Heterospio africana, 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 : 53-56

Heterospio africana new species

Figures 26–27

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Material examined. East Africa, off Mozambique, International Indian Ocean Expedition, R / V Anton Bruun, Cruise 7 , Sta. AB 372 H, coll. 19 Aug 1964, Olga Hartman, Campbell Grab , 24.900ºS, 34.923ºE, 55 m, sand and mud, holotype ( LACM-AHF Poly 13288) .

Description. Holotype (LACM-AHF Poly 13288) complete, 16.6 mm long, 0.25 mm wide across thoracic setigers and 0.41 mm wide across abdominal setigers; with 27 setigers, including 9 thoracic, 14 abdominal, and 4 in posterior bulbous section. Body long, thin, with most abdominal setigers each about as long as entire thoracic region. Thoracic region generally dorso-ventrally flattened, cylindrical in cross section. Dorsal surface of thoracic region with narrow dorsal ridge extending from peristomium to end of setiger 7 ( Fig. 26A ); venter relatively smooth with no ventral ridge or groove ( Fig. 26B ). Color in alcohol opaque white.

Pre-setiger region triangular as long as first three setigers ( Fig. 26A ). Prostomium conical, smoothly rounded on tip ( Fig. 26A–B ); eyes absent; nuchal organs narrow grooves on posterior lateral margins at border with peristomium ( Fig. 26A ). Peristomium divided into the two rings by dorsolateral grooves from which dorsal tentacles arise in other species, but tentacles not attached in holotype. First ring very narrow; second ring as large as following setiger 1 ( Fig. 26A ). Peristomium interrupted dorsally by prominent dorsal crest on setiger 1 and continuing posteriorly as a narrow dorsal ridge to near end of setiger 7 ( Fig. 26A ). Ventrally, peristomium smooth, with oral opening a transverse slit bordered anteriorly by four lobes and posteriorly by a single curved lower lip ( Fig. 26B ); proboscis not observed.

Branchiae present on setigers 2–6 ( Fig. 26A ), with no evidence of scars or stubs on setiger 7 or later even when stained with MG or Shirlastain A; branchiae when present long, thin, rounded in cross section, tapering to rounded tip; branchiae with narrow ciliated groove; internal blood vessel extends along entire length.

All parapodia of thoracic and abdominal setigers biramous with setal fascicles arising from near anterior border of each segment; at least three of four setigers of posterior region biramous; last likely only with notosetae. Thoracic region with eight short setigers, each about twice as wide as long; with setiger 8 slightly longer, about half again as long as setiger 7; setiger 9 first elongated setiger, about 2.5 times longer than setiger 7. Setiger 10 first abdominal setiger, about as long as setigers 1–8 combined; subsequent abdominal setigers 11–23 each of a similar length, about as long as entire thoracic region ( Fig. 27A ). Thoracic notopodia through setiger 9 with notosetae arising as tight fascicles from simple grooves or notches; neuropodia of setigers 1–8 with a short postsetal lamella ( Fig. 26B ). Abdominal parapodia from setiger 10 with parapodia as narrow ridges or rows encircling each segment, with narrow dorsal, ventral, and lateral gaps separating noto- and neurosetae ( Fig. 26A ).

All thoracic noto- and neuropodia of setigers 1–9 with numerous long capillaries in tightly packed, spreading fascicles, of 25 to 30 or more long capillaries ( Figs. 26A , 27A–B ). Abdominal setigers 10–11 with two rows of capillaries, mostly encircling body; capillaries of first row thicker than thin capillaries of second row ( Fig. 26D ). Setigers 12–13 with subuluncini ( Fig. 26C ) and a few acicular spines in first row and thin capillaries in second row. Setigers 14–20 with acicular spines in first row ( Fig. 26E ) and thin capillaries in second row; rarely with aristate spines among the acicular spines. Acicular spines weakly curved, narrowing to narrow blunted tip ( Figs. 26E , 27F– G ). Far posterior setigers 21–23 with subuluncini replacing acicular spines in first row and thin capillaries in second row. Posterior bulbous section with four parapodia each with distinctly curved hooks ( Figs. 26F , 27D–E ); first three of these setigers biramous with two hooks; fourth setiger with only a single notopodial hook.

Posterior bulbous section as long as wide, heavily wrinkled, with parapodia best observed in anterior half ( Fig. 27C ); posterior half with large folds surrounding anal opening.

Methyl Green staining. No pattern.

Remarks. In Heterospio africana n. sp., the large peristomial crest continues along the surface of the first seven setigers as a narrow, but prominent mid-dorsal ridge. Such a prominent ridge has not been observed in other species. In addition, while H. africana n. sp. is one of several species to have setiger 9 as the first elongate setiger, about 2.5 times the length of setiger 8, it is the only species with branchiae limited to setigers 2–6. Species with branchiae from setiger 2–7 and a similarly long setiger 9 include H. guiana n. sp. and H. paulolanai n. sp.; however, both of these species lack a dorsal peristomial crest.

Etymology. The species is named for its occurrence off the SE coast of Africa.

Distribution. East Africa, off Mozambique, 55 m.

Figures

FIGURE 26. Heterospio africana n. sp. Holotype (LACM-AHF Poly 13288): A, anterior end, dorsal view; B, anterior end, ventral view; C, subuluncini, setiger 13; D, capillary seta from setiger 10; E, acicular spines from setiger 14; F, notopodial hooked seta from posterior bulbous section.

FIGURE 27. Heterospio africana n. sp. Holotype (LACM-AHF Poly 13288): A–B, anterior end, right lateral view; C, bulbous posterior section attached to setiger 23, right lateral view; D, two notopodial hooks from bulbous posterior section; E, detail of posterior hook; F, notopodial acicular spines from setiger 15; G, neuropodial acicular spines from setiger 16. Stained with Shirlastain A. Arrows on Figure 2B point to branchial stubs on the right side of setigers 2, 4, and 6.