Glycera sheikhmujibi n. sp. (Annelida: Polychaeta: Glyceridae): A New Species of Glyceridae from the Saltmarsh of Bangladesh

: A new species of glycerid polychaete, Glycera sheikhmujibi , is described from the saltmarsh on the central coast of Bangladesh. The species is identified based on morphological characteristics using both a light microscope and scanning electron microscope (SEM). The species is characterized by the presence of three distinct types of proboscideal papillae: type 1 papillae (conical with three transverse ridges), type 2 (conical with a straight, median, longitudinal ridge), and type 3 (round, shorter, and broader, with a straight, median, longitudinal ridge). It has a Y-shaped aileron with gently incised triangular base, almost equal-size digitiform noto- and neuropodial lobes in the mid-body, and long ventral cirri at the posterior end. The new species is compared with its related species, previously described from the Bay of Bengal region. A key to all these species is provided.


Introduction
The family Glyceridae currently has 87 accepted species (80 species of Glycera, one species of Glycerella, and five species of Hemipodus) (World Register of Marine Species, WoRMS; www.marinespecies.org). Among the three genera, Glycera and Glycerella possess biramous parapodia, whereas Hemipodus includes species with only uniramous parapodia throughout the body [1]. The ailerons, accessory supports on the proboscis, are rod-like in Glycerella, and mostly triangularshaped or a more complicated structure having outer and inner rami in Glycera. Both Glycera and Hemipodus have spinigerous compound chaetae, but in Glycerella, additional compound falcigers are present [1]. Böggemann [2] revised all species of Glycera previously described worldwide and synonymised many of the previously described species (166), accepting only 36 as valid species. This was based on morphological data only, but subsequently he has used molecular studies to support some of these widely distributed species [3,4]. They are easily distinguishable from other polychaetes, as they have a pointed prostomium and eversible axial proboscis with numerous papillae. Glycera are widely distributed from tropical to temperate regions, and from intertidal to abyssal depths, inhabiting mainly soft bottom (sand/mud) sediments [1,3,5,6]. Glycerids are generally considered to be carnivorous burrowers, capturing and killing prey with their strong, well-developed jaws connected to venom glands that supply venom [7,8].
Polychaetes have been poorly studied in Bangladesh. While some benthic ecological studies have been carried out in the area [9][10][11], these studies have provided no taxonomic details, apart from the listing of polychaete species and their abundance data. None of these studies have deposited any material, so the validity of these species cannot be confirmed. Pramanik et al. [12] reported a new record of Glyceridae, Glycera lancadivae Schmarda, 1861 [13], which seems to be similar to Glycera brevicirris Grube, 1870 [14] (known from Sri Lanka and the Andaman Sea).
Of the 80 accepted species of Glycera Lamarck, 1818 [15], only 10 species have been recorded from the Bay of Bengal region (WoRMS; www.marinespecies.org). This region includes Bangladesh, India, Myanmar, Sri Lanka, and the tip of Andaman Nicobar Islands. Only one of these 10 species has been recorded from Bangladesh [12], in the northeastern corner of the Bay of Bengal: G. lancadivae Schmarda, 1861 [13]. Muir and Hossain [16] reported an unidentifiable glycerid fragment from the Halishahar Coast of Bangladesh, and they also provided taxonomic keys for identifying 14 species from the Bay of Bengal and Indo-Pacific regions. Subsequently, Hossain and Hutchings [17] emphasized the possibility of undescribed polychaete taxa from Bangladeshi coastal waters. Hence, the aim of this report is to describe a new species of Glycera from the Bangladesh Coast, and to provide an updated key to all species of Glycera recorded from the Bay of Bengal region.

