Heterospio ehlersi, Blake & Maciolek, 2023

Blake, James A. & Maciolek, Nancy J., 2023, New species and records of Heterospio (Annelida, Longosomatidae) from continental shelf, slope and abyssal depths of the Atlantic Ocean, Pacific Ocean, Indian Ocean and adjacent seas, Zootaxa 5260 (1), pp. 1-74 : 48-50

Heterospio ehlersi new species

Figures 23–24

urn:lsid:zoobank.org:act:5E6FB9FA-CD55-4473-83B1-E1F506B3DCA2

Material examined. South China Sea, Gulf of Thailand, Unocal Thailand Survey , Sta. BWC-1-D-1, 8.958ºN, 101.332ºE, 60–70 m, coll. 03 May 1991, Battelle Ocean Sciences, holotype ( LACM-AHF Poly 13289) .

Description. Holotype (LACM-AHF Poly 13289) only specimen, long, narrow, threadlike; complete with 26 setigers including nine thoracic, 14 abdominal, and three in posterior bulbous section; 10 mm long, 0.25 mm wide across thoracic setigers, and 0.4 mm wide across abdominal setigers. Thoracic region with setigers 1–8 short and crowded, setiger 9 first elongate, as long as 2.5 preceding setigers ( Figs. 23A , 24A ). Abdominal region with elongate cylindrical segments, each about as long as entire thoracic region, terminating in posterior bulbous section bearing at least three parapodia with hooks ( Fig. 24B–C ). Color in alcohol opaque white.

Pre-setiger region short, about as long as first three segments ( Fig. 23A ). Prostomium triangular, tapering anteriorly to narrow, rounded tip ( Figs. 23A–B , 24A ); eyespots absent; nuchal organs narrow slits dorsolateral on border with peristomium ( Fig. 23A ). Peristomium a single ring, interrupted dorsally by thick dorsal crest extending from posterior border of prostomium over setiger 1 to anterior border of setiger 2 ( Fig. 23A ); grooves on either side of dorsal crest likely site where dorsal tentacles arise, but these not present. Ventrally, peristomium entire, interrupted by mouth between prostomium and peristomium ( Fig. 23B ); mouth a transverse groove with shallow vestibule on anterior border and narrow posterior lip with short lobes ( Fig. 23B ); pharynx not observed.

Branchiae present on setigers 2–4 either intact or as stubs; when present, branchiae long, thin, crenulated, with internal blood vessel.

Thoracic region consisting of eight short setigers, each about three times as wide as long and a ninth transitional setiger about 2.5 times as long as setiger 8 ( Figs. 23A , 24A ). All thoracic setigers slightly flattened dorsally with parapodia weakly inflated and elevated over dorsum; ventral similarly inflated, but with broad ventral ridge extending over setigers 1–8 ( Fig. 23B ).

All parapodia biramous with setal fascicles arising from anterior edge of segment. All thoracic noto- and neuropodia of setigers 1–9 with 12–15 long capillaries in spreading fascicles arising from a rounded torus. Elongate abdominal setigers from setiger 10 to about 20 with widely spaced noto- and neuropodia; distinct dorsal, lateral and ventral gaps producing four sets of setae; continuous encircling cinctures not present until last few abdominal setigers (20–23) where reduced gaps result in cinctures of both spines and capillaries. Spines in anterior row numbering about 15–20 per noto- or neuropodium on most abdominal setigers, last few setigers with up to 25 spines per podium; numerous capillaries in posterior row in all abdominal setigers. Acicular spines curved or straight, tapering to narrow tip ( Fig. 23D ); aristate spines and subuluncini not observed.

Posterior bulbous section about as long as wide ( Fig. 24B ), with three parapodia each with 1–2 acicular spines per ramus. Each spine curved, with blunt tip ( Figs. 23E , 24C ).

Methyl Green staining. Dorsal peristomial ring retains stain, otherwise no pattern.

Remarks. Among shallow-water species of Heterospio that lack neuropodial spines on setiger 1, have five or fewer pairs of branchiae, and have setiger 9 as the first elongate setiger, H. ehlersi n. sp. from the South China Sea mostly closely resembles H. africana n. sp. from off Mozambique. They differ in that H. ehlersi n. sp. has branchiae from setigers 2–4, one peristomial ring, and acicular spines from setiger 10 to the end of the abdominal region, whereas H. africana n. sp. has branchiae from setigers 2–6, two peristomial rings, only capillaries on setiger 10. and following setigers with both subuluncini and acicular spines.

Heterospio ehlersi n. sp. also closely resembles H. brunei n. sp., a deep-water species from off Borneo, also in the South China Sea, having a reduced number of branchial pairs, with setiger 9 as the first elongate segment, and with acicular spines present from setiger 10. They differ in that H. ehlersi n. sp. has one peristomial ring instead of two, branchiae on setigers 2–4 instead of 2–5, and an oral opening with short lobes on the posterior lip instead of short lobes on both the anterior and posterior lips. In addition, the nature of the broad ventral ridge observed on H. ehlersi n. sp. is unique among known species of the genus.

Etymology. This species is named for Professor Ernst Heinrich Ehlers (1835–1925), prominent German zoologist and polychaete systematist. He was a Professor at the University of Ĝttingen where he identified and named the genus Heterospio and the type-species, H. longissima , in 1874.

Distribution. South China Sea, Gulf of Thailand, 60– 70 m.

Figures

FIGURE 23. Heterospio ehlersi n. sp. Holotype (LACM-AHF Poly 13289): A, anterior end, dorsal view; B, anterior end, ventral view; C, capillary from setiger 10, posterior row; D, acicular spines from setiger 10; E, notopodial hook from bulbous posterior end.

FIGURE 24. Heterospio ehlersi n. sp. Holotype (LACM-AHF Poly 13289): A, anterior end, dorsal view; B, bulbous posterior end right lateral view; C, bulbous posterior end with detail of notopodial hook. Stained with Shirlastain A.