Naineris bicornis Hartman 1951

Naineris bicornis Hartman, 1951

(Figs 1–3)

Naineris bicornis Hartman, 1951: 72–74, pl. 19, figs 1–6; 1957: 304–305, pl. 40, figs 1–6; 1959: 366.— Perkins & Savage 1975: 43.— Taylor 1984: 1–9, figs 1–5, 1–6a–f.— Salazar-Vallejo 1996: 26.— Perkins 1998: 88.—Felder & Camp 2009: 764.

Material examined. USA, Florida, Franklin County, Alligator Harbor, Florida, Gulf of Mexico, US, North Atlantic Ocean, Sta. 3, coll. 04 Feb 1950, 29.910000°N, 84.395278°W, holotype (LACM-AHF Poly 674). — off Saint George Sound, MAFLA, Sta. 2421, coll. D. Savelle, H. Kritzler, D. Garlick, Sep 1975, 29.62°N, 84.28°W, 19 m, box core (1, USNM 1284135); MAFLA Sta. 2421, coll. D. Savelle, H. Kritzler, D. Garlick, Sep 1975, 29.616667°N, 84.283333°W, 19 m, box core (1, USNM 1284134); MAFLA, Sta. 2420, coll. D. Savelle, H. Kritzler, D. Garlick, 1975, 29.6994°N, 84.1836°W, 19 m (1, USNM 1284133); MAFLA, Sta. 2420, D. Savelle, H. Kritzler, D. Garlick, Jun 1975, 29.6994°N, 84.1836°W, 14 m, (1, USNM 1284132); MAFLA, Sta. 2420, coll. D. Savelle, H. Kritzler, D. Garlick, 1975, 29.6994°N, 84.1836°W, 14 m (1, USNM 1284131). —off Cedar Key, MAFLA Sta. 2317, coll. D. Savelle, H. Kritzler, D. Garlick, 19 Sep 1975, 28.933333°N, 84.100000°W, 29 m, box core (1, USNM 1284136; 1, USNM 1284137; 1, USNM 1284138; 1, USNM 1284139). — off Crystal River, MAFLA Sta. 2316, Nov 1977, 28.700000° N, 84.333333° W, 35 m (1, USNM 090156) (parapodia slides). — off Florida, SOFLA Sta. 16, coll. Mote Marine Lab For Bureau of the Land Management / Minerals Management Service (BLM / MMS), Jul 1981, 25.761667°N, 83.184444°W, 54 m (1, USNM 090154); SOFLA Sta. 02, coll. Mote Marine Lab For BLM/ MMS, May 1981, 26.763889°N, 82.753056°W, 24 m (1, USNM 090153); SOFLA Sta. 46, coll. Environmental Science and Engineering, Inc. /LGL Ecological Research Associates (Ese / Lgl) For BLM/ MMS, May 1984, 26.0144 °N, 82.1319°W, 18 m (2, USNM 112302); SABP Sta. 7B, coll. Texas Instruments for BLM/ MMS, May 1977, 29.4664°N, 80.9525°W, 20 m (1, USNM 59369); MAFLA Sta. 2960, Nov 1977, 25.67°N, 82.33°W, 27 m (1, USNM 90164). — off St. Petersburg, MAFLA Sta. 2207, coll. Aug 1977, 27.950000°N, 83.150000°W, 19 m, (1, USNM 090155). — off Apalachicola Bay, MAFLA, Sta. 2316, coll. D. Savelle, H. Kritzler, D. Garlick, Jul 1975, 28.7003°N, 84.3336°W, 35 m, (2, USNM 1284140; 1, USNM 1284141; 1, USNM 1284670); MAFLA, Sta 48, coll. DG., Jun 1974, 28.48°N, 84.35°W (2, USNM 1284677); MAFLA, Sta 42, coll. DG., Jun 1974, 28.7°N, 84.44°W (1, USNM 1284679). — off Clear Water, MAFLA, Sta. 2207, coll. D. Bishof, D. Savelle, Jul 1975, 27.9497°N, 83.15°W, 19 m, (1, USNM 1284671); MAFLA, Sta. 2209, coll. D. Bishof, D. Savelle, Jul 1975, 27.875°N, 83.5667°W, 34 m, (3, USNM 1284672). — off Charlotte Harbor, MAFLA, Sta. 2104, coll. D. Bishof, D. Savelle, May 1975, 26.4164°N, 83.3833°W, 53 m, (1, USNM 1284678). — off Sanibel Island, MAFLA, Sta. 2101, coll. D. Bishof, D. Savelle, May 1975, 26.4167°N, 82.4169°W, 11 m, (1, USNM 1284683).

Measurements. Holotype is fragmented in three parts. The most anterior 0.75 mm long, 3 mm wide, for 27 chaetigers. Hartman (1951) and Taylor (1984) reported animals reaching 30 mm length and 5 mm width for over 100 segments for specimens from the same localities and sampling events studied.

Diagnosis. Spatulate to slightly indented prostomium. Multiple dorsal sensory organs grouped ten per side in a one row anteriorly, increasing to two on posterior thoracic segments, almost crossing midline; abdominal sensory organs forming two distinct groups irregularly arranged, reduced in number (four to five). Thoracic notopodial lobes may be acute-to-rounded-tipped and with median restriction. Thoracic neuropodial lobe with an upper subtriangular papilla. Thoracic neurochaetae with 5–6 transverse, posterior rows of numerous subuluncini; a transverse, anterior row of about 20 crenulate capillaries; an inferior, anterior, oblique row of about 20 hooded uncini and an inferior, posterior, oblique row of capillaries.

