Leodamas hamatus, Dean, Harlan K. & Blake, James A., 2015

Dean, Harlan K. & Blake, James A., 2015, The Orbiniidae (Annelida: Polychaeta) of Pacific Costa Rica, Zootaxa 3956 (2), pp. 183-198 : 188-191

Leodamas hamatus new species

Figures 2 (F–G), 3 (A–G), 4 (B–G)

Scoloplos (Leodamas) ohlini: Vargas et al. 1985: 336 .— Maurer et al. 1988: 47.— Dean, 1996a: 74; 2009: 146. Not Ehlers, 1901.

Scoloplos (Leodamas) tribulosus: Dean, 1996a: 74 ; 2009: 146. Not Ehlers, 1897.

Material examined. Gulf of Nicoya: Punta Morales, South point, 10°3′30.2″N, 84°57′4.8″W, intertidal, muddy sand, Jul 1995, Holotype ( MCZ 50373); Sta. 2, 9º55′28″N, 84º52ˊ05″ W, 18 m, muddy sand, 13 July 1980 (1); Sta. 24, 9°49′25″N, 84°41′20"W, 11 m, sand, 10 Jul 1980 (1), 1 Oct 1980 (5), 27 Jan 1981, 2 Paratypes ( MCZ 83993) (1), 4 Apr 1982, 1 Paratype ( MCZ 50374); Sta. 28, 9°52′16″N, 84°45′30″W, 26 m, mud, 1 Apr 1982, 2 ( MCZ 83996); Sta. 29, 9°54′55″N, 84°45′15″W, 18 m, muddy sand, 1 Oct 1980, 1 Paratype ( MZUCR 30-3) (6), 27 Jan 1981, (2). Paratypes ( MZUCR 153-01 & MZUCR 31-02) (6), 7 Jun 1981, 1 Paratype ( MCZ 50375) (2), 1 Apr 1982, 2 Paratypes ( MCZ 50377 (SEM) (2); Sta. 30, 9°54′40″N, 84°45′50″W, 18 m, muddy sand, 10 Jul 1980, 1 Paratype ( MCZ 83992); Sta. 31, 9°44′00″N, 84°59′42″W, 20 m, mud/sand, 9 Jul 1980 (1); Sta. 35, 9°55′42″N, 84°47′40″W, 13 m, sand, 12 Jul 1980 (1). Punta Morales: Playa Blanca, 10°04′N, 84°58′W, lower intertidal, muddy sand, 1986, 1 Paratype ( MZUCR 156-01), col: J. A. Vargas; South point, 10°3′30.2″N, 84°57′4.8″W, mid intertidal, muddy sand, 29 Aug 1988, col: H. K. Dean, (2); east of South Point, 10°3′34.9″N, 84°57′6.0″W, intertidal fine sand, col: H. K. Dean, 29 Aug 1988, 2 Paratypes ( MCZ 50378). Guanacaste, Bahia Culebra: Sta. 3, 10 º35′42.9"N, 85º39′16.6″W, 13 m, 19 May 2011 (1); Sta. 12, 10º35′56.5″N, 85º40′34.6″W, 12 m, 19 May 2011 (1).

Description. An elongate species, all specimens incomplete, maximum thoracic width 0.30–1.23 mm.

Holotype incomplete, 32 mm long, 0.8 mm wide with 115 segments ( Figs. 3 A, 4B). Prostomium conical; eyespots absent; paired dorsolateral nuchal organs present. Peristomium slightly shorter than prostomium, subequal to first setiger. Thorax with 13–21 setigers, holotype with 18; transition to abdomen abrupt. Short, conical branchiae from setiger 6 in all specimens, increasing in length posteriorly.

Thoracic notopodial presetal lobe a low ridge, postsetal lobe short, conical at first, increasing in length posteriorly; thoracic neuropodia with low presetal ridge, postsetal ridge somewhat higher ( Fig. 2 F). Abdominal notopodial postsetal lobe conical, shorter than branchiae; abdominal neuropodia with presetal lobe a low ridge, postsetal lobe triangular; with a single well-developed, projecting acicula which enlarges with a hooked tip ( Fig. 3 B, G) and becomes greatly emergent in far posterior setigers ( Fig. 4 G).

Thoracic notosetae camerated capillaries throughout; neurosetae include a small dorsal fascicle of 2‒7 thin capillaries and rows of heavy uncini arranged in 2‒4 complete longitudinal rows, with a partial posteriormost fifth row; uncini with 5‒8 transverse rows of small serrations on shaft ( Figs. 3 C–D, 4–D). First four or five thoracic setigers with narrow uncini with a blunt tip, and thin, appressed hood (sometimes eroded) ( Figs. 3 C, 4C); subsequent thoracic uncini much more robust with thickened hood ( Figs. 3 D, 4D) that together with curved tip, providing uncini with a bifurcate appearance; 5‒8 serrated ridges on shaft ( Figs. 3 E, 4D). Uppermost few uncini short with wide rounded tip and a thick hood projecting slightly beyond the tip in all thoracic setigers ( Fig. 4 E). Abdominal notosetae camerated capillaries accompanied by 1‒3 furcate setae posteriorly ( Figs. 3 F, 4F), each with slightly unequal length tines and coarse spines along the median borders.

