Owenia caissara, Silva & Lana, 2017

Silva, Luiz & Lana, Paulo, 2017, Owenia caissara sp. n. (Annelida, Oweniidae) from Southern Brazil: addressing an identity crisis, Zoologia (e 12623) 34, pp. 1-7 : 2-5

Owenia caissara sp. n.

http://zoobank.org/ D36477B5-63A6-41B4-9D4B-92EA85C330E1

Diagnosis. Crown with five pairs of tentacles. Tentacular branches beginning near collar base, numerous near crown base and apex. Collar rectilinear, with pronounced lateral slit. Two ventrolateral ocelli partially covered by collar. First abdominal segment with rows of up to 23 hooks. Hooks with 0° to 90° angles in relation to anteroposterior body axis, and nuchal shape regularly curved; teeth curvature moderate. Notochaeta scales long and thin with oval transition between A and B ( Fig. 4).

Description (based on holotype; numbers between brackets refer to average measurements in Babitonga and Paranaguá Bay specimens, except body length which represents the maximum and minimum in both places). Body 21 (15–32) mm long. Width at collar height 1.18 (1.16 and 1.24) mm. Body divided into tentacular crown, thorax, and abdomen ( Figs 5, 10). Tentacular crown and thorax separated by a thin membrane forming a collar ( Figs 6, 7, 11, 14, 17, 20). Rectilinear collar with a lateral slit in angle 63° (77° and 67°) on average. Short crown (crown/ abdomen length ratio = 1:2), with five pairs of tentacles ( Fig. 17). Dorsal branches longer than ventral branches ( Figs 7, 13, 17, 20). Tentacular branches 0.83 (1 and 0.89) mm long. Crown/ collar length ratio of 0.70 (0.89 and 0.70). Thorax/collar length ratio of 1.95 (1.97 and 1.84). Thorax with three segments with capillary notochaetae in lateral bundles on first two segments, dorso-lateral on third segment. Thorax 1.6 (2.12 and 2.22) mm long on average. Abdomen with thirteen to eighteen biramous segments, each one with one pair of capillary notochaetae bundles and one neuropodial ring almost encircling the body. Dorsal ridges of the fifth segment with clavate glandular fractures, curved and expanded, almost touching along the middorsal body line. Posterior abdominal region without a dorsal groove. Neuropodial ring with rows of minuscule bidentate hooks.

First abdominal segment with rows of up to 23 hooks ( Figs 18, 21), in 0° to 90° angles in relation to antero-posterior body axis. Teeth on hooks with a space in between, in an inverted V-shape ( Figs 23, 24, 26, 27). Hooks with rectilinear shoulder and regularly curved nuchal shape ( Figs 16, 19, 22). Average teeth protrusion of 2.02 µm ( Figs 4A, 19, 22). Distance between head of shaft and lower part of the teeth (length of opening) 0.83 µm (moderate), ( Fig. 2:Y). Hooks were not measured in the holotype to avoid damage to the individual, and following figures are measurements of five individuals from Paranaguá and Babitonga bays, respectively. Maximum hook width (X + Z) of 4.79 and 5.01 µm ( Fig. 2) and X/Z ratio of 0.73 and 0.67 ( Fig. 2). Moderate teeth curvature, with average angle formed by meeting of L2/L4 tangents from 54° and 63° ( Figs 19, 22). Long and thin scales, total length of notochaetal scales on first abdominal segment (A + B) of 4.87 and 4.29 µm ( Figs 4, 25, 28). A + B/D ratio of 9.9 ( Figs 4, 25, 28). Average length of scale’s free part (C) of 2.5 µm and 2.32 µm ( Fig. 4). Oval transition area between A and B ( Figs 4, 15, 25, 28).

Living specimens with dark brown coloration at the base and terminal region of tentacular branches ( Figs 11, 13). Red tinged thorax and beginning of abdomen due to body transparency, which highlights vascularization; remaining abdomen pinkish ( Figs 5, 10). Color absent in alcohol – preserved animals, except one pair of reddish ocelli at ventrolateral base of tentacular branches, partially covered by collar ( Figs 6, 9), and brown spots basally on tentacular branches and on terminal regions ( Figs 6, 7).

Methyl green staining pattern characterized by tentacular branches unreceptive to staining, dorsal side of the collar and two longitudinal dorso-lateral lines strongly stained. On the ventral side, the two V shaped lines were unreceptive to methyl green but the border of these lines and the collar were strongly stained ( Fig. 29, Table 1).