Redescription. Holotype medium-sized specimen. Color in alcohol pale yellow. Thorax and abdomen distinct, with parapodia inserted laterally in thorax and dorsally in abdomen. Most abdominal branchiae lacking. Ventrally thorax smooth, but abdomen tri-annulate with central ring wider than others.

Prostomium long, spatulate, slightly indented in front end; no eyespots; nuchal organs present at between posterior end of prostomium and anterior end of peristomium (Fig. 1A–B). Peristomium achaetous, as short as following rings. Mouth opening with striated lips; proboscis wide, lobed (Fig. 1D).

Branchiae from chaetiger 6 onward (Figs 1B, 3A), lanceolate, densely ciliated (Fig. 1E–F); first branchiae approximately ⅓ size of abdominal branchiae. Dorsal sensory organs present from chaetiger 12 (Figs 1B, 2B–C, 3B), multiple per segment, oval-shaped; most anterior grouped ten per side forming one row, increasing to two on posterior thoracic segments, almost crossing midline; abdominal sensory organs forming two distinct groups irregularly disposed, reduced in number (four to five). Dorsal crest represented by a straight, consistent, flat curve, low and ciliated (Fig. 1F).

Thorax slightly depressed (Fig. 1E), both fragments with 45 chaetigers (~3 transitional segments with intermediate characteristics between thoracic and abdominal segments) (Fig. 1B–C). Parapodia biramous. Thoracic notopodial postchaetal lobes slightly constricted, lanceolate, with elongated tips (Figs 1E, 2D). Thoracic neuropodial postchaetal lobes represented by a flange with an upper papilla, subtriangular (Figs 1C, E, 2A, D). Abdominal notopodia with postchaetal lobes hardly constricted, pyriform. Abdominal neuropodial lobes are represented by a flange with a triangular lobe, shorter than thoracic (Figs 1F–G, 2E).

Thoracic notochaetae with 20–25 crenulate capillaries in two bundles (Fig. 2D). Abdominal notochaetae with about 20 capillaries and a few furcate chaetae each with unequal tines (Fig. 2E). Thoracic neurochaetae with 5–6 transverse, posterior rows of numerous subuluncini; a transverse, anterior row of about 20 crenulate capillaries; an inferior, anterior, oblique row of about 20 hooded uncini and an inferior, posterior, oblique row of capillaries (Figs 2D, 3C). Abdominal neurochaetae include three acicular spines (Fig. 3D) and 5–8 crenulate capillaries intermixed (Fig. 2E).

Pygidium unknown.

Remarks: Naineris bicornis is mainly distinguished by its slightly indented prostomium. Nevertheless, care is required when using the shape of the prostomium as the main diagnostic character. The shape of the prostomium is as it appears in the holotype is only seen occasionally and tends to be spatulate in specimens from other collections, probably due to fixation (Figs 2A, 3A).

Paired, dark segmental spots at bases of branchiae were not observed in the holotype but were present in chaetigers 5–6 in the additional specimens examined from the type locality or vicinity. They seem to correspond to internal structures that are transparent through the epidermis and must not be confused with the dorsal sensory organs (Fig. 2A–B). These dark, segmental spots were also present in the juveniles of N. australis, the most similar species (see Zhadan et al. 2015, fig. 12D). In addition, dorsal sensory organs were not originally described in N. bicornis. As in N. australis, they are multiple (Figs 2B–C, 3B) and difficult to see in old, preserved specimens.

The chaetal arrangements of the thoracic neuropodia of N. bicornis, N. australis, and N. elegans sp. nov. are all similar. It includes the subuluncini, crenulate capillaries, and hooded uncini. The characters distinguishing N. bicornis from other similar species is based mainly on the features of thoracic notopodial lobes, distribution of multiple dorsal organs, geographic distribution and bathymetry. Thoracic notopodial lobes may be acute-to-rounded-tipped and possess a constriction in the middle, as in N. bicornis. Likewise, dorsal organs they may be grouped in rows or be irregularly distributed and may cross the midline depending on the species. Concerning their distribution, Naineris bicornis is distributed mostly in the Tropical Atlantic, whereas the other species are from the Pacific. Finally, N. bicornis occurs at continental shelf depths, whereas the other similar species are intertidal.

Recent molecular data have shown that N. bicornis is a species complex, and at least two species occur in Brazil (RA unpublished data). Molecular characterization of specimens from the type locality and Brazilian records of N. bicornis are necessary, but they are outside the scope of this study. This species was recorded only once in Brazil (Nonato 1981) and was not abundant in the area (Amaral et al. 2022). Recent sampling along the Brazilian coast resulted in two specimens, which were similar to N. bicornis, but with consistent molecular differences between them (RA unpublished data).

We also examined the holotype of Naineris bicornis minuta Hartmann-Schröder, 1965 (ZMH P-14869, type locality: Oahu, Hawaii). Because of the juvenile morphology of the holotype, it was impossible to find any morphological differences with N. bicornis. Further studies covering different oceans are necessary to clarify the species remaining in this group.

Distribution. Warm Temperate Northwest Atlantic province: Northern Gulf of Mexico ecoregion and Tropical Northwestern Atlantic province: Floridian and Southern Gulf of Mexico ecoregions, 11– 54 m.