Aphelochaeta praeacuta, Dean, Harlan K. & Blake, James A., 2016

Dean, Harlan K. & Blake, James A., 2016, Aphelochaeta (Polychaeta: Cirratulidae) from the Pacific coast of Costa Rica, with a description of five new species, Zootaxa 4103 (2), pp. 101-116 : 108-110

Aphelochaeta praeacuta sp. nov.

Figure 3 D, 4A, 5A–C

Material examined. Bahia Culebra, Sta. 6, 10º35ʹ 35.8″ N, 85º39ʹ 32.1″ W, 13 m. May 2011, Holotype ( MCZ 132801); Sta. 13, 10º36ʹ 19.4″ N, 85º40ʹ 59.9″ W, 28 m. May 2011, 1 Paratype ( MCZ 132802).

Description. A narrow bodied species. Holotype incomplete, 11.0 mm long, 0.8 mm at widest point in anterior abdominal region for 46 setigers; paratype incomplete, 10.3 mm long, 0.8 mm wide for 45 setigers. Thoracic region 12 setigers long, dorso-ventrally flattened, with segments 4.5 times wider than long; first 13–14 abdominal setigers widened, dorso-ventrally flattened, up to six times wider than long; subsequent abdominal segments dorsoventrally rounded, 1.3 times as wide as long. Mid-ventral groove present throughout. Far posterior region widened in holotype ( Fig 5 B), dorso-ventrally flattened, grooves lacking. Pygidium absent. Color in alcohol white.

Prostomium conical, with a narrow pointed tip ( Fig. 4 A), directed dorsally, best seen in lateral view ( Fig. 5 A); pigmented nuchal organs present at posterior border ( Fig. 4 A). Peristomium with two annulations; first as long as wide, extending as a dorsal hood over second annulation, one-fourth length of first, incomplete dorsally; paired dorsal tentacles emerging at border between two peristomial annulations ( Fig. 4 A, 5A). First pair of branchiae arising on enlarged first setiger posterior to dorsal tentacles, second pair of branchiae dorsal to notosetae at posterior of setiger 1, remaining branchiae arising dorsal to notosetae throughout ( Fig. 4 A), first setiger three times as wide as long, with noto- and neurosetae emerging from posterior lateral border; subsequent thoracic setigers five times as wide as long. Parapodia low, fleshy lobes, with setae emerging in a row directly from body wall. Thoracic setae all broad based with long, fine fibrils along one edge ( Fig 5 C), 7–8 in notopodia, 5–8 in neuropodia; abdominal region with up to 12–13 notosetae and 10–12 neurosetae, both broad, fibrillated setae and shorter, thin capillaries apparently lacking emergent fibrils. Swollen far posterior pre-pygidial region two times as long as wide ( Fig. 5 B).

Methyl green staining pattern. Dorsum of thoracic region staining dark blue, remainder of body lighter blue; prostomium unstained ( Fig. 3 D).

Remarks. The relatively large first peristomial annulation extending as a dorsal crest above the second annulation, the darkly pigmented nuchal organs, and the enlarged first setiger bearing the first two pairs of branchiae help to recognize this species. Additionally the lack of well-developed shoulders over the thoracic parapodia is shared with only A. phillipsi Blake, 1996 and A. antelonga sp. nov., both of which have smooth setae. A. bullata Doner & Blake, 2009 also has a similar posteriorly extended dorsal crest and the first setiger is somewhat enlarged but the prostomium and peristomium of that species are inflated and bulbous with a rounded prostomial tip, while A. praeacuta sp. nov. has a narrow anterior end and a sharply pointed prostomium. Additionally, the long fine fibrils on the capillaries of A. praeacuta sp. nov. are different from the smooth capillaries of A. bullata . Aphelochaeta antelonga sp. nov. also has capillary setae with fibrils but the fibrils are not as fine while the elongate anterior region is much different from that of A. praeacuta sp. nov. The biannulate peristomium of this species is also seen in A. multifilis ( Moore, 1909) , and perhaps A. petersenae Blake, 1996 and A. williamsae Blake, 1996 (although these latter two species are described as having 2–3 peristomial annulations) but fibrillated setae are not reported for these species. A. striata sp. nov., described below, also has two peristomial annulations but the prostomium/peristomiun is much longer in that species and the thoracic segments are not as crowded.

Etymology. From the Latin, praeacutus which means sharp, pointed front or anterior, for the sharply pointed, almost digitate, nature of the prostomium.

Distribution. Collected subtidally from sandy sediments at 13 and 28 meters depth from Bahia Culebra, Pacific coast of Costa Rica.

Figures

FIGURE 3. Aphelochaeta antelonga sp. nov. A, Paratype MZUCR 132794; Aphelochaeta glandaria B, voucher specimen (MCZ 132797); Aphelochaeta guimondi sp. nov. C, Holotype MCZ 132798; Aphelochaeta praeacuta sp. nov. D, Holotype MCZ 132801; Aphelochaeta striata sp. nov. E, Holotype MCZ 132803; Aphelochaeta zebra sp. nov. F, Holotype MCZ 132807. A, MGSP of anterior end, ventral view; B, MGSP of anterior end, dorsal view; C, MGSP of anterior end, ventral view; D, MGSP of anterior end, ventral view; E, MGSP of anterior end, ventral view; F, MGSP of anterior end, ventral view. Scale bars; A ‒ F = 500 µm.

FIGURE 4. Aphelochaeta praeacuta sp. nov. A, Holotype MCZ 132801; Aphelochaeta striata sp. nov. B, Holotype MCZ 132803; Aphelochaeta zebra sp. nov. C-D, Holotype MCZ 132807. A, anterior end, dorsal view; B, anterior end, dorsal view; C, anterior end, dorsal view; D, anterior end, lateral view. Scale bars: A ‒ D = 500 µm.

FIGURE 5. Aphelochaeta praeacuta sp. nov. A-C, Holotype MCZ 132801; Aphelochaeta striata sp. nov. D-F, Paratype MCZ 132806. A, anterior end, lateral view; B, posterior end, ventral view; C, thoracic neurosetae; D, notosetae, setiger 10; E, notoseta, setiger 10; F, posterior end. Scale bars: A ‒ B = 500 µm, C ‒ D = 20 µm, E = 5 µm, F = 200 µm.