Study Site Description
The study area is located in an upper tidal channel of the lower Meghna river estuary, the largest estuarine ecosystem of Bangladesh, characterized by sunny tropical weather with monsoonal influence [18,19]. Mean annual temperature and rainfall in the study area are 25.5 °C and 2980 mm, respectively. According to the Köppen-Geiger climate classification, this climate is considered to be Am (tropical monsoon climate). The monsoon is characterized by strong southeastern winds with high rainfall, humidity, cloud cover, thunderstorms, cyclones, and occasional storm surges [18,19]. Almost all year round, the area is influenced by the incoming tide from Bay of Bengal. Tides are of a semi-diurnal type, with two high and two low waters during a lunar day. The tide varies with respect to magnitude, ranging from 0.07 m during neap tide to 4.42 m during spring tide [20]. The wave height of the estuary varies from 0 to 4 m [21]. However, the tidal wave is considerably slanted as it moves inside the channel, so that with increasing distance from the channel opening, the duration of flood becomes shorter than during the ebb tide. The lower, deeper areas near the opening of the channel are characterized by strong estuarine influence, with higher current velocity and stronger tides, while the estuarine water inflow is substantially reduced in the upper shallow areas. In addition, the upper part of the channel receives a continuous freshwater supply, especially during monsoons, through a small system of tidal creeks and streams.

Sample Collection and Analysis
Sediment samples were collected during April 2015 from Chairman Ghat (22°30'48.3876'' N, 91°5'6.6078'' E, Noakhali, Chittagong division), using a hand-held corer with a depth penetration of 10 cm (Figure 1). The collected samples were washed through a 0.5 mm mesh hand sieve, and polychaetes retained on the sieve were placed into plastic vials and fixed with 5% formalin in the field. After 2 days, the samples were washed with freshwater and transferred to 70% ethyl alcohol for further examination [17]. Material was examined using stereo (Motic 6.5x-50X Zoom Stereo) and compound (Carl Zeiss, Oberkochen, Germany) microscopes. Scanning electron microscope (SEM) observations were made with a Zeiss EVO LS15 SEM with a Robinson Backscatter Detector after critical-point drying and coating with 20 nm gold at the Australian Museum [17]. Specimens were photographed using a light microscope (Leica MZ16, Leica Microsystems, Wetzlar, Germany ) and Spot flex 15.2 (Leica Microsystems, Wetzlar, Germany ) with a camera attached. In some cases, the material was stained with methylene blue to increase the resolution of diagnostic characters. All material examined was deposited at the Australian Museum, Sydney (AM).

Material Examined
The

Generic Identification
This species has been placed into the genus Glycera based on its overall morphological similarities with other species of Glycera, including the presence of different types of dense papillae on their proboscis. The genus Glycera Lamarck, 1818 [15] can easily be identified from other genera by the following unique characters [2,15]: acutely pointed, usually ringed prostomium with four terminal tentacles; and a long, eversible, club-like proboscis, provided with four hooked horny jaws and accessory lateral ailerons. The ailerons possess a more complicated structure with outer and inner rami, and sometimes an interramal plate. Parapodia have two anterior lobes with cirri and one or two posterior lobes, as well as the ventral chaetae compound and dorsal capillary chaetae.

Diagnosis
The salient features of the new species are (i) the presence of three types of proboscideal papillae-type 1 papillae (main type), which are conical with three transverse ridges; type 2 papillae, which are conical with straight, median, longitudinal ridges; and type 3 papillae, which are round, shorter, and broader, with straight, median, longitudinal ridges; (ii) Y-shaped ailerons with gently incised triangular bases; and (iii) digitiform noto-and neuropodial lobes of almost equal size in the mid-body and long ventral cirri at the posterior end.

