Alternatipathes bipinnata ( Opresko, 2005 )

Opresko, Dennis, 2017, First record of Alternatipathes bipinnata (Cnidaria: Antipatharia) in the Southern Hemisphere, Zootaxa 4312 (1), pp. 189-193 : 189-190

Alternatipathes bipinnata ( Opresko, 2005) ( Fig. 1 )

Umbellapathes bipinnata Opresko, 2005: 138 , figs 4–5.

Alternatipathes bipinnata, Molodtsova & Opresko, 2017: 10 , fig. 5.

Description. The colony is 210 mm tall with an intact basal attachment plate (about 14 mm in maximum dimensions). The unpinnulated portion of the corallum curves slightly toward the polyp side and then backwards; the pinnulated portion curves forward, with the tip of the corallum pointing downwards. The unpinnulated portion of the stem is 195 mm long and about 1.3 mm in diameter just above the basal plate. The 39 mm long pinnulated section contains 13 pinnules, six on one side and seven on the other. The pinnules on the stem are situated in two lateral rows and are arranged in a regularly alternating pattern. The stem pinnules are inclined toward the distal end of the stem (with a distal angle of about 49° for the lowermost pinnules, decreasing to about 46° for the pinnules at the top). The length of the stem pinnules increases toward the middle of the corallum; the longest simple pinnule is 36 mm and has a basal diameter of about 0.6 mm. The lowermost pinnule on the stem is developed into a 125 mm long pinnate branch with 44 pinnules (21 on one side and 23 on the other), with distal angles of 37° to 51°. This branch is itself branched, with its lowermost pinnule having five pinnules; three on one side and two on the other. Pinnules on the stem and branch are spaced from about 2.5 mm to 4 mm apart on each side of the axis, but some of the lowermost ones on the stem are about 9 mm apart. The average density of the pinnules in each lateral row is three per centimeter, and four to five pinnules per centimeter for both rows. The planes containing the two rows of pinnules and pinnulated branches form an interior angle of 160 to 170°. The spines on the pinnules are concavely conical, with an acute apex; their base is flared out along the axis distally and proximally. They are arranged in regular rows, four or five of which are normally seen in lateral view. Within each row they are spaced at varying distances, from about 289 to 591 µm apart; they are more widely spaced towards the distal part of the pinnules. The pinnular spines are larger on the polyp side of the axis; polypar spines are 95 to 150 µm tall; abpolypar spines range from 40 to 116 µm. No additional small secondary spines are observed. Spines are also present on the stem, extending down to about 4 mm of the basal plate. Those nearest the basal plate are irregularly arranged in two or three rows, higher up they occur in more neat rows; three to five of which are visible in lateral view. The spines on the stem are larger on the polypar side of the corallum; most of them extend out perpendicularly, and only a few of them slant downward towards the base. The spines on the pinnules extend out perpendicularly or are slightly inclined distally. Due to the poor condition of the remaining soft tissue (the specimen is an almost clean skeleton), no characteristics of the polyps could be determined.

Distribution. This species was previously known from three specimens collected in deep waters (1130 to 2085 m) off the Pacific coast of Mexico (31°16.4’ N; 117°34.2’ W to 31°22.0’ N; 117°42.2’ W) and off California, USA in 2634 to 2846 m depth (USNM 1234554, USNM 1234557); the present specimen represents the first record for the species in the Southern Hemisphere ( Fig. 2 ).

Remarks. Overall, the pinnular densities appear to be similar to that of the holotype of A. bipinnata ( Fig. 1 b). In these features, however, our specimen is similar to one of the paratypes which has a maximum pinnular length of 45 mm and a pinnular density of 4 to 5 per centimeter. The skeletal morphology is similar to that of the Northern Hemisphere specimens, with conical, acute spines with flared bases; however, the maximum size of the polypar spines is smaller in the present specimen than in the previously described specimens (159 versus 200 to 300 µm tall, respectively). The additional small secondary spines reported for the holotype ( Opresko, 2005) were not found in the Chilean A. bipinnata ( Fig. 1 c–f). The smaller size of the polypar spines and the absence of secondary spines, suggests that the Chilean specimen may represent a different species. Although spine size can be a valid species-level character, the examination of a larger suite of specimens is needed to eliminate the possibility that the differences reported here represent only intraspecific variability.

Of the approximately 247 known antipatharian species ( Brugler et al., 2013), only eleven of them, or about 4.5 %, occur along the southeastern Pacific off Chile. All of these species only occur in subtidal waters; from 79 m for Plumapathes fernandezi (Pourtalès, 1874) (USNM 99762) from the Juan Fernández Archipelago to a maximum depth of 1800 m for Lillipathes ritamariae Opresko & Breedy, 2010 , from off Caldera, in northern Chile ( Araya et al., 2016a). The modest number of species reported for the area may reflect the lack of sampling in deep waters; from these species four are endemic and three of them have been found only once, while the rest has been collected as bycatch in deep-water fisheries.

Records of unidentified species, in the genera Antipathes Pallas, 1766 ; Cladopathes Brook, 1889 ; Chrysopathes Opresko, 2003 ; Leiopathes Haime, 1849 and Lillipathes Opresko, 2002 , are also known from the area, derived from specimens collected serendipitously in the deep-water fisheries of the Patagonian Toothfish operating at 800–2000 m depth along the entire Chilean coast ( Bravo et al., 2005). Additionally, material obtained in several expeditions along the coasts of the Southeastern Pacific (RV Anton Bruun, HMS Challenger, etc.), accounted for a total number of twelve antipatharian species (including species only identified to genus-level) for Chilean waters ( Häussermann & Försterra, 2007). Unfortunately, species-level identification in these specimens is hindered by the lack of local experts and the scant material deposited in local institutions; they are currently absent in the collections of the MNHNCL at Santiago, Chile (Jorge Pérez-Schultheiss, pers. comm.). This work adds to the scarce information on black corals from the Peruvian province; the present record from northern Chile extends the biogeographical range of this species significantly southwards, and it suggests a continuous distribution of this species along the South American continental margin.

Figures

FIGURE 1. Alternatipathes bipinnata (Opresko, 2005) MPC 280617. a, complete specimen. b, close up view of pinnulated portion of the corallum (abpolypar view). c, SEM of pinnules from pinnulated stem. d, SEM of lateral pinnule. e, detail of spines on pinnulated part of the stem. f, detail of spines on primary branch. Scale equals 20 mm for a and b, and 0.2 mm for c – f.

FIGURE 2. Known distribution of Alternatipathes bipinnata (Opresko, 2005). Red circles indicate previous records and the red star denotes the location of the specimen described in this study.