Microphthalmus Mecznikow, 1865

Georgieva, Magdalena N., Wiklund, Helena, Ramos, Dino A., Neal, Lenka, Glasby, Christopher J. & Gunton, Laetitia M., 2023, The Annelid Community of a Natural Deep-sea Whale Fall off Eastern Australia, Records of the Australian Museum (Rec. Aust. Mus.) 75 (3), pp. 167-213 : 177-180

Microphthalmus Mecznikow, 1865

Microphthalmus sp.

Fig. 11

Material examined. NHMUKANEA 2022.434 , NHMUK ANEA 2022.412 – 420 , NHMUKANEA 2022.437 – 438 , IN2017_ V03 _100; 9 June 2017; off Byron Bay , NSW, Australia, beam trawl, start: 28.05°S 154.08°E, 999 m, end: 28.10°S 154.08°E, 1013 m. DNA vouchers: NHMUK ANEA 2022.434 ( COI, 16 S, 18 S) , WF_SYL_2 (COI, 16S), same locality .

Description. Complete specimens 1.1–1.8 mm long with 18–42 segments, appearingbiannulate ( Fig. 11A ). Body width is similar throughout, with its mid-body chaetigers 0.14–0.24 mm wide, not including the parapodia, only slightly taperingon both ends. Ethanol-preserved specimens appearing white to light brown.

Prostomiumsemicircular, anteriorly slightly cleft, broader thanlong ( Fig. 11B ). Prostomialappendagesare all cirriform. One pair of dorsal antennae and one pair of shorter palps terminally located. Median antenna inserted near posterior end of prostomium. Eyes absent.

First three segments shorter than others andlack chaetae, bearing six pairs of cirriform tentacular cirri ( Fig 11B ). Dorsal and ventral cirri present from segment 4. Dorsal cirri shorter on segment 4 than those on segment 5 onwards. Ventral cirri triangular, shorter, and thicker than cirriform dorsal cirri. Body width similar along most of the length (0.14–0.24 mm).

Parapodia uniramous. Neuropodia with a pointed prechaetal lobe ( Fig. 11C ) and blunt postchaetal lobe ( Fig. 11D ). Length of prechaetal lobe equal to or exceeds that of dorsal cirri. Neurochaetae all heterogomph falcigers with blades of different lengths having serrated edges ( Fig. 11E ).

Pygidium short, with two short anal cirri with swollen bases. Ventral anal lamellae bilobed, with smooth margins and lacking papillae ( Fig. 11F ).

Distribution. IN2017_V03, Station 100. Pilot whale carcass, off Byron Bay, New South Wales, Australia in 999–1013 m.

Remarks. The genus Microphthalmus has been identified in previous studies of whale-fall annelids in the Atlantic ( Sumida et al., 2016) and the Pacific ( Dahlgren et al., 2004) but no descriptions or molecular data for these have been published to date. This genus is also difficult to place phylogenetically ( Fig. 12 ). Sumida et al. (2016) indicatedthat the Microphthalmus collected from the Atlantic whale fall wasanew species, howeverwhether ourspecimens represent the same species cannot be determined at present due to the lack of information from previous studies. Male copulatory organs were not examined, which have been suggested to be the most suitable morpho-anatomical character for differentiating between species ( Westheide, 2013).

Figures

Figure 11. Microphthalmus sp. (A) Photo of an ethanol-preserved specimen (NHMUK ANEA 2022.412–420), scale bar is 0.25 mm; (B) light micrograph of prostomium and three anterior achaetous segments (NHMUK ANEA 2022.434), scale bar is 100 µm; (C, D) light micrographs of parapodium with the prechaetal (C) and postchaetal (D) lobes in focus (NHMUK ANEA 2022.434), scale bars are 50 µm; (E) light micrograph of heterogomph falcigers with different lengths (NHMUK ANEA 2022.434), scale bar is 20 µm; (F) light micrograph of ventral aspect of the posterior end showing anal lamellae (NHMUK ANEA 2022.412–420), scale bar is 100 µm.

Figure 12. Phylogeny for the Hesionidae, Microphthalmidae and Chrysopetalidae families based on Bayesian analysis of a combined dataset of the genes COI, 16S and 18S. Numbers adjacent to nodes indicate posterior probabilities, and taxa for which sequences have been contributed by the present study are indicated in bold.