Tubes with medium and coarse particles (481-586 µm), coalesced by mucus in an imbricated pattern. In cross-section, smaller particles near lumen and larger on tube edge. Quartz particles dominates (99%) followed by magnetite (0.6%), biotite (0.37%), and shell and echinoderm fragments (0.03%). Tubes from 26 to 57 mm long (n = 70).

Material examined. Holotype: ZUEC Polychaeta 17486, 21 mm, Santa Catarina, Babitonga Bay, Paulas Beach, 15/ Jun./2014. Paratypes: ZUEC Polychaeta 17517-17522, Santa Catarina, Babitonga Bay, Paulas Beach, 22/Aug./2014, 6 specimens; Polychaeta 17523-17525, Paraná State, Paranaguá Bay, Cotinga Channel, 4/Jun./2014, 3 specimens; ZUEC Polychaeta 17487-17516, Santa Catarina, Babitonga Bay, Paulas Beach, 3/ Oct./2014, 29 specimens.

Type locality. Paulas Beach, Babitonga Bay , Santa Catarina State, 26°13’S, 48°37’W .

Distribution.Currently known only from estuarine habitats along the coasts of the states of Paraná and Santa Catarina ( Brazil).

Etymology. The species name honors fisherfolk from traditional communities still found along the southern and southeastern Brazilian coasts. We prefer the archaic spelling “caissara ” to the modern “caiçara” to avoid the usage of the cedilla diacritical mark in the taxonomic literature.

Habitat. Populations of Owenia caissara sp. n. are frequent in shallow subtidal bottoms with a predominance of medium sand, at 0.5 to 5 m depth at Babitonga and Paranaguá Bays.

Remarks. Owenia caissara sp. n. has five pairs of tentacles (four in O. fusiformis ), a tentacular branching close to the collar base (clearly more terminal in O. fusiformis ), a collar with a pronounced slit (absent or inconspicuous in O. fusiformis ), ventrolateral ocelli partially covered by the collar (completely exposed in O. fusiformis ), hooks of the first abdominal segment in 0° to 90° angles (varying from 0° to 5° in O. fusiformis ) and the transition between A and B ( Fig. 4) on scales is oval (curved in O. fusiformis, Koh and Bhaud 2003 ), tentacular branches unreceptive to staining (strongly receptive in O. fusiformis tentacular branches) ( Table 1).

The Californian O. johnsoni and O. collaris differ from O. caissara sp. n. in having four tentacular branches with few dichotomies. In O. johnsoni , the crown is long and hooks are in a 45° angle on the first abdominal segment. In O. collaris , the angle of the first abdominal segment ranges from 30° to 45°.

The Korean species O. gomsoni differs from O. caissara sp. n. in having five or more pairs of tentacles (always five in O. caissara sp. n.), a curved collar (straight in O. caissara sp. n.) and a transition area of notochaeta scale angular (oval in O. caissara sp. n.), tentacular branches strongly receptive to staining (unreceptive in O. caissara sp. n. tentacular branches), V shaped lines strongly receptive to methyl green (unreceptive in O. caissara sp. n.) ( Table 1).

Owenia borealis and O. polaris differ from O. caissara sp. n. in having only four pairs of tentacular branches, an angular collar (straight in O. caissara sp. n.) and an angular transition area in notochaeta scale (oval in O. caissara sp. n.). In addition, the dorsal and ventral tentacles do not differ in size in O. polaris , and the tentacular branches are receptive to staining ( Table 1). Owenia persica and O. petersenae differ from O. caissara sp. n. in having only four pairs of tentacular branches. Moreover, O. persica has the dorsal and ventral tentacle branches equal in size, the first tentacular branches are far away from the collar, which is angular, and the hooks lack shoulders. In O. petersenae dichotomies of tentacles are only observed at the distal end, the collar is curved (convex), and the tentacular branches are receptive to staining ( Table 1).

The Australian O. australis , O. mirrawa , O. dichotoma and O. picta differ from O. caissara sp. n. in having four pairs of tentacular branches. Owenia dichotoma has a shorter tentacle crown with fewer ramifications than O. caissara sp. n. and O. picta has fewer tentacle crown ramifications than O. caissara sp. n., and a bilobed structure between the tentacles of the left and right sides in ventral view, which is lacking in O. caissara sp. n. ( Table 1).

The specimens collected in Ubatuba (Northern coast of São Paulo, SE Brazil) differ from O. caissara sp. n. in having four pairs of tentacular branches with dorsal and ventral branches of equivalent length and the angles of the hooksranging from 0° to 45° in the first abdominal segment ( Table 1).