Orbiniella grasslei, Blake, 2020

Blake, James A., 2020, New species and records of deep-water Orbiniidae (Annelida, Polychaeta) from the Eastern Pacific continental slope, abyssal Pacific Ocean, and the South China Sea, Zootaxa 4730 (1), pp. 1-61 : 41-44

Orbiniella grasslei new species

Figure 21

urn:lsid:zoobank.org:act:C1344615-DC39-4782-89FB-F7DBBAB3ECA1

Material examined. East Pacific Rise, hydrothermal vent area at 21°N: HOV Alvin Dive 1221-15, 20°50′N;

109°06′W, 4 May 1982, 1618 m, washings of Riftia pachyptila tubes and Calyptogena magnifica shells, holotype ( MCZ 153574 ) and 3 paratypes ( MCZ 153575 ) ; HOV Alvin Dive 1223-17, 20°50′N; 109°06′W, 7 May 1982, 2616

m, rubble, 4 paratypes ( MCZ 153576 ); HOV Alvin Dive 1223-11, 7 20°50′N; 109°06′W, 7 May 1982, 2616 m, fine fraction from washings, 3 specimens ( MCZ 153577 ) .

Description. Holotype largest specimen, complete, 5.44 mm long and 0.22 mm wide for 26 setigers. Body not divided into distinct thoracic and abdominal regions; body segments all similar. Parapodia reduced, lamellae lacking.

Pre-setiger region thick, with prostomium and peristomium lacking obvious separation dorsally and laterally ( Fig. 21A ). Prostomium broadly rounded anteriorly; eyespots absent, nuchal organs not visible. Peristomium entirely merged with prostomium dorsally; ventrally with a large ventral lip below mouth; two partial annular rings weakly developed, only apparent ventrally ( Fig. 21A ).

Setiger 1 and following segments separated from one another by swollen intersegmental annular rings produc- ing biannulate segments ( Fig. 21A ). Notopodia bearing 2–3 camerated capillaries and three serrated spines from setiger 1; spines reduced to two by setiger 5, continuing to posterior setigers where only a single spine and two capillaries persist ( Fig. 21 B–C). Neuropodia bearing two spines and three capillaries from setiger 1, increasing to three spines and five capillaries by setiger 5, reduced to two spines and 0–2 capillaries in posterior setigers ( Fig. 21 B–C). Spines with distinct serrations along shaft ( Fig. 21C ).

Pygidial segment simple, lacking cirri.

Methyl Green stain. No pattern.

Remarks. Orbiniella grasslei n. sp. is most similar to O. hobsonae Blake & Hilbig, 1990 from hydrothermal vents on the Juan de Fuca Ridge. Both species have long, thin bodies and acicular spines with a row of barbs or serrations along the shaft. Orbiniella grasslei n. sp. differs from O. hobsonae in having a peristomium on which the annular rings are indistinct instead of being present as two distinct rings; in addition, nuchal organs are not visible instead of being prominent laterally on the prostomium. The most conspicuous difference between O. grasslei n. sp. and O. hobson ae, however, is the segmentation. In O. grasslei n. sp., the intersegmental groove is expanded into a large swelling that provides a prominent biannulate appearance to segments along the body. In contrast, the segments of O. hobsonae are entirely uniannulate. There are additional differences in the fine details of the structure of the spines and capillary setae. Another species of Orbiniella , O. aciculata Blake, 1985 , from the vicinity of the Galápagos Rift hydrothermal vents has spines that are smooth instead of serrated, and the body is short and compact instead of long and thin.

Etymology. This species is named for the late Dr. J. Frederick Grassle, prominent deep-sea benthic ecologist of the Woods Hole Oceanographic Institution and the Rutgers University Institute of Marine and Coastal Sciences. As part of his numerous expeditions to deep-sea locations, Dr. Grassle provided this author and other investigators with numerous polychaetes from vents and other habitats that have resulted in a rich harvest of new species.

Distribution. Hydrothermal vents on the East Pacific Rise at 21°N, 1618–2616 m.

Figures

FIGURE 21. Orbiniella grasslei n. sp. Holotype (MCZ 153574): A, anterior end, right lateral view; B, anterior parapodium, anterior view; C, another parapodium showing details of serrated spines.