haptonema

cellstructuremech:haptonema · Appendage · Appendage · Proposed

An elongated, plasma-membrane-bounded, microtubule-supported appendage of haptophyte algae that emerges from the flagellar pole and can coil rapidly during haptonemal motility or participate in particle capture. [DOI:10.1242/bio.036590]

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
haptonemal singlet microtubules	Protein	part of	Reviewed label only (reviewed name; no accession asserted)				A parallel bundle of singlet microtubules that runs through the haptonema and supports rapid coiling. `DOI:10.1242/bio.036590` Nomura et al. 2019 reviewed ultrastructural observations in which six to seven singlet microtubules pass in parallel through a haptonema.

Taxonomic distribution

NCBITaxon:2830 Haptophyta — VARIABLE: The haptonema is haptophyte-specific, but haptophyte algae include lineages that have secondarily lost the haptonema; this row therefore records patchy presence within the clade. [DOI:10.3732/ajb.91.10.1508]

Canonical examples

NCBITaxon:35142 Haptolina hirta — Marine haptophyte, previously Chrysochromulina hirta, in which the haptonema was observed attaching to food particles during phagotrophic feeding. [DOI:10.2216/i0031-8884-30-6-563.1]

Functions

rapid haptonemal coiling — The haptonemal microtubule bundle can undergo rapid calcium-dependent conformational changes that coil the appendage in haptophyte cells.
- DOI:10.1242/bio.036590 Nomura et al. 2019 used microtubule stabilization to show that Ca2+-dependent microtubule conformational changes are required for rapid haptonemal coiling.
haptonemal particle capture — The haptonema can attach to food particles and bring them toward the haptophyte cell surface during feeding.
- DOI:10.2216/i0031-8884-30-6-563.1 Kawachi et al. 1991 observed haptonema-mediated food-particle capture in Haptolina hirta.
- DOI:10.2216/i0031-8884-34-3-193.1 Kawachi and Inouye 1995 characterized functional roles of the haptonema during feeding by Chrysochromulina spinifera.

Mechanism graphs

Haptonemal microtubules support coiling and particle capture (FUNCTION)

Singlet microtubules form the haptonemal core. Calcium-dependent microtubule conformational changes enable rapid coiling, and the protruding haptonema can attach to food particles during haptophyte feeding.

Subject	Predicate	Object	Evidence
haptonemal singlet microtubules	form core of	haptonema	`DOI:10.1242/bio.036590` Nomura et al. 2019 describe prior ultrastructural observations of six to seven microtubules within the haptonema.
calcium-dependent conformational state	modulates	haptonemal singlet microtubules	`DOI:10.1242/bio.036590` Nomura et al. 2019 found that taxol blocked rapid haptonemal coiling. After taxol treatment in calcium-free conditions, calcium addition converted the right-handed helical shape toward a planar bend. This demonstrates a calcium-dependent shape response, not a direct measurement of unchanged Ca2+ influx.
haptonemal singlet microtubules	drive	rapid haptonemal coiling	`DOI:10.1242/bio.036590` Nomura et al. 2019 linked rapid coiling to Ca2+-dependent conformational changes of haptonemal microtubules.
haptonema	attaches to	food particles	`DOI:10.2216/i0031-8884-30-6-563.1` Kawachi et al. 1991 described the haptonema as a food-capturing device in Chrysochromulina hirta.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral groundings for haptonemal tubulins or associated microtubule-linker proteins before adding gene-level components. The first haptonema record curates a morphological microtubule-bundle constituent and avoids guessing whether broad tubulin or ciliary microtubule terms exactly denote haptophyte haptonemal singlets.

Evidence

DOI:10.1242/bio.036590 Nomura et al. 2019, Microtubule stabilizer reveals requirement of Ca(2+)-dependent conformational changes of microtubules for rapid coiling of haptonema in haptophyte algae, Biology Open.
PMID:30700402 PubMed record for the 2019 Biology Open haptonema coiling study.
DOI:10.2216/i0031-8884-30-6-563.1 Kawachi, Inouye, Maeda and Chihara 1991, The haptonema as a food-capturing device: observations on Chrysochromulina hirta (Prymnesiophyceae), Phycologia.
DOI:10.2216/i0031-8884-34-3-193.1 Kawachi and Inouye 1995, Functional roles of the haptonema and the spine scales in the feeding process of Chrysochromulina spinifera, Phycologia.
DOI:10.3732/ajb.91.10.1508 Andersen 2004, Biology and systematics of heterokont and haptophyte algae, American Journal of Botany.

Curation history

2026-09-13T10:39:17Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-13T10:40:05Z codex · EXPANDED_RECORD — Added a label-only haptonemal singlet-microtubule component, Haptophyta scope, a Haptolina hirta canonical example, rapid-coiling and food-particle capture functions, haptonema DOI and PMID evidence, a nonmechanistic haptonemal microtubule function graph, and a microtubule-grounding TODO.
2026-09-13T10:48:57Z codex · ADDRESS_REVIEW — Resolved PR #774 review issue #775 by changing the Haptophyta taxonomic-distribution row from COMMON to VARIABLE and citing Andersen 2004 for haptophyte lineages with secondary haptonema loss.
2026-10-11T04:06:38Z claude · ADDRESS_SAVED_REVIEW — Addressed #2168: bounded the Nomura taxol/calcium evidence note to the observed coiling inhibition and calcium-induced shape response, without treating it as a direct influx measurement.

Source: data/structures/appendage/haptonema.yaml