Aphelochaeta striata, 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 : 110-111

Aphelochaeta striata sp. nov.

Figure 3 E, 4B, 5D–F

Material examined. Gulf of Nicoya. Sta. 24, 9°49ʹ25″N, 84°41ʹ20″W, 11 m, sand, Oct 1980, Holotype ( MCZ 132803)., Sta. 24, 9°49ʹ25″N, 84°41ʹ20″W, 11 m, sand, Oct 1980 (10), Jan 1981 (1), Aug 1981 (1), Oct 1981, 1 Paratype ( MCZ 132804), Aug 1981, 1 Paratype ( MCZ 132805); Sta. 29, 9°54ʹ55″N, 84°45ʹ15″W, 18 m, muddy sand, Jul 1980 (2), Oct 1980 (3), Jan 1981, 1 Paratype ( MCZ 132806 (SEM)) (80), Apr 1981 (6), Jun 1981 (1), Apr 1982 (9); Sta. 30, 9°54ʹ40″N, 84°45ʹ50″W, 18 m, muddy sand, Apr 1981 (1).

Description. Holotype incomplete, 5.7 mm. long, 0.3 mm wide at mid thorax for 23 setigers, paratype MCZ 132804 (dried) complete, 11.4 mm long for 114 setigers, and 0.4 mm wide; paratype MCZ 132805 2.84 mm long 0.2 mm wide in mid thorax with 24 setigers. Thoracic region narrow, twelve setigers long, dorsum somewhat flattened, ventrum rounded, remainder of body dorso-ventrally rounded in cross section; thoracic setigers three times as wide as long; remaining setigers two-thirds as wide as long. With a narrow mid-ventral groove throughout. Posterior end slightly expanded laterally, dorsally and ventrally rounded ( Fig. 5 F), pygidium rounded, anus terminal. Color in alcohol white, unpigmented.

Prostomium conical, with paired nuchal organs at posterior border; peristomium with two annulations; second annulation 3.5 times as long as first ( Fig. 4 B), with slight posterior mid-dorsal triangular projection between tentacles emerging at posterior end of second peristomial annulation. First pair of branchiae emerging from anterior margin of setiger 1, lateral to base of dorsal tentacles; second branchial pair emerging from posterior margin of setiger 1, thus two branchiae on first setiger; subsequent branchiae emerging slightly posterior and medial to notosetae throughout. Noto- and neuropodia greatly reduced with setae emerging directly from body wall throughout ( Fig. 5 D); notopodial region slightly inflated producing weak, low-lying shoulders in thoracic region. Thoracic neurosetae 10–12 per fascicle, abdominal neurosetae 5–8 per fascicle, 18–22 notosetae per fascicle in thoracic region, about 8–10 setae in abdominal fascicles; notosetae longer than neurosetae. Setae with numerous short fibrils and scattered knob-like projections along one side ( Fig 5 D, E), producing a rough, irregular appearance as observed with SEM.

Methyl green staining pattern. Body stains light blue; transverse blue stripes across ventrum of setigers 4–8 ( Fig. 3 E).

Remarks. Aphelochaeta striata sp. nov. is distinguished by the narrow body, the relatively uncrowded setigers in the thoracic region, and the first two pair of branchiae occurring on setiger 1 ( Fig 4 B). Additionally, the bright blue transverse stripes of the thoracic region using methyl green staining easily identify this species ( Fig. 3 E).

This species is similar to Aphelochaeta elongata in having a narrow body, an elongate peristomium, uncrowded thoracic segments and transverse stripes across the ventral surface of posterior thoracic setigers. The prostomium and peristomium of A. elongata are indistinguishable and there are no visible peristomial annulations while in A. striata the prostomium and peristomium are distinct and the peristomium consists of a short anterior and long posterior annulation. The dorsal tentacles of A. elongata arise from the anterior margin of the first setiger and the first branchiae are posterior to the tentacles while in A. striata sp. nov. the first pair of branchiae are lateral to the dorsal tentacles. Additionally, there are median dorsal mounds on thoracic setigers and the posterior region is not expanded in A. elongata but A. striata sp. nov. lacks dorsal mounds and has a somewhat expanded posterior end.

Aphelochaeta striata sp. nov. also shares an elongate peristomium with A. antelonga sp. nov. but that species has a larger first peristomial annulation and the prostomium is more conical than in A. striata sp. nov. The anterior setigers are more crowded and the thoracic region is wider in A. antelonga sp. nov. compared to A. striata sp. nov. Additionally, the long fibrils of the setae of A. antelonga sp. nov. are quite different than the short, beaded projections on the setae of A. striata sp. nov.

Etymology. From the Latin striatum meaning striped, for the blue transverse stripes on the venter of setigers 4–8.

Distribution. Collected subtidally from sand and muddy sand, 11–28 meters depth, the Gulf of Nicoya, 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.