Aphelochaeta antelonga Dean & Blake, 2016

Blake, James A., 2018, Bitentaculate Cirratulidae (Annelida, Polychaeta) collected chiefly during cruises of the R / V Anton Bruun, USNS Eltanin, USCG Glacier, R / V Hero, RVIB Nathaniel B. Palmer, and R / V Polarstern from the Southern Ocean, Antarctica, and off Western South America, Zootaxa 4537 (1), pp. 1-130 : 10-12

Aphelochaeta antelonga Dean & Blake, 2016

Figure 1

Aphelochaeta antelonga Dean & Blake, 2016: 102–104 , figs. 1A, 2A–B, 3A.

Monticellina sp. Soto et al. 2016: Table 2.

Material examined. Off Ecuador, SEPBOP, R / V Anton Bruun Cr. 18B, Sta. 768-D, 10 Sep 1966, 03°36ʹS, 80°38ʹW, ca. 50 m (1, USNM 1490699 ) .— Chile, Valparaiso Bay , USNS Eltanin Cr. 18, Sta. 1437, 25 May 1965, 33.00°S, 71.67°W, 119 m (7, USNM 1490700 ); University of Valparaiso, coll. E.H. Soto, Dec. 2012: Sta. 1, 32.909°S, 71.546°W, 22 m (14, MCZ 14986); Sta. 2, 32.909°S, 71.597°W, 50 m, (6, MCZ 149877 ); Sta. 3, 32.909°S, 71.596°W, 80 m, (7, MCZ 149877 ); LUCE , near Puerto Montt, Estero Reloncavi, Bahía Ralún , Sta. M 29B, 01 Apr 1949, 41.408°S, 72.329°W, 35–40 m in sand (1, SMNH) .

Description. An elongate, threadlike species with narrow thoracic setigers and elongate abdominal segments, but these not moniliform ( Fig. 1A ). Largest specimens 8–10 mm long, 0.2–0.3 mm wide across expanded anterior segments, with about 40 segments; most specimens incomplete, complete specimens with weakly expanded posterior region with segments again becoming narrow and terminating in simple pygidial lobe ( Fig. 1C ). Shallow ventral groove present in anterior thoracic setigers of some specimens, best developed in posterior thoracic and anterior abdominal segments ( Fig. 1B ); absent in middle and posterior segments. Dorsal grooves or ridges not apparent. Color in alcohol opaque white, some specimens transparent; no pigment apparent.

Prostomium conical, narrowing to rounded tip ( Fig. 1B, F ); eyespots absent; nuchal organs narrow transverse slits at posterior margin, dorsal to mouth. Peristomium elongate, narrow, up to 2.5 times as long as wide ( Fig. 1 A–B, F); surface relatively smooth, crossed by several grooves, best seen when stained with Shirlastain A ( Fig. 1F ) or viewed with SEM ( Fig. 1B ). Some specimens with two weakly developed annular rings apparent; first about one-third along peristomium. Peristomium with weakly developed mid-dorsal ridge or crest. Dorsal tentacles arising close to one another from posterior margin of peristomium ( Fig. 1F ). First pair of branchiae also on peristomial margin, lateral to tentacles ( Fig. 1F ). Second pair of branchiae on setiger 1, dorsal to notosetae. Subsequent branchiae in a similar location on following segments ( Fig. 1D ). Branchial scars not evident in posterior half of body.

Parapodia reduced, with setae emerging directly from body wall ( Fig. 1D ). Setae all capillaries with fine fibrils along shaft ( Fig. 1E ). Setae of anterior segments or thoracic region number 4–5 in notopodia and 3–4 in neuropodia, arranged as a group or in a weakly developed double row ( Fig. 1D ); notosetae of anterior abdominal segments increasing to 10–15 in two rows; neuropodia with 8–12 setae in two rows; setae of posterior abdominal segments reduced to 2–4 per fascicle. Long natatory-like setae generally not present, however, far posterior segments with a few long capillaries present on some specimens ( Fig. 1C ).

Methyl Green stain. Three specimens from E.H. Soto’s Sta. 1 in Valparaiso with tip of prostomium retaining weak stain; dorsum of posterior part of peristomium with weak stain; one specimen with a few green speckles on anterior end of parapodia and venter of middle segments. Otherwise no distinctive pattern observed.

Remarks. The elongate peristomium of A. antelonga is relatively smooth compared with other species where the grooves cut deeply and divide the peristomium into prominent annular rings (see other species reported below). The present specimens differ slightly from the original account from Costa Rica in that A. antelonga was described as having two peristomial rings in addition to numerous shallow transverse annulations or grooves. The same numerous annulations or grooves are present in the Chilean specimens but the separation into two rings is vague; in some specimens one can count 3–4 weakly defined rings if the grooves are more prominent, which would likely be due to contraction during preservation. Aphelochaeta antelonga appears to be most similar to A. elongata Blake, 1996 , from California and A. striata Dean & Blake, 2016 , from off Costa Rica. All three species have a presetigerous region 2–3 times as long as wide and relatively smooth rather than divided into prominent annular rings. Both A. elongata and A. striata have the first pair of branchiae on setiger 1; A. striata also has a second pair present on setiger 1. In contrast, A. antelonga has the first pair of branchiae lateral to the dorsal tentacles on the peristomium. Aphelochaeta antelonga also has a longitudinal dorsal crest on the peristomium that is lacking in A. elongata and A. striata .

The overall appearance of the elongate, narrow peristomium and thoracic region is reminiscent of some species of the genus Kirkegaardia (see Blake 2016). However, those species have distinctly serrated or denticulate capillaries and the thoracic parapodia are typically elevated over the dorsal surface producing a furrow that may have a separate dorsal crest.

Habitat. According to Soto et al. (2016), A. antelonga (as Monticellina sp.) was the fifth most abundant polychaete species encountered as part of a survey of Valparaiso Bay, Chile, over quarterly seasonal sampling from December 2012 to December 2013 with an average density of 193.8 individuals m -2. Sediments at stations where A. antelonga was collected consisted of sand (~33%) and mud (~67%).

Distribution. Costa Rica, 11–18 m; Ecuador, 50 m; Chile, 20– 119 m.

Figures

FIGURE 1. Aphelochaeta antelonga Dean & Blake, 2016. Specimens from Valparaiso Bay, Chile: A, anterior and middle body segments in right lateral view; B, anterior end, left ventrolateral view; C, posterior end, ventrolateral view; D, anterior segments, L to R, with branchial scars; E, detail of capillary seta showing fibrils; F, anterior end, dorsal view. A–E, SEMs of specimens collected by E.H. Soto from Valparaiso Bay; F, photomicrograph of specimen from Eltanin Sta. 1437 (USNM 1490700) stained with Shirlastain A. Arrows denote location of weakly developed peristomial grooves revealed after staining.