The taxonomy and systematics of the Annelida have been rapidly changing in recent years. It must be recognised that the classifications used in publications such as Fauvel (1953) and Day (1967) are now very dated. The fauna given in Fauvel (1953) shares many species with his earlier work on the fauna of France (Fauvel 1923, 1927), but it is not now considered likely that so many species from northern Europe would also be found in the Indian Ocean. A more modern classification (although still on classical lines) can be found in Chambers and Muir (1997). More strictly phylogenetic classifications are also available, such as Rouse (2000) and Appeltans et al. (2010). Keys to identify polychaetes to family level can be found in publications such as Fauchald (1977), Chambers and Muir (1997) and Glasby and Fauchald (2000).

Polychaetous annelids are often regarded as a marine group (albeit with some freshwater tolerant species), but it should be noted that non-marine species also exist (see Glasby et al. 2009), including some from Bangladesh (Das and Reynolds 2003 list two species of Aeolosoma).

One specimen was found: length 15 mm, width 0.75 mm for 92 segments, but anal cirri missing. Anteriorly the height of the segments is 1mm, but posteriorly the body becomes dorso-ventrally flattened. This specimen has two pairs of tentacular cirri on the first segment, the dorsal being shorter than the ventral ones (they are both, however, small and difficult to see). The first chaetae are on the second segment. The pharynx is everted, showing a smooth surface and a ring of 12 large subglobular papillae around the opening (Fig. 2). The dorsal cirri are small and rounded, compressed against the side of the body. The ventral cirri, distally rounded, are almost as long as the chaetal lobe anteriorly, but slightly longer posteriorly. The tip of the acicula is just emergent from the chaetal lobe in the anterior part of the body, but in the posterior part of the body is much more protuberant. The specimen is colourless in alcohol except for some brown markings dorsally by the pygidium.

This specimen, especially the structure of the pharynx, displays similarities to Eteone delta Wu & Chen, 1963, which is known from the Yangtze delta, the Pearl River and Zhangjiang estuary, China (Shen and Qi 1982, Chen et al. 2012). There are, however, differences such as the presence of emergent acicula. It is not considered advisable to describe this specimen as a species new to science, partly because there is only one specimen and partly because that specimen is incomplete (the shape of the anal cirri is important at the generic level for this group). It may be that this is a rare species which shows some morphological variation from one extreme of its geographic range to the other. Glasby et al. (2009) list Eteone delta as freshwater tolerant, found in the Palaearctic and Oriental regions inhabiting lake/river freshwater and estuary and coastal lagoons (fresh–brackish) including supra-littoral areas. Shen and Qi (1982) say it is “favored in normal or rich trophic waters”, as opposed to over-trophic or polluted waters.

This is a new record for Bangladesh, no members of the family Phyllodocidae being recorded by Pramanik et al. (2009).

Two specimens from Maungmagaun, Myanmar, in the Natural History Museum, London, (NHMUK ANEA 1935.1.31.34 and NHMUK ANEA 1937.1.4.4) have been identified as Phyllodoce castanea by C.C.A. Monro. On both of these specimens many of the head appendages are missing or regenerating, but the identifications are probably correct. The species is now known as Nereiphylla castanea (see synonymy in Alós et al. 2004). Fauvel (1932) records Phyllodoce madeirensis and Eulalia (Pterocirrus) magalhaensis from a depth of 2 fathoms (3.658 m) in the Mergui Archipelago.

Two species of Eteone are recorded from West Bengal (Misra 1999, Das et al. 2009, Mitra and Misra 2010). Eteone barantollae Fauvel, 1932, is now regarded as a member of the genus Hypereteone (see Wilson 1988). Eteone ornata Grube, 1878, has been referred to the genus Mysta, but may be a misidentification (Uschakov, in Wilson 1988).

In Odisha, Anaitides madeirensis, Eteone (Mysta) ornata and Eteone barantollae have been recorded from estuaries by Misra (1999) and Mitra et al. (2010). Anaitides madeirensis is now generally referred to as Phyllodoce madeirensis, and has a very wide distribution in temperate and tropical waters (Alós 2004).

These species from northern Bay of Bengal waters can be keyed out as follows, but any identifications must be checked against reliable descriptions as many other species are known from the Indo–Pacific area.

The pharynx is often not everted in preserved material, but the jaws and any paragnaths/papillae present may be seen by making a mid-ventral cut backwards from the mouth, cutting through the ventral surface of the pharynx as well as the body wall for several segments, and folding the resulting flaps to the side to reveal the complete jaw apparatus.

