Heterospio indica Parapar & Vijapure & Moreira & Sukumaran & Csir-N 2016, sp. nov.

Heterospio indica sp. nov.

urn:lsid:zoobank.org:act: 8C7B939E-777E-44C6-80F5-1877A49539A4

Figs 1–9; Tables 1–2

Heterospio longissima – Rosenfeldt 1989: 231, fig. 7 (not Ehlers, 1874).

? Heterospio longissima – Hartman 1974: 232 (?not Ehlers, 1874).

Diagnosis

Eight anterior chaetigers short; chaetiger 9 (CH 9) first elongated segment. Eight pairs of branchiae in fully developed individuals. Chaetae forming cinctures from CH 10, provided with both thin and robust capillary chaetae arranged in two rows; both types of chaetae highly flattened in distal half; from CH 14 robust capillary chaetae without fine distal end, subuluncini-like, thicker than on previous chaetigers. Aristate chaetae and acicular hooks not observed on elongated segments.

Etymology

The species is named after the Indian Ocean, where the specimens of the type series were collected.

Type material

Twenty two incomplete specimens and one posterior end were collected in 13 samples along the West coast of India (Table 1; Fig. 1).

Holotype

INDIA: Malvan, postmonsoon, M 4, 29 Jan. 2014, MNCN 16.01 /16996.

Paratypes

INDIA: 1 spec., Malvan, premonsoon, M 2, MNCN 16.01/16997; 2 spec., Ratnagiri, premonsoon, R 3, NIO / MUM /4/2013/1; 3 spec., Ratnagiri, premonsoon, R 4, NIO / MUM /4/2013/2; 1 spec., Mumbai, premonsoon, MY 2, NIO / MUM /3/2013/3; 1 spec., Veraval, premonsoon, V 4, NIO / MUM /3/2013/4; 1 posterior end, Malvan, premonsoon, M 3, MNCN 16.01/16998; 3 spec., Ratnagiri, premonsoon, R 1, MNCN 16.01/16999; 3 spec. on SEM stub, Ratnagiri, premonsoon, R 1, MNCN 16.01/16700; 1 spec., Ratnagiri, postmonsoon, R 4, SMF 24097; 1 spec., Malvan, monsoon, M 4, NIO / MUM /9/2014/5; 1 spec., Ratnagiri, monsoon, R 4, NIO / MUM /9/2014/6; 1 spec., Mumbai, monsoon, MY 4, NIO / MUM /9/ 2014 /7; 1 spec., Veraval, monsoon, V 2, NIO / MUM /9/ 2014 /8; 1 spec. (sequenced), Ratnagiri, postmonsoon, R 4, NIO / MUM /2/2014/R-H; 1 spec. (sequenced), Malvan, postmonsoon, M 4, NIO / MUM /1/ 2014 /M-H.

Type locality

W INDIA: Malvan, 16°01′37.1″ N, 73°25′29.7″ E, 20 m, clayey silt (Table 1).

Molecular identification

COI and 18 S nucleotide sequences of Heterospio indica sp. nov were submitted to GenBank under the accession numbers: COI-KT259053, KU 221229 and 18S-KT259051, KT259052.

Comparative material

One specimen collected by Rosenfeldt (1989) off the coast of Sudan, Red Sea (SMF 3795; labelled as H. longissima).

Description of holotype (SEM images from paratypes)

Longest specimen available, incomplete, 39 mm long and 0.95 mm wide, with 14 chaetigers; body threadlike (Fig. 2A). Prostomium conical, anteriorly rounded (Figs 2B, 4A, 6C, 8C), slightly flattened dorso-ventrally. Eyes absent. Palp present on right side, reaching level of CH 2 (Fig. 2B). Nuchal organs as deep grooves postero-lateral to prostomium, followed by deep peristomial (SG 1) palp scars (Figs 4A, 6 C–E). Pharynx sac-like, eversible and unarmed (Fig. 8 C).

Anterior body region slightly flattened dorso-ventrally (Fig. 8 B). First eight chaetigers (CH 1– CH 8; SG 2– SG 9) short, somewhat more than twice as wide as long. Chaetigers progressively longer from CH 9 (SG 10) onwards. CH 9 first elongated chaetiger (FECH), longer than wide, about twice as long as CH 8 (Fig. 2 B) (length as distance from chaetal bundle to chaetal cincture of CH 10). First chaetiger (CH 1) abranchiate. Eight pairs of filiform branchiae from CH 2 to CH 9, dorsal to notopodia in almost all chaetigers and usually composed by short branchiophores and long branchiostyles (Figs 2 B, 4 B, 6B, F). From CH 10 (SG11) segments strongly elongated and cylindrical in cross section (Figs 6A, 8A); length increasing in posterior segments; CH 10 about five times longer than CH 9; CH 11 (SG12) about 2.5 times longer than CH 10; CH 12 (SG13) more than two times longer than CH 11; CH 13 (SG14) slightly shorter than CH 12; CH 14 incomplete.

