Naineris argentiniensis Blake, 2017, new species

Naineris argentiniensis new species

Figure 51

Material examined. Argentina, Mar del Plata, Rocas Pya Chica, intertidal, Jan 1973, coll. Marchetti, holotype (USNM 1013686); Feb 1970, coll. J.M. Orensanz, 3 paratypes (USNM 1013687).

Description. A small species, holotype incomplete, 12 mm long, 0.8 mm wide for 62 setigers; paratypes of similar size, but not well preserved, one complete. Thoracic region with 12–13 setigers, with transition to abdomen abrupt, characterized by reduction of neurosetae and change from bidentate to unidentate neuropodial uncini.

Prostomium about as wide as long, broadly rounded on anterior margin (Fig. 51 A); no eyespots. Peristomium elongate achaetous region formed of two indistinct rings, more or less fused.

Notopodial postsetal lobes elongate, fingerlike throughout body (Fig. 51 A–B). Thoracic neuropodia swollen, forming rounded tori from which setae emerge; postsetal lobes from setiger 1, continuing through abdominal region.

Thoracic notosetae crenulated capillaries. Furcate setae absent. Thoracic neurosetae including crenulated capillaries with numerous spinelets along shaft (Fig. 51 C) and bidentate ribbed uncini arranged in 2–3 rows; uncini of anterior row shorter, more strongly curved, those of last row longer and straighter (Fig. 51 D–F). Anterior abdominal neurosetae including curved blunt-tipped unidentate uncini and capillaries; posterior abdominal setigers with 2–3 unidentate acicular spines, at least one of which has crenulations (Fig. 51 B). Branchiae from setiger 5–6 continuing to end of body.

Pygidium a rounded lobe with terminal anus; lacking cirri.

Remarks. The specimens studied here are probably juveniles. They are representative of a transitional phase between the traditional definition of a small orbiniid such as Protoariciella, which normally has two achaetous peristomial rings and Naineris, which has one. These specimens are referred to Naineris because juveniles of this genus are known to have two achaetous rings as larvae and juveniles and one as an adult. Naineris argentiniensis n. sp., although represented only by small specimens, has a close relationship with N. grubei, known from the eastern Pacific, in the bifid nature of the neuropodial uncini and occurrence of branchiae from anterior thoracic segments. Naineris argentiniensis n. sp. differs considerably from N. grubei, however, in lacking furcate setae and flail setae, by having a broad, straplike abdominal notopodium instead of one that is thin and fingerlike, having branchiae from setiger 5–6 instead of 4, and by having low, rounded abdominal neuropodia instead of elongate, bilobed ones.

Distribution. Argentina, intertidal.