Leodamas perissobranchiatus, Blake, James A., 2017

Blake, James A., 2017, Polychaeta Orbiniidae from Antarctica, the Southern Ocean, the Abyssal Pacific Ocean, and off South America, Zootaxa 4218 (1), pp. 1-145 : 76-78

Leodamas perissobranchiatus new species

Figure 35

Scoloplos (Leodamas) sp. Hartman 1967: 108 (in part, Sta. 753 only).

Material examined. Western Chile, off Valparaiso, Eltanin Sta. 9-753, 26 Sep 1963, 33.27°S, 71.78°W, 192 m, holotype ( USNM 1013905 ) and 3 paratypes ( USNM 56460 ) .

Description. All types incomplete, largest paratype 17 mm long, 4 mm wide for 44 setigerous segments. Thoracic region broad, dorsoventrally flattened, with 11–13 setigers, narrowing abruptly to more oval-shaped abdominal region. Color in alcohol: brown.

Prostomium reduced, pointed on anterior margin ( Fig. 35 A). Peristomium reduced, hidden by setiger 1 dorsally, reduced ventrally to simple ring around oral opening; nuchal slits present on lateral margins of peristomium; proboscis saclike.

Thoracic parapodia all similar, well developed, with those of anterior segments narrowest. Segmental dorsal sense organs not present. Notopodial postsetal lamellae with broad, flattened bases tapering to narrow tips ( Fig. 35 C); neuropodia consisting of broad tori bearing triangular-shaped postsetal lamellae ( Fig. 35 B–C). Abdominal parapodia all similar, shifted only about 20–45° dorsally; with cirriform postsetal lamellae ( Fig. 35 D).

Branchiae from setiger 4; branchiae single, flattened, acuminate on anterior thoracic setigers ( Fig. 35 C), becoming palmately branched from last thoracic or transitional segment of abdominal region; branchiae formed of two branches ( Fig. 35 A), then increasing to three and finally four branches ( Fig. 35 D); 4-branched arrangement continuing until about setiger 40, thereafter branches reduced to 3, then 2, and 1 in far posterior segments.

Notosetae including dense fascicles of long, crenulated capillaries in thoracic setigers and crenulated capillaries, furcate setae and cross-striated, non-crenulated capillaries in abdominal notopodia; furcate setae with unequal tynes between which fine needles connected in a web on both sides ( Fig. 35 F). Neurosetae of thoracic setigers in 3–4 dense rows of uncini intermixed with few long, thin silky crenulated capillaries ( Fig. 35 B–C); uncini distally curved, notched with lateral sheath and transverse ribs along shaft ( Fig. 35 E); abdominal neurosetae short, non-crenulated capillaries, few in number; tip of single acicula emergent.

Etymology. Perissobranchiatus : perisso, Greek for beyond the regular number or size; branchos, Greek for gill.

Remarks. Leodamas perissobranchiatus n. sp. is most closely related to L. latum ( Chamberlin, 1919) , originally described from 588 m off the Pacific coast of Panama in having branched or multiple branchiae arising from a single location. The species was later reported by Fauvel (1932) from 457 m off Burma. Leodamas perissobranchiatus n. sp. differs from L. latum in having branchiae first present from setiger 4 instead of 5, in having each branchia with maximally four branches in a palmate arrangement instead of nine, and in having 11–13 thoracic setigers instead of 19–20. In addition, the branchial branches of L. perissobranchiatus arise separately, whereas in L. latum , each branch arises from a common raised core. There are also differences with the thoracic neuropodial uncini; in L. perissobranchiatus there is a lateral sheath along the shaft that is not present in L. latum . Unlike most other orbiniids, L. perissobranchiatus n. sp. has the abdominal parapodia in a more lateral position, shifted dorsally to only about 20–45°, probably due to the space taken up from the bases of the additional branchiae; most dorsally oriented branchiae are present in far posterior segments. Another species of Leodamas with branched branchiae is L. cylindrifer ( Ehlers, 1904) from intertidal zones in New Zealand and Australia. However, in this species the branchiae are first present from an anterior abdominal segment and are dendritically branched instead of palmate.

Distribution. Western Chile, 192 m.

Figures

FIGURE 35. Leodamas perissobranchiatus n. sp. Holotype (USNM 1013905). A, anterior end, dorsal view; B, some anterior thoracic setigers in left lateral view; C, thoracic parapodium, anterior view; D, abdominal parapodium, anterior view; E, thoracic neuropodial uncinus; F, furcate seta.