Genus Asclerocheilus Ashworth, 1901

Gwasitoa Chamberlin, 1919: 390–391.

Kebuita Chamberlin, 1919: 390–391.

Type species

Asclerocheilus intermedius (Saint-Joseph, 1894).

Diagnosis

Body elongate, arenicoliform. Prostomium T-shaped with frontal horns. Parapodia of posterior segments reduced; dorsal and ventral cirri absent; interramal papillae or cilia present or absent; postchaetal lamellae absent. Branchiae absent. Chaetae include capillaries, furcate chaetae, and large, conspicuous curved spines on setigers 1 to 4, sometimes accompanied by short spinous setae. Pygidium with long anal cirri.

Remarks

The genus was erected by Ashworth (1901), to include the species A. intermedius (Saint-Joseph, 1894), previously assigned to the genus Lipobranchius Cunningham & Ramage, 1888. In the same work, Ashworth (1901) differentiated Asclerocheilus from Sclerocheilus Grube, 1863 by the absence of parapodial cirri, positioning the genus within the family subgroup I, containing species with an “arenicoliform” body shape. Subsequently, several new species were described. Blake (1981) transferred S. acirratus Hartman, 1966 to Asclerocheilus acirratus (Hartman, 1966) and presented two new species to the genus. Hartmann-Schröder (1994) compared the known species, providing important information on their morphological differences. Blake (2000) referred Kebuita glabra (Ehlers, 1887) to Asclerocheilus glabrus (Ehlers, 1887). The author also followed Hartman's (1938) synonymization of Gwasitoa Chamberlin, 1919 with Kebuita Chamberlin, 1919, and synonymized Kebuita with Asclerocheilus. Moreover, Blake (2000) erected A. victoriensis Blake, 2000 as a new name to replace A. heterochaetus Kudenov & Blake, 1978. This was proposed because Oncoscolex heterochaetus is a synonym of Kebuita glabra (Ehlers, 1887), and K. glabra was transferred to A. glabrus within the same work. In this sense, A. heterochaetus consequently is a junior homonym of O. heterochaetus. Thus, Blake (2000) renamed the homonym A. victoriensis (Hartman 1938; Blake 2000, 2023). Finally, Blake (2023) published the most recent advances on the genus taxonomy and ecology, transferring Oligobregma tasmania to A. tasmanius and describing an abyssal species from Australia.

Currently, the genus Asclerocheilus counts 15 described species, they are A. glabrus (Ehlers, 1887), from the Caribbean Sea; A. intermedius (Saint-Joseph, 1894) from the eastern North Atlantic; A. beringianus Ushakov, 1955 from the Bering Sea; A. capensis Day, 1963 from South Africa; A. californicus Hartman, 1963 from Southern California; A. acirratus (Hartman, 1966) from California; A. ashworthi Blake, 1981 from the Southern Ocean in Sub-Antarctic waters; A. tropicus Blake, 1981 from Ecuador; A. mexicanus Kudenov, 1985 from the Gulf of Mexico; A. shanei Hartmann-Schröder, 1994 from Tasmania; A. kudenovi Blake, 2000 from Central California; A. victoriensis Blake, 2000 from Southeast Australia; A. elisabethae Eibye-Jacobsen, 2002 from the Andaman Sea, Thailand; A. shanonae Eibye-Jacobsen, 2002 from the Andaman Sea, Thailand and A. abyssalis Blake, 2023 from Eastern Australia. Regarding the Brazilian coast, possible occurrences may be related to the species described in the following works: Day (1963, 1967), Blake (1981) and Kudenov (1985). Asclerocheilus tropicus is the only known species of Asclerocheilus found in Brazil, having been redescribed by Nogueira (2002). The material was sampled from Laje de Santos (24°19′ S, 46°11′ W), on 17 March 1996, and Ilha dos Alcatrazes (26°06′ S, 45°42′ W), on 4 December 1996; both localities are rocky shores with large colonies of cnidarians, from which the scalibregmatids were sorted (Nogueira 2002). Moreover, Nogueira (2002) provided an important account on the character variability within the species, such as the horns and prostomium shape, presence or absence of eyes as well as its colour and shape, the acicular spines shape, and the ratio of lyrate chaetae tynes. The latter account is important, because it provided important arguments regarding the validity of this character to separate species, firstly proposed by Blake (1981).