One specimen was found. This species could be regarded as a typical nereidid, having paragnaths on the pharynx and four pairs of tentacular cirri (Fig. 3). The arrangement of the paragnaths agrees with that depicted by Fauvel (1953). Falcigerous chaetae are entirely absent in this species. It is a new record for Bangladesh according to Pramanik et al. (2009). The type locality is Kolkata, West Bengal, and Misra (1999) states that the species is endemic in Indian waters.

This species has no paragnaths on the pharynx and only three pairs of tentacular cirri (Fig. 4). It is, however, not a member of the genus Namanereis because it has parapodia with two distinct branches (notopodium and neuropodium) each with chaetae. Members of Namanereis only have one parapodial lobe with chaetae. This species is not mentioned in Pramanik et al. (2009) but is recorded by Alam et al. (1996) as common on the Halishahar Coast and Misra (1999) states that the species is endemic in north-east coast of India. It is relatively common here, with nine specimens found.

Pramanik et al. (2009) record 12 species of nereidid from Bangladesh: Dendronereides heteropoda, Dendronereis aestuarina, Dendronereis arborifera, Lycastis indica, Namanereis quadraticeps, Nereis caudata, Nereis falcaria, Nereis lamellosa, Nereis mossambica, Nereis operta, Tylonereis bogoyawlenskyi (sic) and Tylonereis fauveli. Alam et al. (1996) add Perinereis nuntia as well as Lycastonereis indica to this list.

The collections from Myanmar in the Natural History Museum, London, include: NHMUK ANEA 1933.3.18.43, NHMUK ANEA 1937.1.4.16-42 Ceratonereis burmensis Monro, 1937, Types; NHMUK ANEA 1931.6.22.70, NHMUK ANEA 2014.7 Namalycastis abiuma species group; NHMUK ANEA 1931.6.22.67-69 Namalycastis multiseta Glasby, 1999, Types; NHMUK ANEA 1931.6.22.71-73 Neanthes meggitti Monro, 1931, Types; NHMUK ANEA 1933.3.18.5-14, NHMUK ANEA 1935.1.31.6, NHMUK ANEA 1935.1.31.7-8 Nereis falcaria; NHMUK ANEA 1933.3.18.15-16 Nereis sp.; NHMUK ANEA 1933.3.18.1-4, NHMUK ANEA 1937.3.10.10-11 Nereis zonata; NHMUK ANEA 1937.3.10.12 Perinereis cultrifera?; NHMUK ANEA 1937.1.4.43-44 Perinereis nuntia; NHMUK ANEA 1932.11.25.5, NHMUK ANEA 1937.1.4.45-66 Perinereis singaporiensis; NHMUK ANEA 1932.11.25.2-3, NHMUK ANEA 1933.3.18.44-46, NHMUK ANEA 1935.1.31.16-18, NHMUK ANEA 1937.1.4.67-68 Pseudonereis trimaculata; NHMUK ANEA 1933.3.18.32-33 Tylonereis bogoyawlenskyi. Fauvel 1932 records Leonnates jousseaumei (from the Mergui Archipelago, shore collecting), Lycastis meraukensis (from Mergui), Nereis onychophora (from the Jack and Una Islands, Mergui Archipelago, shore collecting), Perinereis cultrifera var. helleri (from Mergui), Perinereis singaporiensis (from the Jack and Una Islands, shore collecting) and Tylonereis fauveli (from Mergui harbour, 7 fathoms).

Chandra and Chakraborty (2008), Das et al. (2009), Khan (2003), Misra (1999), Mitra and Misra (2010), Nesemann et al. (2007), Paul and Nandi (2003) and Sarkar et al. (2005) record 18 species (and one variety) of nereidid from coasts, estuaries, rivers and wetlands in West Bengal: Ceratonereis burmensis, Dendronereides gangetica, Dendronereides heteropoda, Dendronereis aestuarina, Dendronereis dayi, Ganganereis sootai, Lycastonereis indica, Namalycastis fauveli, Namalycastis indica, Namalycastis meraukensis, Neanthes chilkaensis, Neanthes chingrighattensis, Neanthes glandicincta, Neanthes meggitti, Perinereis cavifrons, Perinereis cultrifera, Perinereis nigropunctata, Perinereis nuntia, Perinereis nuntia var. typica.

