Harmothoe sp.

Harmothoe sp.

( Figures 11 View Figure 11 , 12 View Figure 12 )

Material examined

Papua New Guinea. One specimen ( MNHN 2015–1870 About MNHN ), Expedition MADEEP, NW Kavieng, RV Alis, Sta . CP4255 ( 02°27 ʹ 55.1988” S, 150° 43 ʹ 33.5928” E), 333–420 m, in wood, 24 April 2014, L . Corbari and S . Samadi, leg.

Type locality

Papua New Guinea, Kavieng , RV Alis, Sta . CP4255 ( 02°27 ʹ 55.1988” S, 150° 43 ʹ 33.5928” E), 333– 420 m.

Diagnosis

Harmothoe with eyes dorsolateral. Cephalic peaks distinct. Elytra minute, subcircular, with fimbriae minute; macro- and microtubercles conical, brownish.

Description of host

Non-type specimen ( MNHN 2015–1870) brownish ( Figure 11 View Figure 11 (A)), bent ventrally, broken in two parts, anterior fragment with most of body, posterior fragment without posterior end; only first right elytron, and on site, all others lost. A female parasitic copepod, H. pabloi sp. n., attached on anterior end ( Figure 11 View Figure 11 (F)). First elytron and right parapodium of chaetiger 12 removed for observation (kept in container); anterior fragment 8 mm long, 4 mm wide, 21 chaetigers, posterior fragment 4 mm long, 3.5 mm wide, 10 chaetigers.

Prostomium subhexagonal, slightly longer than wide, with cephalic peaks distinct ( Figure 11 View Figure 11 (B)). Eyes blackish, anterior and posterior eyes of similar size, anterior ones on the wider prostomial area. Median ceratophore terminal, ceratostyle lost. Lateral ceratophores distinct, ventral to median one, ceratostyles short, about 2 times as long as ceratophores, papillate. Right palp massive, directed ventrally, tapered. Facial tubercle blackish, not visible dorsally.

Tentacular segment with short tentacular cirri, only left lower one present slightly longer than lateral antennae, with 4 chaetae. Second chaetiger without nuchal hood; ventral cirri about 3 times as long as following ones. Nephridial papillae from chaetiger 9, some short globose, other ones tapered. Pharynx not exposed.

Elytra thick, brownish, subcircular, with fimbriae minute ( Figure 12 View Figure 12 (A)). Anterior internal area with small low conical microtubercles ( Figure 12 View Figure 12 (B)), median area with tiny fimbriae, with conical microtubercles and macrotubercles ( Figure 12 View Figure 12 (C)), becoming slightly larger towards external margin ( Figure 12 View Figure 12 (D)). Median internal area with fimbriae and conical microtubercles ( Figure 12 View Figure 12 (E)), continuing along posterior internal area ( Figure 12 View Figure 12 (F)); insertion area with micro- and macrotubercles ( Figure 5 View Figure 5 (G)), external median area with macrotubercles, margin smooth ( Figure 12 View Figure 12 (H)).

Parapodia biramous ( Figure 11 View Figure 11 (C)). A few dorsal cirri on site, tapered, not swollen subdistally, surface papillate. Notopodium with acicular lobe projected with supracicular lobes. Notochaetae coarser than neurochaetae, brownish, upper ones short, directed dorsally, median and lateral ones directed laterally, lower ones shortest. All notochaetae with series of rows of denticles leaving a short distal smooth area, tips unidentate, slightly falcate ( Figure 11 View Figure 11 (D)). Neuropodium larger than notopodium, acicular lobe elongate, with a supracicular lobe. Neurochaetae golden, upper neurochaetae longest, tapered, with rows of denticles almost reaching tips, tips bidentate; lower neurochaetae oar-shaped, with series of denticles along pectinate area, tips bidentate, accessory denticle thin ( Figure 11 View Figure 11 (E)).

Posterior region tapered. Pygidium unknown.

Remarks

Harmothoe sp. belongs in the group having anterior eyes latero-dorsal, and elytra fimbriate, with macro- and microtubercles. It is the only species having tiny elytra, whereas all other species in Harmothoe have elytra large enough to cover most of dorsum.

Elytra reduced in size are known among species of two polynoid genera: Hermenia Grube and Örsted in Grube, 1856, a lepidonotin; and Lepidasthenia Malmgren, 1867 , a lepidastheniin. However, even in these two genera, the first pair of elytra is large enough to cover most prostomial and adjacent areas. In Harmothoe sp. the first pair of elytra is very small, and the only elytron on site is of the same size. This reduction might imply elytra loss and regeneration, with normal-sized elytra being lost after sampling and sieving or fixation, or in case all elytra were tiny, this could be a strange modification needing explanation.

There is no information about parasite-induced morphological modifications in parasitised polychaetes, as has been documented for some insect groups (Wülker 1964), especially ants ( Laciny 2021). This marked reduction in elytral size might be related to the presence of parasites, and additional Harmothoe specimens from the same locality and depth should be studied. This is why describing this specimen as a new species must be postponed until it is possible to examine additional material.

Distribution

Only known from the type locality, in wood, in sediments at 333–420 m water depth.