CH 1– CH 9 provided with biramous parapodia; noto- and neuropodial chaetal fascicles well separated (Figs 2B, 5A, D, 7A, 8D, F). Parapodia from CH 10 backwards as elongated ridges forming a nearly closed flange-like cincture near anterior margin of segment (Figs 2A, 5D, 8B). Chaetae of CH 1– CH 9 simple capillaries, in fan-shaped fascicles (Figs 2B, 4 C–D). Neuropodial hooks not observed. Chaetae of CH 10 backwards shorter than those of anterior chaetigers, arranged in two rows (Figs 2C, 5B, 7C); anterior row of robust capillary chaetae and posterior row of fine capillary chaetae (Fig. 5 E–F). Both types of chaetae circular in cross section at base but quickly flattening outwards and becoming much thinner at distal end (Figs 5C, F, 7B, D, 8E). Distal ends of both types of chaetae very similar in length and width, and provided with an opening at the beginning of the terminal flattening (Figs 5C, 7B, 8E). CH 12– CH 13 (Fig. 2D) also with some robust capillary chaetae lacking flat distal end (i.e., subuluncinilike chaetae); CH 14 (Fig. 2E) with all robust capillary chaetae of subuluncini-like type. No aristate chaetae or acicular hooks observed.

For a description of the posterior end, see below.

Fixed specimens creamy white in colour.

Variations

The first body segments show a certain degree of variation for two relevant taxonomic characters: relative size of first elongated segments and number/size of branchiae. The size of the first elongated segment (CH 9) seems constant, about 2.5–3 longer than any short anterior segment (CH 1– CH 8); the relative size of following elongated segments is somewhat variable: CH 10 is slightly shorter or longer than the anterior body region (i.e., from tip of prostomium to posterior end of CH 9). This variability increases for CH 11, which is longer than CH 10 and may be longer than all preceding segments and prostomium together (cf. Fig. 6A vs 8A). Variability in sizes might be dependent on the degree of contraction of the specimen, but it may still be used as a taxonomic character (see Parapar et al. 2014); however, relative sizes of segments should be reviewed across the genus, because this character has not been properly assessed in descriptions of other species. On the contrary, variability in number of branchiae is likely to be size-dependent. Specimens show a wide range of number and sizes of branchiae that seem to be correlated with the size of individuals (i.e., width at level of anterior non-elongated segments; see Fig. 9). The presence and number of branchial pairs increases from anterior to posterior segments; thus, small specimens (< 0.4 mm wide) bear four pairs while larger individuals (0.7–0.95 mm) show up to 7–8 pairs. The presence and size of branchiophores and branchiostyles also shows certain variability, e.g., in the same specimen there are large and thin branchiostyles indistinctly on large and small branchiophores.

All specimens are broken at the level of the anterior elongated segments (CH 12 to CH 15) but a posterior region could be examined from a posterior end found in a Malvan sample in March 2015. Only one posterior region was found, composed of 7 elongated segments and a bulb-like inflated posterior end provided with 5 chaetigers, a terminal achaetigerous segment and pygidium (Fig. 3A). The last 5 chaetigers are provided with 2–4 acicular hooks (Fig. 3B); the anteriormost elongated chaetiger bears chaetae similar to those of CH 10 of the holotype, with flattened distal ends; the chaetae of the other four elongated chaetigers are similar to those of CH 12–14 of the holotype, i.e., of capillary and subuluncini type.

Specimen from Sudan

The specimen collected by Rosenfeldt (1989) off the coast of Sudan, which was identified as H. longissima (SMF 3795), has also been examined. It is in poor condition, i.e., incomplete, broken in two pieces, twisted and flattened dorsoventrally. According to its width (0.6 mm), this specimen fits within the range of large H. indica sp. nov. and it bears eight pairs of branchiae. Rosenfeldt (1989) highlighted the presence of palps which are now lacking. However, the relevant features of this specimen agree well with the description provided above of H. indica sp. nov.

Distribution and ecology

Heterospio indica sp. nov. was found off the west coast of India (Fig. 1) in shallow water (2.5 to 22 m depth) in mostly clayey silt and sandy silt sediments (Table 1). Hartman (1974) reported H. longissima based on two specimens from off the NW coast of India and Pakistan. In this article, Hartman (1974) only mentioned the papers by Ehlers (1895) and Hartman (1965) and did not provide any comparison with H. mediterranea or H. reducta, the two species described earlier by Laubier et al. (1972 -73) from the Mediterranean Sea. Rosenfeldt (1989) reported H. longissima from Sudan (see above) based on a single specimen. She illustrated chaetae of the second elongated segment but did not provide any comparison with other species of Heterospio. Türkay (1996), Wehe & Fiege (2002), Rao (2005) and Kazmi & Naushaba (2013) mentioned these two records without any discussion of the identification of the reported material. We did not examine the material reported by Hartman (1974) but assume that it may belong to H. indica sp. nov. because of its geographic proximity to our material. The finding of the specimen originally reported as H. longissima by Rosenfeldt (1989) and identified here as H. indica sp. nov. (see above) extends the distribution of the new species to the Red Sea.