Misra (1999), Mitra et al. (2010), Rao (1995) and Soota and Rao (1977) record 17 species of nereidid from coasts, estuaries, the Baitarani River and Chilka Lake in Odisha: Ceratonereis burmensis, Dendronereides gangetica, Dendronereides heteropoda, Dendronereis aestuarina, Dendronereis dayi, Leonnates persica, Lycastonereis indica, Namalycastis fauveli, Namalycastis indica, Neanthes chingrighattensis, Nereis (Neanthes) chilkaensis, Nereis (Neanthes) glandicincta, Neanthes glandicincta, Nereis (Neanthes) reducta, Nereis (Neanthes) willeyi, Nereis (Nereis) persica, Perinereis cultrifera and Perinereis nigropunctata.

Many of these species have had their names changed for taxonomic reasons, or are otherwise worthy of comment.

The genus Ceratonereis has been revised by Hartmann-Schröder (1985), who places the species Ceratonereis burmensis in the subgenus Composetia. Composetia has now been raised to generic level, but more work is needed on this grouping (Bakken and Wilson 2005).

Leonnates jousseamei has been synonymised with Leonnates indicus by Qiu and Qian (2000), who also correct Leonnates persica to Leonnates persicus.

Glasby (1999) states that Namanereis quadraticeps is restricted to the Subantarctic and temperate shores of the Southern hemisphere, and Glasby et al. (2009) refer it to the Namanereis quadraticeps (Blanchard in Gay, 1849) species group.

Glasby (1999) accepts Lycastis indica as a member of the genus Namalycastis, and also places Namalycastis meraukensis in the Namalycastis abiuma (Grube, 1872) species group.

Nereis falcaria was reduced to a subspecies of Nereis jacksoni by Hartmann-Schröder (1974) but the two species were separated again by Wu et al. (1981, see Wu et al. 1985). Wilson (1984) accepts Nereis caudata as a member of the genus Neanthes. Most members of the genera Neanthes and Nereis need to have their type specimens compared with the descriptions in Bakken and Wilson (2005) before their generic placement can be confirmed.

Perinereis nuntia has been studied by Glasby and Hsieh (2006), Wilson and Glasby (1993) and Yousefi et al. (2011), and as Alam et al. (1996) did not give a full description of their specimens, it would be better to refer them to the Perinereis nuntia (Savigny, 1818) species group. The specimen 1937.1.4.43-44 from Maungmagaun, Myanmar, has been studied and identified as Perinereis nuntia as defined by Glasby and Hsieh (2006). Perinereis helleri was kept separate from Perinereis cultrifera by Hutchings et al. (1991), but was synonymised with it by Khlebovich (1996). Problems with species of Perinereis were also discussed by Muir and Bamber (2008).

The very similar species Pseudonereis trimaculata and Pseudonereis variegata have been kept separate by Bakken (2007) and Villalobos-Guerrero and Tovar-Hernández (2013). Most characters seem to overlap completely, but in Pseudonereis trimaculata the dorsal cirrus, rather being sub-terminal, is attached to the notopodium terminally from about chaetiger 40, and the ventral ligule of the neuropodium is 0.5-0.8 times as long as the acicular ligule in anterior chaetigers. In Pseudonereis variegata only the last few dorsal cirri are attached terminally, and the ventral ligule of the neuropodium is as long as the acicular ligule in anterior chaetigers (it is as long as the acicular ligule in posterior chaetigers in both species). It is not surprising, therefore, that Monro labelled sample 1932.11.25.2-3 in the NHM as Pseudonereis trimaculata = variegata. The four samples from Myanmar have now been re-examined, and while some are definitely Pseudonereis trimaculata, others have the longer ventral ligule of the neuropodium in anterior chaetigers of Pseudonereis variegata while also having the dorsal cirrus attached to the notopodium terminally in the last quarter of the body. We are treating all the Myanmar specimens as Pseudonereis trimaculata, but mentioning both species in the key.

The relevant species mentioned above can be keyed out as follows, but any identifications must be checked against reliable descriptions as many other species are known from the Bay of Bengal and other Indo–Pacific areas.

The Lumbrineridae used to be regarded as part of the family Eunicidae (e.g. Fauvel (1953), Day (1967)), but is now regarded as a separate family alongside the Eunicidae and various others in the Order Eunicida (see George and Hartmann-Schröder (1985), Carrera-Parra (2006a)).

