Angursa bicuspis Pollock 1979

Angursa bicuspis Pollock, 1979

Fig. 1

Angursa with presence of median cirrus uncertain; primary clavae longer than lateral cirri; pedestals of primary clavae and lateral cirri absent; morphology of secondary and tertiary clavae unknown; simple, tapering cirri E present; leg I sensory organs present; presence of legs II and III sensory organs uncertain; leg IV sensory organs each as papilla with short, apical spine; robust anal papillae present; presence of seminal receptacles uncertain; presence of proximal pads of internal digits uncertain.

Holotype UNITED STATES OF AMERICA • 1 adult; Massachusetts, Buzzard Bay side of Penzance Point, Woods Hole; 41°31′41″ N, 70°40′41″ W; 9 Jul. 1968; Hummon & Pollock leg.; USNM W 50900.

Angursa bicuspis was described based on the holotype and an additional specimen (Pollock 1979). However, their conspecificity has been doubted by Kaczmarek et al. (2015) owing to the fact that the two specimens were collected from two different environments of distant localities and that they showed morphological differences (Pollock 1979). As there is no positive evidence to regard the two specimens as conspecific, we support the opinion of Kaczmarek et al. (2015) and consider it as sufficient to base our attempt to re-diagnose A. bicuspis on only the holotype.

The holotype is in bad condition. However, our observation confirmed that of Pollock (1979) in the overall body shape (Fig. 1A) and the presence of the internal cirri (Fig. 1B), the external cirri (which is 8 μm, not 5.5 μm as reported by Pollock 1979) (Fig. 1B), the lateral cirri, the primary clavae (Fig. 1B), the leg I sensory organs, the cirri E, the characteristic claws, and the two papillae posterior to the anus (Fig. 1C). Pollock (1979) considered the latter structure as not useful for distinguishing species referring to the variability of the caudal projection of Batillipes Richters, 1909 and the fact that it was not observed in the additional specimen. Villora-Moreno (1998) supported this view, but Noda (1985) and Bussau (1992) used this structure to distinguish this species from its congeners (reason not explained). We agree with Noda (1985) and Bussau (1992) for the following two reasons. Firstly, we consider that this character is not homologous to the caudal projection of Batillipes as Pollock (1979) suggested, but a developed form of the cuticular fold that closes the anus, homologous to the “two weak protuberances” of A. antarctica described by Villora-Moreno (1998). Secondly, as discussed in the previous paragraph, this character’s presence/absence in the two specimens of Pollock (1979) is likely an interspecific variation. Thus, A. bicuspis can be easily distinguished from its congeners by the presence of the well-developed anal papillae (Renaud-Mornant 1981; Noda 1985; Bussau 1992; Villora-Moreno 1998), consequently supporting the species status of A. abyssalis proposed by Bussau (1992).

In addition to confirming and re-interpreting the original observation (Pollock 1979), we recognize three overlooked characters: a paired globular body fringing the mouth (Fig. 1B), the leg IV sensory organs and the peduncles (3 μm) that do not reach the claws (Fig. 1D). Each leg IV sensory organ consists of a spherical papilla and a short, apical spine (Fig. 1C). An enveloping cuticular sheath of the papilla was not evident, but may have been obscured due to the squeezed state of the specimen. The bad condition of the specimen also hindered our decisions on the presence/absence of the median cirrus, the secondary and tertiary clavae, legs II and III sensory organs, proximal pads of the internal digits and the seminal receptacles. Additional collection of specimens from the type locality is necessary for more detailed discussion on this species morphology.