Anguillosyllis Day, 1963

Maciolek, Nancy J., 2020, Anguillosyllis (Annelida: Syllidae) from multiple deep-water locations in the northern and southern hemispheres, Zootaxa 4793 (1), pp. 1-73 : 6-13

Genus Anguillosyllis Day, 1963

Type species Anguillosyllis capensis Day, 1963

Diagnosis (amended). Body very small, meiofaunal, adults with limited and fixed number of setigers. Palps elongated, free to the base or fused partly to completely; prostomium with three club-shaped antennae, without eyes; peristomium with one pair of tentacular cirri similar to or smaller than prostomial antennae. Dorsal cirri smooth, long, filiform, present or (usually) absent on setiger 2. Ventral cirri digitiform, inserted medially to distally on parapodia. Parapodia uniramous, rectangular, truncate, with anterior and posterior lobes developed to varying degrees; with superior (dorsal) lobe that may be contractile (fide Day 1963). Compound setae heterogomph, with falcigers and spiniger-like blades; setae emerging from distal tip and ventral face of parapodium between insertion of ventral cirrus and distal tip. Pharynx straight, eversible, with two (or three) crowns or sections, external one formed by pharyngeal sheath, distal one surrounded by several (10–12) soft papillae, tooth absent. Proventricle barrel- or heart-shaped, usually tapered posteriorly, muscle rows obscure; with associated glandular structure (caeca) wrapped around post-ventricle. Four pygidial cirri, two lateral, two ventromedial.

Remarks. This generic diagnosis elaborates on that provided by Aguado & San Martín (2008). The number of setigers in adults of each species of Anguillosyllis is remarkably consistent: adult specimens can be separated based on the number of setigers, which ranges from eight to eleven (or twelve, if Day’s (1963) account of the 13-segment non-type specimen of A. capensis is included).

Aguado & San Martín (2008) described the antennae and tentacular cirri as papilliform, as did Day (1967), but these structures may be well-formed in some species and much larger than the minute nipple-like structure implied by the term “papilliform.” The proventricle is usually barrel-shaped but may also be distinctly cordate; it usually narrows, sometimes abruptly, toward the posterior end. The muscle rows of the proventricle do not appear as the typical rows of dots or points seen in other syllids; they are fuzzy dark bands that are difficult to see clearly and to count, especially at the anterior and posterior ends of the structure ( Böggemann & Purschke 2005; Aguado & San Martín 2008; this study).

The post-ventricle in syllids often has an associated pair of caeca ( Haswell 1921) that are called “T-shaped glands” ( Jeuniaux 1969) and have been figured as such ( Weidhase et al. 2016). Jeuniaux (1969) stated that these glands are filled with water and probably act as a swim-bladder. Aguado et al. (2015) suggested a glandular function based on their results of staining with MB; they also proposed the possibility of an endocrine function related to reproduction, but later ruled this out and limited the potential role of the caeca to digestion ( Weidhase et al. 2016). In the present study, the caeca were clearly visible in the majority of Anguillosyllis specimens; often appearing to encircle the post-ventricle and with a circlet of cells on the dorsal side that stained deeply with MB or MG.

The dorsal lobe or setal hood on A. capensis was described by Day (1963) as “curious” and “unique” but was not subsequently discussed beyond an uncertain reference by Böggemann & Purschke (2005) and Böggemann (2009) to a small structure seen on the parapodia. This dorsal lobe was seen on all species examined for this study and is included here as a genus-level character. While it cannot be confirmed to be retractile as Day (1963) suggest- ed, larger lobes in, for example, A. palpata were sometimes folded back towards the medial line of the body while smaller ones in other species (e.g., A. andeepia n. sp. and A. sepula n. sp.) appeared as rounded knobby structures; in many species, these lobes appeared to contain glandular structures that exited through the distal part.

Recently, Barroso et al. (2017) amended the generic diagnosis to eliminate the presence of dorsal cirri on setiger 2. However, in the present study, although a cirrus on setiger 2 was almost never seen (i.e., lost or absent), it was observed on two specimens of A. palpata and one specimen of A. hampsoni n. sp. and basal cirrophores were observed on setiger 2 in A. truebloodi n. sp. Also, Day (1963) clearly described and illustrated A. capensis as having a dorsal cirrus on all setigers, including setiger 2, and stubs were illustrated by Böggemann (2009); Hartman’s description of A. palpata implied and the illustration showed a cirrus on setiger 2. Therefore, at this time, this character is retained as a present-or-absent character of the genus.

Anal cirri are easily and often lost but numerous specimens with a partial or full complement of two long, thin, coiled ventromedial ones similar to the dorsal cirri and two wider lateral oval ones allowed clarification of this character. This arrangement was seen in all species of Anguillosyllis examined in this study, with the exception of two species ( A. aciculata n. sp. and A. carolina n. sp.) that had lost all anal cirri. The fifth anal cirrus reported by Böggemann & Purschke (2005) and Böggemann (2009) for their Anguillosyllis from deep water off western Africa was not seen on any specimen of any species examined in this study.

The palps of Anguillosyllis appear to follow a continuum from being completely free to the base; to free dorsally but partly fused basally on the ventral side; to fused both dorsally and ventrally for half or more of their length, sometimes with only the tips free; to completely fused with a narrow more-or-less pointed or softly rounded anterior end. In this paper the species are divided into two groups strictly for convenience: (1) those with palps that appear free to the base or partially fused (including those with only the very distal portion free) and (2) those with palps completely fused with no separation (although two have a minor medial notch, the tips are not free). There are ten species with palps that are entirely free or partly fused, eight of which are named and described as new; and ten species with palps fused for their entire length, eight of which are named and described as new.