The pharynx is usually not everted in preserved material, but the maxillae may be seen by making a lateral cut (not a mid-ventral cut as used for nereidids) backwards from the side of the mouth, cutting through the side of the pharynx as well as the body wall for several segments, and folding the resulting flap to the side to reveal the complete jaw apparatus. If it is necessary to dissect the pharynx in this way, the anterior chaetae should be studied first.

Six specimens of this species (Fig. 5) were found. The species, originally published as Lumbriconereis malayensis, was redescribed by Carrera-Parra (2006a) and transferred to a new genus. It is a new record for Bangladesh according to Pramanik et al. (2009). It is very similar to the description of Eranno papillifera (Fauvel, 1918) by Oug (2002). This latter species was also first published as a Lumbriconereis species. The most important difference is that in Gesaneris the maxillary apparatus has four pairs of maxillae, whereas in Eranno there are five pairs of maxillae.

Previous records of lumbrinerids in Bangladesh are Lumbrinereis heteropoda heteropoda (Marenzeller, 1879) and Lumbrinereis tetraura (Schmarda, 1861), recorded by Alam et al. (1996) and Pramanik et al. (2009).

The collections of the Natural History Museum, London, contain a previously unpublished specimen (NHMUK ANEA 1937.3.10.15) collected by Prof. F.J. Meggitt at Maungmagaun, Myanmar, which can be identified using the key in Fauvel (1953) as Lumbriconereis sphaerocephala. This species has not been re-studied by recent taxonomists but it is similar to Lumbrineris inflata Moore, 1911 (see Carrera-Parra 2006b).

Das et al. (2009) record Lumbrineris heteropoda, Lumbrineris polydesma and Lumbrineris notocirrata from West Bengal.

In Odisha, the species Lumbrineris heteropoda, Lumbrineris notocirrata and Lumbrineris polydesma have been recorded from coasts and estuaries, while Lumbrineris polydesma and Lumbrineris simplex were found in Chilka Lake (Misra 1999, Mitra et al. 2010, Rao 1995).

Lumbrineris heteropoda has been transferred to the genus Kuwaita by Carrera-Parra and Orensanz (2002) and to the genus Scoletoma by Budaeva (2005). The species appears to have a wide geographic range (Sea of Okhotsk to Red Sea) and may well be sub-divided after further study, but for the moment we shall accept the name Kuwaita heteropoda, as Carrera-Parra and Orensanz (2002) studied a specimen from Japan, the type locality.

Lumbrineris tetraura is accepted as a member of the genus Lumbrineris by e.g. George and Hartmann-Schröder (1985) who say it is a cosmopolitan species, but Diaz-Castaneda and Rodriguez-Villanueva(1998), place it in the genus Scoletoma, the members of which only have simple hooded hooks, whereas Lumbrineris species possess both simple and composite hooded hooks. Lumbrineris polydesma may also be better placed in the genus Scoletoma, but it is not formally transferred here because the type specimens have not been studied.

Lumbrineris simplex, having no hooked chaetae and no antennae, is better placed in the genus Arabellonereis.

Lumbrineris notocirrata has been transferred to the genus Ninoe by Fauchald (1970), because of the presence of small branchiae.

The species Lumbriconereis pseudobifilaris Fauvel, 1932, has been recorded from 250 fathoms (about 450 m) depth off Akyab, Myanmar (Fauvel 1932), and from a sewage-fed fish culture pond near Calcutta, West Bengal, India (Mitra and Roy 2010). This species has no hooked chaetae but it does have two very long maxillary carriers. It is not included in the key because these characters make it a member of the family Oenonidae.

Lumbrinereis and Lumbriconereis are incorrect spellings of the generic name Lumbrineris. The northern Bay of Bengal ecoregion species of Lumbrineridae can be keyed out as follows, but any identifications must be checked against reliable descriptions as many other species are known from the Bay of Bengal and other Indo–Pacific areas.

The single 6.5 mm long worm found (Fig. 6) is probably this species, which has been well described by Imajima (1987) under the name Nephtys oligobranchia. The species has been transferred to the genus Micronephthys by Dnestrovskaya and Jirkov (2010), although they say the family needs to be fully reviewed. Glasby et al. (2009) list Nephtys oligobranchia as a freshwater- and saltwater-tolerant species, found in the Palaearctic and Oriental regions inhabiting lake/river freshwater, estuary and coastal lagoons (fresh-brackish) including supra-littoral areas and inland lakes. Shen and Qi (1982) say it is “favored in normal or rich trophic waters”, as opposed to over-trophic or polluted waters.

