. sp., distinguished by a distinctive Methyl Green staining pattern and long branchiae, is described from off Peru.

The phylogenetic position of the polychaete genus Travisia within Annelida is a matter of ongoing debate. Travisia is usually placed within Opheliidae, but morphological similarities with Scalibregmatidae, such as a rugose epidermis, are obvious. To further examine placement of this enigmatic group, we examined 28 annelid species from a range of families, but with special emphasis on Scalibregmatidae and Opheliidae. Our data set consisted of four genes: 16S rDNA, 18S rDNA, 28S rDNA and Histone 3. By combining genes and conducting Maximum Likelihood, Maximum Parsimony and Bayesian analysis, our results strongly support a sister-group relationship of Travisia and Scalibregmatidae. None of the phylogenetic analyses clustered Travisia with or within Opheliidae and such placements are also significantly rejected by hypothesis testing. Moreover, we obtained new insights on relationships within Opheliidae and Scalibregmatidae. Within Opheliidae, the traditional classification into Opheliinae and Ophelininae received strong support. [ABSTRACT FROM AUTHOR]

Annelid systematics and the ingroup relationships of polychaete annelids are matter of ongoing debates in recent analyses. For the investigation of sedentary polychaete relationships a molecular phylogenetic analysis was conducted based on 94 sequences of 18S rDNA, including unpublished sequences of 13 polychaete species. The data set was analyzed with maximum parsimony and maximum likelihood methods, as wells as Bayesian inference. As in previous molecular analyses the monophyly of many traditional polychaete families is confirmed. No evidence has been found for a possible monophyly of Canalipalpata or Scolecida. In all analyses a placement of the Echiura as a derived polychaete ingroup with a close relationship to the Capitellidae is confirmed. The orbiniids appear paraphyletic with regard to Questa. Travisia is transferred from Opheliidae to Scalibregmatidae. The remaining opheliids include a yet undescribed ctenodrilid species from Elba, whereas the other investigated ctenodrilid Ctenodrilus serratus groups with the Cirratulidae and shows a close affinity to the cirratulid genus Dodecaceria. A common ancestry of Branchiomaldane and Arenicola, which has been predicted on morphological data, is confirmed by the analysis and a sistergroup relationship between Arenicolidae and Maldanidae is also recovered. These results support our assumption that on the basis of a broader taxon sampling the phylogenetic position of controversially discussed taxa can be inferred by using 18S rDNA sequence data. [Copyright &y& Elsevier]