Key to species of Asclerocheilus Ashworth, 1901

1. Acicular spines present on chaetiger 1, 1–2 or 1–3 .......................................................................... 2

– Acicular spines present on chaetigers 1–4 ........................................................................................ ............................ A. victoriensis Blake, 2000; from Southeast Australia at shallow subtidal depths

2. Short spinous chaetae present on noto- and neuropodia of chaetigers 1–3 ........................................ .................................... A. abyssalis Blake, 2023; from Eastern Australia at depths of 3952–4280 m

– Short spinous chaetae absent on notopodia ...................................................................................... 3

3. Acicular spines only on chaetiger 1 .................................................................................................. 4

– Acicular spines on chaetigers 1–2 or 1–3 ......................................................................................... 8

4. Lyrate chaetae from chaetiger 2 or further on neuropodium ............................................................ 5

– Lyrate chaetae from chaetiger 1 on neuropodium ............................................................................ 6

5. Short spinous chaetae present on chaetiger 1 neuropodia .................................................................. .......... A. shanonae Eibye-Jacobsen, 2002; from the Andaman Sea, Thailand, at depths of 70–76 m

– Short spinous chaetae absent A. glabrus (Ehlers, 1887); from the Caribbean Sea at depths of 320 m

6. Prostomium with a pair of thin lateral horns ...................................................................................... ........................................ A. acirratus (Hartman, 1966); from California at shallow subtidal depths

– Prostomium with a pair of distally rounded lateral lobes ................................................................. 7

7. Prostomium T-shaped with a pair of stout lateral lobes ...................................................................... ................................... A. mexicanus Kudenov, 1985; from the Gulf of Mexico at depths of 2–75 m

– Prostomium heart-shaped, with a pair of flaring lobes; prostomium generally entire, but sometimes separated by a median sulcus in some specimens .............................................................................. ................................................................ A. tropicus Blake, 1981; from Ecuador at depths of 8–9 m

8. Acicular spines on chaetigers 1–2. ................................................................................................... 9

– Acicular spines on chaetigers 1–3 .................................................................................................. 14

9. Lyrate chaetae from chaetiger 2 on notopodium ................................................................................. A. ashworthi Blake, 1981; from the Southern Ocean in Sub-Antarctic waters at depths of 200–400 m

– Lyrate chaetae from chaetiger 3 on notopodium ............................................................................ 10

10. Notopodial and neuropodial lobes simple or reduced .....................................................................11

– Notopodial and neuropodial lobes long and enlarged from chaetiger 6 ............................................. .......................... A. californicus Hartman, 1963; from Southern California at depths of 542–890 m

11. Prostomium triangular to trapezoidal ............................................................................................. 12

– Rounded prostomium ..... A. kudenovi Blake, 2000; from Central California at depths of 90–120 m

12. Lyrate chaetae from chaetiger 1 on neuropodium ......................................................................... 13

– Lyrate chaetae from chaetiger 2 on neuropodium .............................................................................. ......... A. elisabethae Eibye-Jacobsen, 2002; from the Andaman Sea, Thailand, at depths of 0–80 m

13. Prostomium triangular, bearing two recessed horns directed upwards; chaetiger 1 uniannulated, chaetiger 2 triannulated, then quadriannulated from chaetiger 4 up to posterior end of the body ..... ................................. A. beringianus Ushakov, 1955; from the Bering Sea at depths of 986–2006 m

– Prostomium sub triangular, bearing two large rounded horns directed laterally; chaetigers 1–7 biannulated, then quadriannulated ...................................................................................................... ........................................................ A. capensis Day, 1963; from South Africa at depths of 9 –26 m

14. Acicular spines with capillaries on chaetigers 1–3 ......................................................................... 15

– Acicular spines without capillaries on chaetigers 1–3 ........................................................................ .......................................... A. shanei Hartmann-Schröder, 1994; from Tasmania at depths of 125 m

15. Lyrate chaetae from chaetiger 2 in neuropodia ............................................................................... 16

– Lyrate chaetae from chaetiger 4 .......................................................................................................... ................ A. intermedius (Saint-Joseph, 1894); from the eastern North Atlantic at depths of 551 m

16. Acicular spines with rounded tips present .......................................................................................... ........................................... A. geiseae sp. nov.; from the Espírito Santo Basin at depths of 11–50 m

– Acicular spines with rounded tips absent ........................................................................................... ................. A. blakei sp. nov.; from the Espírito Santo and Campos basins at depths of 683–1908 m