Marphysa acicularum Webster 1884

Marphysa acicularum Webster, 1884

Figures 2, 3, 10

Marphysa acicularum Webster, 1884: 19, Pl. 10, Figs 50–53; Treadwell 1921: 57 –59, Pl. 5, Figs 1–4, text–figs 184–193.

Material examined. Type material: Two syntypes USNM 4793 (and 4 slides with parapodia), Bermuda, 32°19'48.11" N 64°44'59.98'' W, 1876, col. G.B. Goode.

Description. Syntype complete, broken into two fragments, with 289 chaetigers (anterior fragment with 124), L10= 11 mm, W10= 4 mm, TL= 125 mm. Anterior region with convex dorsum, venter flat, without groove; body depressed from chaetiger 6, widest at chaetiger 20, tapering after chaetiger 51. Dorsally dissected from prostomium to chaetiger 5.

Prostomium bilobed, 2 mm long, 2.7 mm wide; lobes frontally rounded; median sulcus shallow (Fig. 2 A), ventral sulcus deep. Prostomial appendages in semicircle, median antenna isolated by gap. Palps reaching first peristomial ring; lateral antenna reaching first chaetiger; median antenna reaching second chaetiger. Palpophores and ceratophores ring-shaped, short, thick; palpostyles and ceratostyles tapering, slender, without articulation. Eyes rounded, dark, between palp and lateral antenna.

Peristomium (2 mm long, 4 mm wide) clearly wider than prostomium, first ring three times longer than second ring, separation between rings distinct on dorsal and ventral sides, faintly visible laterally (Fig. 2 A). Inferior lip with a slight central depression, with a couple of shallow wrinkles.

Maxillary apparatus with four pairs and one single maxillae; MF= 1+1, 4+4, 5+0, 3+7, 1+1; other syntype MF= 1+1, 4+4, 6+0, 4+7, 1+1 (Fig. 2 B). Maxillary carriers 2.4 times shorter than MI, anterior region rectangular, posterior end triangular, with a pair of oval wings situated at the laterals of maxillary carriers. MI forceps-like, without attachment lamella; maxilla with falcal arch at right angles, poorly developed. Closing system 3.7 times shorter than MI (Fig. 2 B); ligament between MI and MII, rectangular, dark. MII wide, without attachment lamella; with triangular teeth, distal tooth directed laterally, others recurved; cavity opening oval, 4.4 times shorter than MII; rectangular ligament between MII and MIII and right MIV, slightly sclerotized (Fig. 2 B). MIII short, curved, forming part of distal arc; with blunt teeth; attachment lamella rectangular, situated only in the center of posterior edge of maxilla (Fig. 2 B). Left MIV with small basal tooth; narrow attachment lamella, semicircular, situated along posterior edge. Right MIV with distal tooth longest; attachment lamella wide, more developed in the central portion, situated along posterior edge (Fig. 2 B). MV rectangular, slightly longer than wide, with a short rounded tooth (Fig. 2 B). Mandibles not examined.

Branchiae pectinate with up to three filaments, present from chaetigers 26R–27L to 282 (Fig. 2 E–F). First pair and the last 24 with one filament; with three filaments in chaetigers 44–210 (Fig. 10). Branchial filaments longer than dorsal cirri, except last nine branchiae, which are reduced to a globular expansion.

First two parapodia smaller; best developed along chaetigers 3 to 13, following parapodia gradually smaller. Notopodial cirri without articulation; longer than ventral cirri, conical, with broad base, best developed in chaetigers 3–15, posterior ones gradually decreasing in size, being smaller from chaetiger 44 (Fig. 2 C–F). Prechaetal lobes as transverse fold in all chaetigers (Fig. 2 C–F). Chaetal lobes rounded with aciculae emerging dorsal to midline in anterior chaetigers; from chaetiger 41 becoming smaller with acicula emerging in midline, longer than other lobes (Fig. 2 C–F). Postchaetal lobes best developed along chaetigers 1 to 38, first three digitiform, from chaetigers 4 to 38 auricular, from chaetigers 17 to 38 progressively reducing in length; posterior ones inconspicuous (Fig. 2 C–F). Ventral cirri in chaetigers 1–3 digitiform; from chaetiger 4 to the last one with an oval swollen base and digitiform tip, gradually reducing in size (Fig. 2 C–F).

Aciculae blunt, reddish, darker in anterior chaetigers. First 10 chaetigers with two or three aciculae, chaetigers 11–33 with three or four, from chaetigers 34 to 48 with five, from chaetigers 49 to 102 with four, from chaetigers 103 to 122 with three, from chaetigers 122 to 269 with two or one, last 10 with only one acicula (Fig. 3 D).

Most chaetae broken. Chaetae limbate supracicular, large, reduced in number around chaetiger 30. Two types of pectinate chaetae, anterior and median chaetigers with 2 or 3 isodonts narrow with short and fine teeth, with up to 15 teeth (Fig. 3 A); in median and posterior chaetigers with 3 anodonts wide with long and slender teeth, with up to 10 teeth (Fig. 3 B). Compound spinigers subacicular, present in all chaetigers, with blade of two sizes in the same chaetiger, shorter in anterior region of chaetiger; longer in posterior region (Fig. 3 C). Subacicular hooks bidentate (Fig. 3 E), yellow, present along chaetigers 34R–35L to 133, one per chaetiger, absent from chaetiger 134. Proximal and distal teeth worn, rounded, some hooks appear unidentate probably from wear (Fig. 3 F).