Nephtys oligobranchia is the only nephtyid recorded by Pramanik et al. (2009) from Bangladesh. It is also recorded by Fauvel (1932) from Mergui, Myanmar.

Nephtys oligobranchia and Nephtys polybranchia Southern, 1921, have both been recorded from West Bengal (Misra 1999) and the Ganges river system (Nesemann et al. 2007). Das et al. (2009) record Nephtys dibranchis and Nephtys oligobranchia. Nephtys dibranchis was placed in the genus Aglaophamus by Hartman (1950).

Nephtys oligobranchia is recorded from the Baitarani River, Odisha, by Misra (1999). Nephtys oligobranchia and Nephtys polybranchia are both recorded from the Chilka Lake (Misra 1999, Mitra et al. 2010).

The northern Bay of Bengal ecoregion species of Nephtyidae can be keyed out as follows, but any identifications must be checked against reliable descriptions as many other species are known from the Bay of Bengal and other Indo–Pacific areas.

Specimens of Capitellidae, having no head appendages and usually no obvious parapodial lobes, can easily be mistaken for oligochaetes (e.g. Stephenson 1908, 1910). Without studying the reproductive system in detail, the most useful distinguishing character is the presence of hooked chaetae with a terminal hood covering the hook, which are found on the abdomen of capitellids (absent from oligochaetes).

Green (2002) gives a key to members of the genus Heteromastus found in the Indian Ocean. Unfortunately, there are variations in the descriptions of Heteromastus filiformis (Claparède, 1864) specimens described by different people. The three specimens found in this collection (Fig. 7), having expanded neuropodial lobes in the posterior abdomen and abdominal hooded hook chaetae with three teeth above the main fang, are more like those described by Day (1967) than those described by Hutchings and Rainer (1981), which had expanded notopodial lobes in the posterior abdomen and abdominal hooded hook chaetae with 11–13 teeth above the main fang. The type locality of Heteromastus filiformis is in the Mediterranean (see Green 2002), so Day’s specimens from South Africa could be a different species to Claparède’s. Glasby et al. (2009) list Heteromastus filiformis as freshwater tolerant, but say that multiple species may have been reported under this name.

This is a new record according to Pramanik et al. (2009).

Pramanik et al. (2009) give Dasybranchus caducus as the only capitellid species they know from Bangladesh.

The Natural History Museum, London, has a specimen of Notomastus near latericeus Sars, 1851 sensu Green 2002 (NHMUK ANEA 1933.3.18.71) and the type specimens of Parheteromastus tenuis Monro, 1937, from Maungmagaun, Myanmar (NHMUK ANEA 1937.1.4.151-163).

Matla bengalensis Stephenson, 1908, was described as a new genus and species of oligochaete from West Bengal, but is now (Stephenson 1910) recognised as a capitellid polychaete similar to Capitella capitata. Alam et al. (2010), Chandra and Chakraborty (2008), Das et al. (2009), Misra (1999), Mitra and Misra (2010) and Sarkar et al. (2005) report Barantolla sculpta Southern, 1921, Capitella capitata (Fabricius, 1780), Mastobranchus indicus Southern, 1921, and Parheteromastus tenuis Monro, 1937, from coasts, mangroves, lakes and rivers of West Bengal.

In Odisha, five species of capitellid have been reported (Rao 1995), all of them from the Chilka Lake – Barantolla sculpta, Capitella capitata, Heteromastus similis, Notomastus latericeus and Pulliella armata. Magalhães and Bailey-Brock (2012) consider Pulliella to be a junior synonym of Scyphoproctus.

There follows a key to the reported species of capitellid from the Northern Bay of Bengal ecoregion, but any identifications must be checked against reliable descriptions as many other species are known from the Bay of Bengal and other Indo–Pacific areas. In particular, Green (2002) suggested earlier records of Heteromastus similis may be suspect. Also, as noted above, the type locality of Capitella capitata is West Greenland (Blake 2009). In both these cases further taxonomic work is needed, including the careful study of type specimens and probably comparisons of DNA, to see whether the Bay of Bengal specimens have been misidentified and actually represent new species (see, for example, Blake (2009), Blake et al. (2009), Wu et al. (1991)).

Most keys to capitellid genera start with the number of segments in the thorax. There may be a sudden change in size or shape of the segments at the start of the abdomen, but in many cases it is easier to make a temporary whole mount of the specimen and count the segments with capillary chaetae.