Tharyx maryae, Blake, James A. & Göransson, Peter, 2015

Blake, James A. & Göransson, Peter, 2015, Redescription of Tharyx killariensis (Southern) from Ireland and description of two new species of Tharyx from the Kattegat, Sweden (Polychaeta, Cirratulidae), Zootaxa 4039 (4), pp. 501-515 : 505-508

publication ID	https://doi.org/ 10.11646/zootaxa.4039.4.1
publication LSID	lsid:zoobank.org:pub:4B12AA52-6A3F-44B9-BBEC-EBABF0E22DF5
DOI	https://doi.org/10.5281/zenodo.5658079
persistent identifier	https://treatment.plazi.org/id/EE2B2061-FFC3-0270-FF2F-0BCEFC03FA62
treatment provided by	Plazi
scientific name	Tharyx maryae
status	sp. nov.

Treatment

Tharyx maryae View in CoL new species

Figures 2 View FIGURE 2 , 3 View FIGURE 3 A–C

Material examined. SWEDEN, Kattegat, near Varberg, 0 3 Aug 2012, in sediments near eelgrass beds, 57.11501°N; 12.22611°E, 0.3–1.7 m depth, coll. P. Göransson, holotype ( SMNH 8754), four paratypes ( SMNH 8755).

Description. A moderate-sized species, holotype complete, 10 mm long, 0.5 mm wide across thorax, 0.8 mm wide across expanded posterior end for 115 setigerous segments; paratypes all incomplete (lacking posteriormost segments), up to 9 mm long, 0.5 mm wide, with about 70 setigerous segments. Color in alcohol light tan to opaque white; lateral black pigment spots present on peristomium of some specimens ( Fig. 3 View FIGURE 3 A), faded or not apparent on others; some specimens with brown pigment spots in intersegmental grooves along body. Body elongate, laterally expanded through first 20–25 thoracic setigers with narrow crowded segments ( Figs. 2 View FIGURE 2 A, 3C); abdominal segments narrower, longer and rounded, but not moniliform; posterior 20–25 segments becoming enlarged, forming expanded posterior end with narrow segments, tapering to pygidium with dorsal anus and bulbous ventral lobe ( Figs. 2 View FIGURE 2 B, 3B). Dorsum of thoracic region broad between notopodia, with segmentation evident ( Fig. 2 View FIGURE 2 A); dorsal groove absent. Venter generally flattened with mid-ventral line of ridges along entire body from setigers 2–3 ( Fig. 3 View FIGURE 3 C); ridges formed from ventromedial bulges or pads associated with each segment.

Prostomium triangular, tapering to pointed tip on anterior margin ( Figs. 2 View FIGURE 2 A, 3A), broadening posteriorly, nuchal organs narrow slits on posterior margin of prostomium, inconspicuous, not pigmented; eyes absent. Peristomium as long as wide, with two annuli surmounted by longitudinal dorsal crest ( Fig. 2 View FIGURE 2 A). Paired dorsal tentacles on posterior margin of peristomium, with first pair of branchiae located immediately posterior to tentacles on peristomium ( Fig. 2 View FIGURE 2 A); second pair of branchiae on posterior margin of setiger 1, dorsal to notosetae. Branchiae present on most segments through middle of body.

Noto- and neuropodia with setal fascicles arising close together; anterior parapodia with spreading fascicles of about 5–6 capillary setae in notopodia and 6–7 capillaries in neuropodia; middle body segments with about 9–10 capillaries in notopodia and 5–6 in neuropodia; far posterior notopodia with 4–5 narrow capillaries; neuropodia with 3–4 capillaries and 1–3 short, curved, spines in posteriormost 4–5 setigers ( Fig. 2 View FIGURE 2 C). Neuroacicular spines initially as straight pointed spine ( Fig. 2 View FIGURE 2 D) transitioning over next four setigers to blunt-tipped spine ( Fig. 2 View FIGURE 2 E), then spines with knob-like tips ( Figs. 2 View FIGURE 2 F–G). On holotype of 115 setigers, neuroacicular spines limited to posteriormost five setigers (111–115).