1. Anguillosyllis species with palps entirely or partially free:

1. Anguillosyllis aciculata n. sp.

2. Anguillosyllis acsara n. sp.

3. Anguillosyllis capensis Day, 1963

4. Anguillosyllis carolina n. sp.

5. Anguillosyllis denaria n. sp.

6. Anguillosyllis hadra n. sp.

7. Anguillosyllis hampsoni n. sp.

8. Anguillosyllis palpata ( Hartman, 1967)

9. Anguillosyllis taleola n. sp

10. Anguillosyllis truebloodi n. sp.

2. Anguillosyllis species with palps completely fused:

1. Anguillosyllis andeepia n. sp.

2. Anguillosyllis blakei n. sp.

3. Anguillosyllis bruneiensis n. sp.

4. Anguillosyllis elegantissima n. sp.

5. Anguillosyllis enneapoda n. sp.

6. Anguillosyllis hessleri n. sp.

7. Anguillosyllis inornata n. sp.

8. Anguillosyllis lanai Barroso, Paiva, Nogueira & Fukuda, 2017

9. Anguillosyllis pupa ( Hartman, 1965)

10. Anguillosyllis sepula n. sp.

Species in each group are compared in Tables 1 and 2 and are separated according to the following key. Except for A. palpata and possibly A. pupa , species appear to be restricted to geographical areas and depth ranges, so researchers should not assume that a species described from the South China Sea will occur, for example, off the coast of South America or Africa; in many cases, techniques in addition to morphological analyses may be required to separate species (e.g., Nygren 2014, Aguado et al. 2019).

Tables

TABLE 1. Characters of Anguillosyllis species with palps that are partly or entirely free.

Species/ Character	Type Locality	Depth (m)	# Set.	Max. length (mm)	Annulation	Palps
aciculata n. sp.	South China Sea	2162	11	2.9	None, but slight wrinkling in mid- dle setigers	Free dorsally, joined ventrally on proximal half
acsara n. sp.	North Carolina, USA	1505–1996	11	2.5	Clearly biannulate setigers 2–5 (larger one)	Free dorsally, joined ventrally
capensis Day, 1963	Cape Town, SA	183	11 (?)	3.5	Not mentioned	Fused halfway or more; tips free
capensis sensu Böggemann & Purschke (2005)	West coast of Africa	5389–5449	up to 11	2.5	Not mentioned, but possibly bian- nulate anteriorly (Fig. 1A–B)	Fused with notch
carolina n. sp.	North Carolina, USA	720–2999	10	1.2	Slightly biannulate anteriorly	Free dorsally, possibly slightly joined ventrally on proximal half
denaria n. sp.	South China Sea	1171–1967	10	1.9	None	Fused 1/2–2/3, tips free
hadra n. sp.	South China Sea	1015–1329	11	1.5	Slightly biannulate anteriorly	Free dorsally, joined ventrally on proximal half
hampsoni n. sp.	New England shelf	142–151	11	2	Slightly biannulate anteriorly	Free dorsally, joined ventrally on proximal three-quarters
palpata Hartman, 1967	Antarctica	210–4652	11	2.8	Slightly biannulate anteriorly	Free dorsally, joined ventrally on proximal half
taleola n. sp.	South China Sea	1294–1958	10	1.8	None	Entirely separate both dorsally and ventrally
truebloodi n. sp.	Pacific Ocean, CCFZ1	4516–4861	11	1.2	None	Fused 1/2, tips free

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TABLE 2. Characters of Anguillosyllis species with palps that are entirely fused.

Species/ Character	Type Locality	Depth (m)	# Set.	Max. length (mm)	Annulation	Palps (anterior tip)	Nuchal organs
andeepia n. sp.	Antarctica	4551	8	1+	None	Narrow, pointed	Not evident (no cilia seen)
blakei n. sp.	Northern California	995–1820	10	1.4	Setiger 1 biannulate, sometimes setiger 2	Narrow, pointed	Small patch between pro-and peristomium
bruneiensis n. sp.	South China Sea	1234	8	1	None	Wide, rounded	Small patch, visible with stain
elegantissima n. sp.	South China Sea	1050–2162	10	3.4	Biannulate 1-4, then triannulate	Conical, arched dorsally	Not evident; largest specimen with possible sense organ.
enneapoda n. sp.	South China Sea	1242–2117	9	1	None	Narrow, pointed	Small oval patches
hessleri n. sp.	Pacific Ocean (CCFZ)1	4480–4518	11	3.8	None	Wide, blunt, small medial notch	Small patch, visible with stain but no cilia seen
inornata n. sp.	Northern California	2005–3864	9	2	None	Narrow, pointed	Small oval patches
lanai Barroso et al., 2017	Brazil	1035–2997	10	2	Not mentioned	Narrow, acute	Not mentioned
pupa ( Hartman, 1965)	W Atlantic Ocean, continental slope off New England	168–805	9	2	None	Broad, rounded	Not evident
sepula n. sp.	South China Sea	1234–1487	10	1.2	None	Narrow, slightly pointed	Not evident
sp.	Pacific Ocean (CCFZ) 1	4851	9	1+	None	Narrow, pointed	Not evident

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