Aphelochaeta antelonga, 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 : 102-104

Aphelochaeta antelonga sp. nov.

Figures 1 A, 2A–B, 3A

Aphelochaeta longisetosa: Dean 1996a (in part). Not Hartmann-Schröder, 1965. Not Carrasco, 1977. Aphelochaeta glandaria: Dean 2004 (in part). Not Blake, 1996.

Material examined. Gulf of Nicoya: Station (Sta.) 30, 9°54ʹ40ʹʹN, 84°45ʹ50″W, 18 m, muddy sand, Aug 1981, Holotype ( MCZ 132794); Sta. 29, 9°54ʹ55″N, 84°45ʹ15″W, 18 m, muddy sand, Oct 1980, 1 Paratype ( MCZ 132796), (2), Jan 1981, (1), Apr 1981 (2), Jul 1981, 1 Paratype ( MCZ 132795 (SEM)), (1), Apr 1982 (1). Bahia Culebra: Nicoyan Peninsula (NP) Sta. 15, 1036ʹ35.4″N, 85°40ʹ43.1″W, 18 m, sandy mud, Dec 1985, 1 Paratype ( MZUCR 362-01); Sta. NP 16, 10°37ʹ9.1″N, 8540ʹ28.3″W, 22 m, sandy mud, Dec. 1985 (1); Sta. Bahia Culebra (BC) 6, 10°35ʹ41.6″N, 85°39ʹ3″W, 16 m, May 2011 (1); Sta. BC 16, 10°37ʹ9.1″N, 85°40ʹ28.3″W, 22 m, May 2011 (1).

Description. A narrow-bodied species, thoracic region wider than remainder of body with 13 segments each 7.5 times wider than long ( Fig. 1 A, 2A), thorax dorso-ventrally rounded in cross section; abdominal setigers 1.5– 2.0 times longer than wide, dorso-ventrally rounded. Holotype incomplete, 9.0 mm long, thoracic region 0.5 mm wide, remainder of body 0.25 mm wide for 38 setigers. All specimens incomplete, pygidium absent. Color in alcohol cream white.

Prostomium short, narrow, rounded on anterior margin, as long as wide; nuchal organs rounded, small, located beneath peristomium at postero-lateral prostomial border; peristomium 2.5 times as long as wide with a weak, rounded dorsal crest and two annulations, second longer than first; both annulations with numerous transverse creases apparent with SEM; dorsal tentacles emerging from posterior margin of peristomium ( Fig. 1 A, 2A). First pair of branchiae arising posterior-lateral to dorsal tentacles on peristomium, subsequent branchiae postero-dorsal to notosetae from setiger 1. Parapodia in thoracic region low swellings, with setae emerging directly from body wall throughout. Setae thin capillaries with blade-like base and occasional fine fibrils; SEM revealing numerous long thin, pointed, fibrillar endings along one side of seta, some protruding ( Fig. 2 B); setiger 1 with three notosetae and four neurosetae, remainder of thoracic setigers with 8–10 notosetae and 6–8 neurosetae; abdominal setigers with 25–28 notosetae and 16–20 neurosetae, each setal fascicle elongate capillaries with an anterior row of 5–8 shorter capillaries.

Methyl green staining pattern. Body uniform light green, venter of thoracic setigers 8–12 darker green, prostomium and peristomium unstained ( Fig. 3 A).

Remarks. The most striking characteristic of this species is the long, biannulate peristomium and the relatively narrow prostomium that is rounded on the anterior margin ( Fig. 1 A, 2B). The posterior end is unknown but the elongate peristomium is most similar to that of Aphelochaeta elongata Blake, 1996 from Tomales Bay in northern California. Both these species also have a slightly expanded thorax relative to the rest of the body. The first pair of branchiae is found on the peristomium in A. antelonga sp. nov. but on setiger 1 in A. elongata ; a median dorsal thoracic ridge is present in A. elongata while no such ridge occurs in A. antelonga sp. nov. Additionally, the thoracic segments are more crowded and the setae are fibrillated in A. antelonga sp. nov. whereas A. elongata has less crowded thoracic segments and the setae are smooth when using a light microscope; details using SEM are not known. The methyl green staining patterns of the two species also differ. Aphelochaeta elongata has transverse stripes on the thoracic venter while A. antelonga sp. nov. has a light blue staining thorax but no transverse stripes. Aphelochaeta malefica Elías & Rivero, 2009 also has an elongate prostomium-peristomium with three peristomial annulations and fibrillated setae but the thoracic segments are not crowded, the prostomium is much more conical and pointed and the setal fibrils are shorter than in A. antelonga sp. nov.

Etymology. The specific name is from the Latin ante, in front of, and longus, meaning elongate.

Distribution. Known from 11–18 m in sandy to muddy sand sediments in the Gulf of Nicoya.

Figures

FIGURE 1. Aphelochaeta antelonga sp. nov. A, holotype (MCZ 132794); Aphelochaeta guimondi sp. nov. B-C, holotype (MCZ 132798). A, anterior end, dorsal view; B, anterior end, dorsal view; C, anterior end, lateral view. Scale bars: A ‒ C = 500 µm.

FIGURE 2. Aphelochaeta antelonga sp. nov. A – B, paratype (MCZ 132795); Aphelochaeta glandaria C, voucher specimen (MCZ 132797); Aphelochaeta guimondi sp. nov. D, paratype (MCZ 132799). A, anterior end, lateral view; B, neurosetae, setiger 4. C, neurosetae, setiger 2. D, noto- and neurosetae, mid body. Scale bars: A = 200 µm, B = 5 µm, C = 10 µm, D = 20 µm.

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.