Methyl Green Stain. Most of body staining initially, tip of prostomium and dorsal peristomial crest clear; stain retained laterally in irregular patches on sides of peristomium and intersegmentally on dorsum, between parapodia, and mid-ventrally on thoracic region where ventral ridges are located sometimes producing a line of paired spots along the venter. The most conspicuous stain is present intersegmentally between the parapodia; no distinct pattern on prostomium and peristomium.

Remarks. Because of the expanded posterior end on the holotype of T. maryae n. sp., the specimen was initially thought to be a species of Aphelochaeta . However, careful inspection of the posterior parapodia revealed the presence of short, curved, blunt-tipped spines ventral to the capillaries in the posteriormost five neuropodia.

These spines transition from curved pointed setae among capillaries to short curved blunt-tipped spines with knoblike tips in the very last setigers. No spines were observed in the notopodia. Because the neuropodial spines are limited to the very posteriormost setigers, they will not be observed in fragmented specimens. Therefore other characters will be required in order to identify the species. Other features of the body are similar to related species of Tharyx . These include the raised crest on the peristomium, the occurrence of lateral black pigment spots on the peristomium; the position of the paired dorsal tentacles on the posterior margin of the peristomium followed by the first pair of branchiae also on the peristomium and the generally elongated form of the body. In addition, the methyl green staining pattern in conjunction with the paired peristomial pigment spots readily differentiates this species from other cirratulids observed in these collections.

Tharyx maryae n. sp. differs from all other species of the genus in having an expanded posterior end and with the neuropodial spines limited to the five posteriormost setigers. The expanded posterior end suggests a close relationship of T. maryae n. sp. with species of Aphelochaeta also having this character. Among eight species of Aphelochaeta described by Blake (1996) from the eastern Pacific, six species had the posterior end expanded in some form. Of these, none had the first pair of branchiae positioned immediately posterior to the dorsal tentacle on the peristomium as is typical for species of Tharyx . When branchiae were present on the peristomium, they were positioned lateral to the tentacles. There are no described species of Aphelochaeta from European waters that have characters similar to those of T. maryae n. sp.

Etymology. This species is named for the late Dr. Mary Elizabeth Petersen, in recognition of her numerous contributions to polychaete systematics and research on cirratulids.

Biology. The specimens of Tharyx maryae n. sp. were collected by one us (PG) in connection with a benthic macrofauna mapping project in sediments in and outside eelgrass ( Zostera marina ) beds near Varberg on the west coast of Sweden. Salinity and temperature variation in this shallow area is high (20–30 PSU; <0°C to>25°C). The worms occurred in four of 30 quantitative haps-corer samples, calculated to each contain 160–400 ind/m2 with a biomass of <0.01–0.8 g /m2 (variation in specimen length was 6–12 mm). These samples were taken at 0.3–1.7 m depth in coarse to fine sand with a low organic content (about 1–2 % loss on ignition) and almost no vegetation, outside or in the margin of the eelgrass bed. The associated fauna were relatively scarce in most samples (6–12 species and 3,093 ind/m2) and were dominated by Hediste diversicolor ( O.F. Müller, 1776) , Peringia ulvae Pennant, 1777 , Tubificoides benedii Udekem, 1855 , and Scoloplos armiger ( O.F. Müller, 1776) . The fauna in the eelgrass beds was richer and more diverse in most samples, with a representation of polychaetes and several species of crustaceans and molluscs.

Both Tharyx maryae n. sp and T. robustus n. sp. (described below) were found in the same sample together with an anterior fragment of Aphelochaeta sp., also likely new to science. These specimens were taken in relatively fine sediment with higher organic content outside the eel grass beds where small patches of the algae Ruppia spp. and Fucus vesiculosus (Linnaeus, 1753) were found; however, cirratulids were recorded in sediments almost entirely free of vegetation in three of the four samples. These results suggest that T. maryae n. sp. and T. robustus n. sp. are very tolerant of variations in salinity and temperature and prefer relatively coarse sand with almost no vegetation and low competition from other species.

Distribution. Known only from the west coast of Sweden in low water.