Pygidium with two pairs of pygidial cirri, without articulation; dorsal pair as long as last four chaetigers; ventral pair short, as long as last chaetiger.

Variation. Second syntype complete with 155 chaetigers, L10= 4.0 mm, W10= 4.0 mm. Palps reaching second peristomial ring, lateral antennae reaching chaetiger 2, median antenna reaching chaetiger 3. Branchiae along chaetigers 22 to 145 with up to 2 filaments. Parapodia with postchaetal lobes better developed along chaetigers 2 to 28; subacicular hooks bidentate from chaetigers 27 to 110, posterior ones discontinuous.

Habitat. In muddy sediments, coquina and coralline rocks in shallow waters (Treadwell, 1921).

Distribution. Bermuda, Dry Tortugas, Florida and Tobago.

Discussion. Marphysa acicularum was described with some specimens collected by the ichthyologist George Brown Goode in 1876 from Bermuda; additionally, the species was recorded in Dry Tortugas and Tobago (Treadwell 1921). The original description lacked some important details such as the maxillary apparatus, pectinate chaetae and subacicular hooks. However, Treadwell (1921) made a more detailed characterization including the maxillary apparatus. In turn, he described the variety M. acicularum brevibranchiata. Unfortunately, the type material of this subspecies is apparently lost, and its taxonomic status cannot be assessed. Hartman (1956) stated that the type was deposited in the National Museum of Natural History, Smithsonian Institution, but is not in this collection, nor in the American History Natural Museum of New York, where many of the materials described by Treadwell were deposited.

Marphysa acicularum belongs to group B2 (Fauchald 1970), which is characterized by having only compound spinigers and branchiae present along the body. Marphysa acicularum resembles M. brasiliensis (Hansen, 1882) (from Brazil), M. elityeni (from South Africa), M. mullawa (from Australia), M. sanguinea (from England), and M. viridis by having spinigers present in all chaetigers and bidentate subacicular hooks. Marphysa sanguinea and M. mullawa differ from M. acicularum in the size of teeth present in anodont pectinate chaetae, being long and thick in M. sanguinea and M. mullawa, while in M. acicularum are long and slender. Further, the first two species have wide isodont pectinate chaetae; whereas M. acicularum has narrow isodont pectinate chaetae. Also, M. sanguinea and M. acicularum differ in the maximal number of branchial filaments and beginning of subacicular hooks; the former (specimen with 290 chaetigers) has 6 branchial filaments and subacicular hooks starting in chaetiger 21; while the latter (specimen with 289 chaetigers) has only 3 filaments and subacicular hooks starting in chaetiger 34. In addition, in M. mullawa the postchaetal lobe is three times longer than chaetal lobe, while in M. acicularum it is slightly longer than chaetal lobe. Marphysa elityeni is a species that reaches large size (170–850 mm), which may explain the late start of branchiae (chaetigers 36–42) and subacicular hooks (chaetigers 60–70); in contrast, our longest specimens of M. acicularum are shorter (around 125 mm), and have branchiae (chaetigers 22–26) and subacicular hooks (chaetigers 27–34) beginning more anteriorly. In addition, both species differ in the type of isodont pectinate chaetae, M. acicularum has a narrower blade, while M. elityeni has a wider blade. Furthermore, M. viridis has a larger number of abranchiate posterior chaetigers (23–50 chaetigers) than M. acicularum (7–10 chaetigers). Also, both species differ in the proportion of maxillary carriers and closing system relative to MI; maxillary carriers and closing system are 2.4 and 3.7 times shorter than MI in M. acicularum, whereas in M. viridis the maxillary carriers are 4 times and closing system is 6 times shorter than MI. Moreover, in M. viridis the ventral cirri with swollen base end 23–49 chaetigers before the pygidium; whereas in M. acicularum they are present up to the last chaetiger. In addition, M. viridis has rounded postchaetal lobes; while it is auricular in M. acicularum. Moreover, M. acicularum (TL= 125 mm) differs from M. brasiliensis (TL= 100 mm) by having an earlier start of branchiae, beginning from chaetiger 26, whereas in M. brasiliensis branchiae start after chaetiger 31.

In the Grand Caribbean region, M. acicularum could be confused with M. nobilis (see below) because in larger specimens some subacicular hooks may be worn and look unidentate such as in M. nobilis; nevertheless, these species differ in the size of postchaetal lobes in anterior chaetigers and the beginning and ending of the ventral cirri with swollen bases. In M. nobilis, the postchaetal lobe is 2 times longer than chaetal lobe, and the ventral cirri with swollen base always start after chaetiger 10 and ending 61 chaetigers before the pygidium; while in M. acicularum the postchaetal lobe is slightly longer than the chaetal lobe and the ventral cirri with swollen base start in chaetiger 4 and are present until the last chaetiger. Furthermore, both species differ in the proportion of maxillary carriers and closing system relative to MI; in M. nobilis the maxillary carriers and closing system are 4 and 7 times shorter than MI, respectively; while in M. acicularum the maxillary carriers is 2.4 and closing system is 3.7 times shorter than MI.