Melinnopsis chadwicki, Gunton & Kupriyanova & Alvestad, 2020

Gunton, Laetitia M., Kupriyanova, Elena & Alvestad, Tom, 2020, Two New Deep-water Species of Ampharetidae (Annelida: Polychaeta) from the Eastern Australian Continental Margin, Records of the Australian Museum 72 (4), pp. 101-121 : 111-114

Melinnopsis chadwicki sp. nov.

urn:lsid:zoobank.org:act:FD5DA304-2BBB-4CB3-85F3-11D285CA149E

Figs 6–7

Holotype incomplete missing part of long buccal tentacle: AM W.52950, IN2017_ V03 operation ( OPS) 104 Australia, Queensland, off Moreton Bay, Beam Trawl (start 26°57'39.6"S 153°50'52.8"E, 1071 m; end 26°59'27.6"S 153° 50'49.2"E, 1138 m) 10/06/2017 . Paratypes mounted for SEM AM W.52537 and AM W.52538, OPS 104 Australia, Queensland, off Moreton Bay, Beam Trawl (start 26°57'39.6"S 153°50'52.8"E, 1071 m; end 26°59'27.6"S 153°50'49.2"E, 1138 m) 10/06/2017 .

Other material examined. Total 58 specimens. (17 specimens) AM W.50417, W.50416, W.52980, W.52949, W.52979, W.50737, W.52948, W.52999, W.53000 OPS 121 Australia, Queensland, Coral Sea Commonwealth Marine Reserve, Beam Trawl (start 23°35'13.2"S 154°11'38.4"E, 1013 m; end 23°37'1.2"S 154°11'42"E, 1093 m) 13/06/2017. (4 specimens) AM W.50404, W.52997, W.50406, W.50405 OPS 080 Australia, New South Wales, Central Eastern Commonwealth Marine Reserve , Beam Trawl (start 30°5'56.4"S 153°35'45.6"E, 1257 m; end 30°7'40.8"S 153°34'15.6"E, 1194 m) 05/06/2017. (36 specimens) AM W.50415, W.50414, W.52981, W.52950, W.52951, W.52965, W.52975, W.52955, W.52961, W.52958, W.52973, W.52954, W.52956, W.52952, W.52953, W.52969, W.52976, W.52959 OPS 104 Australia, Queensland, off Moreton Bay , Beam Trawl (start 26°57'39.6"S 153°50'52.8"E, 1071 m; end 26°59'27.6"S 153°50'49.2"E, 1138 m) 10/06/2017. (1 specimen) W.50403 OPS 069 Australia, New South Wales, Hunter Commonwealth Marine Reserve , Beam Trawl (start 32°28'44.4"S 152°59'38.4"E, 1006 m; end 32°30'25.2"S 152°59'27.6"E, 1036 m) 03/06/2017 .

Description (based on holotype). Holotype 22 mm length for more than 55 chaetigers, widest at post-branchial region 1 mm ( Fig. 6A ), thereafter gradually tapering to abdomen (0.5 mm width) and pygidium. Thorax with 16 chaetigers, neurochaetae as small acicular spines on segments II to V and uncini on remaining 46 chaetigers.

Prostomium with well-defined anterior and posterior sections separated by a pair of deep transverse nuchal slits that meet mid-dorsally ( Fig. 6C ). Pigmented glandular bands above nuchal slits ( Fig. 6C ). Anterior part of prostomium whole, without any distinct lobes, and with a slightly raised lip. No eyespots present. Segments I and II obscured by branchial ridge. Segment I continued ventrally to form lower margin of the mouth no crenulations.

Buccal tentacles in holotype one short stump, three small tentacles, arising from a large membranous lip ( Fig. 6B ). Small tentacles smooth and grooved. In other specimens, one long buccal tentacle, smooth along length, twisted and ventrally grooved ( Fig. 7A ), generally around 5 mm in length. In many specimens long buccal tentacle broken off, four smaller tentacles (three and one on each side) although probably six in total (two pairs of three).

Lateral wings of anterior body between prostomium and segment V highly arched ( Fig. 6B ).

Segment I collar-like, laterally and ventrally encompassing head region. Branchiae emerging together on dorsal branchial ridge at level of segment II–III ( Fig. 7A ), arranged in two basally fused groups of four, three branchiae in front and one pair slightly behind (towards anterior). Inner- and anteriormost branchia of each group not joined by membrane. Branchiae circular in cross section, slightly ridged ( Fig. 7A ), dorsal groove, gently tapering to filiform tips. Branchiae roughly one third the length of longest buccal tentacle. Outer pair of branchiae longest ( Fig. 6B ).

