Aphelochaeta guimondi Dean & Blake, 2016, sp. nov.
Creators: name: Dean, Harlan K.
name: Blake, James A.
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Annelida
Polychaeta
Terebellida
Cirratulidae
Aphelochaeta
Aphelochaeta guimondi

description: Aphelochaeta guimondi sp. nov.
Figures 1 B–C, 2D, 3C
Aphelochaeta longisetosa: Dean 1996a (in part). Not Hartmann-Schröder, 1965. Aphelochaeta glandaria: Dean 2004 (in part). Not Blake, 1996.
Material examined. Gulf of Nicoya; Sta. 24, 949ʹ25″N, 84°41ʹ20″W, 11 m, sand, Oct 1981, Holotype (MCZ 132798); Sta. 24, 9°49ʹ25″N, 84°41ʹ20″W, 11 m, sand, Oct 1980 (71), Jan 1981 (2). Oct 1981, 1 Paratype (MZUCR 363-01); Sta. 28, 9°52ʹ16″N, 84°45ʹ30″W, 26 m, mud, Oct 1980 (3); Sta. 29, 9°54ʹ55″N, 8445ʹ15″W, 18 m, muddy sand, Jul 1980 (3), Oct 1980 (2), Jan 1981 (1), Jun 1981, 4 Paratypes (MZUCR 364-01), 1 Paratype (MCZ 132799 (SEM)) (1), Aug 1981 (2), Apr 1982 (4); Sta. 30, 9°54ʹ40″N, 84°45ʹ50″W, 18 m, muddy sand, Jan 1981, 2 Paratypes (MCZ 132800) (1), Aug 1981 (1).
Description. An elongate, narrow species, holotype in two pieces (anterior 2.4 mm, posterior 17.6 mm), 20.0 mm long, 0.3 mm wide in thoracic region, slightly narrower in abdomen, expanded posterior end 0.4 mm wide; with 118 setigers, thoracic region 18 setigers, eight times as wide as long, slightly rounded dorsally with median ridge (Fig. 1 B, 3C), flattened ventrally, larger specimens with more greatly expanded thoracic region; remainder of body rounded dorsally, flattened ventrally with mid ventral groove, setigers two times as wide as long; expanded posterior end with 27 crowded setigers, with wide, shallow, ventral furrow, setigers up to ten times as wide as long; pygidium simple ventral lobe. Color in alcohol white.
Prostomium narrow, conical with rounded tip, slightly longer than wide, with prominent dorsal crest, continuing over dorsum to about setiger 10; unpigmented nuchal organs present on posterior-lateral margin of prostomium. Peristomium as long as wide, with three annulations, second annulation about one-half length of first, third almost three times length of second; dorsal tentacles located at posterior border of peristomium and setiger 1, lateral to dorsal crest (Fig. 1 B–C). First branchiae posterior-lateral to dorsal tentacles at anterior border of setiger 1; subsequent thoracic branchiae at dorsal posterior border of notopodial lobe becoming more dorsal, shifting medially and further separated from notosetae on medial surface of shoulder; branchiae in abdominal region at posterior border of notopodia, dorso-lateral to and some distance from notosetae.
Thoracic parapodia robust ridges, with notosetae emerging dorso-laterally with swollen notopodial lobes extending medially, forming a well-defined channel along dorsum (Fig. 1 B); abdominal setigers with parapodia poorly developed with setae emerging from lateral body wall. Notosetae and neurosetae emerging close to one another throughout (Fig. 2 D). Setae capillaries with occasional fibrils visible using oil immersion (1000 x), SEM revealing numerous, long delicate fibrils emerging along one side of seta providing a plume-like appearance to setae (Fig. 2 D). Thoracic region with 8–14 long, fibrillated notosetae, mid-body with up to 15 notosetae occurring in double rows, including up to five thin, smooth natatory setae in anterior row and 7–10 slightly shorter but wider fibrillated notosetae in posterior row (Fig. 2 D), reduced to 4–6 in posterior segments; neurosetae 7–8 fibrillated setae in thorax, 7–12 in mid-body, reduced to 3–5 setae in posterior segments.
Methyl Green Staining Pattern. Venter of posterior half of thorax staining dark blue, prostomium and peristomium unstained, remainder of body weak blue-green (Fig. 3 C).
Remarks. Important in the identification of Aphelochaeta guimondi sp. nov. is the wide mid-dorsal channel along the thorax and the extension of the prostomial dorsal crest as a mid-dorsal thoracic crest (Fig 1 B). The long fibrils of the setae (often not visible with light microscopy) is a noticeable character for this species. The long narrow, pointed prostomium of A. guimondi sp. nov. is similar to that of A. monilaris (Hartman, 1960), as is the expanded thorax and posterior end. The peristomium is longer than wide in A. guimondi sp. nov. and subequally as wide as long in A. monilaris. The first branchial pair occurs on setiger 1 in A. guimondi sp. nov. and on the peristomium in A. monilaris, additionally the thoracic branchiae of A. guimondi are dorsally separated from the notosetae becoming located on the edge of the mid-dorsal channel, whereas in A. monilaris they are close to the notosetae. The middle body setigers of A. monilaris are typically moniliform but are not in A. guimondi sp. nov. While both species stain intensely on the ventral surface of thoracic segments, the stain forms bands on the anterior segmental margins of A. monilaris, whereas in A. guimondi sp. nov. the staining is more uniform over the ventral surface; the tip of the prostomium is unstained in A. guimondi sp. nov. but is stained in A. monilaris.
Etymology. This species is named after Professor Robert Guimond, University of Massachusetts, Boston in recognition of his dedication to his students and in the friendship and kindnesses to the first author (HKD) which have sustained his academic career and research efforts for many years.
Distribution. Collected in the Gulf of Nicoya from 11–26 m in mud, muddy sand, and sandy sediments.
description: Published as part of Dean, Harlan K. & Blake, James A., 2016, Aphelochaeta (Polychaeta: Cirratulidae) from the Pacific coast of Costa Rica, with a description of five new species, pp. 101-116 in Zootaxa 4103 (2) on pages 106-108, DOI: 10.11646/zootaxa.4103.2.1, http://zenodo.org/record/259134