Holotype
The holotype has an incomplete, cylindrical body, which is elongated and tapered at both ends ( Figure 2A,B). The body reaches up to 42 mm long, with up to 158 segments, and has a width of 2.2 mm in the middle part of the body; preserved specimens in alcohol are whitish with numerous scattered small black pigmented spots ( Figure 2C,D). The body segment is biannulate ( Figure 2E), and the anterior annulus slightly shorter than posterior annulus.
The prostomium is conical, pointed, and distinctly separated into about ten rings; the terminal ring has four antennae, and no nuchal organs or eyes (Figures 2A,B and 3A,C).
The parapodia of the first two segments are uniramous, with a prechaetal and a postchaetal lobe, while the subsequent parapodia are biramous ( Figures 2B and 3D). There are two unequal, triangular to digitiform, prechaetal and postchaetal anterior lobes, and lobes of similar length in mid-body (Figures 2C, 3D, and 4A,D). Knob-like dorsal cirri from the second parapodium are inserted most clearly at the base of the anterior parapodia, as well as on the body wall far above parapodial base in the mid-body, and again near the posterior base ( Figure 2D-F). Ventral cirri are not distinct in the anterior part, but are well-developed in the posterior part ( Figure 4F). Retractile branchiae are present at chaetigers 27-31. Notochaetae slender capillaries with one margin covered with spines or hairs ( Figure 4A,C). There are neurochaetae homogomph spinigers (based on SEM) ( Figure 4B), as well as a pygidium with a terminal pair of slender, elongated cirri ( Figure 3G).
The proboscis is very long, equal to 28 segments, bell-shaped, and densely covered with papillae, which are arranged in distinct longitudinal rows (Figures 2A and 3A,B). The papillae consist of three types: (1) numerous, conical papillae with three "V"-shaped ridges on posterior surface from top to bottom ( Figure 5C,D); (2) a few long, conical papillae, with one straight, median longitudinal ridge ( Figure 5C,D); and (3) very few, slightly shorter and broader, rounded papillae with a single very distinct median longitudinal ridge ( Figure 5C,D). Among the three types, type 2 is the longest. All papillae have small ciliated pores ( Figure 5D) and are smooth anteriorly. The terminal part of proboscis has four black hook-shaped jaws and accessory "Y"-shaped ailerons with gently incised triangular bases ( Figure 3B).    has also decided to jointly celebrate the "Mujib Year" with Bangladesh at its 40th General Assembly.

Distribution, Ecology, and Habitat
Glycera sheikhmujibi n. sp. is one of 11 species in the genus Glycera distributed in the Bay of Bengal region, and is the second species from Bangladeshi coastal waters. Currently, it is only known from the type locality on the central coast of Bangladesh; however, increased sample collection from other parts of the coastline might extend its distribution range. Sympatric species include Nephtys bangladeshi, Lumbrineris spp., Capitella spp., Goniada spp., Nereis spp., Magelona spp., and Naidadae, as well as the crustacean groups Ocypodidae, Palaemonidae, Gammaridae, and Harpecticoida. The species was collected from the muddy saltmarsh zone (intertidal zone), with a water depth range of 0.5 to 1.0 m during high tide. The zone is densely covered with the grass Spartina spp. and connected to the Meghna River Estuary, which falls to the Bay of Bengal near Hatiya and Swandwip islands. The average salinity, dissolved oxygen, pH, alkalinity, and temperature was 6 ppt, 9.15 ppm, 7.72, 180 ppm, and 29 °C, respectively.