Postbranchial dorsal membrane not visible. Postbranchial hooks absent. Segmentation not visible dorsally in postbranchial area. No visible nephridial papillae.

Capillary notochaetae present in 14 thoracic chaetigers, starting from segment IV. In holotype, anterior end notopodial chaetae damaged. In paratypes, chaetiger 3 (segment IV) with few fine notochaetal capillaries and chaetiger 4 (segment V) with more abundant fine notochaetae arising from body wall. Short, cylindrical notopodia with thicker capillaries starting from chaetiger 6. Notochaetae arranged in double rows, roughly the same length. Microfiber ends on notochaetae visible ( Fig. 7C ).

Abdominal notochaetae lacking. No small, papilliform projections evident in notopodial positions.

Neurochaetae as small acicular spines with lanceolate tips, on segments II to V ( Fig. 7B ). Neuropodial uncini from chaetiger 5 (segment VI) present in 12 thoracic uncinigers. Holotype complete with more than 40 abdominal uncinigers.

Holotype damaged at end of thorax beginning of abdomen. In other specimens, thoracic uncini emerge subdistally on short flaps until chaetiger 16, distally on narrow lappets on chaetigers 17 and 18. In holotype, abdomen uncini arranged on narrow lappets decreasing in size until pygidium, similar to last two thoracic chaetigers.

Thoracic uncini in single line of around 43 ( Fig. 7D ). Abdominal uncini in a single line of 14 ( Fig. 7E ). Uncini of thoracic uncinigers with two teeth in one vertical row over rostral tooth, subrostral process and basal prow ( Fig. 7D ). Uncini of abdominal uncinigers with numerous teeth over rostral tooth, subrostral process and basal prow ( Fig. 7E ).

Pygidium with terminal crenulated anus, bounded by 4 small indistinct lobes. No anal cirri. ( Fig. 6a ).

Methyl blue staining pattern. Use of methyl blue in holotype revealed light staining of prostomium except nuchal slits. Stained bands (anterior/ posterior direction) on prostomium ventral lobe absent, however stained band along anterior edge of prostomium ventral lobe present. Strong staining in segments I to IV. Light staining branchiae. Variation, specimens occasionally have stained dorsal banded region as in M. gardelli sp. nov., but less distinct and until chaetiger 5. Light speckling between thoracic chaetigers. Stained ventral shields, shields cover entire ventral surface of the segment. Indistinct number of shields on holotype due to damage. Light speckles staining on abdomen. No staining on neuropodial lappets.

Tube. In holotype, sediment tube with small green veins running throughout and Foraminifera attached ( Fig. 6D ). Tube similar length to the specimen. Tube varies among specimens, may not have green veins and Foraminifera attached.

Distribution. Coral Sea Marine Park to Hunter Commonwealth Marine Reserve. Eastern Australia

Etymology. This species is named after Clarence (Clarry) Chadwick for his endowment that supports the Chadwick Biodiversity Fellowship at the Australian Museum Research Institute.

Remarks. Melinnopsis chadwicki sp. nov. appears to be closely related to M. gardelli sp. nov. by acicular neurochaetae on segments II–V, one large buccal tentacle and multiple smaller ones, four branchiae and branchial arrangement and 12 thoracic uncini, however, it can be differentiated from the latter by the shape of the thoracic uncini which have 2 rather than 3 teeth above the rostral tooth, the distinct presence of pigmented glandular bands above nuchal slits and the lack of a conspicuous stained band ending between chaetigers 9 and 10. The two species are found at different depths: M. chadwicki sp. nov. around 1000 m and M. gardelli sp. nov. around 2500 m. The difference between new species of Melinnopsis and others with 12 thoracic uncini are discussed in the remarks of M. gardelli sp. nov. above and in Table 3.

Figures

Figure 6. Melinnopsis chadwicki sp. nov. light microscope images. (A) holotype (AM W.52950) lateral view of entire specimen, (a) pygidium; (B) holotype lateral view of anterior part; (C) AM W.52981 prostomium, arrows indicate transverse nuchal organs; (D) holotype sediment tube. Scale bars: A, B 1 mm; C 0.5 mm; D 2 mm.

Figure 7. Melinnopsis chadwicki sp. nov. SEM micrographs of paratypes (W.52537 and W.52538). (A) AM W.52538 dorsal view of anterior section; (B) W.52538 acicular chaetae segment 3 and 4; (C) W.52537 close up of notochaetae microfiber endings; (D) W.52537 thoracic uncini; (E) W.52537 abdominal uncini. Scale bars: A 1 mm, B 20 µm, C 2 µm, D 5 µm, E 10 µm.