Aphelochaeta readi, Blake, 2023

Blake, James A., 2023, New Species of Cirratulidae (Annelida) from Continental Slope and Abyssal Depths off Eastern Australia, Records of the Australian Museum (Rec. Aust. Mus.) 75 (3), pp. 249-270 : 251-254

publication ID	https://doi.org/ 10.3853/j.2201-4349.75.2023.1799
DOI	https://doi.org/10.5281/zenodo.10988919
persistent identifier	https://treatment.plazi.org/id/03B987C1-FFCE-ED46-B5AC-F9EF6F60F8D8
treatment provided by	Felipe
scientific name	Aphelochaeta readi
status	sp. nov.

Treatment

Aphelochaeta readi View in CoL sp. nov.

urn:lsid:zoobank.org:act:8E09CD78-35D3-46EE-8BEB-5DE6E5C4F55E

Figs 2–3 View Figure 2 View Figure 3

Holotype: Abyssal plain off eastern Australia, off Byron Bay, New South Wales, RV Investigator, Sta. 098, coll. 8 June 2017, Brenke sledge, start 28.371°S 154.647°E, 3811 m to end 28.389°S 154.612°E, 3754 m ( AM W.52714). GoogleMaps

Description. A small species, holotype only specimen, complete with 28 setigers, 3.2 mm long and 0.47 mm wide across anterior setigers. Body expanded over first nine setigers, then narrowing to consistent width along rest of body ( Figs 2A View Figure 2 , 3A View Figure 3 ). First 8–9 individual setigers short, each 11–12 times wider than long, following segments longer, about three times wider than long ( Fig. 2A View Figure 2 ); far posterior segments becoming rounded, weakly moniliform ( Fig. 2C View Figure 2 ). Each segment separated from following by relatively deep intersegmental grooves. Dorsal surface of all segments smooth without dorsal longitudinal grooves or ridges. Ventral surface of body with prominent mid-ventral ridge line composed of transverse raised ridges that together form a line of ridges along body ( Fig. 2B View Figure 2 ); ventral ridges of anterior setigers about half as wide as ventral surface, narrowing to short ridge in posterior segments. Colour in alcohol light tan.

Pre-setiger region relatively short, thickened, about as long as first six setigers ( Fig. 2A View Figure 2 ). Prostomium short, pear-shaped, tapering to narrow tip ( Figs 2A–B View Figure 2 , 3A–B View Figure 3 ); eyespots absent; nuchal organs not observed. Peristomium with three annular rings and one narrow achaetous segment, all complete dorsally ( Fig. 2A View Figure 2 ); these all merged ventrally providing smooth ventral surface from anterior margin of peristomium to setiger 1 ( Fig. 2B View Figure 2 ). Mouth of opening anteriorly, visible only in frontal view, a only visible ventrally as narrow slit between first peristomial ring and prostomium. Dorsal tentacles arise from middle of third peristomial ring ( Fig. 2A View Figure 2 ); first pair of branchiae arises on achaetous segment anterior to setiger 1; subsequent branchiae arise on posterior margin of individual segments dorsal to notosetae ( Fig. 2A View Figure 2 ). All branchiae missing or broken, represented only by scars or short stubs.

Parapodia relatively simple throughout, not producing prominent lobes or shoulders anywhere along body; setae arising directly from body wall ( Figs 2A–B View Figure 2 , 3A–B View Figure 3 ). Pre- and post-setal lobes or lamellae entirely absent. Setae all smooth capillaries, not limbate or granulated; fimbriated borders not present. Anterior and middle setigers with 8–9 capillaries in notopodia and 6–7 in neuropodia; posterior setigers with 3–4 notosetae and 4–5 neurosetae.

Pygidial segment elongate, with anal opening terminal; without anal lobes or cirri ( Fig. 2C View Figure 2 ).

Methyl Green staining. Weak stain on prostomium and in intersegmental areas of anterior segments where subdermal glands occur; otherwise no pattern.

Remarks. To date, only 12 valid species of Aphelochaeta have been described from abyssal depths of about 3000 m or greater ( Blake, 2018, 2019, this study). Aphelochaeta readi sp. nov. is the twelfth species in this group and the only one having multiple peristomial rings that cross the dorsal surface, yet do not cross the ventral surface leaving it smooth. In addition, the distinct widening of the first 8–9 setigers followed by a narrow middle and posterior body with a few far posterior moniliform segments terminating in a simple pygidial lobe is distinctive. Unlike other cirratulids encountered in this study and at other deep-water locations, A. readi sp. nov. is the only one to have the mouth opening directed frontally, not visible in ventral view.

Etymology. This species is named in honour of Dr Geoffrey Read, Marine Biologist with the National Institute of Water & Atmospheric Research Ltd (NIWA), Wellington, New Zealand in recognition of his long-time role as Chief Editor of annelids for the World Register of Marine Species (WoRMS). In addition, Dr Read has long maintained a website site dedicated to polychaetes and provides a wide range of assistance in addressing problems with zoological nomenclature and locating references, many of which are long out of print.

Distribution. Abyssal plain off Byron Bay, NSW, eastern Australia, 3754–3811 m.