Discussion
The main diagnostic characteristics for the identification of glycerid species include shape and number of pre-and post-chaetal lobes, presence or absence of branchiae, shape of the aileron, and the structure of proboscidial papillae [2]. However, Fiege and Böggemann [23] and Rizzo et al. [1] found that parapodial lobes and branchiae are not reliable characters, because branchiae are retractable in some species, and the shape (size) and number of pre-and post-chaetal lobes are difficult to evaluate for some species. Therefore, they suggested the proboscidial papillae and ailerons to be the most reliable characters for the identification of species of Glycera. Glycera sheikhmujibi n. sp. can easily be distinguished from all other species of Glycera by the presence of three distinct types and shapes of proboscidial papillae (Table 1).  [25] n/a n/a G. embranchiata Krishnamoorthi, 1962 [26] Nomen dubium Böggemann [2] reported as a nomen nudum  [29] Nomen nudum Böggemann [2] reported as a nomen nudum G. sagittariae Fauvel, 1932 [27] Aileron with two long dagger-like processes Parapodia with two equal elongated, tapering anterior lobes, and two equal, blunt, triangular posterior lobes; dorsal cirrus more or less remote Present, simple and short beginning at 40th segment n/a G. subaenea Grube, 1878 [30] n/a Posterior parapodial lobes longer than the anterior ones; lower lobes triangular and wider than the upper ones, anterior lobes equally long, rounded Branchiae present and positioned at the anterior wall of parapodium, separated into 2-3 fingerlike filaments, longer than ventral cirrus n/a G. tesselata Grube, 1863 [31] n/a n/a n/a n/a Glycera sheikhmujibi n.sp.
Dark, hookshaped jaws and ailerons with gently incised bases Parapodia with digitiform prechaetal and postchaetal lobes; knob-like dorsal cirrus along the body and long ventral cirrus present posteriorly Branchiae present, retractile, commencing from the 27th to 31st segments 5-6 slender capillary notochaetae Glycera sheikhmujibi n. sp. shares no diagnostic characteristics with either Glycera lancadivae, the only known species from Bangladesh [12], or fragments of another glycerid described by Muir and Hossain [16]; however, it clearly differs in many other aspects, especially in the form of three distinct types of proboscidial papillae. Again, Böggemann [2] mentioned that G. lancadivae is a nomen dubium, and it is almost similar to G. brevicirris. Glycera sheikhmujibi n. sp. seems to resemble Glycera nicobarica Grube, 1867 [32] and Glycera macintoshi Grube, 1877 [33] in the shape of ailerons, parapodial lobes, and types and shapes of the proboscidial papillae (Table 1). However, G. nicobarica and G. macintoshi have only two different types of papillae: G. nicobarica possesses few ovate papillae without ridges, and numerous leaf-like ones with five to six "U"-shaped ridges, and G. macintoshi has conical proboscidial papillae with three transverse ridges. Recently, G. nicobarica has been synonymized with Glycera unicornis Lamarck, 1818 by Read [24]. It has been argued that the proboscidial papillae may vary due to preservation, sample preparation, and development of papillae; however, for the sample collection and preservation of G. sheikhmujibi n. sp., standard procedures were followed.
In addition, G. sheikhmujibi n. sp. differs from G. macintoshi by the presence of two equal triangular pre-and postchaetal lobes, whereas shorter, rounded neuropodial postchaetal lobes are present in G. macintoshi. Glycera. embranchiata Krishnamoorthi, 1962 [26] (known from India) is a nomen dubium, as there is no description of the species in the original report, and G. rutilans Grube, 1877 [33] (known from Sri Lanka) is nomen nudum, as reported in Böggemann [2]. Glycera convoluta, G. longipinnis, G. rouxii, and Glycinde oligodon, all reported from the Bay of Bengal region, have not been accepted by Böggemann [2], as G. convoluta is a junior synonym of G. tridactyla, G. longipinnis is a junior synonym of G. sphyrabrancha, G. rouxii is a junior synonym of G. unicornis, and Glycinde oligodon belongs to the family Goniadidae. Although Glycera tesselata Grube, 1863 [31] is a good species and is accepted by Böggemann [2] and Read [24], it is poorly described in the original description.
The first procedure in any ecological work or applied research with organisms is an exercise in taxonomy. Taxonomy provides the fundamental understanding about the components of biodiversity, which is badly needed for effective decision-making regarding conservation, management, and sustainable use of the studied organisms. In addition, the loss of biodiversity due to human activities and climate change should be of major concern to everyone, because it threatens the functioning of an ecosystem. Despite this, there is very little information on the taxonomy of polychaetes from Bangladeshi coastal waters compared with those of neighbouring countries. To date, only thirty species have been identified from Bangladesh, which is a very low number compared to known polychaete species (~10,000) in the world. With a diverse coastline of about 720 km, it is hoped that the number of polychaete species will be increased with further studies.
Key to the species of genus Glycera from the Bay of Bengal region (modified from Muir and Hossain [15]) is as follows: 1 Proboscideal papillae do not have a terminal fingernail structure 2 -Proboscideal papillae have a terminal fingernail structure 6 2 There is one postchaetal lobe in all parapodia 3 -There are two postchaetal lobes (at least) on the mid-body parapodia 5 3 Mid-body, the notopodial prechaetal lobes are shorter than the neuropodial lobes, and branchiae are absent Glycera lapidum Quatrefages, 1866 [24]. -Mid-body, the prechaetal lobes are about same length or longer than the notopodial lobes. Branchiae are present or absent 4 4 The proboscideal papillae are digitiform and without ridges, ailerons have deeply incised bases, and simple digitiform branchiae are situated termino-dorsally on the parapodia Glycera sphyrabrancha Schmarda, 1861 [12]. -Conical proboscideal papillae with 5-20 transverse ridges, ailerons have slightly arched bases, and branchiae are absent Glycera oxycephala Ehlers, 1887 [25]. 5 Ailerons have gently incised bases; long, mid-body postchaetal lobes are digitiform and of about equal length; three types of proboscideal papillae, with the main type having fewer than three ridges; and branchiae are absent Glycera sheikhmujibi n. sp.