Daylithos amorae, Salazar-Vallejo, 2012

Salazar-Vallejo, Sergio I., 2012, 3562, Zootaxa 3562, pp. 1-62 : 48-50

Daylithos amorae n. sp.

Figure 19

Pherusa sp. Amor 1994:342–345 , Figs 1–4.

Type material. Southwestern Atlantic Ocean, Argentina. Holotype ( MACN-38946 ) and paratypes (7 in MACN 38947 , 4 in ECOSUR 144 ), Santa Clara del Mar (37º50'30" S, 57º29'58" W), Buenos Aires, intertidal, boring limestone, Feb. 1974, J.M. Orensanz, coll. (paratypes ECOSUR, three complete, two mature females, 38–43 mm long, 3.0– 3.5 mm wide, cephalic cage 6 mm long, 88–118 (32–36 + 55–82) chaetigers; oocytes 125 µm in diameter; paratypes MACN, seven complete, three mature females, 37–50 mm long, 2.8–4.5 mm wide, cephalic cage 5–8 mm long, 86–102 chaetigers (32–36 + 52–69); oocytes 125 µm in diameter).

Additional material: Southwestern Atlantic Ocean, Uruguay. An anterior fragment (MUNHINA-1267), RV Hero, cruise 3A, Stat. 22 (34°12' S, 53°40' W), between Valizas and Punta Palmar, shells, 12 m, 23 Jul. 1972 (5 mm long, 1.8 mm wide, cephalic cage 4 mm long, 26 chaetigers; first falcate neurohooks in chaetiger 6) .

Description. Holotype (MACN-38946) mature male, pale, subcylindrical, becoming progressively wider in the region preceding the posterior region or cauda ( Fig. 19A); 57 mm long, 3.5 mm wide, cephalic cage damaged, 6 mm long, 99 (36 + 63) chaetigers. Tunic thin, free from sediment cover, mostly detached from body wall, integument smooth; body papillae short, globose, arranged in single rows per segment ( Fig. 19B), smaller, fewer papillae spread over each segment.

Cephalic hood not exposed; anterior end observed in one paratype. Prostomium projected lobe, four black eyes, not coalescent. Caruncle well-developed, lateral ridges elevated, median lobe depressed, almost reaching the branchial plate posterior margin ( Fig. 19D). Palps long, pale; palp keels rounded, projected outwards. Lips projected, observed in another paratype with siphon exposed; dorsal lip rounded, lateral lips larger, expanded, ventral lip reduced.

Branchiae cirriform, arranged in two lateral groups, each with about 70 filaments in concentric lines, larger filaments dorsal or marginal, inner or ventral filaments smaller; largest about as long as palps. Nephridial lobes in the inner margin of the fourth or fifth row of branchial filaments; each delicate, thin, whitish, with delicate basal bulbs.

Cephalic cage chaetae about 1/10 as long as body length, or twice as long as body width. Chaetigers 1–2 involved in the cephalic cage; chaetiger 3 with chaetae longer than those present in following chaetigers, but not contributing to the cage. Cephalic cage chaetae arranged in short ventrolateral lines; chaetiger 1 with 12 noto- and 14 neurochaetae, chaetiger 2 with 14 noto- and 17 neurochaetae per bundle.

Anterior dorsal margin of first chaetiger papillated; anteriorly projected plate not visible. Anterior chaetigers with longer papillae, close to chaetal lobes. Chaetigers 1–3 progressively longer; chaetiger 3 the longest, especially on its dorsal side. Sand cemented anterior shield dorsal, extended over chaetigers 1–4 ( Fig. 19C) with a small median projection reaching chaetiger 5. Chaetal transition from cephalic cage to body chaetae gradual; chaetigers 5-6 with straight anchylosed neurohooks; falcate transparent neurohooks from chaetiger 7. Gonopodial slits in chaetiger 5, pale.

Parapodia poorly-developed, chaetae emerge from the body wall. Parapodia lateral, median neuropodia ventrolateral. Noto- and neuropodia as low lobes, without associated papillae; 1–2 larger interramal papillae, becoming more prominent in posterior chaetigers ( Fig. 19F). Noto- and neuropodia well separated.

Median notochaetae arranged in short, transverse rows; all notochaetae multiarticulate capillaries, about 1/5 as long as body width, 5–6 per bundle; basal articles medium-sized, some irregularly short articles medially. Neurochaetae multiarticulate capillaries in chaetigers 1–4; chaetigers 5–6 with transitional, anchylosed, shorter neurochaetae ( Fig. 19E). Slightly curved, transparent neurohooks in chaetigers 7–9, replaced by larger neurohooks from chaetiger 10; arranged in transverse rows, 3–4 in anterior chaetigers, 4 in median trunk chaetigers, 2 in precaudal chaetigers; caudal chaetigers with thin, small neurohooks, 2–3 per bundle. Trunk neurohooks golden, medially wider, distally expanded, acute, becoming eroded to blunt neurohooks ( Fig. 19G).

Posterior end subdistally swollen, tapering to a blunt cone; pygidium with anus terminal, as a longitudinal slit, without anal cirri.

Etymology. The species is named after the late Argentinian scientist, Dr. Analía Amor, who made a very detailed study on several aspects of the morphology, biology and ecology of the species, including some details on boring, and tube calcification. Material described in this paper was collected from her study site.

Remarks. Daylithos amorae n. sp., belongs to the group of species provided with few neurohooks (2–4) in far posterior chaetigers, which also includes D. dieteri n. sp. and D. nudus ( Caullery, 1944) n. comb. However, D. dieteri can be distinguished from the other two as its dorsal shield has a posterior projection (as opposed to having a smooth margin or a small posterior projection). Thus, D. amorae is more closely related to D. nudus , but they differ in the relative number of anterior multiarticulate neurospines and in the number of transverse series of body papillae; D. amorae has 4–5 multiarticulate neurospines in chaetigers 5–6, and the body papillae are in single rows, whereas in D. nudus there are 2 multiarticulate neurospines in chaetigers 4–5, and the body papillae are arranged in two rows per segment.

The nephridial lobes are very thin, arising about the fifth branchial row. They are not restricted to pores postioned about the middle of the branchial plate, as in Amor’s figure 3a ( Amor 1994:343), but rather they were shown in her SEM photo as her figure 3b. These nephridial lobes are under 100 µm in diameter and therefore are not involved in gamete release. The gametes are released through the gonopodial slits in chaetiger 5.

The species was found to be very abundant (14 specimens per 100 cm 2) and to have indirect development from the southern summer (November to February), with larval stages found among the coralline algae ( Amor 1994:345).

Variation: The first falcate transparent neurohooks started in chaetiger 7 in almost all specimens (just one from chaetiger 8, and in chaetiger 6 in the smallest specimen); however, it was in the following 2–3 chaetigers that the neurohooks were noticeably larger and thicker. In some specimens there was a fine dark line along the gonopodial slits; the variation of pigmentation mayt be due to the relative tunic erosion or removal. The relative number of neurohooks per chaetiger and their mean were as follows: 10: 3–4(3.3), 20: 3–5(3.9), 30: 2–3(2.9), 40: 2–3(2.9), and 50: 2–3(2.4).

Type locality. Santa Clara del Mar , Buenos Aires, Argentina, in intertidal and shallow subtidal rocky bottoms, covered by coralline algae .

Distribution. From central Uruguay to Northern Argentina in intertidal or shallow subtidal hard bottoms.