Remarks. Blake (2000) noted that Leodamas should be recognized as a genus separate from Scoloplos as its thoracic neuropodial spines are thicker than the narrow, pointed spines of Scoloplos and are not accompanied by numerous capillaries in the setal fascicle (see S. cryptosetosa n. sp. below) as occurs in Scoloplos . Blake (1996) considered the subgenus Scoloplos (Leodamas) to differ from Scoloplos (Scoloplos) in that the onset of branchiae occurred anterior to setiger 7 rather than posterior to setiger 8. Later, Blake (2000) treated Leodamas as a full genus and noted that while most species in this genus have the first branchiae on the anterior part of the thorax at about setiger 6, there is one group of species represented by L. treadwelli (see below) where the branchiae begin more posteriorly; the generic status of this group of species is currently being reviewed (Blake, in prep.).

Leodamas hamatus n. sp. is unusual in the structural differences of the neuropodial uncini along the thorax. Blake (in prep.) has noted a similar transition in the neuropodial uncini along the thorax of L. cochleata Ehlers, 1900 from Patagonia. The uncini of the first 2–3 setigers of L. cochleata are straight shafts with a rounded apex, weak transverse ridges, and an elongate groove along one side. In the remaining thoracic setigers, however, the uncini have well-developed transverse ridges and a more expanded distal end with a round, cup-like concavity (see Ehlers 1901: pl. 21, Figs. 20–21). The thoracic uncini of L. hamatus n. sp. also exhibit a transition in morphology of the uncini along the thorax but the uncini of anterior setigers are more pointed than those of L. cochleata , have a thin, distal hood, and more robust transverse ridges. These thoracic uncini are replaced posteriorly to setiger 5 by heavily ridged, thick uncini with a slightly curved apex and a thickened, oblique hood, sometimes giving the appearance of a biramus end ( Figs. 3 E, 4D). Also, L. hamatus n. sp. has a single, large, curved neuropodial acicular spine in posterior abdominal segments ( Fig. 4 g). L. cochleata possesses 1‒2 weakly curved spines in both the notopodia and neuropodia of abdominal segments.

The unusual thickened hood in middle and posterior thoracic neuropodial uncini appears similar to the uncini of L. chevalieri ( Fauvel, 1902) ( Fauvel 1902, Fig. 26) but there is no mention of variability of the uncini along the thorax of that species. L. chevalieri is similar to L. hamatus n. sp. based on the length of the thorax, first occurrence of branchiae and morphology of the abdominal parapodia but lacks the large emergent, curved acicular spines in the posterior neuropodia ( Figs. 3 B, G; 4E) as well as the furcate setae present in the posterior notopodia of L. hamatus n. sp. ( Figs. 3 F; 4E, F).

Etymology. Hamatus is Latin for hooked, referring to the large curved neuropodial spines found on this species.

Distribution. Collected in muddy to sandy sediments from 11–26 m in the Gulf of Nicoya and from 12–13 m in Bahia Culebra, Costa Rica.

Figures

FIGURE 2. Leitoscoloplos multipapillatus: A, Anterior end, lateral view. Leitoscoloplos panamensis: B, Station 29, Gulf of Nicoya specimen, anterior end, lateral view. Leitoscoloplos pugettensis: C, Station 22, Gulf of Nicoya specimen, anterior end, lateral view; D, Station 9, Bahia Culebra specimen, midbody abdominal setiger, anterior view; E, Station 9, Bahia Culebra specimen, posterior abdominal setiger, posterior view. Leodamas hamatus n. sp.: F, Holotype, posterior thoracic setiger, anterior view; G, Holotype, Posterior notopodial emergent hook. Scale bars: A, C = 1000 µm, B = 500 µm, D, E = 100 µm, F = 50 µm G = 10 µm.

FIGURE 3. Leodamas hamatus n. sp.: A, holotype, anterior end, dorsal view; B, Holotype, posterior abdominal setiger, anterior view; C, Holotype, anterior thoracic mid-neuropodial spine; D & E, Holotype, posterior thoracic mid-neuropodial spines; F, Holotype, abdominal notopodial furcate setae; G, Holotype, posterior neuropodial emergent hooked spine. Scale bars: A = 200 µm, B = 100 µm, C ‒ G = 10 µm.

FIGURE 4. Leitoscoloplos multipapillatus: A, Setigers 17 – 19, ventral view. Leodamas hamatus n. sp.: B, Paratype XXX Anterior region, lateral view; C, Anterior thoracic spines, setiger three, mid-neuropodial region; D, Posterior thoracic spines, setiger 15, mid-neuropodial region; E, Posterior thoracic spines, upper neuropodial region; F, Furcate notosetae, posterior abdominal region; G, Posterior emergent neuroaciculum, posterior abdominal region. Scale bars: A = 200 µm, B = 500 µm, C ‒ E, F, G = 10 µm. h = hoods, stp = stomach papillae.